Functional Segregation of Color
and Motion Processing in the
Human Visual Cortex: Clinical
Evidence

Lucia M. Vaina

Anatomical and physiological investigations indicate
two major distinct functional streams within the extrastriate visual cortex of the macaque monkey, and
behavioral observations suggest that the ventral (occipitotemporal) pathway is the cornerstone for object
recognition whereas the dorsal (occipiioparietal) pathway is primarily involved in visuospatial perception
and visuomotor performance. In the context of this dichotomy we conducted a psychophysical and neuropsychological study of visual perceptual abilities in
two stroke patients, each with lesions involving several extrastriate areas. Magnetic resonance imaging
demonstrated bilateral lesions; in one patient (E.W.) the
lesion involves the ventral medial portions of the occipital and temporal lobes, and in the other (A.F.) the
lesion involves dorsally the occipital-parietal area, including the region of the temporal-parietal-occipital
junction. E.W. suffers from achromatopsia of central origin, prosopagnosia, visual agnosia, and alexia without
agraphia. His depth and motion perception, including
recognition of moving objects, are normal. He has superior visual field loss bilaterally, and slightly impaired
acuity, and complains that the world appears in a deep
twilight even on a sunny day. In contrast A.F. shows
specific deficits of stereopsis, spatial localization, and
several aspects of motion perception. He is also impaired at recognizing objects presented from unconventional views, but recognition of prototypical views
of objects, and color and form discrimination are normal, as is his ability to recognize faces.

Studies of the visual system of the macaque monkey
provide the best structural and physiological model of
the human visual system. Both they and we are Old
World primates, and the physiology and anatomy of
the macaque visual system are well studied. At subcortical levels, the anatomy of the macaque brain is
very similar to our own. At the cortical level, a great
deal is now known about the macaque but relatively
little is known about the human visual system.
A wealth of anatomical and physiological studies
concerned with the characterization of visual properties in the extrastriate regions of the macaque have
led to the hypothesis that each of these areas is specialized in a particular aspect of vision. In one of the
most influential schemes for the functional parcellation of extrastriate visual cortex, Ungerleider and
Mishkin (1982) propose two major "parallel" streams
of processing, both originating in VI. One stream progresses toward the temporal lobe via V4, and is involved in the analysis of visual information relevant to
object recognition. The other stream courses toward
the parietal lobe via MT, and is indispensable for the
perception of visual information relevant to spatial position and visuomotor coordination. Recently, this
sharp separation in the visual system has been challenged (for a critical review, see Merigan and Maunsell,
1993) partly due to the discovery of abundant interconnections among the extrastriate areas (for review,
see Felleman and Van Essen, 1991). However, abundant cross-connections at various stages between extrastriate visual areas in functionally different pathways are still consistent with anatomical segregation
over substantial portions of the parietal and temporal
pathways (Merigan and Maunsell, 1993). For example,
interconnections may evoke one pathway to suppress
another in the mechanism of selective visual attention.
Most of the direct comparisons that have been made
between the parietal and temporal pathways emphasize primarily the contributions to visual analysis of
areas MT and V4. The major distinctive properties of
these areas appear to be strong selectivity to motion
in MT, accompanied by indifference to color and form,
and conversely conspicuous selectivity for color and
orientation in V4 along with insensitivity to changes
in motion. The selectivity for color persists along the
occipital-temporal pathway (Gross et al., 1972), whereas the selectivity for motion-related information persists along the occipital-parietal pathway (Bruce et al.,

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The anatomical characteristics of the lesions of
these two patients permit a direct experimental comparison of the effects of lesions confined to the parietal
or temporal pathways. E.W.'s and A.F.S performance on
the psychophysical and neuropsychological tasks discussed here supports the functional distinction between a dorsal and a ventral extrastriate system but
additionally suggests the existence of a pathway involved in identification-from-motion that is separate
from both the dorsal early motion/spatial analysis pathway and the ventral color/static-form pathway.

Intelligent Systems Laboratory, Departments of
Biomedical Engineering and Neurology, Boston
University, Boston, Massachusetts 02215, Center for
Biological and Computational Learning,
Massachusetts Institute of Technology, Boston,
Massachusetts, and Departments of Neurology and
Surgery, Brigham and Women's Hospital, Harvard
Medical School, Boston, Massachusetts 02115

In this study we report the results of detailed psychophysical and neuropsychological tests from two
patients (E.W. and A.F.) who have bilateral lesions in
conjunction with particularly selective visual deficits.
Patient E.W. showed deficits in color discrimination in
the total absence of deficits in motion perception. Patient A.F. showed the opposite pattern of deficits; that
is, he was impaired on motion but not color. A.Es visual motion deficits have been discussed before (Vaina
et al., 1990a,b). Although other perceptual deficits
were found concurrently, the present results provide
further support for the idea that different visual cortical streams process color and motion aspects of vi-

Functional Segregation of Color and Motion " Vaina

sual stimuli. Furthermore, the location of these human
cortical areas is consonant with the general scheme
of parietal and temporal pathways of information processing proposed in the monkey visual cortex (Ungerleider and Mishkin, 1982; Ungerleider and Desimone, 1986; Maunsell and Newsome, 1987) and
dealing respectively with the position or the identity
of objects.
The Patients
The localization of the lesion in both patients was
done by magnetic resonance imaging (MRI), and acuity, visual fields, and eye movements were measured
formally in neuro-ophthalmological examinations.
Both patients underwent a detailed evaluation of their
perceptual abilities concerning form, color, motion,
binocular stereopsis, and their abilities to recognize
objects and actions. Normal subjects naive as to the
purpose of the tasks used in this study were used as
control subjects. The two patients and the control subjects gave written consent to all the procedures after
they had been explained.
Case 1: KW.
E.W. is a 63-year-old right-handed man, a retired highschool science teacher who was referred to us for the
clinical evaluation of perceptual and cognitive deficits.
His neurological problems date from March 1988,
when he suffered a right occipitotemporal infarction.
He was then maintained on anticoagulation therapy
with Coumadin, which was stopped in July 1988
when he underwent surgery for the removal of a coIonic polyp. A few days later he developed headache,
nausea, vomiting, gait instability, and global visual
changes. The patient's clinical condition was consistent with a new left occipitotemporal cerebrovascular
accident (CVA) that was revealed by MRI studies.
The neuro-ophthalmological investigation revealed
normal fundus in both eyes, normal pupils, and normal
optokinetic nystagmus. Acuity was 20/40 in both eyes
without correction. Visual fields on Goldmann perimetry (Fig. lA,ff) demonstrated a superior latitudinal
defect in both eyes that is characteristic, although not
diagnostic, of patients with cortical achromatopsia
(Meadows, 1974). The MRI obtained at the time of our
study (Fig. IC-F) showed bilateral occipital lobe lesions, more extensive in the right hemisphere than the
left. The lesions extend ventrally into the medial temporal area, involving the hippocampus and parahippocampal gyrus, and slightly into the parietal lobe, medial and posterior to the trigone of the lateral
ventricle. The neurological examination did not reveal
any paresis, ataxia, akinesia, or apraxia and there were
no somatosensory deficits, including stereognosis. On
neuropsychological evaluation, the results on subtests
of the Wechsler Adult Intelligence Scale Revised
(WAIS-R) showed that his score on the verbal scale
(VIQ = 136) was above average, whereas on the performance scale he showed a severe deterioration from
the premorbid level (PIQ = 76). Memory, especially
visual and topographic, was severely impaired. Problem-solving ability and reasoning were remarkably

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1981; Van Essen and Maunsell, 1983; Cowey and Marcar, 1993; Marcar and Cowey, 1993).
Functional segregation between the properties of
the parietal and temporal pathways in humans has
also been demonstrated in PET studies of normal subjects. Most notably, Watson et al.(1993) and Zeki et al.
(1991) have shown substantial spatial segregation in
cortical activation when subjects view color or moving stimuli, and Haxby et al. (1991) showed similarly
separate patterns of activation when subjects perform
a spatial task underlying either judgements of face recognition or spatial relationships. Consistent with neurophysiological data, these neuroanatomy studies support the model of a major segregation of the
extrastriate visual cortex into at least two functional
streams.
This segregation is reinforced by studies of lesions
in restricted regions of the human visual cortex,
which often lead to specific deficits in visual perception. Vaina (1989) showed that patients with occipitaltemporal lesions are impaired at discriminating form
whether it is defined by orientation differences (texture), stereopsis, or motion, yet their performance is
normal on a large class of motion discrimination tasks.
The converse holds for patients with occipital-parietal
lesions, whose perceptions of motion and stereopsis
are impaired, although their form discrimination ability is generally unaffected. [There is, however, evidence that large parietal lobe lesions do not impair
global stereopsis in monkeys (Cowey, personal communication), while temporal lobe lesions do (Schiller
et al., 1993)] Vaina et al.(1989) and Rizzo et al.(1992)
presented evidence for the dissociation of color and
motion perception in patients with central achromatopsia. Although in humans such well-circumscribed
lesions are even more rarely exactly where one would
want them to be, it is important to study their effects
psychophysically for a number of reasons. First, it
helps to map areas in human visual cortex that are
homologous and/or analogous to areas in monkeys
where we can learn much more about the cell physiology and connectional anatomy. Second, verbal reports by human subjects of damaged visual percepts
are incomparably more detailed and informative than
purely psychophysical data from animals with specific
lesions. When the link between human and monkey
visual cortical areas can be made with greater confidence, it will be much clearer how to interpret properties of cells in a given functional/anatomical area.

