The Kinetic Occipital Region in Human
Visual Cortex
Patrick Dupont1,2, Bart De Bruyn1, Rik Vandenberghe1,
Anne-Marie Rosier1, Johan Michiels3, Guy Marchal4, Luc
Mortelmans2 and Guy A. Orban1
1
Laboratorium voor Neuro- en Psychofysiologie, KULeuven,
Medical School, Campus Gasthuisberg, B-3000 Leuven,
2
Centrum voor Positron Emissie Tomografie, Dept. Nucleaire
Geneeskunde, UZ Gasthuisberg, B-3000 Leuven, 3Laboratorium
voor Medische Beeldverwerking, ESAT Radiologie, KULeuven,
B-3000 Leuven and 4Afdeling Radiologie, UZ Gasthuisberg,
B-3000 Leuven, Belgium
In the present study we showed that the kinetic occipital (KO)
region, located laterally in occipital cortex ∼20 mm behind human
MT/V5, can be strongly and bilaterally activated under passive
viewing conditions. We used continuous, randomly changing visual
stimulation to compare kinetic gratings to uniform motion and kinetic
gratings to luminance defined gratings. The KO activations under
these passive conditions are stronger than those observed when the
two types of gratings are compared under active conditions, i.e.
while subjects perform a task (counting gratings of a given
orientation). Region KO was shown to process both shape and
motion information, the conjunction of which is typically present in
kinetic contours. Area MT/V5 also processes these two aspects of
visual stimulation but favors motion signals. Clear segregation
of shape and motion processing was observed only in occipitotemporal and parietal regions respectively. Although neurons with
properties similar to those derived from the conditions activating the
KO region have been documented in the macaque monkey, their
location seems inappropriate for them to correspond to the KO
activation observed in humans.
Kinetic contours are generated by differences in motion. They
can be created by differences in direction or speed of motion on
either side of the contour as well as by the juxtaposition of
coherent and noncoherent motion or motion and nonmotion. All
these types of contours are computationally important because
they allow the visual system to disambiguate luminance edges
and separate object boundaries from shadows and surface
markings. Here we restrict ourselves to kinetic boundaries
created by differences in direction, because their extraction
requires the processing of the direction of motion rather than
the mere processing of motion per se or the coherence of that
motion. Furthermore, this type of kinetic boundary excludes any
contribution from nonmotion cues, such as blur or temporal
frequency, to the contour generation. Such contours are
probably very important for breaking camouf lage when the
subject is moving, such as when a predator is pursuing its prey,
and are the only cues available when color, luminance and stereo
cues are absent. Humans are very accomplished at using such
contours for different aspects of spatial vision, including vernier
acuity, orientation discrimination, contour localization, shape
perception and letter recognition (Regan, 1986, 1989; Regan and
Hong, 1990; Regan and Hamstra, 1991, 1992; Sáry et al., 1994;
Rivest and Cavanagh, 1996).
Some progress has been made into our understanding of the
processing of kinetic contours in the primate brain. Recent
evidence has shown that these contours are processed in the
ventral pathway (Ungerleider and Mishkin, 1982) together with
luminance defined contours. Indeed, neurons selective for
orientation of luminance and motion defined contours have
been reported in areas V2 and IT (Marcar et al., 1992, 1994; Sáry
et al., 1995), and TE shape selective cells are selective both for
kinetic and luminance defined shapes (Sáry et al., 1993). Similar
mechanisms might operate in humans, since the activation
of human visual cortex obtained by comparing orientation
discrimination to a passive viewing control was very similar
whether kinetic or luminance defined gratings were used
(Orban et al., 1995). On the other hand, it is not as clear where
the initial motion preprocessing of the kinetic contours occurs,
i.e. the extraction of motion direction necessary for the creation
of the kinetic boundary. Initially Marcar and Cowey (1992) had
suggested that this preprocessing was accomplished in area
MT/V5, which is known to project to areas V2 and V4 (Maunsell
and Van Essen, 1983; Ungerleider and Desimone, 1986). In these
two ventral areas the direction signals could then be used to
extract orientation selectivity for kinetic boundaries. Marcar and
Cowey (1992) obser ved deficits in kinetic shape perception
after lesions of area MT/V5 and the surrounding areas. The lack
of selectivity for the orientation or position of kinetic boundaries
in the MT neurons themselves (Marcar et al., 1995) is not
contradictory to the view that area MT/V5 plays a role in the
preprocessing of the kinetic contours. However, lesions restricted to area MT/V5 (Lauwers et al., 1995) only mildly impair
orientation discrimination of kinetic boundaries, suggesting that
other early cortical areas might also contribute to the motion
preprocessing required for the extraction of kinetic contours.
Indeed, Orban et al. (1995) described a motion area in human
lateral occipital cortex which could play this role. This region
was differentially activated when subjects counted the kinetic
gratings of a given orientation compared with when they
performed the same task for luminance defined gratings.
