Case report

Conscious visual
abilities in a patient
with early bilateral
occipital damage
Deborah Giaschi* PhD, Associate Professor, Department of
Ophthalmology, University of British Columbia (UBC);
James E Jan MD FRCP(C), Professor;
Bruce Bjornson MD FRCP(C), Clinical Assistant Professor,
Department of Pediatrics, UBC;
Simon Au Young MSc, Research Assistant, Department of
Pediatrics, British Columbia’s Children’s Hospital;
Matthew Tata MSc, Graduate Student, Department of
Psychology, UBC;
Christopher J Lyons MB BSc FRCS(C), Associate Professor,
Department of Ophthalmology, UBC, Vancouver, British
Columbia, Canada.
William V Good MD, Clinician-Scientist, Smith-Kettlewell
Eye Research Institute, San Francisco, CA, USA.
Peter K H Wong BEng MD FRCP(C), Professor, Department
of Paediatrics, UBC, Vancouver, British Columbia, Canada.
*Correspondence to first author at Department of
Ophthalmology, BC’s Children’s Hospital, Room A146,
4480 Oak Street, Vancouver, BC, V6H 3V4, Canada.
E-mail: giaschi@interchange.ubc.ca

A 21-year-old male presented with occipital lobes that were
extensively damaged by bilateral infarcts present at birth. The
absence of the striate cortex was confirmed with anatomic and
functional MRI and high-resolution EEG. His cortical visual
impairment was severe, but he retained a remarkable ability to
see fast-moving stimuli. Horizontal optokinetic nystagmus
could be elicited from either eye. Resolution acuity was close
to normal providing the patient was allowed to move his head
and eyes. The direction of motion in random-dot patterns could
be discriminated with perfect accuracy at speeds above 2 deg/s,
and the patient reported that he could ‘see’ the motion at fast
but not at slow speeds. This conscious residual vision for
motion is known as Riddoch’s phenomenon, but it has never
been reported in the complete absence of the striate cortex.
Functional neuroimaging revealed activation that was outside
the motion-responsive regions of the extrastriate cortex. This
case demonstrates remarkable plasticity in the human visual
system and may have implications for understanding the
functional organization of the motion pathways.

772

Developmental Medicine & Child Neurology 2003, 45: 772–781

Damage to the striate cortex (Brodmann area 17) produces
regions of blindness in the visual field. The extent and density of the visual field defects, measured with standard perimetry, reflect the site and completeness of the lesion. Conscious
vision, therefore, is classically believed to require intact striate cortex. Three decades ago, it was noted that humans with
damage to the striate cortex may demonstrate residual visual
functions within their corresponding clinically blind visual
fields, but with no acknowledged awareness (Pöppel et al.
1973, Weiskrantz et al. 1974). Weiskrantz and his colleagues
termed this phenomenon ‘blindsight’. When forced to guess,
a variety of visual capacities have been demonstrated, including localization of targets by saccadic eye movements; pointing or reaching; detection of static, flickering, or moving
targets; and discrimination of stimulus orientation, direction
of motion, colour, or simple shapes (reviewed in Weiskrantz
1996, Stoerig and Cowey 1997). More recently pupillary reflexes have been used to indicate residual processing of visual
stimuli in the absence of awareness (Weiskrantz et al. 1998).
The possibility that blindsight could be caused by light scattered into the intact part of the visual field has been discussed
(Campion et al. 1983), but this artifact was controlled for in
more recent studies (reviewed in Weiskrantz 1996).
There are a number of retinal projections that could mediate vision in the absence of the striate cortex (reviewed in
Stoerig and Cowey 1997). Two projections in particular have