B
RIGHT EYE

LEFT EYE

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Figure 1. Visual fields and MRI of patient E.W.S brain 3 months following a hemorrhagic stroke and the localization of the axial scans on the lateral view of a
human brain. A and B show EW.'J visual fields by Goldmann perimetry. The crosshatched area shows E.W.S bilateral upper visual field loss. Isopters for targets
lie and //Me are indicated. C-Fshow axial slices of LVV.'s T2-weighted MRI studies (Tr, 2000 msec; Te, 80 msec) revealing large lesions, consistent with infarcu,
along the medial margins of both temporal lobes (C), into the medial portions of the occipital lobes. The posterior portion of the lesion in the left hemisphere
does not extend quite as far medially as in the right hemisphere. Some small slight patchy hyperintense areas are seen at the cortical margin of the right posterior
temporal-parietal-occipital region of the right hemisphere (C, D), suggesting some tissue loss as well, but the margins of the area are not well-enough defined
to be certain of discrete tissue loss. E extends through the frontal and occipital homs of the lateral ventricles. The lesion in the nght hemisphere extends about
the margins of the occipital hom of the lateral ventricle, extends up higher than on the left, and is still seen behind and slightly lateral to he body of the right
lateral ventricle (F\. ft also extends up medially to the occipital hom, in front and behind the parietal-occipital sulcus. Numerous bright foci are also seen scattered
in the basal ganglia; the most prominent one {small whits arroWi lies at the lateral posterior margin of the right thalamus. For C-F (Figs. 1 and 2): W, body of the
lateral ventricle; ft frontal lobe; h, hemosiderin; oh, occipital hom of the lateral ventricle; po, parietal-occipital sulcus; ptol, parietotemporo-occiprtal fossa; ssc,
supersellar cistern; t, trigone of the lateral ventricles. For 6 (Figs. 1 and l\. IFg, inferior frontal gyrus; ITg, inferior temporal gyrus; UFg, middle frontal gyrus; MTg,
middle temporal gyrus; MTS, middle temporal sulcus; PO, parietal occipital sulcus; PoCg, postcentral gyrus; PrCg, precentral gyrus; SFg, superior frontal gyrus;
STg, superior temporal gyrus; STS, superior temporal sulcus; SYl Sytvian fissure; PTOFu the panetal-temporal-occipital fossa from Poiyalc (1957, fig. 271), which
several authors have suggested corresponds to the human homolog of the macaque MT. The horizontal lines denote the levels of the axial slices corresponding
to C-F.

Cerebral Cortex Scp/Oct 1994, V 4 N 5 557

He had severe deficits in recognizing familiar objects, photographs, and drawings (visual object agnosia), and was unable to find his way even in the most
familiar surroundings (topographic agnosia). Even
when he recognized objects, such as shoes or clothing
items, for example, he could not distinguish between
those that were his own and those that belong to
someone else, such as his son or son-in-law, for example.
Case 2: A.F.
Details of patient A.F. have been reported in detail in
Vaina et al. (1990a) and are summarized here. A.F. is a
60-year-old left-handed man, retired from a white-collar job, who suffered an acute hypertensive hemorrhage that required emergency hospitalization and
subsequently the evacuation of a large hematoma.The
neurological examination did not reveal any paresis,
ataxia, akinesia, or apraxia. An MRI study (Fig. 1C-F)
showed bilateral lesions involving the temporal-parietal-occipital junction. The right hemisphere lesion was
larger than the left but both extended dorsally into
the posterior parietal lobes. The left hemisphere lesion shows tissue loss from an old infarct extending
along the lateral margin of the lateral ventricle and
around the margins of the occipital horn, going upward posterior to the body of the lateral ventricle and
into the medial portion of the parietal lobe.
Visual field charted by Goldmann perimetry revealed a dense congruous loss of the left inferior visual field bilaterally (Fig. 2A,B). There was a minimal
loss in the upper visual field. Letter acuity with appropriate correction glasses was 20/30. On the examination of ocular motility there was no strabismus, and
saccadic eye movements were normal both to the

Functional Segregation of Color and Motion • Valna

right and to the left. He substituted saccades for
smooth pursuit when following a smoothly moving
target. This occurred both to the right and to the left.
He was unable to maintain fixation of left lateral gaze
and tended to drift back toward the central fixation.
Though arm movements were intact and he could
clearly perceive objects in the visual field, he was
somewhat inaccurate in touching objects placed in his
reach (more in the left visual field than in the right).
He complained of difficulties with reading and written
calculations, but he showed no deficits in oral calculations. Copying and drawing were poor and lacked
perspective. Printing in uppercase letters was very disorganized when he wrote looking at the page, but
when blindfolded or when writing cursive he was not
impaired. The difficulties of reading and writing in
print were entirely derived from his inability to locate
letters and numbers on the page under visual control.
As expected, writing cursive with lowercase letters
was good, since this does not require specifically visual positioning of each individual letter. On basic neuropsychological evaluation with the WAIS-R, A.F. obtained an average VIQ of 104 and a severely depressed
PIQ of 68.
General Methods and Results
The psychophysical tasks for assessing the patients'
contrast sensitivity and perceptual abilities for form,
motion, and spatial location were generated and presented by an Apple Macintosh Fix computer on standard Apple monitors (the Pelli attenuator was used in
the contrast sensitivity tests for displaying low-contrast stimuli). The monitor was 13 inches along the
diagonal with a frequency of the vertical retrace interrupt of 67 Hz. Viewed from 60 cm from the screen,
a pixel subtended 2 X 2 arcmin. In most tests, stimuli
were displayed by the constant stimuli method to
compute the percentage of correct responses to stimuli with graded level of difficulty. In the contrast sensitivity and motion coherence tests stimuli were presented by a staircase procedure. In all the motion tasks
random dots were used to minimize familiar position
cues and to isolate the detection of motion per se,
because in such displays it is impossible to track the
individual elements across frames by a shift in attention (Nakayama and Tyler, 1981). All the computerpresented tasks were conducted at photopic light levels. Every new test was introduced by examples to
assure that the subject understood the task. During
the example session feedback was given. For the computer-presented tasks, each trial was initiated by the
subject by pressing a specially designated key and observers were asked to maintain fixation on a small
black mark in the center of the display. An exception
to this was the motion coherence task, in which the
stimuli were presented separately in each visual field
and the subjects fixated on a mark placed 2° to the
left or to the right of the border of the stimulus aperture.
Binocular stereopsis was measured with the clinical
Randot test (Randot Stereotests, Stereo Optical Co.,
Chicago, IL) and with a set of stereograms from the

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good. There was no discernable aphasia or agraphia.
Calculations were normal. Copying was excellent. In
contrast, drawing from memory was very impaired.
Thus, when asked to draw a banana, which he could
copy very well, he drew a large L-shaped form with
the corner well emphasized.
E.W. had persistent significant visual deficits consistent with central achromatopsia, prosopagnosia, loss
of topographic memory, alexia without agraphia, and
visual object agnosia. He reported that the world
looked as if in a continuous "twilight and drained of
color." His prosopagnosia was extremely severe, he
was not able to recognize any of the members of his
family or to identify himself in a recent photograph,
and he could not identify any particular objects beyond their general category. He could, however, recognize people by their voice, posture, and gait. At the
hospital he could recognize familiar nurses as soon as
they moved, but when they were seated in front of
him he failed to identify any of them. E.W. could see
letters and words, but could not identify them. He
could write well, and legibly, but was not able to read
his own writing (alexia without agraphia). In occupational therapy and at home he went through many
sessions of retraining his reading of letters and words,
but he did not make any progress by the time of this
study (2 months after the second stroke).

