Full text of DOI:10.1016/S0896-6273(00)00032-5

Neuron, Vol. 27, 227–235, August, 2000, Copyright  2000 by Cell Press
A Human Extrastriate Area
Functionally Homologous
to Macaque V4
Case Study
J ack L. Gallant,* Rachel E. Shoup,
and J ames A. Mazer
a different perspective by focusing on form processing
and visual attention.
Department of Psychology
University of California, Berkeley
Berkeley, California 94720
Area V4 is one of the largest visual areas in the ma-
caque, occupying about 10% of visual cortex and 5%
of neocortex as a whole (Felleman and Van Essen, 1991).
Anatomically, V4 lies on the prelunate gyrus, immedi-
ately anterior to area V2 and dorsal to area V3 (Zeki,
1
975; Gattass et al., 1988). V4 receives most of its visual
Summary
input from area V2, and it projects primarily to area
TEO (Felleman and Van Essen, 1991). (There is some
disagreement about the extent of TEO; here, we refer
to the retinotopic area immediately anterior to V4, which
is roughly coextensive with PIT in the nomenclature of
Felleman and Van Essen [1991].) Based on anatomical
connections alone, V4 appears to be an intermediate
processing stage in the ventral visual processing stream
Extrastriate area V4 is crucial for intermediate form
vision and visual attention in nonhuman primates. Hu-
man neuroimaging suggests that an area in the lingual
sulcus/fusiform gyrus may correspond to ventral V4
(V4v). We studied a human neurological patient, AR,
with a putative V4v lesion. The lesion does not affect
early visual processing (luminance, orientation, and
motion perception). However, it does impair hue per-
ception, intermediate form vision, and visual attention
in the upper contralateral visual field. Form deficits
occur during discrimination of illusory borders, Glass
patterns, curvature, and non-Cartesian patterns. At-
tention deficits occur during discrimination of the rela-
tive positions of object parts, detection of low-salience
targets, and orientation discrimination in the presence
of distractors. This pattern of deficits is consistent
with the known properties of area V4 in nonhuman
primates, indicating that AR’s lesion affects a cortical
region functionally homologous to macaque V4.
(
Ungerleider and Mishkin, 1982).
Neurophysiological studies have shown that macaque
area V4 contains a high proportion of cells selective for
color (Schein and Desimone, 1990; Zeki, 1975, 1983).
Color selectivity in V4 is more complex than that ob-
served in earlier areas such as V1 and V2, and V4 has
been postulated to play an important role in color con-
stancy (Zeki, 1980; Zeki et al., 1999). Early neurophysio-
logical evidence of color processing in primate V4 has
served to focus subsequent experimental attention on
color processing in human V4, as discussed below.
Several neurophysiological studies in nonhuman pri-
mates have also demonstrated that V4 neurons are sen-
sitive to specific aspects of stimulus shape (Desimone
and Schein, 1987; Gallant et al., 1993; Kobatake and
Tanaka, 1994). For example, V4 neurons are selective
for non-Cartesian grating patterns (Gallant et al., 1993,
Introduction
1
996; Kobatake and Tanaka, 1994) and contour curva-
Much of our current understanding about the function
of human visual cortex comes from studies of visual
cortex in the macaque monkey. The human and ma-
caque visual systems appear to share a similar anatomi-
cal organization (Sereno et al., 1995). In addition, the
early visual systems of the two species (i.e., retina, visual
thalamus, and primary visual cortex) appear to be func-
tionally homologous (DeValois et al., 1974). Beyond area
V1, however, functional homology between human and
macaque visual cortices is unclear.
In this report, we examine functional homology be-
tween extrastriate visual area V4 in humans and ma-
caques by behavioral assessment of visual function in
a human achromatopsic patient. The patient, AR, has a
small unilateral lesion at the temporal–occipital junction,
in the lingual sulcus/fusiform gyrus. This region corre-
sponds to an area identified in functional imaging stud-
ies as the ventral portion of human V4, called V4v (Ser-
eno et al., 1995; DeYoe et al., 1996; Hadjikhani et al.,
ture (Pasupathy and Connor, 1999), two aspects of stim-
ulus structure not explicitly represented in earlier visual
areas. Neurophysiological studies have shown that cells
in area V2 are sensitive to second-order visual stimuli
such as illusory contours (Peterhans and von der Heydt,
1
987; von der Heydt and Peterhans, 1987) and ampli-
tude-modulated (AM) sinusoidal gratings (Zhou and
Baker, 1994, 1996; Mareschal and Baker, 1998). To date,
no single-unit studies have examined this issue in V4.
However, because V2 projects directly to V4, second-
order contours are also likely to be represented in V4.
Lesion studies in nonhuman primates have confirmed
these physiological results. V4 lesions in macaques af-
fect intermediate aspects of stimulus form while sparing
stimulus properties explicitly represented in V1 (Schiller
and Lee, 1991; Schiller, 1995; Merigan and Phan, 1998).
For example, V4 lesions reduce the ability to discrimi-
nate the orientation of illusory contours (De Weerd et
al., 1996) and to identify borders defined by texture dis-
continuities (Merigan, 1996).