The present experiments were undertaken to obtain further
evidence that this lateral occipital region is indeed specialized in
the processing of kinetic contours. In the original experiment in
which kinetic gratings and luminance gratings were contrasted,
there was a possible confounding factor, in that motion is
present between the kinetic boundaries in the kinetic grating
stimuli. Thus the differential activation observed in the
subtraction kinetic gratings minus luminance gratings might be
due to the local motion rather than to the kinetic boundaries. In
the original study (Orban et al., 1995) we argued that this was
unlikely since the difference between kinetic and luminance
grating conditions in the KO region was maximal when subjects
counted the orientations of the gratings. Yet there is a
straightforward way to eliminate this confounding factor:
namely to show that the KO region is also differentially active
when kinetic gratings are compared with uniform motion. The
first aim of the present experiments was to compare these two
conditions. Since it is impossible to find contour-related
attributes which subjects could use in a task performed with the
kinetic gratings as well as with the uniform motion, we resorted
to passive stimulation. Thus we compared kinetic gratings with
Cerebral Cortex Apr/May 1997;7:283–292; 1047–3211/97/$4.00
uniform motion while the subjects performed a fixation task and
remained passive to the stimuli. We also repeated the
comparison of kinetic and luminance gratings under the same
conditions. All three types of stimuli were generated with
randomly textured patterns and were presented continuously.
For the grating stimuli the four main orientations were presented
in random order, to match the presentation of motion along the
four main axes in the uniform motion conditions (Zeki et al.,
1991; Watson et al., 1993; Dupont et al., 1994).
In the three conditions (uniform motion, kinetic and
luminance gratings) motion and shape cannot easily be
disentangled since comparing kinetic gratings with luminance
gratings isolates motion and comparing kinetic gratings with
uniform motion isolates shape. The addition of a fourth
condition, a static randomly textured pattern, allows the study of
the main effects of motion and shape as well as their
interactions. The addition of this fourth condition also enabled
us to locate MT/V5 (Zeki et al., 1991; Watson et al., 1993;
Dupont et al., 1994) and compare it with the kinetic occipital
region in the same group of subjects, something we could not do
in the initial publication (Orban et al., 1995). Finally, we
replicated the two conditions which defined the kinetic
occipital region in the original experiment (Orban et al., 1995),
counting gratings of a given orientation for kinetic and
luminance defined gratings. This allowed us to compare the
differential activation strength of region KO when the subjects
performed a task with a visual stimulus and when they remained
passive during continuous and randomly changing stimulation.
These experiments demonstrate the existence of a lateral
occipital region which is specialized for the processing of
kinetic boundaries, and which is distinct from area MT/V5.
Materials and Methods
Ten young (mean age ± SD, 22.5 ± 2 years) male subjects participated in
the study which was approved by the Ethical Commission of the
KULeuven Medical School. All were right-handed, had normal vision and
no neurological history, were not on any medication and had a normal
MRI scan. They were trained in two sessions prior to the PET scanning.
Fixation was controlled by EOG, and all subjects fixated steadily.
Stimulus Characteristics and Tasks
Six stimulus conditions were used: two in which the subjects performed
the same task (counting) with the visual stimulus while fixating, as in
Orban et al. (1995), and four conditions in which the subject remained
passive to the visual stimulus and only fixated. Each condition lasted 2
min.
In the active trials (counting tasks) series of 9, 10 or 11 gratings were
presented for 200 ms at a rate of 3/s: 4, 5 or 6 gratings were vertical and
the others slightly oblique (orientation difference 5.8 ± 1.4° for
luminance defined and 14 ± 2° for kinetic gratings). The task of the
subjects was to count the nonvertical stimuli and press the right or left
key depending on whether or not this number was 5. This task was
performed both with luminance defined (CLUM) and kinetic gratings
(CKIN).
Stimuli were exactly the same as those used in our previous study
(Orban et al., 1995). Rectangular gratings were created by an Atari
computer at 70 Hz. The stripe width was 0.66°, the diameter was 3° and
mean luminance was 47.5 cd/m2. Stimuli were centered on the fixation
point. They were generated by modulation of random textured patterns
(50% white and dark pixels of 1 arc min) and the stripes differed either in
luminance (28.8 versus 66.1 cd/m2) or in motion direction. In the kinetic
and uniform motion stimuli, pixels moved at 4°/s. In the conditions in
which subjects judged the orientation of kinetic gratings, motion was
upward and downward and the nearly vertical orientation of the kinetic
boundary was manipulated independently of the defining cue. In the
passive conditions, the direction of motion was always parallel to the
kinetic boundary.
284 Kinetic Occipital Region • Dupont et al.
Figure 1. Stimuli used in the four passive conditions. Upper left: a stationary randomly
textured pattern; upper right: same randomly textured pattern moving uniformly in a
single direction; lower left GKIN: kinetic grating generated by pixels of the randomly
textured pattern moving in opposite directions, parallel to the boundary; lower right
GLUM: luminance defined grating by luminance modulation of the randomly textured
pattern.