RIGHT EYE

B

LEFT EYE

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Figure 2. Visual fields and MRI of patient A.F.'s brain 3 months following a hemorrhagic stroke and the localization of the axial scans on the lateral view of a
human brain. Perimetry results obtained on the Goldmann perimeter are shown in A and B. Isopters for targets I4e and IH4e are given, as well as the dimensions
of A.F.'s bilateral congruous loss of the left inferior visual field and a small loss in the upper visual field [crosshatched area). C-Fne the relevant slices in axial
view of T2-weighted MRI studies (Tr, 2000 msec; Te, 80 msec; see 6). In C the picture shows the temporal horns of the lateral ventricles and some patchy
hyperintensities at their margins, more on the right In D the picture shows local tissue loss in the right hemisphere at the sites of the hemorrhagic stroke in the
parietal lobe just medial to the occipital horn of the lateral ventricle and anterior to the parietal occipital sulcus. There is also some patchy hyperintensity in the
temporal lobe along the lateral margin of the right occipital horn. Localized hyperintense areas are seen in the left temporal lobe adjacent to the lateral proximal
margin of the occipital horn and in the margins of the occipital horn, f and Fshow bilaterally larger patchy areas of hyperintensity posterior, medial, lateral, and
above of the trigones and at the margins of the bodies of the lateral ventricles. Tortuous narrow bands of hemosiderin (labeled h) are seen in both images at
the site of the recent hemorrhage. G, A schematic drawing of adult human brain showing the major gyri and sulci in lateral view.

series generated by Julesz (1971). For evaluating color
vision, both patients were given the Farnsworth-Munsell 100 Hue Test (Farnsworth, 1943). Two additional
color tasks were given to E.W. since he was clinically
diagnosed as having central achromatopsia: a classical

wavelength discrimination task and flicker photometry to measure the photopic spectral sensitivity. These
tests were done by the method of adjustment. Neuropsychological tasks of perceptual categorization (silhouette matching, Gollin pictures, unusual views) and
Cerebral Cortex Sep/Oct 1994, V 4 N 5 559

100

Perceptual Categorization Tasks

> 80
IN

O

u 60

I

40

A
A E.W.
E.\
A.F.
O Controls
(n-15)

Figure 3. Shape discrimination task: percentage correct performance of five
normal controls and of F_W and A.F. on shape discrimination for three ratios
plotted as decreasing difficulty.

Contrast Sensitivity
The patients' contrast sensitivity for ID gratings was
measured with the Vistech chart' (Vistech Cons. Inc.,
Dayton, OH) and with computer-displayed sinusoidal
gratings. In the computer-based test, both static and
moving stimuli were used, with spatial frequency ranging from 0.4 to 5 cycles/degree. E.W. and A.F scored
within the normal range for both the detection and
discrimination of static and moving stimuli (direction).
Static Form Perception
Shape Detection
This is a task of figure-ground discrimination closely
adapted from Warrington and Taylor (1973). The stimulus consists of a fragmented background on which
was superimposed a fragmented letter, either an X or
an O. The degree of difficulty of the detection was
manipulated by varying the ratio of black to white in
the figure in relation to the black/white ratio in the
background. This was a yes/no task in which the subject had to report whether the letter was present in
the display. Both A.F. and E.W. obtained perfect, 100%
correct scores.
Shape Discrimination
This task is a close replication of Efron's "square" test
(Efron, 1968; Warrington and James, 1988). The target
stimulus was a square 5° X 5° and the distractors were
oblongs with one areal dimension of 5.25° X 4.77°,
4.6° X 5.5°, or 6.5° X 4° (Fig. 3; shapes under the plot
represent each particular shape pair). For each of
these dimensions 10 squares and 10 oblongs were presented for 0.5 sec, singly in pseudorandom order. Subjects were asked to judge whether the shape was a
square or an oblong.
A.Fs. performance on this task was normal. E.Ws
performance was in the impaired range as compared
with age-matched normal control subjects and with
A.E, except for stimuli that differed by the largest ratio
of the lengths of the sides of one of the components

560 Functional Segregation of Color and Motion • Vaina

Unusual Views
This test, adapted from Warrington and Taylor (1973),
consists of black-and-white photographs of common
objects shown from an unconventional angle but still
in a relatively familiar view. Visual difficulty is manipulated by changing the angle from which the object
is photographed. The observer is asked to recognize
the objects presented in an unusual view. The patients
who fail this task are subsequently asked to identify
the same objects presented from a front view (the
conventional view). Since, as discussed in detail in the
next section, E.W. could not recognize objects presented even in the prototypical, front view, we did not
give him this test. The test is very sensitive to right
posterior parietal lobe damage (Warrington and Taylor, 1973), and as expected, A.F. was severely Impaired
on it. He could recognize all these objects when presented as photographs taken from the usual, canonical
view. When presented with pictures of noncanonical
views of a bucket or a basket, for example, A.F. described them as "a slice taken from the trunk of a
tree," a glove he described as an "overshoe or a boot,"
and a frying pan as a "magnifying glass."
Gollin Pictures
This test consists of a graded series of incomplete outline drawings of objects (Gollin, I960). There were in
total five drawings for each item. An error score was
obtained by summing the number of additional drawings of the stimulus required for correct identification.
A.E was given 14 total stimuli. E.W. was so severely
impaired on visual recognition of objects that tasks
that manipulate visual complexity of objects were inappropriate. We did, however, administer a short exploratory test using only seven stimuli.
A.F. scored 29 of 52, which is worse than the 5%
cutoff score in the normal population. For E.W. it was
meaningless to apply the usual scoring procedure,
since he was unable to recognize the objects. Nonetheless, his responses were interesting. Similar to the
recognition of photographs or of full drawings of objects, when an incomplete drawing contained a relevant feature of an animate object, such as the legs, he
could correctly assign the drawing to the correct category. Thus, for example, a cow was in the first at-

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of object and face recognition were presented as
drawings or as photographs.

Matching Silhouettes to Objects
In this test, the subject is asked to first pick out the
photograph that correctly matched a silhouette of an
animate object (kangaroo, giraffe, dog, cow, horse) or
an inanimate one (roller skates, truck, doll, train, car),
and then to name or describe the objects. The silhouettes and the target objects were photographed from
prototypical, front view. All 10 silhouettes and the 10
colored photographs of the corresponding objects
were shown side by side. A.F. scored 100% correct on
this task. E.W. also was able to match correctly all silhouettes to photographs of objects even if he could
not identify the object (e.g., roller skates were identified as "an animal, a cat?").

tempt described as "a four-legged animal," and even
when the full drawing was shown, he could not provide a more specific description. The only item that
he could identify' correctly when presented as a complete drawing was the pig: "the cute curly tail, must
be a pig." However, when he was shown any drawing
of an inanimate object, he often could not identify it
even when the full drawing was presented.

