Improved motion perception and impaired spatial suppression following disruption of cortical area MT/V5.
ABSTRACT As stimulus size increases, motion direction of high-contrast patterns becomes increasingly harder to perceive. This counterintuitive behavioral result, termed "spatial suppression," is hypothesized to reflect center-surround antagonism-a receptive field property ubiquitous in sensory systems. Prior research proposed that spatial suppression of motion signals is a direct correlate of center-surround antagonism within cortical area MT. Here, we investigated whether human MT/V5 is indeed causally involved in spatial suppression of motion signals. The key assumption is that a disruption of neural mechanisms that play a critical role in spatial suppression could allow these normally suppressed motion signals to reach perceptual awareness. Thus, our hypothesis was that a disruption of MT/V5 should weaken spatial suppression and, consequently, improve motion perception of large, moving patterns. To disrupt MT/V5, we used offline 1 Hz transcranial magnetic stimulation (TMS)-a method that temporarily attenuates normal functioning of the targeted cortex. Early visual areas were also targeted as a control site. The results supported our hypotheses and showed that disruption of MT/V5 improved motion discrimination of large, moving stimuli, presumably by weakening surround suppression strength. This effect was specific to MT/V5 stimulation and contralaterally presented stimuli. Evidently, the critical neural constraints limiting motion perception of large, high-contrast stimuli involve MT/V5. Additionally, our findings mimic spatial suppression deficits that are observed in several patient populations and implicate impaired MT/V5 processes as likely neural correlates for the reported perceptual abnormalities in the elderly, patients with schizophrenia and those with a history of depression.
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ABSTRACT: The pursuit-pursuing illusion is a visual illusion where a circular object placed in the centre of a radial pattern consisting of thin sectors is seen to move in the pursuit eye movement direction. The present study investigates the role of the surrounding texture, replacing the sectors with random dots or stripes in an orientation that was orthogonal, parallel or oblique to the pursuit direction. The experiments demonstrate that the acquired illusory effect was large for the orthogonal stripes. However, each surrounding texture produces a relatively smaller effect than the radial sectors. These results suggest that a hypothesis based on the property of a centre-surround relative-motion detector cannot fully explain the illusion and that the radial stimulus structure itself plays an important role in this illusion.Perception 01/2014; 5(1):20-40. · 1.11 Impact Factor
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ABSTRACT: In addition to motion perception per se, we utilize motion information for a wide range of brain functions. These varied functions place different demands on the visual system, and therefore a stimulus that provides useful information for one function may be inadequate for another. For example, the direction of motion of large high-contrast stimuli is difficult to discriminate perceptually, but other studies have shown that such stimuli are highly effective at eliciting directional oculomotor responses such as the ocular following response (OFR). Here, we investigated the degree of independence between perceptual and oculomotor processing by determining whether perceptually suppressed moving stimuli can nonetheless evoke reliable eye movements. We measured reflexively evoked tracking eye movements while observers discriminated the motion direction of large high-contrast stimuli. To quantify the discrimination ability of the oculomotor system, we used signal detection theory to generate associated oculometric functions. The results showed that oculomotor sensitivity to motion direction is not predicted by perceptual sensitivity to the same stimuli. In fact, in several cases oculomotor responses were more reliable than perceptual responses. Moreover, a trial-by-trial analysis indicated that, for stimuli tested in this study, oculomotor processing was statistically independent from perceptual processing. Evidently, perceptual and oculomotor responses reflect the activity of independent dissociable mechanisms despite operating on the same input. While results of this kind have traditionally been interpreted in the framework of perception versus action, we propose that these differences reflect a more general principle of modularity.Journal of Vision 03/2014; 14(3). · 2.73 Impact Factor
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ABSTRACT: Recent evidence suggests that normal aging is typically accompanied by impairment in the ability to perceive the global (overall) motion of visual objects in the world. The purpose of this study was to examine the interplay between age-related changes in the ability to perceive translational global motion (up vs. down) and important factors such as the spatial extent (size) over which movement occurs and how cluttered the moving elements are (density). We used random dot kinematograms (RDKs) and measured motion coherence thresholds (% signal elements required to reliably discriminate global direction) for young and older adults. We did so as a function of the number and density of local signal elements, and the aperture area in which they were displayed. We found that older adults' performance was relatively unaffected by changes in aperture size, the number and density of local elements in the display. In young adults, performance was also insensitive to element number and density but was modulated markedly by display size, such that motion coherence thresholds decreased as aperture area increased (participants required fewer local elements to move coherently to determine the overall image direction). With the smallest apertures tested, young participants' motion coherence thresholds were considerably higher (~1.5 times worse) than those of their older counterparts. Therefore, when RDK size is relatively small, older participants were actually better than young participants at processing global motion. These findings suggest that the normal (disease-free) aging process does not lead to a general decline in perceptual ability and in some cases may be visually advantageous. The results have important implications for the understanding of the consequences of aging on visual function and a number of potential explanations are explored. These include age-related changes in spatial summation, reduced cortical inhibition, neural blur and attentional resource allocation.Frontiers in Aging Neuroscience 08/2014; 6:199. · 2.84 Impact Factor
As stimulus size increases, motion direction of high-contrast patterns becomes increasingly harder to perceive. This counterintuitive
behavioral result, termed “spatial suppression,” is hypothesized to reflect center–surround antagonism—a receptive field property
these normally suppressed motion signals to reach perceptual awareness. Thus, our hypothesis was that a disruption of MT/V5 should
visual areas were also targeted as a control site. The results supported our hypotheses and showed that disruption of MT/V5 improved
motion discrimination of large, moving stimuli, presumably by weakening surround suppression strength. This effect was specific to
high-contrast stimuli involve MT/V5. Additionally, our findings mimic spatial suppression deficits that are observed in several patient
Center–surround antagonism is a simple, yet powerful recep-
tive field property that is found across sensory modalities,
ranging from vision to electroperception (Tadin and Lappin,
2005a). In vision, center–surround antagonism is typically
manifested as the reduction of a neuron’s firing when the
surround region. Consequently, such neurons respond poorly
to large, uniform stimuli. Theoretical and neurophysiological
work associates this basic mechanism with key neural pro-
cesses, including redundancy reduction, input normalization,
figure-ground segregation and computation of object motion
(Born et al., 2000; Vinje and Gallant, 2000; Schwartz and Si-
moncelli, 2001; Pack et al., 2005).
