Inhibited head
movements: A risk
of combining
phoning with
other activities?

Abstract—Studies of cellular phone use while driving have attributed impaired performance to the distractions of conversation. We determined that
holding an inactive phone to the ear reduces the probability of eccentric head
positions, potentially indicating reduced ability to monitor the visual surround.
This effect may constitute a risk of cellular phone use independent of conversation and peculiar to handheld models.
NEUROLOGY 2005;65:754–756

Brian S. Oommen, MS; and John S. Stahl, MD, PhD

Cellular phone conversations are often conducted in
settings in which unexpected hazards may approach
from the side. Because the range of the eyes within
the head is only approximately ⫾50 degrees, using
vision to monitor the world for hazards requires a
person to repeatedly turn the head.1 Mechanical impediments to head rotation depress the propensity to
make head movements.2 We questioned whether
handheld cellular phones exert similar effects that
might constitute an unrecognized risk of these devices, one unrelated to distraction and hitherto unexplored in studies of the impact of phoning on driving
safety. To answer this question, we investigated
whether seated subjects reduce their propensity to
maintain eccentric head positions when holding an
inactive cellular phone to the ear.
Methods. Twenty-six subjects (10 women, 16 men, aged 22 to 64
years) were tested in the seated position in settings that featured
unobstructed fields of view exceeding ⫾90 degrees and fairly homogeneous distributions of objects that might attract a subject’s
visual attention. Horizontal position of the head with respect to
the world was measured by a miniature heading sensor (3DM-G,
Microstrain, VT) attached to the vertex of a conventional baseball
cap worn by the subject. Sensor output was sampled at 50 Hz on a
laptop computer, which logged each orientation value to a histogram spanning ⫾180 degrees in 0.1-degree “bins.”
Each experiment was divided into two 10-minute epochs in which
the seated subject either did or did not hold an inactive cellular
telephone to the preferred ear, as if to engage in a phone conversation. The order of the epochs was randomized. Subjects were instructed only to regard the world about them in a natural fashion.
Each experiment yielded two histograms representing the distribution of horizontal head-in-space orientation during each 10minute epoch. Histograms were individually scaled so that the
area under the curve was 1.0 and shifted so that the 50% point of
the cumulative area under the curve coincided with the histogram’s center (0 degrees) bin. Span of head orientation was initially quantified by the angular range of the histogram
encompassing the central 90% of the area under the curve (head
range). Additionally, we determined the effect of the phone on the

This article was previously published in electronic format as an Expedited
E-Pub on July 6, 2005, at www.neurology.org.
From the Department of Neurology, Louis Stokes Cleveland Department of
Veterans Affairs Medical Center (B.S. Oommen and Dr. Stahl), and Department of Neurology, Case Western Reserve University (Dr. Stahl), Cleveland, OH.
Supported by the United States Department of Veterans Affairs.
Received March 17, 2005. Accepted in final form May 23, 2005.
Address correspondence and reprint requests to Dr. John S. Stahl, Department of Neurology, Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH 44106-5040; e-mail: jss6@case.edu
754

Copyright © 2005 by AAN Enterprises, Inc.

most eccentric head positions as follows: In the without-phone
histogram, we determined the angles delimiting the left and right
5% extremes of the area under the curve. We found the total area
lying outside the same boundary angles in the with-phone histogram and divided this value by 0.1 (the total area of the 5%
flanking regions in the without-phone histogram). The resultant
value (eccentric orientation propensity) expresses the change in
probability of the head being found within the most eccentric 10%
of the orientations the subject assumed in the without-phone condition. We also determined the analogous, separate measures of
the alteration in probability on the side ipsilateral and contralateral to the phone. For instance, for the side on which the subject
held the phone, we determined the area under the curve of the
with-phone histogram for eccentricities outside the 5% probability
point of the corresponding side of the without-phone histogram.
We divided this area by 0.05 (the area under each 5% tail of the
without-phone histogram) and expressed the ratio of areas as a
percentage.