1
998; Beauchamp et al., 1999). Many previous studies
of human V4 have focused on color vision and have not
produced definitive evidence of homology (Heywood et
al., 1991; Zeki et al., 1991; Rizzo et al., 1993; McKeefry
and Zeki, 1997; Beauchamp et al., 1999; Zeki et al.,
Both physiological and lesion studies in nonhuman
primates suggest that area V4 is important for allocating
visual attention. Attentional modulation appears to in-
crease the selectivity of V4 cells by improving spatial
selectivity and neuronal tuning (Moran and Desimone,
1
999). Here, we address the question of homology from
1
985; Haenny et al., 1987; Maunsell et al., 1991; Motter,
*
To whom correspondence should be addressed (e-mail: gallant@
1994; McAdams and Maunsell, 1999). Attentional modu-
lation of spatial receptive field profiles in V4 may also
socrates.berkeley.edu).

Neuron
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2
Figure 1. Location of Lesion
AR’s lesion is shown in coronal (left), axial (middle), and saggital (right) sections. Sections were selected to illustrate the maximum extent of
the lesion in each plane. The small, right-hemisphere lesion (arrows) is located close to the temporal–occipital junction. The lesion is about
4
mm at its longest extent and runs along the fusiform gyrus and into the lingual sulcus, with little involvement of the underlying white matter.
Images were acquired using T1-weighted MR imaging at 1.5 T.
reflect the representation of the relative position of im-
age features within a single object (Connor et al., 1996,
likely to be affected by V4 lesions, such as detection
and discrimination of static Glass patterns (Glass and
Switkes, 1976), also remain to be tested. Psychophysical
(Wilson et al., 1997), electrophysiological (Allison et al.,
1999), and neuroimaging (James et al., 1999, Invest.
Ophthalmol. Vis. Sci., abstract) studies in normal hu-
mans all suggest that human V4 explicitly represents
curvature, although this hypothesis has not been tested
in patients with V4 lesions.
Despite extensive neurophysiological evidence from
macaques that V4 plays an important role in visual atten-
tion, few studies have investigated the effects of V4
lesions on attention in humans. To our knowledge only
one human lesion study has specifically assessed atten-
tional allocation using a task similar to those used in
animal studies (Mendola and Corkin, 1999). This study
reported deficits similar to those reported by Schiller
and colleagues (Schiller and Lee, 1991; Schiller, 1995)
in macaques. However, the lesion described by Mendola
and Corkin was relatively large and encompassed areas
beyond V4, making it unclear exactly which area is spe-
cifically responsible for the observed behavioral deficits.
1
997). Lesions of area V4 in nonhuman primates disrupt
attentionally demanding visual search tasks. V4 lesions
bias attentional allocation, making highly salient (e.g.,
brighter, bigger) stimuli more detectable than stimuli of
lower salience (Schiller and Lee, 1991; Schiller, 1995).
Similar lesions also impair target selection in the pres-
ence of flanking distractors (De Weerd et al., 1999).
Recent functional magnetic resonance imaging (fMRI)
studies in humans have revealed the functional topogra-
phy and organization of several early visual areas in
human occipital cortex. One of these areas represents
the upper visual field and appears to be homologous to
macaque V4v (Sereno et al., 1995; DeYoe et al., 1996).
To date, the dorsal subdivision of V4 (V4d) has not been
identified in humans.
Whether or not human area V4v is functionally homol-
ogous to macaque V4v is still a matter of substantial
debate. Many studies have examined patients with tem-
poral–occipital lesions encompassing putative area V4v
(Kolmel, 1988; Rizzo et al., 1993; Cowey and Heywood,
1
995; Heywood et al., 1995; Heywood and Cowey, 1998;
Mendola and Corkin, 1999). Unfortunately, these lesions
are typically quite large and often involve both striate
and extrastriate areas other than V4, as well as underly-
ing white matter (but see the report of Merigan et al.
Results
In this paper, we describe deficits in color perception,
intermediate form vision, and visual attention in a 56-
year-old male patient, AR, following a right hemisphere
posterior cerebral artery infarct two years prior to this
study. Neurological examination following the infarct re-
vealed achromatopsia confined to the left upper visual
quadrant, with no other significant visual or cognitive
deficits (see Experimental Procedures). Subsequent MR
imaging revealed a small (2–4 mm) right hemisphere
lesion in the lingual sulcus/fusiform gyrus close to the
temporal–occipital junction (see Figure 1). This lesion
is coincident with putative human V4v (Kolmel, 1988;
Sereno et al., 1995; DeYoe et al., 1996; Hadjikhani et al.,
1998) and substantially smaller than most previously
reported human V4 lesions (Zeki, 1990; Cowey and Hey-
wood, 1995; Heywood et al., 1995; Heywood and Cowey,
1998; Mendola and Corkin, 1999).