Face Recognition
Facial recognition ability was tested informally. E.W.
always knew when he was looking at a face and he
quickly and accurately noted missing parts in incomplete drawings of faces. However, he consistently
failed to identify whose face it was, and could not
even recognize himself in a photograph. Family photographs were meaningless to him; he described them
as "a bunch of people together." He was unable to
judge correctly the age or the mood of photographs
of faces, and could not interpret accurately the emotional content of photographs or drawings of faces.
This failure to recognize facial expression (i.e., sadness, happiness, surprise, anger, or fear) was more pronounced with static expressions, as shown in drawings or photographs. However, when a facial
expression was pantomimed in front of him, he carefully observed the movement and could recognize
quite accurately, although hesitantly, the specific face
expression. When asked to mimic sadness, anger, surprise, or happiness, his facial expressions were always
accurate.
Recognition of Objects and Actions
E.W. failed to recognize real objects and colored pictures, although by making use of specific details he
was usually able to identify the general category' (e.g.,
a four-legged animal) but not the subordinate category
of the object (a dog). It did not matter whether the
objects were shown as 3D reproductions of the real
object or as colored or black-and-white photographs.
Although he almost always failed to recognize the
stimulus as a whole, often he quickly identified a salient part of the stimulus and used it as a basis for
reasoning about the possible identity of the object. For
example, when shown (without being allowed to
touch it) a gray toy elephant that was a veridical reproduction of an elephant, at first he said that he had
no idea what it was, but then continued, "long nose,
big ear, busy ears, prehensile nose, the only animal
with prehensile nose is. . .hmm, elephants have big
noses, they are gray or brown, but this is not an ele-

In contrast, his recognition of drawings of actions
(i.e., dancing, fighting, exercising, riding a bicycle,
hammering, sawing) and of pantomimed actions was
perfect. When he watched television he could correctly identify actions with no difficulty. He was able
to characterize gaits accurately (e.g., sporty, tired, limping) and without failure could recognize people by
how they moved. He loved watching sports on television and he could anticipate accurately the moves
of the players.
Color Perception
The Farnswortb-Munsell 100 Hue Test
This is a test of color discrimination, consisting of 85
chips of different hues, in four groups. The patient is
given all chips in one group and is asked to arrange
them in a line according to hue. The first and last chip
are fixed at the ends of the group and serve as a frame
of reference. Figure 4, A and B, shows that while E.W
was severely impaired on this task, A.Fs score was
normal.
Wavelength Discrimination
In order to look at the wavelength discrimination deficits of E.W. in more detail, he was tested additionally
as follows (since no color deficits were obvious in A.F.,
his color vision was not tested further). The output of
two slit monochromators (slit bandwidth = 10 nm)
was projected, side by side, onto a plain white screen.
The relative luminance of the two monochromators
was systematically varied by interposing neutral density filters into the light path, out of sight of the subject. The reference monochromator was set at a fixed
wavelength (440-640 nm, in 20 nm steps). E.W. was
asked to match, as closely as possible, the color of the
reference monochromator by adjusting the second
monochromator until the colors appeared equal. Four
CcrcbraJ Cortex Scp/Oct 1994, V 4 N 5 561

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Recognition: Faces, Objects, and Actions
In addition to his inability to discriminate colors of
objects, E.W. failed to recogni2e even the most familiar
faces and was severely impaired on object recognition.
These deficits were noted by the patient himself and
by his family and people surrounding him. In contrast,
A.F. had no problems in this area and since his results
on the neuropsychological tests in this section were
totally unremarkable, they will not be discussed further.

phant, elephants have a trunk, this is not a trunk, is a
hell of a nose. This is a wild, ferocious animal." When
he took it in his hand, he passed the fingers around
it, slowly, and said "still I don't know, some strange
beast! with four legs." However, when he looked at an
excerpt of a videotape showing an elephant walking
in the field, he immediately recognized it—"an elephant!" He described the picture of a cow as "an animal in disguise, the ears do not give a clue, skinny
legs, big body, could be a dog," a horse as "a dog, its
gait is common to dogs and horses," a seal as "it has
whiskers, so may be it is meant to be a cat. No tail,
very unrealistic," and a fry as "a four-legged animal
with wings. That's strange, no flying animal has legs."
Recognition of inanimate objects was even more impaired. He described a little blue toy car as a "fourlegged animal," and he still continued to describe it as
a four-legged animal when he held it in his hand.
When shown a picture of a telephone he described
the telephone cord in detail, but failed to put together
the object "for the foot, that goes around the ankle, to
secure it," the picture of an ice-cream bar as "a torch,
a lantern," and a camera as "a clock, some man-made
thing."

B

If": -

,

\ i

/ /,

values were taken for each reference wavelength. The
standard deviation of these values from the reference
was calculated for E.W. and two normal controls, as a
measurement of wavelength discrimination abilities
(Fig. 5).
The shape and the values of the wavelength discrimination curves for the two normal control subjects are typical of normal observers described in earlier studies (e.g., Wright, 1947). Relative to the
controls, discrimination values for E.W. are clearly elevated, as one would expect from an "achromatopic"
subject. However, the figure shows that discrimination
values were clearly better than random, and apparently better on long-than short-wavelength settings.
Though E.W. complained initially that he could not
discriminate colors at all, he could in fact discriminate
one end of the spectrum from the other, and never
matched a red with a blue, or vice versa. However, the
subject did take an extremely long time (>1 min) to
make each match, and expressed little confidence in
the final values. This is in contrast to his quick, confident, and good performance on the motion tasks.

I 40]

Controls

• 30
•o

E.W.

Pbotopic Spectral Sensitivity
like the previous task, this task was used solely with
E.W. Flicker photometry at 15 Hz was done on a CRT
screen, in which E.W. was asked to match the luminance of white to either the blue, green, or red gun
over a range of luminance values (1-21 cd/m2)- The
results of the test are shown in Figure 6, which shows
luminance values of the red, green, and blue guns of
the stimulus CRT, at values matched by E.W. to the
luminance of a white patch with which it was alternating. For each of the three colors, the function relating white luminance to color luminance is essentially linear, indicating that the spectral sensitivity does
not change in shape over this range in luminances;
that is, there is no Purkinje shift. Second, the values of
the color/white ratios given by E.W. were entirely
within the normal range; that is, the photopic spectral
sensitivity curve was normal.
We also tested the equiluminance point somewhat
informally. The subject viewed either a red-green
• R/al:2.43, aO:-5.38
• G/al:1.82,a0:0.948
A
B/al:3.00, a0:38.00

20

3 10
t 0

•2 400
Q

10

500

600

30

40

White entries
700

Wavelength (nm)

Figure 5. Results from EW. and two normal control subjects on the wavelength discrimination test

SS2 Functional Segregation of Color and Motion • Valna

20

figure 6. Results from EW. on the flicker photometry test The figure shows
luminance values of the red, green, and blue guns of the stimulus on the
CRT, at values matched by E.W. to the luminance of a white patch against
which the stimulus was flickering Fof each of the three colors, the function
relating white luminance to color luminance is essentially linear.

Downloaded from http://cercor.oxfordjournals.org/ at Cambridge University on August 25, 2015

Rgure 4. Results of the Farnsworth-Munsell 100 Hue Test from EW. [A) and A.F (fl). Errors are plotted radially, and position on the circumference represents
points along a continuum of hue.

square wave or a sine wave grating, in which the intensities of the red and green could be independently
and continuously varied. There was no point, in either
type of stimulus, at which the grating appeared as a
uniform field to E.W., although the stripes appeared
much more faint at intensity values corresponding to
expected normal equiluminance values.

Binocular Stereopsts
Static binocular stereopsis was first measured with the
Randot Stereotest (Stereo Optical Co., Chicago, IL) and
with red-green stereopatterns from the series generated byjulesz (1971). In both tests, in 75% of the trials
with binocular fusion a central figure (e.g., letter E or
T, a square, a circle, a triangle, or a star) stands out in
front of the surround. In the remaining 25% of the
trials the display contained only random dots.
The Randot test uses random dot stereograms printed on polarized cards. With appropriate polarized
glasses each eye views a different image. The test measures stereoacuity in a series of stereograms of different disparities. In Julesz's random-dot stereograms,
when viewed monocularly, each target appears as a
random array of small light and dark squares in which
no form or depth is apparent. The two random-dot
patterns are identical except that in one pattern a contiguous cluster of dots in the central region has been
displaced laterally with respect to the same region in
the other pattern. The patterns were printed in pale
red and green ink. When viewed with a green filter
over one eye and a red filter over the other, the central
figure is seen in front of the surround. We used 16
random-dot stereograms with the disparity ranging between 120 and 300 arcmin. In both stereotests, the
subjects' task was to say whether they saw a central
figure standing away from the surround and then to