The four passive conditions (Fig. 1) included presentation of kinetic
(GKIN) and luminance defined gratings (GLUM), of uniform motion
(UNIFORM) and of a static randomly textured pattern (STATIC). The
kinetic gratings and uniform motion were presented with pixels moving
along horizontal, vertical and both oblique (45 and 135°) axes. In these
stimuli the pixels moved backward and forward along a single axis for a
total of 856 ms before switching randomly to another axis. In the static
condition the same random textured pattern remained stationary
throughout the entire 2 min period. In the kinetic and luminance defined
gratings vertical, horizontal and both oblique orientations were
presented. These stimuli switched to another randomly chosen
orientation every 856 ms, in the kinetic gratings this change was coupled
to the change in motion axis since the pixels always moved parallel to the
kinetic boundary. It should be noted that locally (over a diameter smaller
than the stripes of the kinetic stimuli) the motion was exactly the same in
the kinetic and uniform motion condition; the rate of change in motion
direction was also exactly the same in these two types of stimuli and the
rate of change in orientation was exactly the same in luminance defined
and kinetic gratings.
Data Acquisition
During the PET session, the subject had to perform the tasks while lying
in the PET scanner (Siemens-CTI 931/8/12). The subjects viewed the
stimuli in a dimly lit room at a distance of 114 cm. The order of conditions
was randomized according to a latin square design. The head of the
subject was immobilized with a foam headholder (Smither Medical
Products, Akron, OH). The start of the task coincided with the start of the
injection of 40 mCi (1.48 Gbq) H215O. The injection lasted 12 s and the
scan began when activity reached the brain, which was clearly marked by
a sharp rise in counts (∼30 s post-injection). Scanning lasted 40 s and
occupied the middle third of the period during which the subjects
performed the task. Each subject underwent six emission scans while
performing one of the six tasks. Scans were separated by a 15 min time
interval for decay of the tracer.
The PET scanner measured 15 planes (slice thickness 6.75 mm)
parallel to the inferior orbito-meatal line. Prior to the emission scans, a
transmission scan was acquired which was used to correct for
attenuation. The (attenuation corrected) images were reconstructed
using filtered back projection with a Hanning filter of cut-off frequency
0.5 cycles/pixel. Each reconstructed image represents the activity
distribution during the measurement which is related to the regional
cerebral blood f low (rCBF).
A fter the PET scanning, each subject underwent a magnetic
resonance imaging (MRI) scan. The MRI images were acquired using a
three-dimensional Magnetization-Prepared Rapid Gradient Echo
(MPR AGE) sequence (Mugler and Brookeman, 1990). Acquisition
parameters were: repetition time 10 ms, echo time 4 ms, f lip angle 8°,
field of view 256 mm, acquisition matrix 256 × 256. The 3-D volume had
a thickness of 160 mm, partitioned into 128 sagittal slices.
Data Analysis
The data were analyzed with statistical parametric mapping (SPM95,
software from the Wellcome Department of Cognitive Neurology,
London, UK) implemented in MATLAB (Mathworks Inc., Sherborn, MA).
Statistical parametric maps are spatially extended statistical processes
that are used to characterize regionally specific effects in imaging data.
Statistical parametric mapping (SPM) combines the general linear model
(to create the statistical map of SPM) and the theory of Gaussian fields to
make statistical inferences about regional effects (Friston et al., 1991,
1994; Worsley et al., 1992).
Spatial Realignment and Normalization
The scans from each subject were realigned using the first scan as a
reference. The six parameters of this rigid body transformation were
estimated using a least squares approach (Friston et al., 1995a). Following
realignment, all images were transformed into a standard space (Talairach
and Tournoux, 1988). This normalizing spatial transformation matches
each scan (in a least squares sense) to a reference or template image that
already conforms to the standard space. As a final pre-processing step the
images were smoothed using a Gaussian kernel (20 × 20 × 12 mm full
width at half maximum).
Statistical Analysis
After specifying the appropriate design matrix, the condition, subject
and covariate effects were estimated according to the general linear
model at each voxel (Friston et al., 1995b). The design matrix included
global activity as a confounding covariate and this analysis can therefore
be regarded as an ANCOVA (Friston et al., 1990). To test hypotheses
about regionally specific condition effects the estimates were compared
using linear contrasts. The resulting set of voxel values for each contrast
constitute a statistical parametric map of the t-statistic SPM(t).
The SPM(t) were transformed to the unit normal distribution [SPM(Z)]
and thresholded at 3.09 (P < 0.001 uncorrected) and at 4.10 (P < 0.05 after
the correction for multiple comparisons as used in SPM95).
MRI images of each subject were registered, after segmenting the
brain (ANALYZE, Mayo Clinic USA), to the corresponding PET images
using automatic image registration (Woods et al., 1993). Then the same
transformations into the standard space as those used for the PET images
were applied to the resampled (and registered) MRI images. An averaged
(for the group of subjects) MRI image in the standard space was
constructed and the thresholded parametric maps were projected onto
these images for visualization.
Table 1.