[1997], which studied a patient with a focal lesion com-
parable to the one examined here). As noted above,
many of these studies have focused on achromatopsia
(Zeki, 1990). It is unclear whether achromatopsia is due
specifically to V4 damage (Kolmel, 1988; McKeefry and
Zeki, 1997); several studies now suggest that this syn-
drome may in fact be a consequence of collateral dam-
age to visual processing modules that receive input from
area V4 (Cowey and Heywood, 1995; Heywood et al.,
1
1
995; Hadjikhani et al., 1998; Heywood and Cowey,
998).
A few studies of putative human V4 lesions have ex-
amined intermediate form vision (Rizzo et al., 1993; Meri-
gan et al., 1997). However, these studies did not evaluate
the full range of stimuli that, based on studies in nonhu-
man primates, would be expected to require V4. Human
functional imaging studies suggest that V4 might be
sensitive to the orientation of illusory contours (Mendola
et al., 1999), but these stimuli have not been used in
human V4 lesion studies. Other second-order tasks
Detection and discrimination thresholds were esti-
mated using a nonparametric staircase procedure (Lev-
itt, 1970). For each task, behavioral thresholds were
obtained concurrently in each quadrant of the visual

Case Study
29
2
Figure 2. Hue Discrimination Thresholds in the Lesioned Upper Left
Quadrant Are Significantly Higher than Those Observed in the Three
Remaining Quadrants
(A) Hue discrimination thresholds for a red reference patch. The
ordinate gives thresholds obtained in the upper right (UR), upper
left (UL), lower left (LL), and lower right (LR) quadrants, respectively.
The lesion affects the upper left quadrant, and the corresponding
threshold is shown in black. Asterisks indicate significant (p Ͻ 0.01)
differences between the lesioned quadrant and each normal
quadrant.
(B) Hue discrimination thresholds for a green reference.
Figure 3. Stimuli Used in the Various Tasks Discussed in This Report
field using four independent interleaved staircases. All
stimuli were flashed briefly in the relevant quadrant while
AR fixated a spot at the center of the display (see Experi-
mental Procedures for details).
The stimuli are shown for illustration purposes and do not necessar-
ily reflect the range of thresholds.
(
A) Circular luminance patches.
(B) Oriented sinusoidal gratings.
C) Drifting sinusoidal gratings (motion shown schematically).
D) Sinusoidal gratings containing a second-order oriented border.
E) Concentric Glass patterns differing in signal-to-noise ratio. To
preserve visibility, only three large patterns are shown in this panel.
F) Non-Cartesian spiral sinusoidal gratings.
G) Radial-frequency-modulated circles. See Experimental Proce-
(
(
(
Color Perception
A hue-matching task was used to assess both the spatial
extent and degree of achromatopsia. Each trial con-
sisted of a brief reference patch that appeared at fixa-
tion, followed by a brief test patch that could appear in
any visual quadrant (stimuli not shown). Red and green
reference hues were tested in separate sessions. The
test stimulus could either have the same hue as the
reference or a different hue as determined by the stair-
case. AR had to indicate whether or not the test hue
was the same as the reference hue. The results revealed
that AR has a significant deficit in color perception that
is confined to the upper left quadrant (see Figure 2).
The remainder of our experiments can be divided into
two broad categories: early and intermediate vision
tasks. Early vision tasks are those that macaques can
perform accurately following lesions of area V4 (Schiller,
(
(
dures and text for details of psychophysical procedures.
verbal instructions. For luminance, AR had to indicate
whether the brightness of the test patch was different
from the background. In the orientation task, he had
to indicate whether the test grating was horizontal or
oblique. In the motion task, he had to indicate whether
the test grating drifted to the left or right.
In contrast to AR’s clear color perception deficit, he
showed no significant impairment on any of the early
form vision tasks (see Figures 4A–4C). This is generally
consistent with previous results obtained in both human
achromatopsic patients (Kolmel, 1988; Rizzo et al., 1993;
Merigan et al., 1997) and nonhuman primates with V4
lesions (Schiller and Lee, 1991; Schiller, 1995; Merigan,
1996; Merigan and Phan, 1998). Note, however, that
the patient examined by Merigan et al. (1997) showed
impaired contrast sensitivity, while AR appears to have
normal contrast sensitivity. This may reflect subtle dif-
ferences in experimental procedures or differences in
the extent of the lesion or involvement of the underlying
white matter in the two cases.
1
995; Schiller and Lee, 1991; Merigan, 1996; Merigan
and Phan, 1998). Intermediate vision tasks are those
affected by V4 lesions in macaques (Schiller and Lee,
1
1
991; Schiller, 1995; Merigan, 1996; Merigan and Phan,
998; De Weerd et al., 1999) and those selected based
on published physiological properties of macaque V4
neurons (Gallant et al., 1993, 1996; Connor et al., 1997).
Intermediate vision tasks include both form vision and
visual attention tasks.