been implicated in blindsight (Fig. 1): the projection from the
superior colliculus to ipsilesional extrastriate cortex via the
inferior pulvinar and the direct projection from the interlaminar regions of dorsal lateral geniculate nucleus to ipsilesional extrastriate cortical areas (Cowey and Stoerig 1991). It has
also been suggested that with unilateral lesions the intact
contralesional hemisphere mediates blindsight via transcallosal or intertectal connections (Baseler et al. 1999, Ptito et
al. 1999), particularly in cases of surgical hemispherectomy
(Wessinger et al. 1996, Bittar et al. 1999). Alternatively, blindsight abilities have been attributed to intact areas of damaged
striate cortex in the lesioned hemisphere (Campion et al.
1983, Fendrich et al. 1992), but there is convincing evidence
that this is not so in all cases (Weiskrantz 1996, Stoerig et al.
1998, Kleiser et al. 2001). In support of a non-geniculostriate
basis for blindsight, functional neuroimaging studies found
activation in the superior colliculus, pulvinar, and extra-striate cortical areas V3/V3a and V5 by stimuli presented in the
blind visual field (Sahraie et al. 1997, Stoerig et al. 1998,
Bittar et al. 1999, Ptito et al. 1999).
Regardless of the specific pathways involved, blindsight
implies that conscious awareness of visual stimuli requires
an intact striate cortex and that cortical activity in other visual
areas cannot sustain conscious vision. Motion perception
may be the exception because some degree of awareness for
rapidly moving stimuli has been reported (reviewed in Zeki
and ffytche 1998). This residual vision for motion is also
known as Riddoch’s phenomenon after the British neurologist who first characterized it (Riddoch 1917). Riddoch examined the visual abilities of 10 soldiers with visual field defects
from occipital wounds. Five of these patients could detect
the presence of motion within their blind fields without
being able to characterize the other attributes of the stimulus. There are several more recent reports of patients with
conscious perception for various types of motion stimuli on
detection (Blythe et al. 1987, Azzopardi and Cowey 2001),
speed discrimination (Barbur et al. 1980, Mestre et al. 1992,
Morland et al. 1999), and direction discrimination (Perenin
1991, Mestre et al. 1992, Benson et al. 1998, Schoenfeld et al.
2002) tasks. Thus, it seems that activity in brain regions outside of striate cortex must be sufficient for mediating awareness of motion.
Blindsight refers to those functions occurring with no
conscious awareness, but in residual vision some conscious
perception is registered. Blindsight and residual vision may
be expressions of similar neural mechanisms with earlier
damage leading to more awareness (Blythe et al. 1987).
Alternatively, blindsight and residual vision may represent
independent processes (Weiskrantz et al. 1995). Residual
motion perception has been attributed specifically to cortical area V5 based on the pattern of activation by moving stimuli in blind regions of the visual field (positron emission
tomography: Barbur et al. 1993, electroencephalogram [EEG]:
ffytche et al. 1996, magnetoencephalography: Holliday et al.
1997, functional magnetic resonance imaging [MRI]: Zeki
and ffytche 1998, Schoenfeld et al. 2002) and the lack of
residual motion perception in persons with a hemispherectomy who lack V5 (Perenin 1991, Azzopardi et al. 2001). One
preliminary study reported a shift in activation from the
superior colliculus and medial prefrontal cortex when the
patient was unaware of the moving stimuli, to prestriate and
dorsolateral prefrontal cortex when the patient was aware of

the moving stimuli (Sahraie et al. 1997).
In all previous cases of residual motion perception, however, there was at least some intact striate cortex in the ipsilesional or the contralesional hemisphere which could be
responsible for residual visual abilities. Previous reports on
patients with total bilateral destruction of area 17 indicate
total permanent visual loss (Brindley et al. 1969, Celesia et al.
1991). In a study of nine patients with cortical visual impairment due to bilateral occipital lesions, residual motion perception was observed in only four patients (Celesia et al.
1991). Each of these patients had functional remnants of area
17 confirmed by CT and SPECT. The remaining five patients
with no residual vision had more extensive lesions and no
functionally intact regions. It was concluded that the extrageniculostriate visual system is functional in humans but is
not capable of providing conscious visual perception. A
recent review of blindsight results in human and non-human
primates concluded that ‘we must await an unequivocal
demonstration of conscious vision in the absence of all striate
cortex’ to resolve this issue (Stoerig and Cowey 1997, p 555).
Here we present a case that we believe provides such a
demonstration.
This case report is of a young adult whose occipital lobes
were extensively damaged by infarction present at birth. His
case study at age 6 years has previously been published (Jan
et al. 1986). At the age of 21 years, our patient underwent
extensive clinical, psychophysical, electrophysiological, and
neuroimaging studies at British Columbia’s Children’s Hospital
over a 3-day period.
Case report
HISTORY