Results. Figure 1 shows the distribution of head orientation for the with-phone and without-phone conditions in
one subject, and demonstrates that head orientations were
more narrowly distributed in the with-phone condition. We
summarized these plots by determining head range as described above. Figure 2 plots head range for the withphone condition vs the without-phone condition for all 26
subjects. The majority of subjects fell below the superimposed equivalence line, indicating that eccentric head positions were less probable in the with-phone condition.
Overall, head range averaged 77.6 ⫾ 22.9 degrees in the
without-phone condition and 59.1 ⫾ 26.0 degrees in the
with-phone condition (paired t test, p ⫽ 0.0002), an average reduction of approximately 24%.
The 24% value, however, understates the effect on eccentric head orientations. The head-range measure is dominated by the most common head orientations. Eccentric
head positions may be particularly critical for detecting
peripheral hazards, but being less common than central
orientations, any reduction in their probability would have
a proportionately smaller impact on head range. Accordingly, we devised a more sophisticated measure (eccentric
orientation propensity), which focuses on changes in the
likelihood of eccentric head orientations. Eccentric orientation propensity was reduced to an average of 58.7 ⫾ 47.6%
(range, 1.4% to 178.9%) in the with-phone condition, or an
average 41.3% reduction in the time the head occupied the
extreme orientations achieved in the unencumbered state.
When calculating the eccentric orientation propensity
above, we combined the left and right directions of head rotation. We also considered the two directions separately, as it
was conceivable that holding the phone would interfere preferentially with head movements directed toward or away
from the side of the phone. Because we were concerned with
answering the question of whether reductions in head range

Figure 1. Head orientation histograms. Histograms obtained
from one subject who viewed his surroundings without the
phone (gray area) and with the phone held to the ear (solid
line). Vertical dashed lines mark the eccentricities of the
flanking 5% areas of the without-phone histogram.

were specific to the side on which the phone was held, we
limited our analysis to the 23 subjects whose head range
actually decreased while holding the phone. This analysis
demonstrated that there was no consistent relationship between the change in head orientation probability and the side
of the phone. Eccentric head orientations decreased on average to 49.3 ⫾ 53.3% on the phone side and 48.2 ⫾ 72.5% on
nonphone side (p ⫽ 0.957, paired t test). Plots (not shown) of
this percentage for the phone side vs the nonphone side exhibited a wide scatter on either side of the line marking a 1:1
ratio. Thus while there was no consistent asymmetry in the
probability ratios, we cannot exclude the possibility that individual subjects exhibit asymmetries in the effect on head
movements related to the side of the phone.

Discussion. To date, studies of cell phone safety
have concentrated on the impact of phoning on driving. These studies have demonstrated that cellular
phone use is associated with reduced awareness of
salient visual stimuli, an effect that has been attributed to the cognitive burdens of maintaining a

Figure 2. Comparison of head ranges in the with-phone
and without-phone conditions. Each data point represents
one subject. Dashed line indicates a 1:1 ratio.

conversation.3-9 Ours is the first study to demonstrate an effect of phoning that is unlikely to be
attributable to cognitive loading, as the cognitive demands of the with-phone and without-phone conditions were identical. The results suggest that
combining handheld phone use with other activities
may engender a risk related to reduced monitoring of
the visual surround, independent of the degree to
which a conversation is mentally taxing. One way
the effect might arise is if the handheld phone engenders a subconscious awareness that moving the
head would disturb the optimal relationship between
the ear and receiver. In this case, our results may
apply to other situations. For instance, a user of a
hands-free phone with a poorly fitting earpiece
might avoid rapid or large amplitude head movements because of a similar subconscious recognition
that such movements could dislodge the earpiece.
Although previous studies5,8 concluded that the
risks of handheld and hands-free phones are identical, our results might have predicted a greater risk
of handheld phones due to suppression of head movements. There are several possible explanations as to
why this result has not been obtained. First, the
effect would be expected to have the greatest impact
under conditions in which scanning the periphery is
important, as in changing lanes or crossing intersections. Thus it would not have been observed in driving studies comparing the effects of different phone
designs based on reactions to stimuli presented to
central vision.5,7,10 Second, the tendency of conversation to narrow the span of visual attention4,9 (and
thus restrict head range) could occlude the
conversation-independent effect of the handheld
phones. Third, reductions in the range of head movements could be compensated by an increase in the
range of eye movements.
The current study was limited in two respects. First,
since we did not assess eye movements, we can only
hypothesize that holding a phone affects the span of
visual exploration. Second, the degree to which the
phenomenon we demonstrated during spontaneous
viewing applies to the more structured task of driving
is unknown. It is conceivable that the learned patterns
of driving—for instance, the pattern of looking to the
left and right when preparing to cross an intersection—would override the suppressive effects on head
movements. However, it should be recognized that not
all of the gaze-shifting sequences during driving are as
strongly patterned as those associated with intersection crossing. Maintaining awareness of the visual surround while driving requires periodic glances to
mirrors that are not occasioned by specific procedures,
and these less stereotypic redirections of gaze may be
more akin to the spontaneous shifts made by subjects
in our experiment. Ultimately, the degree to which the
effect we have demonstrated impacts driving performance needs to be explored in a driving simulator using relevant tasks.
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755