Early Vision Tasks
We examined early vision using three different tasks:
luminance detection, orientation discrimination, and
motion direction discrimination (see Figures 3A–3C). In
all three tasks, a single test stimulus appeared briefly in
one of the four visual quadrants, and AR had to indicate
whether it matched a reference stimulus specified by
Intermediate Form Vision Tasks
We investigated the effects of AR’s lesion on intermedi-
ate vision by measuring detection and discrimination
thresholds in several different tasks. First, we measured
AR’s ability to discriminate the orientation of illusory
contours formed by the addition of an oriented phase

Neuron
30
2
dots appeared briefly in one of the four visual quadrants.
The staircase controlled the ratio of signal to noise dots.
AR had to indicate whether the dots formed a Glass
pattern or were distributed randomly. Radial and con-
centric patterns were tested in different sessions.
Pilot studies with normal observers in our laboratory
indicate that Glass pattern discrimination at peripheral
locations is a demanding psychophysical task. Consis-
tent with this, AR’s overall performance was poor in all
quadrants, and absolute threshold values varied sub-
stantially across testing sessions. However, within each
session his performance was consistently and signifi-
cantly worse in the lesioned upper left quadrant than in
the other three quadrants (see Figure 5B).
Finally, we evaluated AR’s perception of curvature
using two different tasks. The first task employed spiral
gratings modulated in non-Cartesian polar coordinates
(Gallant et al., 1993, 1996; also see Figure 3F). On each
trial a spiral reference grating appeared briefly at the
fixation point, followed by a spiral test grating that could
appear in any visual quadrant. AR had to indicate
whether the concentric frequency of the test grating was
the same or higher than the reference (i.e., whether it had
higher spiral curvature). He had a significant behavioral
deficit in the upper left visual quadrant (see Figure 5C).
The second curvature task used radial-frequency-
modulated circles as test patterns (Wilkinson et al.,
Figure 4. Early Form Vision Thresholds for the Lesioned Quadrant
Are Not Significantly Different from the Three Normal Quadrants
(
(
(
A) Luminance detection thresholds. ns, not significant.
B) Orientation discrimination thresholds.
C) Motion direction discrimination thresholds.
shift to a sinusoidal grating (see Figure 3D). On each
trial, a single illusory contour stimulus appeared briefly in
one of the four visual quadrants, and AR had to indicate
whether the illusory contour was horizontal or oblique.
His thresholds were significantly higher when stimuli
appeared in the upper left quadrant; thresholds in the
other three quadrants were comparable to those ob-
tained with conventional gratings (see Figure 5A).
Next, we examined AR’s ability to distinguish radial
and concentric static Glass patterns from random noise
patterns (Glass and Switkes, 1976; Wilson et al., 1997;
Wilson and Wilkinson, 1998; also see Figure 3E). On
each trial, a single Glass pattern composed of Gaussian
1
998; also see Figure 3G). One of two stimuli could
appear on any trial: a single circle or a radially deformed
circle containing five lobes. AR had to indicate whether
a circle or deformed circle had appeared. Once again,
he showed a significant deficit in circle discrimination
restricted to the upper left quadrant (see Figure 5D).
Attention Tasks
We examined the effects of the lesion on visual attention
using three different tasks. First, we designed a task to
assess the effect of AR’s lesion on his ability to discrimi-
nate the relative positions of object parts (Logan, 1994).
For this task, stimuli were bipartite circular disks, half
white and half black, divided horizontally. On some trials
the white half was above the black, while on others the
black half was above the white. A single disk appeared
in one quadrant on each trial; AR had to indicate whether
the white half was above or below the black half. In
this experiment, the staircase determined the display
duration rather than stimulus structure. In all three unle-
sioned quadrants, AR was able to perform this task in
a single video frame (14 ms). In contrast, the patterns
had to be displayed for over 100 ms to achieve equiva-
lent performance in the lesioned quadrant (see Figure
6
A).
To verify that AR was able to detect the presence of
the contrast border, we used similar bipartite stimuli in
two control tasks. In the first, the border could be ori-
ented either horizontally or vertically, and AR indicated
the border orientation on each trial. In the second, AR
had to discriminate between bipartite and solid (white
or black) disks. AR could easily perform each of these
tasks equally well in the lesioned and unlesioned quad-
rants (data not shown). These results confirm that the
lesion impairs judgment of the relative position of the
parts of an object but not detection of the component
parts.
Figure 5. Intermediate Form Vision Thresholds Are Significantly Ele-
vated in the Lesioned Quadrant
(
(
A) Second-order border orientation discrimination thresholds.
B) Concentric Glass pattern discrimination thresholds. Similar re-
sults are obtained with radial Glass patterns.
C) Spiral non-Cartesian grating discrimination thresholds.
D) Radial-frequency-modulated circle discrimination thresholds.
(
(
The abscissa represents arbitrary units of curvature; see Experimen-
tal Procedures for details.
We also investigated whether the lesion affected AR’s

Case Study
31
2
Figure 7. Distractors Elevate Orientation Discrimination Thresholds
in the Lesioned Quadrant
Figure 6. Spatial Position Discrimination and Visual Search Thresh-
olds Are Higher in the Lesioned Quadrant than in the Normal Quad-
rants
(A) Orientation discrimination in the presence of distractors. Each
trial included one oriented sinusoidal grating that could appear alone
or flanked by three white or black distractors.