This 21-year-old right-handed white male was born weighing
3kg at 43.5 weeks, by dates. The pregnancy was complicated by
maternal toxemia and weight gain of 21.4kg. Labour was
remarkable for fetal distress; delivery was by high forceps. The
infant required initial resuscitation and had seizures within a
few hours of birth. Apgar scores were 1, 4, and 9 at 1, 5, and 10
minutes respectively. He required tube feeding for a few days
before discharge with a diagnosis of hypoxic brain insult.
Subsequently, he has been in generally good health, except for
occasional seizures treated with carbamazepine and topiramate. Early developmental milestones were age appropriate; he
walked and began to speak words at 1 year of age. However, by 5
months of age his parents suspected visual impairment. At the

V2

Retina

LGN

V1

V3
V4

Superior
colliculus

V5
Pulvinar

Figure 1: Projections from retina to extrastriate cortex (V2,
V3, V4, V5) that survive damage to striate cortex (V1) in
macaque monkeys and have been implicated in cases of
blindsight in humans. LGN, lateral geniculate nucleus.

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773

Direction discrimination (% correct)

age of 2 years, he was referred to the visually impaired program
and received a diagnosis of congenital cortical visual impairment (a term that is gradually replacing cortical blindness).
Electroretinograms, most recently obtained at the age of 3
years, were normal. Full-field flash visual evoked potential
results obtained at the same time and more recently, however,
showed no occipital responses. Repeated EEGs showed a slow
posterior background without alpha rhythm, no responses on
eye opening and closure, and occasional epileptiform activity.
Psychological testing was done most recently at the age of
11 years. The following verbal scaled scores were obtained
on the Wechsler Intelligence Scale for Children–Revised
(Wechsler 1971): Information (9), Similarities (8), Arithmetic
(8), Vocabulary (7), Comprehension (5). Scores between 9 and
11 are considered average for normally sighted children. Our
patient appeared to have good auditory memory skills and
somewhat impaired verbal reasoning. He received his education in the mainstream school system, with supportive care for
blind students, and although he was noted to have some learning difficulties, he graduated from high school.
His past eye and neurological examinations were repeatedly normal. Recognition acuity was very difficult to measure
and he was considered to have minimal ‘count-fingers acuity’. He was able to name a few colours; could not read, write,
or sign his name; could not recognize himself or others in
photographs; and appeared to have minimal visual concepts
about his environment and even described his dreams without visual content. With great difficulty, he identified a few
simple shapes, by scanning them repeatedly, approximately
5cm away from his eyes. He could appreciate size differences
and count coins, without touch, only when they were widely
separated. When asked to draw a picture of himself, he needed to touch his face and body. The resulting figure was not
recognizable. In school he was taught Braille and learned to
use a cane when travelling.
Since childhood, the patient behaved as profoundly visually impaired except for a remarkable ability to perceive
rapid movements. He participated in various ball games and
running events. He rode a bicycle and safely avoided people,

100

Patient

CURRENT CLINICAL EXAMINATION

Our patient’s neurological examination at 21 years of age
was essentially normal. His pupils were equal in size and
responded normally to light. Cycloplegic refraction was normal and his fundi showed no abnormalities, apart from slight
disc pallor. There was no indication of optic nerve atrophy
or hypoplasia. During conversations his head was flexed forward and he made no eye contact. There was no blink
response to threat. He could look at near objects without
nystagmus, but tended to fixate on a point just below them.
Visual fields were attempted but could not be evaluated
with Goldmann perimetry due to poor fixation. Kinetic
perimetry with a moving target (Mohn and van Hof-van Duin
1986) suggested extensive field loss, with sparing of the central 10 degrees. When the kinetic perimetry target was held
stationary, it could not be detected reliably anywhere within
the visual field.
Voluntary saccades were inaccurate and smooth pursuit
in all directions showed saccadic intrusions. His voluntary
up-gaze was limited. In the right eye, optokinetic nystagmus
to a moving stripe pattern was of equal amplitude with nasally and temporally directed movements. In the left eye the
temporally directed movements resulted in diminished
responses compared to nasally directed movements. Vertical
optokinetic nystagmus was essentially absent. Eye movement data are based on inspection.
He had light perception, but his recognition acuity on a
Snellen chart could not be determined from any viewing distance. Binocular resolution acuity for gratings was obtained
by two experienced examiners using the Teller Acuity Cards
(McDonald et al. 1985). The patient quickly located the stripes,
while his head and eyes rapidly moved from side to side. The
movements became more vigorous when the cards contained
higher spatial frequencies. The resolution acuity on several
occasions was 9.8 cycles/deg (20/66) at 38cm. This is within
normal limits for a 3-year-old child and well above the mean
newborn resolution acuity of 0.66 cycles/deg (Salomao and
Ventura 1995).
The patient was able to name the colour of large red,
green, and blue targets, but he made many errors in color
discrimination on the Quantitative Color Vision Test (large
stimuli, 16 hue; Precision Vision, IL, USA).