UNIFORM – STATIC
Talairach coordinates (mm)a
x
y
z
–40
40
34
–26
60
–22
24
–70
–64
–48
–92
–34
–60
–10
–4
4
40
–4
20
40
48
Z-score
Anatomical description
6.30*
5.91*
4.45*
3.66
3.61
3.52
3.49
L GOm BA19/37 (MT/V5)
R GOm BA19/37 (MT/V5)
R LPi BA40
L GOi BA18 (KO)
R sulc. lat.
L LPs BA7
R GPrC BA6
In this and subsequent tables all differential activation regions reaching P < 0.001 uncorrected are
tested. GOm: medial occipital gyrus, GOi: inferior occipital gyrus, LPi: inferior parietal lobule, LPs:
superior parietal lobule; GPrC: precentral gyrus.
a
Distance laterally from the midline (x) with right positive, anterior–posterior distance (y) from
anterior commissure (AC) with forward positive and distance (z) above (positive) and below
(negative) the anterior–posterior commissure line.
*P < 0.05 after correction.
al. (1995) (25, –88, –1) to find the most significant voxels in the
comparison between counting kinetic gratings and counting
luminance defined gratings. No correction for multiple
comparison is needed in such a hypothesis-testing experiment.
We were unable to find a voxel reaching the required level of
significance (P < 0.05) in the right hemisphere, but did find one
in the left hemisphere with coordinates –24, –96, –4. Thus we
replicated the result of Orban et al. (1995), except for the right
lateralization of the focus.
Comparison of Static and Uniform Motion: Passive
Viewing
This comparison provides background information regarding
the location of human MT/V5 in the subjects of the present
study. The results are shown in Table 1 and Figure 2A. The most
significant differences were obser ved over regions which
correspond to right and left human MT/V5. Another very
significant activation was observed in right Brodmann area (BA)
40. Weaker activations reaching only a significance of P < 0.001
(uncorrected) were observed in the left lateral occipital cortex,
presumably corresponding to the kinetic occipital (KO) region,
right lateral sulcus, left BA7 and right precentral gyrus (Table 1).
Behavioral Results
The subjects performed the two counting tasks equally well:
mean % correct was 93.3 ± 4.7% and 90 ± 8.2% for luminance
defined and kinetic gratings respectively. This is slightly higher
than reported in Orban et al. (1995).
Comparison of Uniform Motion and Kinetic Gratings:
Passive Viewing
The result of subtracting uniform motion from kinetic gratings is
given in Table 2 and Figure 2B. Only two regions in the lateral
inferior occipital cortex yielded a significant difference when
corrected for multiple comparisons. These regions must
correspond to region KO, since kinetic contours are present in
the kinetic gratings but not in uniform motion. This designation
is supported by the location of the two activations: the one in the
left hemisphere lies close to the region defined by the active task
in the present study and the one in the right hemisphere near the
coordinates of the kinetic region observed by Orban et al.
(1995). Weaker activations were observed in the right fusiform
gyrus, close to the border with the lingual gyrus and in the left
lingual gyrus (Table 2).
Comparison of the Two Active Conditions
We used the active conditions to locate the kinetic occipital
region exactly as it was defined in Orban et al. (1995). In both
hemispheres we looked within a radius of 10 mm (Haxby et al.,
1994; Grabowski et al., 1996) from the focus given in Orban et
Comparison of Kinetic and Luminance Defined
Gratings: Passive Viewing
Although this comparison is similar to that originally used to
define the kinetic occipital region, there might be a difference
between active conditions and passive conditions. Indeed, in the
Results
Cerebral Cortex Apr/May 1997, V 7 N 3 285
Figure 2. Statistical parametric maps showing the differential activation in UNIFORM – STATIC (A), GKIN – UNIFORM (B) and GKIN – GLUM (C) at seven horizontal levels from –12
to +12 mm with respect to the anterior commissure (AC)–posterior commissure (PC), superimposed on the average MRI of the 10 subjects. Yellow pixels indicate activation
significant at P < 0.001 (uncorrected) and black pixels activation significant at p < 0.05 (corrected). L indicates left side of the brain. Vertical line: midline; horizontal lines: line
through the AC and PC respectively.
Figure 3. Coronal sections at –48, –68 and –90 (from left to right) showing average MRI with indication of the three main regions: right BA40, right and left MT/V5, and right and
left KO. The cross in the –90 section indicates the position of the most significant voxel in the neighborhood of region KO obtained by the subtraction CKIN – CLUM. For color code
and conventions see Figure 2.
active conditions, subjects must use the boundary information to
solve the task. This probably explains why the differential
activation of KO in the Orban et al. (1995) study was stronger in
the active than in the passive conditions.
The results of subtracting luminance defined from kinetic
gratings are given in Table 3 and Figure 2C. The three major
differentially active regions are the left and right MT/V5 and left
KO. As can be seen from the comparison of Figure 2A and C,
activation of the right KO is fused with the right MT/V5. A
286 Kinetic Occipital Region • Dupont et al.
weaker activation was observed in the left BA7 (Table 3). The
fact that these activations are very similar to those observed in
the subtraction uniform-static strongly suggests that in the
passive conditions it is mainly the presence or absence of motion
which produces the differential activation in the kinetic versus
luminance defined gratings comparison. It is noteworthy that
the right parietal BA40 region was not activated in the kinetic
versus luminance defined grating comparison but was activated
in the uniform motion versus static comparison. This might
Table 2.