(A) Relative position discrimination thresholds.
(
B) Visual search for an odd item. Each trial consisted of eight identi-
(B) Thresholds for orientation discrimination in the presence of dis-
tractors. Black bars show thresholds observed when no distractors
were present. White bars show the thresholds obtained with white
distractors. Similar results were obtained with black distractors.
Distractors impaired orientation discrimination performance in the
lesioned quadrant but had no effect in the unlesioned quadrants.
cal items (not shown) or seven identical items and one odd item,
as illustrated here.
(C) Visual search thresholds. White bars show thresholds obtained
when the spatial frequency of the target pattern was higher (i.e.,
less salient) than that of the distractors. Black bars show thresholds
observed when the frequency of the target pattern was lower (i.e.,
more salient) than that of the distractors. Search asymmetry is signif-
icantly greater in the lesioned than in the unlesioned quadrants.
Similar results were obtained with circular outlines of different sizes.
6
C). These results are consistent with studies of both
animals (Schiller and Lee, 1991; Schiller, 1995) and hu-
mans (Mendola and Corkin, 1999).
Finally, we examined the allocation of spatial visual
attention in the presence of distractors (De Weerd et
al., 1999). On each trial a single sinusoidal grating ap-
peared at the center of one visual quadrant. On half of
the trials, the grating appeared alone, while on the other
half it was surrounded by three circular distractors (see
Figure 7A). Trials with and without distractors were ran-
domly interleaved within each session. White and black
distractors were tested in different sessions. The stair-
case controlled the orientation of the grating. In all cases
AR had to determine whether the grating was vertical
or oblique. AR showed a significant performance deficit
restricted to the lesioned quadrant in the distractor-
present condition, relative to the distractor-absent con-
dition (see Figure 7B). The deficit was independent of
distractor polarity. This finding is consistent with the
results of an earlier lesion study in macaques (De Weerd
et al., 1999).
ability to distinguish between stimuli differing in percep-
tual salience (Schiller and Lee, 1991; Schiller, 1995; Men-
dola and Corkin, 1999). For these experiments, we used
a conventional visual search procedure (see Figure 6B).
Each search display was composed of eight items ar-
ranged in a circle around the fixation point. A given trial
contained either eight identical items or seven identical
items and one odd item that could appear at any of
the eight locations. Two different stimulus classes were
tested in different sessions: high contrast, white circular
outlines and high contrast checkerboard patterns with
random luminance polarity phase. High-salience and
low-salience target items were tested in separate ses-
sions on the same day. The high-salience circles were
larger than the distractors, and the high-salience checks
had lower spatial frequency than the distractors; the
low-salience circles were smaller than the distractors,
and the low-salience checks had higher spatial fre-
quency than the distractors. Distractor salience was
held constant throughout a session, while the staircase
controlled the salience of the odd items. In all cases AR
simply had to indicate whether or not the search display
contained an odd item.
Discussion
AR shows no deficit on early vision tasks such as lumi-
nance detection and orientation and motion discrimina-
tion. In contrast, he shows profound deficits on color,
intermediate form, and visual attention tasks. Moreover,
these deficits are confined to the lesioned visual quad-
rant. The fact that both visual acuity and early form
and motion discrimination are unaffected by the lesion
suggests that information explicitly represented in pri-
mary visual cortex can bypass the lesioned area, possi-
bly via the dorsal visual processing stream (Ungerleider
and Mishkin, 1982). Unimpaired performance in the early
Previous psychophysical studies have demonstrated
a small performance asymmetry for stimuli differing in
perceptual salience; detection and discrimination of
more salient items is better than that for less salient
items (Treisman and Gormican, 1988). Consistent with
this, AR’s performance was generally better when the
targets were more salient than the distractors. However,
the asymmetry was significantly larger in the lesioned
quadrant than in the unlesioned quadrants (see Figure

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vision tasks also suggests that the observed deficits are
not simply due to a general attentional deficit.
deficits than those resulting from V4 lesions (Heywood
and Cowey, 1987; Heywood et al., 1995).
The form and attention deficits observed here are
consistent with those reported in lesion studies of non-
human primates. V4 lesions in macaques impair per-
ception of second-order stimuli such as texture-defined
borders (Merigan, 1996). Likewise, AR has difficulty
discriminating second-order stimuli (illusory contours)
in the lesioned quadrant. V4 lesions in macaques also
impair performance in attentionally demanding tasks
such as visual search; the lesions appear to make it
difficult for the animals to exclude irrelevant or more
salient distractors (Schiller and Lee, 1991; Schiller, 1995;
De Weerd et al., 1999). In similar search tasks, AR shows
deficits that are restricted to the lesioned quadrant.