Comparison

90

PSYCHOPHYSICS

80
70
60
50

0

2

4

6

8

10

12

14

Dot speed (deg/s)

Figure 2: Percentage correct direction discrimination (up
or down) for a moving dot pattern as a function of speed.
Patient’s performance was similar to that of comparison
individuals for speeds above 3.5deg/s.

774

and parked and moving cars. He also played video games
that were based on movement.

Developmental Medicine & Child Neurology 2003, 45: 772–781

Motion perception was evaluated with computer-generated
movies of random dot patterns. The patterns comprised 1 pixel
(0.76 arc min) white dots on a black background (32dots/deg2).
The speed of the moving pattern was increased by increasing
the distance each dot moved between subsequent frames of
the movie. Each movie lasted for 850ms. The patient could verbally report the direction of motion (up or down) with 100%
accuracy at speeds between 3.5 and 10 deg/s (Fig. 2). At speeds
below 3.5deg/s his accuracy fell to chance performance. He
also reported that he could ‘see’ the motion at the faster
speeds but not at the slower speeds. Three adult volunteers
(one male, two females) with normal or corrected to normal
vision and a mean age of 25 years provided comparison data
on this task. Comparison participants could accurately judge
the direction of motion for speeds as slow as 0.05deg/s. At

speeds above 10deg/s, the perception of motion in a single
direction disappeared and accuracy decreased to chance performance. These results indicate that the patient had normal
direction discrimination for moderate to fast motion. He
showed no evidence of better than chance guessing at slower
speeds when he became unaware of the stimuli.
ELECTROPHYSIOLOGY

Visual evoked potentials were recorded with a Manscan system (Sam Technology, San Francisco, CA) using 128 scalp
electrodes applied with an elastic cap. The position of each
electrode was applied in accordance to the 10–10 convention,
digitized and coregistered with skull landmarks. Binocular

flash (transient EP, 1Hz rate, 2-minute duration) and checkerboard pattern-reversal visual stimuli were used (steady-state,
7.14Hz rate, 2-minute duration, full-field, 4deg square checks,
both black–white and red–green check). Due to the patient’s
impaired vision, there was difficulty with fixation, and numerous artifacts were present.
No reproducible response was present with flash stimuli
after averaging more than 100 flashes. Black–white checkerboard pattern reversal showed a small response that was
maximal in the right parietal area. This response was larger
with red–green colour reversals. There was a slow positive
response component at 81ms maximal over the right parietal
cortex, but possibly involving central–parietal and pari-

Frontal

Right
central

Left
central

Occipital

Figure 3: Topographic scalp voltage map at P6 (right parietal) electrode response peak, showing response maxima confined to right
parietal and occipital-temporal areas. This probably reflects islands of functional neuronal elements and is consistent with
sparing of extrastriate cortex in right relative to left hemisphere (see Figure 4). Normally, response peak should be maximal at
midoccipital area, decreasing laterally and anteriorly. Black, positive; white, zero.

Case Report

775

etal–occipital areas. There was no response over the occipital
region. Figure 3 shows the scalp electrodes superimposed
onto a topographic voltage map of the peak positive response
at the time of the positive peak at electrode P6 (lateral right
parietal). There were several maxima seen on the map rather
than a single large peak though all were at the right posterior
quadrant.
NEUROIMAGING

Whole brain anatomic and functional MRI data were acquired
at 1.5 T on a Picker Edge PowerDrive System. Anatomic MRI
showed occipital lobe destruction involving Brodmann areas
17, 18, and 19 in the left hemisphere and areas 17 and most of
18 in the right hemisphere (Fig. 4). Structures in the retinotectal pathway appeared to be intact. An additional area of
infarction was identified in the left frontal lobe.
Functional MRI was used to determine the brain regions
activated by slow and fast motion. A pattern of high-contrast