Spatial Perception
Point Discrimination
The task consisted of two adjacent squares (each subtending 6° X 6°), one with a black dot (subtending 4
arcmin2) printed in the center and the other with a
black dot printed off center (the task is similar to that
described by Warrington and James, 1988). From trial
to trial the deviation of the dot from the center varied
from 2 arcmin to 2°. For each trial the assignment of
the dot to the center of the square or off center was
random, but so that in 50% of the trials the left-hand
square contained the dot in the center. In a two-alternative forced-choice task and constant stimuli, the observers were ask to choose the point that was in the
center of the square. E.Ws score was perfect on this
task. A.F. scored 60% correct when the off-center dot
was off by 1° or less. For larger offsets his performance
was perfect, thus indicating that he did not have any
difficulties in understanding the task per se.
Discrimination of Line Orientation
Line orientation discrimination was evaluated with a
task developed by Benton (Benton et al., 1977) that is
widely used in clinical neuropsychology for the assessment of spatial perception abilities. The stimulus
consists of two lines oriented at an angle between 0°
and 180° (the target), and 11 line segments arranged
in a semicircle radiating outward from the center. The
subject must decide which two lines among the 11
lines exactly match the orientation of the two target
lines. All the lines have equal length. E.Ws score was
almost perfect (59 of 60). On the other hand, A.Fs
score of 31 of 60 suggests a severe deficit of spatial
perception.
Spatial Discrimination
A basic task of spatial discrimination is that of line
bisection. The patient is presented with a line and
asked to mark the central point. Thirty lines of different lengths and orientations were used. A.F. was severely impaired on this task (2 of 30). He was not able
to mark accurately the center of lines, even if the examiner placed them carefully within his intact visual
Cerebral Cortex Sep/Oct 1994, V 4 N 5 563

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Color Ordering and Naming
The stimuli consisted of colored Munsell papers differing in saturation and hue. All the hues were represented by 3 X 5 cm rectangular patches that were
presented binocularty in a random arrangement on a
neutral gray flat surface. There were 15 papers in each
of three widely separated parts of the spectrum, namely, reds, yellow/greens, and blues. The first task was to
put the color patches of similar hues into a smooth
order of color. The second task was to name the colors. A.F. showed no deficits on the color ordering and
naming task. E.W. could name and choose colored
patches of paper at levels somewhat above chance,
but often used brightness cues to make the choices.
He could not distinguish blues, greens, and grays, and
had difficulties with reds and yellows. Thus, similar to
his performance on the wavelength discrimination
task, E.W. was better at discriminating and naming
long wavelengths than short wavelengths. He could
correctly, but effortfully and slowly, name yellows (578
nm) and reds (630 nm) but not blues (480 nm), which
he described variously as blue, green, or yellow. Apparently this ability to identify long-wavelength hues
prevented him from making widely discrepant matches on the wavelength discrimination task.

identify the shape of the figure (e.g., a square, a triangle in different orientations, a star, or a circle). E.Ws
performance on binocular stereopsis was intriguing.
In both tests, he reported correctly that he perceived
a figure and he correctly identified the random-dot
patterns in which there was actually no figure present.
Asked to draw what he saw in the random-dot patterns, he reproduced the forms perfectly and then (often without looking at it) he could correctly identify
it. In contrast, A.E lacked binocular stereopsis; in all
the displays he reported seeing in the random-dot stereograms "just dots, no pattern or form at all." Surprised
by his failure on these tests, A.F. commented that in
the past he enjoyed resolving anaglyphs of Julesz's
type like the ones he was looking at now, and that
years ago he used to watch 3D movies and had never
had any problems with depth vision.

field. (At close examination, A.Fs errors did not reveal
a specific pattern.) In contrast, E.W. indicated correctly
the center of the all the lines presented (30 of 30).
Spatial Location
The stimuli consist of two outline squares, one containing 14 randomly placed symbols (single digit numbers and letters) and the other containing a small
black square subtending 5.6 arcmin2 (MacQuarrie,
1953). The subject's task is to identify the symbol in
the top square corresponding to the position of the
black mark in the bottom square. A.F. scored 50% correct (10 of 20), which was at a severely impaired level
(his scores were below the 5% scores obtained in an
age-matched control group; Warrington and James,
1988). E.Ws performance was normal.

2D Form from Motion
The sensation of two moving textured planar surfaces
was elicited by two patches of contiguous random
dots uniformly displaced from one frame to the next
in horizontal translational motion across the randomdot display that formed the stationary background
(Fig. 7A). The subjects are asked to determine whether the two translating forms have the same shape
(square, circle, triangle, cross, or oblong). Both subjects
performed normally on this task (Fig. IB).
Boundary from Differences in Motion Direction
This test (adapted from Hildreth, 1984) is described
in detail in Vaina et al. (1990a) and Vaina and Grzywacz (1992). In summary, the display (subtending 10°
X 10°) contains two adjacent regions translating coherently, but in different directions, thus producing a
discontinuity in the velocity field (Fig. 1C). The discontinuity appears as an imaginary vertical line with
a notch. The notch (subtending 1.4° X 1.4°) was always presented within 2° above or below the center
of the imaginary boundary. Five angular differences
between the two areas are used: 18.4°, 37.1°, 45°, 90°,
and 180°. In a two-alternative forced-choice procedure
the observers are requested to determine whether the
notch was above or below the center of the display.
E.Ws score was perfect on this task. A.F. also scored

554 Functional Segregation of Color and Motion • Vajna

2D Form from Relative Motion
This task (described in Vaina et al., 1990a) involves
comparison of velocity magnitude without any difference in direction. An example of the display is portrayed in Figure IE. In summary, the figure (subtending roughly 2° X 2°) is presented roughly in the
middle of a 6° X 3.75° aperture consisting of a dense
random-dot pattern. Both the figure and the background are displaced in the same direction but with
different speeds. In 60% of the trials the background
speed was slower than the figure and in 40% of the
trials the background was faster than the figure. The
speed ratios between the figure and the background
using as a reference the speed of the background (37
sec) had the following values: 3/2, 2, 3, 2/3, and 1/2.
Observers were asked to make a six-alternatives
forced-choice judgment indicating which of the six
figures displayed at the bottom of the screen constituted the correct match for the moving shape. There
were 60 trials and each one of the six shapes was the
correct answer 10 times.
The results for this experiment are shown in Figure
IF. The normal control group had near perfect performance, approximately 95% correct, whereas A.Fs
was strikingly impaired. His score of 17% correct responses was at chance level. E.Ws score was below
that of the normal controls but still significantly above
chance (70% correct).
Local Speed Discrimination
The stimuli consist of two sparse dynamic random-dot
kinematograms each comprising 20 computer-generated dots. The kinematograms were displayed in two
rectangular apertures arranged one above the ouier,
each subtending an area of 4° X 2.5°, thus giving a
dot density of 2 dots/degree2 (Fig. &4). The distance
between the centers of the apertures was 2.75°. In any
single trial each dot took an independent, 2D "random-walk" of constant step size defined by the speed.
The direction in which any dot moved was independent of its previous direction and also of the displacements of the other dots. The speeds of the dots, defined as a function of the distance a dot was displaced
between successive frames, was uniform within an aperture and was assigned independently for each aperture. A base speed of 3°/sec was always compared
to five other speeds, giving five speed ratios of 1.1,
1.47, 2.2, 3.6, and 55. The assignment of the highest
speed to the top or bottom aperture was pseudorandomly selected.
Subjects were asked to determine which of the two
apertures contained the faster moving dots. A two-alternative forced-choice procedure was used for measuring the subject's ability to detect difference in
speed. In comparison to the age-matched control
group, and E.W, who was performing almost perfectly
for 2:1 speed differences, A.F. had a severe deficit on
this task (Fig. SB). He failed to discriminate reliably
speed ratios smaller than 5 5 and was performing near

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Motion Perception
We tested several aspects of motion perception. The
tests and A.Fs performance are described in detail in
Vaina et al. (1990a,b). In the first three tasks we wanted to learn whether E.W. and A.F. could see form or
boundary from differences in motion in neighboring
spatial regions. These tasks use highly coherent dense
motion fields to address the problem of perceptual
segregation by different motion cues. The next three
tests evaluate the patients' ability to discriminate
speed in randomly moving dots, to detect coherent
motion defined by a small number of dots embedded
in noise, and to perceive 3D structure solely from motion cues. Finally, we addressed E.Ws and A.Fs ability
to identify different patterns of biological motion only
from the trajectory of a small set of moving points.

well, except for the smallest angle (18.4°), for which
his performance was impaired (Fig. ID).

gDLK

?!

i
B
HIIB
p
i

chance

1

1

'}

Controls
(n = 6)

j

E.W.

A.F.

Controls

45

135

90

(n=15)

180

Angle Difference

E

i

m

r

i

i

100-1

1

1

I
•••+1!

Controls
(n = 6)

E.W.

A.F.