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NeuroImages
Figure. (A) Patient’s drawing of her
experience: the dark area is intended to
represent her loss of vision in the right
hemifield, and bright colors represent
her visual hallucinations. (Although
she drew the dark area slightly across
the midline, on confrontational testing
the area of visual loss was restricted
to the right hemifield.) (B) Photograph
of patient’s eyeglasses, showing the
cardboard masks she constructed to
minimize light stimulation of her right
visual fields (arrowheads). (C) FLAIR
MRI demonstrates increased signal in
the gray matter of the left occipital
lobe, consistent with an ischemic stroke
(arrow in enlarged region of interest).
(D) T1 MRI with gadolinium shows
gyriform enhancement consistent with
subacute infarction (arrow in enlarged
region of interest). (E) SPECT scan
shows a focal region of hypoperfusion
in the left occipital cortex.

Vivid visual hallucinations from occipital
lobe infarction
Alexander C. Flint, MD, PhD; John P. Loh, MD;
and John C.M. Brust, MD, New York, NY
Infarction of the occipital pole causes homonymous hemianopia, and release hallucinations occasionally occur in the region
of the field defect.1,2
A 64-year-old woman developed acute right homonymous
hemianopia with vivid hallucinations in the right visual field. She
drew what she experienced, including colored pinwheels and lines
at right angles (figure, A). Because light exacerbated the positive
phenomena, she constructed a cardboard mask on her eyeglasses

Disclosure: The authors report no conflicts of interest.
Address correspondence and reprint requests to Dr. John C.M. Brust, Harlem Hospital, 506 Lenox Avenue, Dept. of Neurology, 16th Floor, MLK
Bldg., New York, NY 10037.

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September (1 of 2) 2005

to minimize light entering her right visual field (figure, B). FLAIR
MRI demonstrated subtle signs of ischemic infarction of the left
occipital pole (figure, C). T1 imaging with gadolinium showed
gyriform enhancement in the same region (figure, D). Focal hypoperfusion was evident on SPECT (figure, E). EEG was normal
except for borderline slowing in the left occipital region.
The positive symptoms abated over a week. The hallucinations
may have resulted from infarction, with disinhibition of higher
visual centers, or from simple partial seizures not detected by
surface EEG. The prolonged symptoms and finding of hypoperfusion by SPECT during the phenomena argue against an epileptiform etiology.
Copyright © 2005 by AAN Enterprises, Inc.
1. Brust JC, Behrens MM. “Release hallucinations” as the major symptom
of posterior cerebral artery occlusion: a report of 2 cases. Ann Neurol
1977;2:432–436.
2. Lance JW. Simple formed hallucinations confined to the area of a specific
visual field defect. Brain 1976;99:719–734.

Vivid visual hallucinations from occipital lobe infarction
Alexander C. Flint, John P. Loh and John C.M. Brust
Neurology 2005;65;756
DOI 10.1212/01.wnl.0000180350.58985.5f
This information is current as of September 12, 2005
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