GKIN – UNIFORM
Talairach coordinates (mm)
x
y
z
34
–28
30
–14
–88
–94
–62
–84
0
–4
–16
–16
Z-score
Anatomical description
5.38*
4.77*
3.88
3.33
R GOi BA18 (KO)
L GOi BA18 (KO)
R GF BA19
L GL BA18
GOi: inferior occipital gyrus, GF: fusiform gyrus, GL: lingual gyrus.
*P < 0.05 after correction.
Figure 4. Functional profiles of the left and right MT/V5 areas: the adjusted rCBF
(arbitrary units) is shown for each of the six conditions. Vertical bars indicate SE. The
coordinates of the voxels are those indicated in Table 1.
Table 3.
GKIN – GLUM
Talairach coordinates (mm)
x
y
z
–36
38
–26
–16
–70
–68
–92
–52
0
4
0
44
Z–score
Anatomical description
6.37*
5.70*
4.57*
3.49
L GOm BA19/37 (MT/V5)
R GOm BA19/37 (MT/V5)
L GOi BA18 (KO)
L LPs BA7
*P < 0.05 after correction.
indicate that this parietal region requires more spatial
summation in moving stimuli.
Region KO is Distinct from Area MT/V5
The present results indicate that the right and left KO regions
defined by the subtraction of uniform motion from the kinetic
gratings correspond to the region defined originally by the
orientation counting tasks. These two regions are clearly distinct
from the MT/V5 areas. The locations of these areas in coronal
section are shown in Figure 3. On average, region KO is located
25 mm more posterior than MT/V5, with average (over right and
left) coordinates of 31, –91, –2 for KO and 40, –66, 0 for MT/V5.
Hence they are clearly distinct areas, even taking into account
the low resolution of the average subject PET technique. This is
amply confirmed by the difference of the activation profiles of
the two areas, shown in Figures 4 and 5 respectively. The profiles
of the right and left KO areas are clearly very similar: both
regions are more strongly activated by kinetic gratings than by
uniform motion or luminance defined gratings, and static
random textured pattern is the weakest stimulus. The profiles of
areas MT/V5 are clearly different from those of regions KO, the
main difference being that uniform motion is almost as effective
a stimulus in activating MT/V5 as is a kinetic grating, and is
clearly better than either the static randomly textured pattern or
luminance defined gratings.
These activation profiles also demonstrate the robustness of
the differential activation of region KO in the two main
subtractions. In the subtraction GKIN – GLUM the mean percent
change in rCBF is 5.5% in left KO and 5.7% in right KO. In
the subtraction GKIN – UNIFORM the values were 5.5% in
left KO and 7.1% in right KO. In contrast, in the subtraction
CKIN – CLUM the mean percent change in rCBF was only 1.3%
in left KO and 0.5% in right KO. The differential activations
obtained in the passive conditions in KO region compare
favorably with the mean percent change in MT/V5 yielded by
the subtraction UNIFORM – STATIC: 8% in left MT/V5 and
6.8% in right MT/V5.
Figure 5. Functional profiles of the left and right KO regions. The coordinates of the
voxels are those indicated in Table 2. The same conventions as in Figure 4 apply.
Main Effects of Motion and Shape
Given the activation profiles of KO and MT/V5, it is not
surprising that the main effect of motion defined as (GKIN +
UNIFORM) – (GLUM + STATIC) was significant in both right and
left MT/V5 and in left KO (Table 4). In contrast, the main effect
of shape defined as (GKIN + GLUM) – (UNIFORM + STATIC) was
significant in right and left KO and in several inferior occipital
regions (Table 5). The interaction between the motion and
shape effects failed to reach significance anywhere (Tables 4 and
5), although there was a trend towards a positive interaction in
the right KO region (z = 1.55, P < 0.12). Thus region KO is only
marginally more strongly activated when shape is defined by
motion than when defined by luminance. These data support the
view that area MT/V5 is activated by motion more than by shape,
while region KO is activated equally by both. This is also clearly
shown in Figure 6, where the regions activated by motion and
shape are shown in coronal sections. Posteriorly in the occipital
lobe, the motion and shape effects overlap considerably,
including at the level of region KO. As one moves forward the
two effects tend to become dissociated, particularly in the right
hemisphere. Motion dominates in the parietal regions and the
middle temporal gyrus, whereas shape dominates in the
fusiform gyrus.
Discussion
Comparison with Our Previous PET Study (Orban et al.,
1995)
Our results show that very robust activations of the KO region
Cerebral Cortex Apr/May 1997, V 7 N 3 287
Table 5.
Main effect of shape (GKIN + GLUM) – (UNIFORM + STATIC)
Table 4.