Rgms 7. Motion tasks. A 20 form from motion in a static background. The display consisted of a fine-grained (pixel size = 1.72 arcmin) random-dot pattern
containing 50% black and 50% white dots. Two patches of contiguous dots were coherently translated across the static background and with equal speeds. The
observer's task was to determine whether the two translating 20 shapes were the same or different B, Percentage correct responses as a function of correct
matches of die moving shapes. The graph shows the mean percentage correct responses and error bars for E.W. and A.F. and mean percentage of correct
responses and standard deviations for the normal control group. C, Boundary localization test The differential movement of the two adjacent areas of the pattern
reveals a boundary with a rectangular notch defined solely by the difference in die directions of motion of the two areas. The position of die notch and of the
invisible dividing line between the two areas in relative motion vary randomly within 1° on the x-axis. The heavy square indicates the fixation mart D, Percentage
correct responses for correctly identifying the location of die notch (above or below die fixation mark) for the following angular differences of directions of motion
between die two areas: 18.4°, 37.1°, 90°, and 180°. The shaded area indicates the percentage of correct responses of die control group ± 1 SD obtained under
identical conditions. £, 20 form from differences of velocity magnitudes: iPustration of the stimulus. The background scrolls vertically and a central patch of
contiguous dots subtending 2° x 2° moves in the same direction as the background with different speed. The shape of the central patch is randomly assigned
to one of the six shapes illustrated on the bottom of die display. F, The bar graphs plot percentage correct responses of the total number of trials for E.W. and
A.F. and for die normal controls together with the standard deviation for the normal group and die SE of die patients.

Cerebral Cortex Sep/Oct 1994, V 4 N 5 565

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E.W.
A.F.

B

1

*

*
*

£

chance

N <- S

E.W.
A.F.

S

Controls (n = 26)

2

0

3
4
Speed

i
i
0%

i
50%

100%

Controls
(n=16)

E

E.W.

A.F.

100i

chance
E.W.
A.F.
Controls

(n-ll)

20

40

60

80

100

% Structure
Rgors 8. Motion tasks. A Local speed discrimination: a schematic representation of the stimuli employed. The display consisted of two sparse random-dot fields
each displayed in a rectangular aperture subtending 4° x 2.5°. Within each aperture the dots, plotted here as vectors, move in random distributed directions
with constant speed. The observer's task is to decide in which of the two apertures the dots move faster. B, Results for LW., AJ., and normal controls. The
graphs plot the percentage of correct answers as a function of the speed ratios between the two apertures. C, Motion coherence: schematic representation of
the dynamic random-dot stimuli employed. Each stimulus presented dots in rapid succession and each dot survived for a brief period of time before being
replaced. In the 0% correlation case [left the replacement dots were plotted at random locations within the aperture so that the dot field appeared as twinkling
visual noise without motion in any single direction In the 100% correlation case (right) each dot was replaced by a partner with a constant offset in space and
time, so that the dot field appeared to move in a single coherent direction. For intermediate states, such as that for 50% correlation displayed in the middle, a
prespecified percentage of the dots carried the correlated motion signal while the remaining dots provided a dynamic masking noise. The stimulus is presented
2° to the left or to the right of a fixation mark. A four-alternative forced-choice procedure was used to determine the threshold correlation for which observers
could successfully discriminate the direction of motion. D, The graph plots die threshold correlation for normal controls and E.W and A.F £, Structure from
motion, schematic representation of the two dynamic random-dot fields employed. On the left is portrayed the structured stimulus generated by the

565 Functional Segregation of Color and Motion * Vaina

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i

chance when normal observers and E.W. were performing better than 90% correct.

E.Ws score was normal for presentation in either
visual field. A.F., on the other hand, had elevated
thresholds for motion coherence for stimuli presented
in either visual field (Fig. BD). It is possible that this
deficit demonstrates a deficit of spatial integration of
motion signal, or an inability to filter out motion noise
(Baker et al., 1990; Pasternak et al., 1991; Pasternak and
Merigan, 1994).
3D Structure from Motion: The Rotating Cylinder
This experiment examined the patients' ability to recover 3D information from the relative motions of elements in the changing 2D image. [A similar task has
been used by Siegel and Andersen (1988) in monkeys
with MT lesions.] The display (Fig. 8£) consisted of
two dynamic random-dot kinematograms presented simultaneously, each subtending an area of 3° X 3°. Each
kinematogram was composed of 128 dots with an average point density of 14 dots/degree2, which ap-

Biological Motion Recognition
Johansson (1973) demonstrated the sufficiency of biological motion for form perception by placing lights
on the points of articulation of a human actor in darkness. The form of such an actor remains obscure while
the person is static or even while the light points
translate without any articulation. But as they articulate, the shape becomes immediately obvious. The
only information available in the display is provided
from the dynamic source alone. The display shows
only the pattern of lights attached to the joints of the
human actor during the performance of some prototypical actions: walking, stair climbing, riding a bicycle,
push-ups, two men walking, shaking hands, and hugging. The stimulus was presented to E.W. and A.F. on
a videotape using scenes from the original Johansson
movie. Both E.W and A.F. had perfect scores on this
test. They quickly recognized that the movement of
the lights portrayed a man and correctly identified all
the actions.
Topographic Disorientation
E.W s topographic memory was very poor. His family
described that when going for a walk in the neighborhood, E.W. could not remember how to get back

orthographic projection at a square-shaped random-dot velocity field onto a transparent cylinder that is rotated. On the right is portrayed a velocity field
representing the unstructured stimulus. The dot survival time and the percentage of structure in the structured stimulus were independently varied in the display.
F Comparison of ELW.'s and A_F.'s results with normal controls where percentage of structure was varied in the cylinder (point lifetime was constant at 400 msec).

Cerebral Cortex Scp/Oct 1994, V A N 5 567

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Motion Coherence
This task is adapted from Newsome and Pare (1988)
and the specific test used here is described in detail
in Vaina et al. (1990a). In summary, the stimuli were
dynamic random-dot kinematograms with a correlated
motion signal of variable strength embedded in motion noise. The strength of the motion signal, that is,
the percentage of the correlated dots moving in the
same direction, varied from 0% to 100%. For strengths
less than 100%, the dots carrying the motion signal
were embedded in a field of dots moving in random
directions. The direction of signal flow could not be
determined by following a single dot because the signal and the noise dots were spatially intermingled, and
between frames varied in assignment between the signal and the noise group. Thus, to do the task, the subject was required to detect the global direction of
flow, which involved integrating the motion signal
over the whole display. The percentage of signal intensity for which a subject could reliably discriminate
the direction of motion, up, down, left, or right, constituted the threshold (Fig. 8C). The stimulus consisted of a dynamic random-dot display presented in a
square 10° X 10° aperture situated at 2° left or right
of a white fixation mark. The subject is instructed to
maintain fixation on the fixation mark for the entire
testing period. Dot density used in this test was 2
dots/degree2. [Other densities were explored but the
range of densities used did not have an effect on performance. This is consistent with the findings of
Downing and Movshon (1989) in the similar displays.]
The speed of motion, denned as a function of the distance a dot is displaced between successive frames,
was 3°/sec.

peared to be optimal for the normal control group. At
the end of its lifetime the point disappeared and was
replotted at a new random location on the screen
(within the boundary of each display) and it began a
new trajectory. One kinematogram (structured display) portrayed the dots painted at random location
on the orthographic projection of a transparent rotating imaginary cylinder, and the other (unstructured)
showed a pattern of scrambled velocities. The angular
velocity of the cylinder rotating around its vertical
axis was 30°/sec. The maximum distance traveled by
a dot between two consecutive frames was 4.3 arcmin. The dots had limited point-lifetime (400 msec).
The percentage of structure, that is, percentage of dots
actually projected on the imaginary surface of the rotating hollow cylinder, varied as follows: 100%, 90%,
80%, 70%, 65%, 42%, 27%, 11%. The spatial positions
(left vs right) of the structured field and the unstructured field were randomly assigned. There were 20
trials for each condition (in total 160 trials).
For high percentage of structure in the cylinder
both patients scored very well on this task (Fig. 8F).
Both patients scored close to the normal control
group for fractions of structure in the cylinder above
42%. As the proportion of noise increased, the patients' performance dropped significantly. Since for A.F.
this was similar to the level of noise that he could
tolerate in the motion-coherence task, it is possible
that his structure-from-motion recognition was limited
by his ability to cope with noise in the stimulus.