Our findings are also consistent with single-unit stud-
ies of macaque V4. Several neurophysiological experi-
ments have demonstrated that macaque V4 neurons
preferentially represent curvature (Pasupathy and Con-
nor, 1999) and non-Cartesian patterns (Kobatake and
Tanaka, 1994; Gallant et al., 1996) not explicitly repre-
sented in area V1. Although AR can normally judge the
orientation of simple gratings, he is severely impaired
at discriminating non-Cartesian patterns presented in
the lesioned quadrant. This novel result confirms recent
neurophysiological evidence suggesting that non-Carte-
sian patterns are processed preferentially in human ex-
trastriate cortex (Allison et al., 1999). Neurophysiological
studies also suggest that single neurons in macaque V4
may encode the position of object parts relative to the
current focus of attention (Connor et al., 1996, 1997).
AR’s lesion impairs his ability to identify the relative
position of parts of objects, though he has no difficulty
detecting their presence. This is direct evidence sug-
gesting that human V4 might be involved in encoding
the relative positions of object parts.
In summary, there are currently insufficient data to
allow us to unequivocally determine whether AR’s lesion
is restricted only to area V4v. However, the pattern of
deficits indicates that any damage beyond area V4v is
most likely confined to a limited region of TEO/V8.
Color Vision
In addition to form and attention deficits, AR exhibits
a profound color discrimination deficit in the lesioned
quadrant. The functional implications of this deficit are
unclear. Zeki and colleagues have argued that V4 lesions
are the underlying cause of achromatopsia (Zeki, 1990;
Zeki et al., 1999). However, similar lesions in nonhuman
primates have been consistently reported to produce
only mild color deficits (Cowey and Heywood, 1995;
Merigan et al., 1997).
There are three possible explanations for this appar-
ent species difference. First, it could reflect differences
between human and macaque experimental methods.
Animal experiments tend to involve significantly more
training than similar experiments on human neurological
patients. This additional training might enable animals
to compensate for some of the perceptual deficits ac-
companying V4 lesions. Second, the difference could
reflect a real and important functional difference in color
processing between the two species; area V4 could be
important for color perception in humans but not in ma-
caques. Third, AR’s achromatopsia might reflect focal
damage to TEO/V8, anterior to area V4v. In this case
there would be no discrepancy to resolve, because le-
sions anterior to V4 appear to affect color perception in
both species (Heywood et al., 1995).
Conclusion
We tested the hypothesis that human V4 is functionally
homologous to V4 in the macaque by testing a neurologi-
cal patient, AR, with a putative V4v lesion. In every form
vision and visual attention task we examined, AR’s per-
formance was consistent with the predicted effects of
a V4 lesion based on anatomical, lesion, and neurophysi-
ological data from the macaque. The only inconsistency
involves color vision; AR showed clear color vision defi-
cits in the lesioned quadrant, but the role of V4 in ma-
caque color vision is currently unclear. Taken together,
these data provide strong evidence that a retinotopic
region in the human lingual sulcus/fusiform gyrus is
functionally homologous to area V4v in the macaque.
Moreover, our data indicate that this region is crucial
for normal intermediate visual form processing and at-
tention in humans. This leads us to conclude that, with
respect to form vision and visual attention, the human
and macaque visual systems are functionally homolo-
gous up to the level of V4.
Location of Lesion
The data presented here demonstrate that AR’s focal
lesion encompasses a human extrastriate visual area
functionally homologous to macaque area V4. Previous
functional neuroimaging studies suggest that human
V4v lies along the lingual sulcus and fusiform gyrus (Ser-
eno et al., 1995; DeYoe et al., 1996; Hadjikhani et al.,
1
998; Beauchamp et al., 1999), and anatomical MRI con-
firms that AR’s lesion is also located at this site. It is
possible that the lesion may also affect adjacent anterior
extrastriate areas. However, because AR’s deficits are
confined to a single visual quadrant, collateral damage
must be both confined to retinotopic areas and limited
in scope. Only area TEO (Boussaoud et al., 1991) and
the recently reported V8 (Hadjikhani et al., 1998) meet
these requirements.
Ideally, we could resolve this issue by testing AR using
a task that would unambiguously distinguish between
V4 and TEO/V8. Unfortunately, at this time we don’t
know enough about the role of these anterior areas in
form vision and attention to devise appropriate psycho-
physical tasks. Shape selectivity in TEO is similar to
V4, although TEO neurons have more complex tuning
Experimental Procedures
Patient
AR is a 56-year-old male diabetic with chronic hypertension. At age
5
2, 2 years prior to the beginning of this study, AR suffered a right
(Kobatake and Tanaka, 1994) and larger receptive fields
hemisphere lesion near the temporal–occipital junction following a
posterior cerebral artery infarct. Immediately after the infarct, AR
reported a transient blindness that resolved without treatment within
(Boussaoud et al., 1991). In macaques both V4 and TEO
lesions produce small form vision deficits on simple
tasks but large deficits on tasks that engage attention
1
2 hr. A subsequent neurological exam and visual field map revealed
(De Weerd et al., 1999). TEO lesions have also been
persistent achromatopsia confined to the upper left quadrant and
reported to produce more profound color perception
a small perifoveal scotoma (about 0.5Њ diameter at 2Њ eccentricity).