Main effect of motion (GKIN + UNIFORM) – (GLUM + STATIC)
Talairach coordinates (mm)
Z–score
x
y
z
–38
–70
0
7.67*
38
–66
4
7.2*
–26
22
–92
–94
0
–12
5.38*
4.55*
32
–18
58
–48
46
–10
24
–48
–56
–34
–28
–26
–92
–10
44
44
16
28
32
–16
48
4.46*
4.13*
3.88
3.47
3.37
3.36
3.18
Anatomical
description
Z–score interaction
L GOm BA19/37
(MT/V5)
R GOm BA19/37
(MT/V5)
L GOi BA18 (KO)
R GL BA17/18
(V1/V2)
R LPi BA40
L LPs BA7
R Sulc.Lat.
L LPi BA40
R LPi BA40
L GL BA18 (V1/V2)
R GPrC BA6
0.27
0.30
0.91
0.15
1.83 (P = 0.07)
0.06
0.75
0.35
0.22
1.07
1.87 (P = 0.06)
can be obtained under passive conditions. This was true for the
subtraction of uniform motion from kinetic gratings and to a
slightly lesser degree for the subtraction of luminance defined
gratings from kinetic gratings. In the present experiment the
differential activation in the active condition (counting the
nonvertical gratings) was weaker than in the previous study and
located in the opposite hemisphere. The number of subjects was
smaller in the present study than in the previous study and the
task was slightly easier, which might account to a certain extent
for the weaker activation. Both experiments taken together
suggest that the counting of nonvertical gratings task is a less
optimal way of activating region KO. This fact, together with
interindividual differences in KO activation strength and
lateralization which we have documented in our subsequent
fMRI study (Van Oostende et al., 1996a,b), combined with
inherent limitations in the sensitivity of the PET technique,
might explain the variability in lateralization observed between
the two studies.
Another apparent discrepancy between the two studies is that
the comparison of kinetic with luminance defined gratings
under passive viewing yielded a stronger differential activation
than the active comparison in the present study, while the
opposite was true in the previous study. There are, however, two
major differences between the passive conditions of the two
studies. Here subjects were stimulated continuously compared
with 60% of the time in the previous study. More importantly,
multiple orientations of kinetic gratings and hence multiple
directions of motion were used in the present study. If the tuning
for the axis of motion is narrow enough in region KO, the use of
four axes of motion rather than one may result in stimulation of
four times as many neurons. Of course, at the level of neuronal
activity only a single population (tuned to one axis) will be active
at a time. However, due to the slow nature and spatial extent of
circulatory responses (Malonek and Grinvald, 1996), the change
in rCBF induced by the neuronal activity will outlast the
neuronal response and hence the rCBF changes induced by the
different axes of motion will summate. We have obtained direct
confirmation of this effect by comparing the fMRI signal over
area MT/V5 when stimulated with one or four axes of motion
(Cornette et al., 1996). Hence, combining the two effects, one
could expect an increase in rCBF by a factor of up to 6.6. This is
not very different from the factor of 7.2 observed between the
two studies using the active task as a common reference. In the
previous study the active condition was 1.75 times more
288 Kinetic Occipital Region • Dupont et al.
Talairach coordinates (mm)
Z–score
Anatomical
description
Z–score interaction
0
–4
–12
0
5.99*
5.61*
5.29*
4.50*
1.55 (P = 0.12)
0.90
0.55
0.50
–20
–20
–20
4.38*
3.50
3.85
R GOi BA18 (KO)
L GOi BA18 (KO)
R GOi BA19
L GOm BA 19/37
(MT/V5)
R GF/GOi BA19
L GOi BA19
R GOi BA18
x
y
z
34
–28
46
–36
–90
–92
–78
–76
34
–40
24
–68
–80
–90
0.11
0.89
0.31
effective than the passive condition (comparing the percentage
change in rCBF in right KO), while in the present study the
passive condition was 4.1 times more efficient (in left KO). Thus
both duration and range of stimulation contribute to the
effectiveness of the stimulus in activating region KO. When
using an active task the modulation by attention has to be quite
substantial before it can compensate for the reduction in
activation produced by using stimuli differing only slightly and
presented brief ly.
Definition and Selectivity of Region KO
We refer to the region selectively activated by kinetic boundaries
as the kinetic occipital area. This is used in a descriptive sense
since the three subtractions which yield differential activation in
this region all rely on a kinetic grating presentation as the
experimental condition. However, the kinetic boundaries were
always produced by pixels moving in opposite directions. Hence
we do not know whether the kinetic boundaries themselves or
the pixels moving in opposite directions are the critical aspect of
the stimulus. The initial experiment (Orban et al., 1995) might
provide some enlightenment in this respect. Subjects could base
their judgements only on the kinetic boundaries in the active
conditions and thus the task dependent increase in activation in
region KO in that experiment could be considered as evidence
that region KO is involved in the processing of kinetic
boundaries. Our subsequent fMRI experiment definitively
resolved the issue in favor of kinetic boundaries (Van Oostende
et al., 1996a,b).