Table 1
A qualitative summary of E.W.'s and A.F. s results on the static psychophysical
tasks

Table 3
A qualitative summary of LW.'s and A.F.S results on the visual recognition
tasks

Test results

E.W.

A.F.

Test results

E.W.

A.F.

Contrast sensitivity
Shape detection
Shape discrimination
Farnsworth-Munsell test
Wavelength discrimination
Photopic spectral sensitivity
Color naming
Binocular stereopsts
Line orientation
Point location
Spatial location

Normal
Normal
Impaired
Impaired
Impaired
Impaired
Impaired
Normal
Normal
Normal
Normal

Normal
Normal
Normal
Normal
N/A
N/A
Normal
Impaired
Impaired
Impaired
Impaired

Face recognition
Matching silhouettes to objects
Gollin pictures
Unusual views
Object recognition (drawings)
Object recognition (objects)
Memory for objects
Topographic memory

Impaired
Normal
Impaired
N/A
Impaired
Impaired
Impaired
Impaired

Normal
Normal
Impaired
Impaired
Normal
Normal
Normal
Normal

home or which street to turn on, and that when they
returned to their street he did not recognize it as familiar. He thought that the neighbor's house, a few
doors down the street, was theirs. In general he failed
to use familiar landmarks to find his way around. In
contrast, A.F. had no deficits in this area.
Discussion
The focus of this study was the comparison of results
on visual-cognitive and psychophysical tasks in two
patients with focal bilateral brain lesions. The patients'
results on the psychophysical tasks are summarized in
Tables 1-3.
The results show that these patients present a clearcut dissociation of deficits at the earlier stages of visual processing. E.W. was impaired on color and form
discrimination, but not on motion or stereopsis. He
was also impaired on perceptual categorization and
recognition of objects and faces, but he could recognize correctly actions, even in degraded stimuli (biological motion task). A.F. was impaired on spatial relations, binocular stereopsis, and motion, but not on
form and color discrimination. He was also impaired
on aspects of perceptual categorization, but faces and
object recognition were normal, as was his ability to
recognize biological motion.
In both patients localization of lesions by MRI
Table 2
A qualitative summary of E.W.S and A.F. s results on the motion tasks
Test results

E.W

A.F.

2D form from motion
Boundary by direction difference
2D form from speed difference
Speed discrimination
Motion coherence
3D structure from motion
Biological motion

Normal
Normal
Good
Normal
Normal
Normal
Normal

Normal
Good
Impaired
Impaired
Impaired
Normal
Normal

"Good," patient's results are below those of the normal controls, with a statistical significance of the difference in the range of 0.05 < p < 02.

Functional Segregation of Color and Motion • Valna

showed involvement of the visual association cortex.
A.Fs lesions were relatively dorsal, involving the parietal-occipital-temporal junction bilaterally. He has severe motion deficits. PET scan studies done by Zeki
and his collaborators (Zeki, 1991; Watson et al., 1993)
suggest that the region activated during the perception of movement in humans coincides with the
heavily myelinated region labeled by Flechsig (1920)
as area 16. This region probably includes the homolog
of the macaque MT complex and higher motion-responsive areas (e.g., MST, FST). Several studies suggested that the human homolog of area MT corresponds to the occipital-parietal-temporal fossa (area
PTOF of Polyak, 1957), or in Brodmann terms to the
junction of the area 19 and the inferior portion of area
37 (Miezin et al., 1987; Tusa and Ungerleider, 1988;
Vaina et al., 1989; Clarke and Miklossy, 1990). The location of A.Fs lesion is consistent with his symptoms,
which illustrate misperception of spatial position of
visual stimuli and the ensuing inability to relate positions of objects in visually represented space. This deficit was manifested both visually and by reaching under visual guidance. Taken together these deficits are
components of the syndrome of visual disorientation
found in patients with bilateral posterior parietal lobe
damage (Holmes, 1918a,b). Although visual motion
mechanisms are severely impaired in A.F., color and
form perception and object and facial recognition are
normal.
E.Ws lesions were also bilateral and symmetric, affecting the occipital and ventral medial temporal
structures. The location of his lesions is consistent
with lesion locations leading to achromatopsia and associated prosopagnosia in other human patients. Recent PET studies confirmed that the ventromedial surface, particularly the occipitotemporal junction, is
implicated in face recognition (Damasio et al., 1982;
Sergent et al., 1992). Specifically, the authors suggest
a crucial role for the right parahippocampal gyrus in
linking perceptual and memory information about faces.
Thus, on both anatomical and behavioral grounds it
is likely that E.W7s and A.Fs lesions involved different
streams of processing in the extrastriate cortex: E.Ws
lesion can be associated with the ventral visual system,
while A.Fs lesion may be associated with the dorsal
system.

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"N/A," task was not administered to the subject "Normal," patient's results
are not statistically different from the results of the normal controls; "Impaired," patient's scores are significantly below those of the age-matched
normal controls [p < 0.05)

E.Ws impaired fine discrimination of shapes (Fig. 3)
suggests a selective partial deficit of visual analysis,
prior to the perceptual categorization level. His performance on the two smaller ratios of the shape discrimination test was similar to that of Mr. S reported
by Efron (1968). Mr. S is considered one of the classical cases of apperceptive agnosia. Interestingly, Efron
commented that "the various tasks that Mr. S. cannot
perform are the identification of objects, geometrical
figures, letters, numbers, and people. Is there one attribute of these various existents which must be perceived for the identification? The answer is inescapable: they are all identified by the attribute of shape."
Efron concluded that the ability to discriminate between shapes is necessary for recognition and identification.
E.W. also failed to recognize letters, drawings, and
pictures of objects presented from prototypical, front

views. His descriptions of objects presented as photographs or drawings were always guided by the identification of a part (the ears or the legs of an animal)
and then by trying to associate them by inference to
an object from a small repertoire of objects that he
could remember (e.g., he identified most animals as
dogs). This is similar to Mr. S, who "knowing the entire
repertoire. . .could deduce which object was before
him from the attributes he could identify," and to the
patient described by Landis et al. (1982). It is possible
that, at least in part, E.Ws deficits of face and visual
object recognition and his inability to read can be explained by an apperceptive disorder of static shape
discrimination. His partial achromatopsia but normal
motion perception and normal binocular stereopsis
strongly indicate that his lesion selectively involved
the ventral, occipital-temporal pathway. Moreover,
E.Ws slight deficit on form from speed differences is
consistent with the recent results of a study by Britten
et al. (1992), which showed that in monkeys with inferotemporal lesions the discrimination of familiar
forms (learned prior to the lesion) denned by motion
cues was somewhat impaired.
It is thus probable that E.W. suffered from visual
apperceptive agnosia, defined as impaired recognition
due to a deficit of perceptual categorization and percept formation despite intact early sensory processing
(lissauer, 1890), or as "a disturbance of the synthesis
or fusion of impressions in a single modality" (Iiepmann, 1908). Numerous cases of apperceptive visual
agnosia have been described in the literature (see
Griisser and Landis, 1991, for a review), and most
agree that it is a syndrome with devastating consequences for the patient, leaving him in a condition of
severe perceptual handicap. E.W. described suggestively how he perceived the world: "The impression I
have is that if you only turn the light on I would see,"
referring to his inability to "see" objects and faces so
that he recognizes them.
Impaired Binocular Stereopsis, Motion and
Spatial Perception: A Deficit in the
Dorsal Pathway?
A.F. and E.W. were tested on six motion tasks: 2D form
from motion, 2D form by relative motion, speed discrimination, motion coherence, 3D structure from motion, and biological motion recognition.Table 1 shows
that E.W. performed very well on these tasks while
A.E was very impaired on four of the six motion tasks.
On the speed discrimination task A.F. could not discriminate speed ratios smaller than 3, which is within
the range of the performance of patients with right
occipital-parietal lesions reported in Vaina et al.
(1989). On the 2D-form-by-relative-motion task he
scored at chance level, which is well below the range
of the right-occipital parietal group, who were themselves impaired on this task. He was also severely impaired on the motion coherence task, and showed a
mild impairment on the 2D-form-from-motion task. In
a striking departure from these findings, he had no
problems on the structure-from-motton task. His good
performance on this task was surprising since A.F. had
Cerebral Cortex Sep/Oct 1994, V 4 N 5 569