white dots was generated on a computer, projected onto a
screen at the end of the scanner and viewed in a mirror
mounted above the patient’s eyes. The dots alternated every
17.5s between fast radial motion (20deg/s) in and out from
the centre of the pattern, slow radial motion (2deg/s), and no
motion for a total run of 262.5s. The patient reported that he
could ‘see’ the fast motion but not the slow motion or the stationary dots. In a second run, a pattern-reversal (7.14 Hz)
high-contrast checkerboard alternated with a steady grey
field every 21s for a total of 252s.
Although area V5 appeared to be anatomically intact in the
right hemisphere (Fig. 5), no functional activation was observed
in this region. Instead, fast radial motion activated regions in
right premotor cortex (Brodmann area 6), right medial posterior cingulate (Brodmann area 23), right medial precuneus
(Brodmann area 31), left anterior superior temporal gyrus
(Brodmann area 38), and left and right posterior superior
temporal sulcus (Brodmann area 22; Fig. 6). There was no

a

b

Figure 4: Anatomic MRI images showing extent of patient’s lesions. There is (b) extensive gliosis in right occipital horn. Also
note (a) smaller infarct involving left frontal lobe. Slice number in each frame corresponds to horizontal section defined in
stereotaxic atlas of Talairach and Tournoux (1988).

776

Developmental Medicine & Child Neurology 2003, 45: 772–781

activation in any cortical region by slow motion or by pattern
reversal. These stimuli, however, activated posterior visual
areas in comparison participants (Fig. 7). These results
demonstrate a lack of functional striate cortex in our patient.
Discussion
Some aspects of this case are consistent with the complete
absence of striate cortex. Normal pupillary reactions to light,
normal electroretinograms, and normal appearance of the
fundi are usually seen in adults with pure cortical blindness
(Reese 1954, Bergman, 1957, Nepple et al. 1978) and in children with cortical visual impairment (Good et al. 1994). In
non-human primates, occipital lobe ablation results in transsynaptic neuronal degeneration and eventual optic atrophy
(Cowey 1974). This is rare in humans (Miller and Newman
1981) and we saw no evidence of transsynaptic degeneration
in our patient, but it has been documented in a 9-year-old child
with a 4-year history of visual involvement (Sachdev et al.
1990). The absence of a blink response to threat is also consistent with previous reports in humans (ter Braak et al.
1971) and in non-human primates (reviewed in Stoerig and
Cowey 1997). Smooth pursuit is often severely abnormal in
those with bilateral occipital lesions, particularly when
extrastriate areas are damaged as well (Good et al. 1994). It
has been suggested that an intact foveal representation in
occipital cortex is required for the development of smooth
pursuit (Rizzo and Hurtig 1989).
Other aspects of this case are unexpected and may change
our understanding of the functional organization of the
human visual system.
OPTOKINETIC NYSTAGMUS

The status of optokinetic nystagmus following striate cortex
damage is controversial. In animals, the passive subcortical
component of optokinetic nystagmus survives removal of
striate cortex and shows a strong directional preponderance
for movement in the temporal-nasal direction (reviewed in
Heide et al. 1990). In humans, this asymmetry is normal in
infants and disappears around the 20th postnatal week
unless the child has a binocular impairment. Optokinetic
nystagmus may be driven by indirect subcortical pathways
initially until the cortical pursuit mechanisms mature (reviewed
in Preston and Finocchio 1993). Following unilateral striate
cortex damage, passive optokinetic nystagmus often persists and the directional asymmetry is observed with large
lesions that extend to prestriate regions (Heide et al. 1990).
Optokinetic nystagmus is usually absent in cases of complete
bilateral cortical visual impairment (Bergman 1957, Brindley
et al. 1969, Aldrich et al. 1987, Celesia et al. 1991, Perenin 1991,
Dalman et al. 1997). There are a few reports of residual passive optokinetic nystagmus in bilateral cases (ter Braak et al.
1971, Mehdorn 1982, Heide et al. 1990, Celesia et al. 1991).
Directional asymmetry was observed in some of these cases,
but it could not be attributed exclusively to subcortical structures because the destruction of visual cortex was not complete (Mehdorn 1982, Heide et al. 1990). Smooth pursuit was
severely impaired in our patient and destruction of striate cortex was complete, therefore, his residual optokinetic nystagmus is likely to be subcortical in nature. The directional
asymmetry in his left eye only is consistent with the total
destruction of his left occipital lobe if extrastriate cortical
areas, which appear to be intact in his right hemisphere, make a

necessary input to the subcortical optokinetic nystagmus system (Mehdorn 1982, Heide et al. 1990, Perenin 1991).
COLOUR VISION