Case Study
33
2
An anatomical MRI scan taken 2 years after the injury revealed a
report here are conservative in the sense that any uncontrolled eye
movements will tend to minimize the apparent effect of the lesion.
small right hemisphere lesion of the lingual sulcus close to the
temporal–occipital junction. The lesion extends ف4 mm along its
longest axis from the lingual sulcus into the fusiform gyrus with little
involvement of the underlying white matter. This unilateral lesion
encompasses the putative human area V4v (Kolmel, 1988; Zeki,
Color (Hue) Discrimination
To estimate color discrimination thresholds, we presented a refer-
ence stimulus (6Њ) at the fovea for 250 ms following fixation. Two
hundred and fifty milliseconds after the reference stimulus was ex-
tinguished, the test stimulus appeared in one quadrant, chosen at
random. Colors were specified using hue, saturation, and brightness
(HSB) coordinates. A slice through HSB space in which brightness
is held constant can be visualized as a circle, where hue is given
by the angular component around the circumference of the circular
slice, and saturation is given by the radial component. By convention
red is located at 0Њ, green at 120Њ, and blue at 240Њ. For the current
experiments, saturation and brightness were both held constant (at
1
990; Sereno et al., 1995; DeYoe et al., 1996; Hadjikhani et al., 1998).
A neurological examination conducted at the beginning of these
experiments confirmed the persistence of AR’s achromatopsia but
revealed no additional visual deficits. AR reports no difficulties in
form vision other than occasional problems resolving written text
in the left perifovea, consistent with his small scotoma. AR continues
to work and drive normally.
Stimulus Presentation
AR sat 50 cm from a high-quality computer display (Sony Trinitron,
8
0% of the maximum screen saturation and 40% of the maximum
screen brightness) while hue angle was varied systematically to
estimate color discrimination thresholds. We tested red and green
reference hues in different sessions. On trials in which the test
stimulus did not match the reference stimulus, hue could vary in
either direction from the reference hue (i.e., with a red reference
hue, the test hues could vary either toward yellow–green or toward
magenta–blue; with a green reference hue the test hues could vary
either toward yellow–red or toward cyan–blue). In all cases AR had
to indicate if the reference and test stimuli were the same or different.
7
2 Hz, 40Њ horizontal, 1280 ϫ 1024 pixels). During testing, his head
was stabilized at a constant distance from the monitor using a chin
rest. With one exception (orientation discrimination in the presence
of distractors, see below), test stimuli were 6Њ in diameter, appeared
at 12Њ eccentricity, and were blended smoothly into a neutral gray
background to eliminate potential edge artifacts. These parameters
were chosen to ensure that stimuli were confined to a single quad-
rant while avoiding the vertical and horizontal meridians (except for
the perceptual saliency task, as noted below), the visual blindspot,
and AR’s perifoveal scotoma.
Luminance Detection
Luminance detection thresholds were measured by varying the lumi-
nance of circular patches relative to the background (ف10–15 cd/
m , though monitor luminance and ambient brightness could not be
controlled perfectly in the clinical setting). Each trial contained either
a circular patch that was brighter or darker than the background,
or no circular patch (i.e., a patch that was the same brightness as
the backround). The circular patch could appear in any quadrant.
AR had to indicate whether the trial contained a patch the same as
or different from the background.
Psychophysical Methods
Detection and discrimination thresholds were estimated using a
standard nonparametric staircase procedure (Levitt, 1970). Thresh-
olds were obtained simultaneously in each visual field quadrant
using four independent, interleaved staircases. The discriminability
of stimuli in each quadrant was decreased after three correct trials
in a row in that quadrant and increased after one error in that quad-
rant. This 3-down/1-up procedure converges on a stimulus level that
corresponds to 80% correct responses regardless of the underlying
psychometric function. Data from pilot studies in normal subjects
and AR were used to set the stimulus parameters for each task so
that targets were initially highly discriminable. The first four steps
of the staircase were relatively large to facilitate rapid convergence.
Trials continued in all four quadrants of the visual field until at least
2
Conventional Orientation Discrimination
Thresholds were measured by varying the orientation of sinusoidal
gratings (1.33 cycles/Њ, 50% contrast) around the horizontal. On
each trial a single horizontal or oblique grating appeared in one
quadrant. Oblique gratings could be tilted either clockwise or coun-
terclockwise from the horizontal. AR had to indicate whether the
grating was horizontal or oblique.
1
2 reversals occurred in each quadrant. Threshold values were com-
puted separately for each quadrant by averaging stimulus values
at the last six reversal points.
Significance was assessed using nonparametric randomization
or permutation) tests (Manly, 1991). For all experiments, the mean
Motion Discrimination
(
Thresholds were measured by varying the Michelson contrast (0% –
stimulus level of the last six staircase reversals obtained in the
lesioned quadrant was compared to the mean stimulus level of the
last six reversals in each of the unlesioned quadrants. Statistical
significance was estimated by comparing the measured mean differ-
ence to the distribution of 100 random permutations of the same
data obtained in lesioned and unlesioned quadrants. For all experi-
ments reported here, significance was set at p Ͻ 0.01.