Although at present the subtraction ‘kinetic grating minus
uniform motion’ is the optimal comparison with which to
visualize region KO, we do not imply that KO is the only region
active in this subtraction. What really defines region KO is its
functional profile based on a set of comparisons. In our opinion,
this represents the counterpart for functional imaging of using
the functional properties of neurons as a criterion for
distinguishing monkey visual cortical areas, along with
architectonics, connections and topographical organization.
Indeed, the functional profile of region KO was clearly different
from that of area MT/V5.
Comparison with Other PET Studies of
Form-from-Motion
Zeki (1993) brief ly reported a PET experiment in which
form-from-motion was compared with (the average of) uniform
motion and form-from-luminance. The stimulus was somewhat similar to ours in that stripes of different widths were
used, but as no details concerning stimulus size, element density
or speed of motion were provided, comparison with our results
is difficult. Judging from the figure provided, it is likely that
Figure 6. Statistical parametric maps showing the main effects of motion (green) and of shape (blue) superimposed on coronal sections (from –96 mm to –48 mm behind
the AC) of the average MRI of the 10 subjects. The contours are the outline of SPMs (up to y < –45 mm) thresholded at z = 3.09 (P < 0.001 uncorrected) projected
onto the nearest section. The white crosses indicate zero z and x Talairach coordinates at each y level. The red circles and crosses indicate the positions of region KO and
area MT/V5 respectively.
region KO was included in the region of activation. Furthermore, from the subtraction used by Zeki it is difficult to know
whether it is the motion, the shape of the kinetic contour
stimulus or both that caused the activation observed. Our
experiment clearly shows that both motion and shape activate
region KO.
Gulyás et al. (1994) also studied form-from-motion by comparing a form discrimination (using a form defined by motion)
with a motion discrimination (in a shape defined by motion).
Although many regions were activated in this subtraction, none
were near region KO. Several regions were located ventrally in
the fusiform gyrus, some of them close to the inferior
occipital/fusiform regions in which we observed a shape effect
(Table 5). This study only underscores the difficulty of
comparing kinetic shape and uniform motion in a paradigm
other than a passive fixation paradigm. The two dimensions to
be discriminated in the Gulyás et al. (1994) experiment were
very different: degree of coherence of motion and squareness of
a shape. It is difficult to see how comparison of these two
dimensions could isolate the processing of kinetic contours.
There is, however, agreement between the Gulyás et al. study
and ours in that form-from-motion is processed further along the
ventral pathway (Haxby et al., 1994). Our experiments show
that for these ventral regions form-from-motion is not different
from form-from-luminance, since interactions between motion
and shape main effects were absent.
Location of Region KO with Respect to Other Visual
Areas in the Human Brain
Our results clearly show that region KO is distinct from area
MT/V5, which is usually considered the most prominent motion
area in human cortex (Zeki et al., 1991; Tootell et al., 1995b;
Ungerleider, 1995), although many regions of the human brain in
fact process motion, as shown by the present results, as well as
those of Dupont et al. (1994), Dale et al. (1995) and Sunaert et
al. (1996). Another brain region responding to motion is area
V3A (Tootell et al., 1995a). The central vision representation in
area V3A is located higher and more medially than region KO
Cerebral Cortex Apr/May 1997, V 7 N 3 289
(Sunaert et al., 1996). Region LO defined by Malach et al. (1995)
is located posteriorly and ventrally to area MT/V5. Region KO
thus seems to be located dorsally and posteriorly to region LO.
Finally, region KO lies in front of the tier of three retinotopically
defined areas, V1, V2 and V3 (Sereno et al., 1995; Shipp et al.,
1995). However, comparisons across group studies are difficult
and further work is required to clarify the relationships of region
KO with areas V3 and V3A and region LO. Such experiments
using fMRI to map region KO and the other areas in a single
subject have shown that region KO is distinct from all three areas
(Van Oostende et al., 1996a,b). However, the present study
allows us only to conclude that region KO is selective for kinetic
boundaries and we must leave open the possibility that this
represents a new selectivity of an existing area rather than a new,
separate area of the human brain.
Dissociation of Visual Cortical Regions Processing
Shape and Motion
Although the functional profiles of area MT/V5 and region KO
are clearly different, both areas still process motion and shape
information. Thus in these posterior, middle occipital regions
the segregation of motion and shape is incomplete, although in
human area MT/V5 motion is clearly the dominant effect. This
latter observation is in good agreement with the monkey single
cell data as MT/V5 neurons are best driven and are most selective
for moving stimuli but also react to static luminance patterns and
are orientation selective (Albright, 1984; Marcar et al., 1995). In
this respect it is worth noting that when mapping the dorsal and
ventral occipito-temporal streams in human cortex, using
attention to locations and to faces respectively (Haxby et al.,
1994), the segregation was incomplete in posterior occipital
regions surrounding striate cortex.
Our results also show that beyond the middle occipital regions
there is a clear segregation, at least in the right hemisphere,
between ‘motion’ and ‘shape’, as more dorsal parietal areas are
significantly activated only by motion and more ventral
occipito-temporal areas are significantly activated only by shape.