Residual colour naming has also been observed in children
with cortical visual impairment (Jan et al. 1987, Good et al.
1994). Colour vision was not routinely investigated in older
studies of individuals with cortical visual impairment. A few
persons with unilateral striate cortex damage show good
wavelength discrimination on forced-choice psychophysical
tasks (Stoerig and Cowey 1992, Brent et al. 1994) and with
pupillometric methods (Weiskrantz et al. 1999), but with no
conscious perception of colour. Functional MRI studies have
revealed activation by coloured stimuli of the superior colliculus (Barbur et al. 1998) and the posterior fusiform gyrus
(Goebel et al. 2001). Our patient appears to have poorer
colour perception yet better awareness than previous individuals studied, but further investigations are required.
GRATING ACUITY

Previous studies have shown that when the optic radiation
and/or striate cortex are damaged by various neurological
disorders, resolution acuity is impaired (Hertz et al. 1988,
Birch and Bane 1991, Ipata et al. 1994). Resolution acuity,
however, is usually less impaired than recognition acuity
(Sokol et al. 1983, Mayer et al. 1984, Kushner et al. 1995). It is
generally assumed that both resolution and recognition acuity reflect the intactness of the geniculostriate visual system.
However, the exact neurological substrate needed for each
type of acuity remains unclear. Damage to the geniculostriate
system may have a more detrimental effect on recognition
acuity that requires foveal retinal mechanisms than on resolution acuity that may use parafoveal or peripheral retinal
mechanisms (Mayer et al. 1984).
There is one previous report of a patient with unilateral
hemianopia and only slightly reduced resolution acuity of
15.8 cycles/deg in the blind hemifield (20 cycles/deg in the

Sylvian fissure

Superior
temporal
sulcus

Ascending
limb of ITS
Posterior
continuation
of ITS

Inferior
temporal
sulcus (ITS)

Figure 5: V5 is usually in region of ascending limb of
inferior temporal sulcus (ITS) and posterior continuation
of ITS (Dumoulin et al. 2000).

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777

normal hemifield; Weiskrantz et al. 1974). This finding and
our case report suggest that resolution acuity may be mediated
by extra-geniculostriate pathways. These pathways may be
particularly sensitive to moving stimuli given that head and
eye movements, which create stimulus movement on the retina, were required for our patient to locate the stripes.
MOTION PERCEPTION

As reviewed in the opening section, there are several previous
reports of residual direction discrimination, especially for
fast motion (Perenin 1991, Mestre et al. 1992, Benson et al.
1998, Schoenfeld et al. 2002), and V5 has been implicated as
the source. Residual motion perception is a rare finding in
individuals with striate cortex lesions (Barton and Sharpe
1997), and there are conflicting reports of its occurrence
within individual patients (Azzopardi and Cowey 2001). This
is the first report of such strong motion perception leading to
useful vision for locomotion in the total absence of striate cortex. Mestre and colleagues described an individual with cortical visual impairment who could move freely in a cluttered
environment and could discriminate different speeds and
directions of motion (Mestre et al. 1992). His striate lesions
were not complete, however, and his vision was intact in
foveal and parafoveal regions. Perenin (1991) described
three cases of complete cortical visual impairment, due to
bilateral lesions of striate cortex, and accurate direction discrimination on a forced-choice motion task. All three patients
described a vague sensation of a shadow moving in front
of them, but they could not describe what was moving.
Unfortunately, we have no information on the speed tuning of
this residual vision, and the completeness of the lesions was
not confirmed with MRI and/or functional neuroimaging.

LEFT

The speed tuning of our patient’s residual motion perception is consistent with the suggestion that signals from slow
moving stimuli reach V5 via the classical sequential route
through striate cortex, while signals from fast moving stimuli
reach V5 directly via a fast route from the pulvinar (ffytche et
al. 1995, Buchner et al. 1997). This suggestion is compatible
with the residual motion processing documented for slow
motion in humans with V5 lesions (Hess et al. 1989) and for
fast motion in humans with unilateral striate cortex lesions
(Barbur et al. 1993). Other aspects of this suggestion remain
controversial (Anderson et al. 1996, Azzopardi and Cowey
2001). Functional neuroimaging studies confirm that V5
remains active in the absence of V1 (Holliday et al. 1997, Zeki
and ffytche 1998, Goebel et al. 2001), but in these studies V5
was activated by slow as well as fast motion.
The V5 region appeared to be intact in our patient’s right
hemisphere, but this region was not activated by moving
dots at either speed in the functional MRI study. Fast-moving
dots produced activation that was outside the early motionresponsive regions of the patient’s occipital lobe. Given the
congenital nature of his injury, the activation in his brain by
fast motion may be due to atypical cortical functional organization. It is also possible, however, that the sites activated are
part of the normal network of motion-sensitive cortex. The
posterior superior temporal activation, in particular, may be
of importance to his residual motion perception. In nonhuman primates the superior colliculus and pulvinar project
to the posterior superior temporal gyrus (superior temporal
polysensory area), an area with direction-selective neurons
(Gross 1991). In human functional neuroimaging studies,
activation has been reported in this area in persons with normal motion processing (Ahlfors et al. 1999, Sunaert et al.