1
00% ) of vertical sinusoidal gratings (1.33 cycles/Њ) drifting to the
left or right (0.6 cycles/s). The staircase controlled the contrast of
the grating. Each trial contained a single moving grating in one
quadrant, and AR had to determine whether the grating drifted to
the left or the right.
Except where noted below, all experiments followed the same
trial structure. A fixation target appeared at the center of the screen.
AR was instructed to fixate and then press a key. After a 600 ms
delay, the test stimulus appeared for 200 ms accompanied by a
brief tone. After another 300 ms, the fixation spot was extinguished
Second-Order Orientation Discrimination
The methods for this experiment were identical to those used to
measure conventional orientation discrimination thresholds, except
that the stimuli contained a second-order illusory contour. The sec-
ond-order contour was created by introducing an oriented phase
shift along a diameter of a vertical sinusoidal grating. Although the
carrier grating was always vertical, the magnitude and orientation
of the second-order contour varied across trials. AR was instructed
to indicate whether the illusory contour was horizontal or oblique.
Discrimination thresholds were measured by varying the orientation
of the second-order contour according to the staircase procedure.
and
a response screen appeared, indicating two possible re-
sponses. AR then responded by pressing a left or right key. Stimulus
location was varied randomly to eliminate any anticipation effects.
Responses were not timed and AR was allowed to take short breaks
as required.
AR received substantial practice (2–5 hr) on each task before data
reported here were collected. Pilot experiments and early practice
sessions were conducted without feedback, while later sessions
and all of the data reported here were conducted with feedback.
Eye position was not monitored, but brief presentations were used
to minimize the effects of voluntary eye movements. AR’s lesion
affects only one quadrant. If he attempted to improve performance
by shifting fixation toward the lesioned quadrant, it would improve
his performance in the lesioned quadrant while reducing perfor-
mance in the opposite quadrant. The magnitude of the deficits we
Glass Pattern Discrimination
Static Glass patterns were generated by uniformly distributing
Gaussian dots (3 pixel diameter) on a rectangular grid. Dot coordi-
nates were rotated or translated relative to the center of the grid and
redrawn to form concentric or radial Glass patterns, respectively. For
concentric Glass patterns, dots were rotated such that each dot
translated the same distance in rectangular coordinates (as op-
posed to a constant angle in polar coordinates). This procedure

Neuron
34
2
produces a Glass pattern with no density cues near the center that
might be used for detection. For presentation all patterns were
presented on a black background and were masked with a circular
aperture. During testing, each Glass pattern was combined with a
random noise signal (uniformly distributed Gaussian dots). On each
trial, AR indicated if the test pattern was a Glass pattern or a noise
pattern. Detection thresholds were measured by using the staircase
to vary the ratio of signal to noise dots, keeping overall dot density
constant. Concentric and radial Glass patterns were tested in sepa-
rate sessions.
Orientation Discrimination in the Presence of Distractors
On each trial a single sinusoidal grating (4Њ diameter, 1.33 cycle/
deg, 50% contrast) appeared at one of four locations at the center
of each visual quadrant (9Њ eccentricity). AR had to indicate whether
the grating was vertical or oblique. On half of the trials the grating
appeared alone, and on half it was surrounded by three circular
distractors arranged in a triangle centered on the grating (3.8Њ diame-
ter, centered 4Њ from center of grating). Trials with and without dis-
tractors were interleaved within each session, and thresholds were
estimated simultaneously and independently in each quadrant.
White and black distractors were tested in separate sessions.
Non-Cartesian Spiral Frequency Discrimination
Spiral sinusoidal gratings were constructed using the method of
Gallant et al. (1996). Each sinusoidal luminance grating was modu-
lated in polar coordinates to produce a spiral pattern. For these
experiments the radial frequency component was fixed at 5 cycles/
Acknowledgments
We gratefully acknowledge and thank Dr. Robert Knight for his neu-
rological acumen in identifying AR and bringing him to our attention.
We also thank Donatella Scabini for patient scheduling and Nina
Dronkers for helping us obtain the structural MRI. This study was
partially funded by Whitehall and Sloan Foundation grants to J. L. G.
R. E. S. was supported by a National Institutes of Health grant to
Dr. Robert Rafal.
3
60Њ. Thresholds were measured by increasing the concentric fre-
quency component beyond its baseline value of 8 cycles/stimulus.
On each trial a test grating appeared at fixation, and after it was
extinguished a single spiral grating appeared in any one quadrant.
AR had to indicate whether or not the test grating matched the
reference.
Received March 3, 2000; revised July 11, 2000.
Radial-Frequency-Modulated Circle Discrimination
Radial-frequency-modulated circles were constructed according to
the method of Wilkinson et al. (1998). The cross-sectional luminance
profile was defined by the radial fourth derivative of a Gaussian.
The circles were radially deformed by a circular sinusoid with 5
cycles/360Њ. As the radial amplitude modulation increases in these
patterns, stimuli become increasingly distorted and total curvature
increases. During testing, the staircase controlled the radial ampli-
tude, and AR was asked to indicate whether each stimulus was
circular or noncircular.
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