This again is in agreement with the monkey data, which have
shown that in inferotemporal cortex and in V4 neurons can be
selective for orientation or shape irrespective of whether the
defining cues are motion or luminance differences (Sáry et al.,
1993, 1995; Logothetis and Charles, 1990). The strongest ventral
activation by shape occurred in a region (46, –78, –12)
corresponding relatively well to region LO (Malach et al., 1995),
the branching point of which was located at 43, –73, –18. It is
noteworthy that activation in this region was recently reported
by Goebel et al. (1996) in the comparison of letters defined by
motion and uniform motion. Again our results show that this
region is not exclusively involved in processing of kinetic
boundaries (the conjunction of shape and motion) but rather of
form, whether defined by motion or luminance.
Comparison with Lesion Studies
It has been reported that both cortical lesions (Regan et al.,
1992) and multiple sclerosis (Regan et al., 1991) affect the
perception of kinetic shapes much more than the perception of
luminance defined shapes. However, the widespread nature of
the lesions in both studies make a comparison with our results
difficult. Although at first glance the preferential impairment of
kinetic shape perception over that of luminance defined shapes
suggests that the motion preprocessing is affected in these
lesions, this need not necessarily be the case. Kinetic shape
perception might be more vulnerable to neuronal damage since
290 Kinetic Occipital Region • Dupont et al.
the proportion of neurons in the ventral pathway which are
shape selective for kinetic defined shapes is small compared
with those selective for luminance defined shapes (Sáry et al.,
1993, 1995).
Comparison with Monkey Data
It is well established that area MT neurons in monkeys respond
less vigorously to kinetic grating stimuli than to uniformly
moving random dot and random textured patterns (Snowden et
al., 1991; Marcar et al., 1995). Hence it may seem surprising that
in our experiments area MT/V5 is slightly more activated by
kinetic gratings than by uniform motion. However, during the
kinetic grating presentation, the MT neurons will be driven by
both forward and backward motion, while during the uniform
motion presentation they will be driven only by a single
direction. Thus, during a given presentation, twice as many MT
neurons respond to the kinetic gratings than to uniform motion.
Since the response of individual cells to kinetic gratings is more
than half that of uniform motion (Marcar et al., 1995), one would
expect a slightly larger population response to the kinetic
gratings than to the uniform motion.
Since kinetic gratings drive twice as many neurons as uniform
motion, it is sufficient that KO neurons simply respond equally
well to uniform motion and to kinetic gratings to explain the
profile of region KO we observed. Their response to local
motion would suffice to explain the KO activation in the
subtraction of luminance defined gratings from kinetic gratings.
We cannot, however, exclude the possibility that KO neurons are
selective for the orientation of kinetic boundaries. The results of
Snowden et al. (1991) suggest that KO neurons should have to be
nondirection selective to respond as much to kinetic gratings as
to uniform motion. Sensitivity to the motion discontinuities
similar to those which have recently been reported for
orientation discontinuities in V1 (Sillito et al., 1995) would
further accentuate the difference in the population response to
kinetic gratings compared with uniform motion. Preliminary
experiments in our laboratory have shown that some neurons in
areas V2 and V4t, which are not direction-selective, show an
enhanced and direction-selective response to a foreground
stimulus moving in the direction opposite to a slowly moving
background (Orban et al., 1989).
As in humans, an area other than MT/V5 also appears to
preprocess the kinetic grating motion signals in monkeys, since
lesions of area MT/V5 only mildly impair the discrimination of
kinetic grating orientation discrimination (Lauwers et al., 1995).
Which other areas of the monkey visual cortex may perform this
function is presently unclear. Both of the areas suggested by the
preliminary physiological recordings are unlikely choices. V2 is
located too posteriorly to correspond to region KO. Area V4t is
also unlikely, since it was probably included in the lesions of the
Lauwers et al. (1995) study. Thus this still leaves us with no clear
indication of which monkey cortical area contains neurons with
the properties accounting for the selectivity for kinetic gratings,
displayed by region KO in the human brain. Further experiments
both in humans and in monkeys are presently being undertaken
to address this question.
Notes
We are indebted to Prof. R. Frackowiak for making available the SPM
software. The technical help of M. De Paep, S. Vleugels, L. Verhaegen,
M. Heroes, T. De Groot, P. Kayenbergh, G. Meulemans and Y. Celis is
gratefully acknowledged. We thank S. Raiguel for comments on earlier
versions of the manuscript. This work was supported by Grants 9.007.88,
3.0043.89, 3.00227.95 and S 2/5-AV-E208 from the Belgian National
Research Council. P.D., B.D.B and A.R. are research associates of the
Belgian National Research Council. R.V. is a research assistant of the
National Research Council of Belgium.
Address correspondence to: Prof. Dr G. A. Orban, Laboratorium voor
Neuro- en Psychofysiologie, Katholieke Universiteit te Leuven, Campus
Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.
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