RIGHT

a
c
b

d

e

Figure 6: Functional MRI activation maps for patient. White regions are brain areas that were statistically more active
(p<0.05 corrected) when dots moved rapidly than when dots did not move. Arrows point to (a) right premotor cortex,
(b) right medial precuneus, (c) right medial posterior cingulate, (d) left anterior superior temporal gyrus, and (e) left and
right posterior superior temporal sulcus.

778

Developmental Medicine & Child Neurology 2003, 45: 772–781

e

1999) and in two patients with residual motion perception
(Zeki and ffytche 1998, Vanni et al. 2001).
VISUAL AWARENESS

Our patient’s abilities are different from those termed ‘blindsight’ in patients with striate cortex damage because he claims
to be aware of the stimuli he can accurately discriminate. His
vision may be similar to the residual vision known as Riddoch’s
phenomenon (Zeki and ffytche 1998), although he cannot
adequately describe his visual experiences and he has no
standard for ‘normal’ vision.

Figure 7: Functional
MRI activation maps for
two representative
comparison individuals
with normal vision
(both aged 21 years).
(a) Fast radial motion
versus stationary dots.
(b) Slow radial motion
versus stationary dots.
(c) Counterphaseflickering checks versus
a grey field. All three
stimuli normally
activate posterior visual
areas.

a

LEFT

He is also different from adults with visual anosognosia
(Anton syndrome) who deny blindness but are clinically blind
due to acquired bilateral occipital lobe damage (Bergman 1957,
Aldrich et al. 1987, Goldenberg et al. 1995). Such individuals
confabulate visual experiences and bump into things. Vision
often returns in those who survive (Argenta and Morgan 1998).
The fact that our patient’s brain damage occurred at birth
may be important. Human (Blythe et al. 1987, Payne et al.
1996) and animal studies (Spear et al. 1988, Moore et al. 1996)
have shown that blindsight and visual awareness can be
more developed when the damage to the striate cortex

RIGHT

b

c

Case Report

779

occurs early in life. In cats, this is attributed to a pathway
from the dorsal lateral geniculate nucleus to motion sensitive
regions of the cortex that normally retracts in adulthood but
is retained and expanded when the striate cortex is damaged
in infancy (Payne et al. 1996). A similar transient extra-geniculostriate pathway may be responsible for residual vision in
monkeys and humans, although no evidence for such a pathway has been found (Sorenson and Rodman 1999). It has even
been hypothesized that there is a period in infancy when visual awareness is partially due to activities in the superior colliculus (Sewards and Sewards 2000).
Conclusion
Conscious vision is reportedly impossible when striate cortex
is absent (Celesia et al. 1991). This is clearly not true in this
particular case in which the absence of striate cortex was confirmed based on the following set of findings: lack of alpha
rhythm on EEG, no flash or pattern-reversal visual evoked
potentials recorded over the occipital area including the
pole, no functional MRI activation by pattern reversal, and
no striate cortex tissue visible on anatomic MRI. (This is the
standard by which other patients have been assessed, but
post-mortem examination is required to prove the absence
of striate cortex.) Cortical area V5 has been implicated in
residual motion perception, however, we observed no activation in this area in our patient. Instead, we suggest that the
posterior superior temporal sulcus is involved in his residual
motion perception. This may represent a reorganization of
his visual system to compensate for the absence of striate cortex such that the functionally defined motion sensitive area
V5 is no longer in the expected anatomic location. The intact
network of cortical and subcortical motion-sensitive regions
in this patient appears to be sufficient for conscious perception. This represents a dramatic demonstration of the plastic
nature of the human brain during early development.
DOI: 10.1017/S0012162203001439
Accepted for publication 28th May 2003.
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