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Achromatopsia and Impaired Shape
Discrimination: A Deficit in the
Ventral Pathway?
One might perhaps argue that E.Ws complaint that
the "world looks as if it was in deep twilight, even on
a sunny day" and was "devoid of color" can be explained by preferential sparing of magnocellularstream cortical areas, which might lead to such a perception, since there is evidence that the rod signals
are directed preferentially to the magnocellular LGN
layers (e.g., Purpura et al., 1988), and magnocellular
cells are poor at color discriminations (e.g., Derrington et al., 1984). However, E.Ws photopic spectral
sensitivity curve showed no hint of rod intrusion.
E.Ws wavelength discrimination was significantly impaired, particularly on the short-wavelength end of the
spectrum, but he could discriminate one end of the
spectrum from the other. He correctly reported red,
but was unable to identify blue, gray, or greens. This
partial sparing of color vision has been previously reported in achromatopsia (Meadows, 1974; Victor et al.,
1989).
In a series of studies Zeki (summarized in his recent
monograph, Zeki, 1993) argued that total (bilateral)
achromatopsia is a result of bilateral damage to area
V4 of the human brain. MRI studies (Kolmel, 1988)
and brain autopsy in achromatopsic patients (Meadows, 1974; Damasio et al., 1982) implicate the ventral
occipital cortex in the deficit, which was indeed involved in E.Ws lesion. Moreover E.Ws loss of upper
visual field perception (Meadows, 1974) and his mild
deficit on the shape discrimination task are consistent
with an involvement of V4 in the lesion. However, if
the human homolog of V4 is anything like the macaque V4, E.Ws color deficits cannot be accounted
for only on the basis of such a lesion. There is strong
evidence that lesions of macaque area V4 produce
only mild deficits on form discrimination and wavelength discrimination tasks and it has been suggested
(Dean, 1976;Cowey, 1982;Heywood and Cowey, 1987;
Schiller et al., 1990; Heywood et al., 1991; Schiller and
Lee, 1991; Schiller, 1993) that perhaps V4 is concerned
with color constancy rather than wavelength discrimination, with form, and with perceptual context.

A.F. was severely impaired on spatial perception
tasks and, despite his normal object recognition, was
severely impaired at identifying degraded structural
descriptions of familiar objects (as shown by his poor
performance on the unusual-views test and on the
Gollin pictures). In contrast, E.Ws spatial perception
abilities were normal. His failure on the Gollin pictures
test can be accounted for by his impaired object recognition discussed above.
hi conclusion, A.F. was selectively impaired on aspects of visual motion analysis, discrimination of spatial relations, and binocular stereopsis, which are tasks
engaging visual processes along the dorsal pathway.
Asked what disturbed him most, A.F. said, "I never
know exactly where things are, and when I walk I
often wonder whether all the drivers in [his town]
are drunk or high, and whether on top of the stroke
I'll have now someone crashing into me. It always
seems that they are going faster than they actually do."
A System for Identification from Motion?
The anatomical segregation of the patients' lesions is
clear-cut and shows good evidence of two complementary classes of visual defects, one associated with
lesions along the ventral system and the other asso570 Functional Segregation of Color and Motion • Vaina

ciated with lesions corresponding to the dorsal system. E.W. could not recognize objects or faces, but he
never failed to identify correctly objects in motion or
even to recognize facial expression from pantomime.
Recognition of biological motion and structure from
motion were normal. A.F. was severely impaired on a
large class of motion and spatial tasks, but his performance was normal on the recognition of biological
motion and on the 3D-structure-from-motion task. The
spared recognition and identification from motion in
both patients are surprising. It suggests the existence
of a higher-level visual motion system involved in motion recognition that does not require the motion
pathway to area MT. Indeed, cells sensitive to particular "biological" types of motion have been found
within the STS in STP (Bruce et al., 1981; Perrett et
al., 1985). It is possible that in addition to supplying
motion information useful to the posterior parietal
cortex for visuomotor tasks and for navigation, the
dorsal stream also supplies to the anterior temporal
lobe motion information useful for recognition of objects and actions. Our previous findings in patients
with right hemisphere lesions of a dissociation between motion analysis and motion recognition (Vaina
and LeMay, 1992) support this hypothesis. In an elegant recent study, Boussaoud and Ungerleider (1990)
showed that, in the macaque, areas specialized for various stages of motion analysis, such as MT, MST, and
FST, not only send inputs to the ventral and dorsal
system, but also supply strong input to the STS. Thus,
this area may constitute a further stage in the system
underlying motion, and specifically it may be involved
in recognition. MT was clearly spared in E.Ws lesion,
and thus information could arrive at the STS by and
large avoiding the ventral system. MT appeared to be
involved in A.Fs lesion, but probably not MST or FST,
and motion information could reach the STS by an
alternate route, via PO or V3A, for example. Another
possibility is that motion information necessary for
recognition is routed to STS through V4 and the inferior temporal cortex (IT)
Notes
1. The Vision Contrast Test System (VCTS) consists of six
rows of 1-cm-diameter patches of gratings obtained from
photographing computer-generated sine wave gratings, each
row having patches of different spatial frequency: 1.5, 3, 6,
12, and 18 cycles/degree. Each row contains, from left to
right, one sample patch and eight test patches. The contrast
of these patches ranges from 0 contrast to contrast above
and below normal threshold in roughly 0.1 log unit steps.
The gratings are tilted in one of the three orientations: - 15°,
0°, +15° The contrast and orientation of test patches are
randomized for each row to control for guessing. The observer holds the chart at 56 cm distance positioned vertically
at eye level and contrast sensitivity is assessed for each eye
separately. The observer is shown a high-contrast sample
grating at the three possible orientations. The task is to determine whether each sequential grating patch on a specific
row was blank or at a particular orientation. The procedure
is repeated for the remaining rows of grating patches The
test method is a four-alternative forced-choice procedure.
Contrast sensitivity threshold is determined from an answer
key provided by VCTS on the basis of an extensive data base
of results from a large number of observers.
This research was supported by N1H Grant EY-RO1-07861

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impaired several early motion mechanisms, such as
speed discrimination and motion coherence, which
according to current theoretical models may underlie
the computation of structure from motion (LonguetHiggins and Prazdny, 1980; Koenderink and van
Doom, 1986;Treue et al., 1991, 1994). In our reports
(Vaina et al., 1990a,b) on A.Fs motion perception, we
suggested that either these cues are not necessary and
A.F. might have used different cues (e.g., position), or
that structure-from-motion tasks may not require the
precision of motion signals implied by the many computational theories relying on velocity difference. Even
more surprising was A.Fs normal performance on the
biological motion test. We suggested (Vaina et al.,
1990a,b) that A.F's perfect performance may be explained by the existence of a separate motion pathway specialized for object recognition and perception
of action. There is evidence from physiological studies
in the monkey that this type of motion may be perceived in the rostral portion of the superior temporal
sulcus (STS) (Bruce et al., 1981; Perrett et al., 1985).
Our own data from patients with anterior temporal
lesions are consistent with this physiological hypothesis (Vaina and LeMay, 1992; Vaina, unpublished observations). The MRI study suggests that A.Fs lesion
involves the putative human homolog of MT, but that
it does not directly involve higher-order areas such as
MST or STP (superior temporal polysensory area). This
is consistent with his deficits on speed discrimination
(Pasternak and Merigan, 1994), motion coherence
(Newsome and Pare, 1988), and impaired smooth pursuit (Wurtz et al., 1990). Indeed, A.Fs configuration of
deficits selective to aspects of motion perception is
similar to the deficits previously reported in patients
with lesions selectively involving the dorsal (occipitalparietal) pathway (Vaina, 1989; Vaina et al., 1991; Regan et al., 1992).

and McDonnell-Pew Foundation Grant T89-01245-017.
Thanks are due to Drs. Roger Tootell and Nikos Logothetis
for the help with the evaluation of color vision of patient
E.W., to Dr. Marjorie LeMay for help with the interpretation
of the MRI scans of the patients, and to Dr. Don Bienfang for
sharing the interpretation of the neuro-ophthalmologicai
findings. I thank Hillary Rodman, Charles Gross, and Alan
Cowey for critical comments on an early version of the
manuscript.Jeremy Lambert and Ivans Chou helped with the
manuscript preparation.
Correspondence should be addressed to Dr. Lucia M. Vaina,
Intelligent Systems Laboratory - Vision Research, ERB-331,
Department of Biomedical Engineering, Boston University, 44
Cummington Street, Boston, MA 02215.

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