Despite their omnipresence at the neural level, we have rela-
subjects. In motion perception, it has been proposed that spatial
suppression—a counterintuitive elevation of direction discrimi-
nation thresholds with increasing stimulus size—is a direct per-
ceptual correlate of center–surround antagonism within cortical
area MT/V5 (Tadin et al., 2003). This linking hypothesis is sup-
ported by several studies offering largely correlational evidence.
For example, the dependency of spatial suppression on stimulus
size and eccentricity matches that of center–surround MT/V5
foreshadowed the discovery of contrast-dependent center–sur-
round antagonism in MT/V5 (Pack et al., 2005).
Our first aim was to investigate the hypothesized causal in-
volvement of human MT/V5 in spatial suppression of motion
signals. The assumption was that a disruption of neural mecha-
nisms critically involved in spatial suppression could allow these
normally suppressed motion signals to reach perceptual aware-
ing would reduce spatial suppression and improve motion
the intended effect of MT/V5 disruption would effectively be
the Harvard-Thorndike Clinical Research Center at Beth Israel Deaconess Medical Center [National Center for Re-
TheJournalofNeuroscience,Month??,2011 • 31(xx):xxx-xxx • 1
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we used offline 1 Hz TMS—a technique that temporarily atten-
uates normal functioning of the stimulated cortex with an effect
that outlasts the period of stimulation (Boroojerdi et al., 2000;
Battelli et al., 2009). In addition to MT/V5, we targeted early
visual areas (EVA) because they also contain center–surround
neurons (Jones et al., 2001; Shushruth et al., 2009) and make
direct projections to MT/V5 (Born and Bradley, 2005). This ad-
ditional target site is a valuable active control of nonspecific and
indirect effects of TMS.
The feasibility of observing spatial suppression impairments
that are evident as better-than-normal perception of large mo-
populations, including the elderly (Betts et al., 2005, 2009), pa-
tients with schizophrenia (Tadin et al., 2006), and history of de-
comparable to spatial suppression abnormalities that are found
of observed deficits.
We studied six subjects (ages 22–32 years, 1 female) all of whom passed
TMS exclusion criteria (Rossi et al., 2009) and gave written informed
consent (approved by the Beth Israel Deaconess Medical Center’s Insti-
tutional Review Boards). No subject experienced any adverse effects.
attenuate TMS noise.
Selection of coil location for MT/V5 stimulation.For five subjects, we used
functional magnetic resonance imaging (fMRI) MT/V5 localization and
et al., 2006; Battelli et al., 2009) (supplemental Fig. 1, available at www.
jneurosci.org as supplemental material); for the remaining subject,
localized using standard neuroimaging procedures (described below).
These functional images were overlaid on structural brain scans and
coregistered to the subject’s head using Brainsight Frameless stereotaxy
studies demonstrating that left MT/V5 TMS is more effective at causing
appropriate coil location was confirmed by inducing moving phos-
phenes using short trains of 10 Hz stimulation. The TMS coil was held
at a 45° angle.
was localized functionally using phosphene induction (Fernandez et al.,
near the occipital pole targets these early visual areas (Kastner et al.,
left hemisphere 2 cm rostral and 2 cm lateral to the inion. The subjects
then viewed a circle (8° radius) at 9° eccentricity in the right visual field,
corresponding to the large stimulus used in the study (see below). The
experimenter then adjusted the coil location until a subject reported a
the target for TMS of EVA, henceforth “EVA TMS.” The TMS coil was
held in place with its handle facing upward.
TMS stimulation. TMS was administered with a Magstim 2T Rapid
delivering biphasic pulses. Stimulation intensity was 75% of maximal
described locations. Brainsight was used to continuously monitor coil
position and assure consistent targeting (Gugino et al., 2001).
Previous studies have shown that 1 Hz TMS temporarily reduces ex-
citability of the cortex within the stimulated area and that this effect
2004; Allen et al., 2007). The time required to perform the below-
described psychophysical task (?13–16 min) is within that for which 1
Hz TMS has been shown to have lasting effects in parietal regions as well
as in MT/V5 (Hilgetag et al., 2001; Silvanto et al., 2008; Battelli et al.,
we statistically examined trends across three trial blocks following each
TMS session. The rationale was that if the effect of TMS did not outlast
0.74, p ? 0.51).
Center for Biomedical Imaging). Standard procedures were used to lo-
calize MT/V5 (Tootell et al., 1995). Briefly, MT/V5 was localized as the
region on the ascending branch of the inferior occipital sulcus that ex-
hibited the stronger blood oxygenation level-dependent responses dur-
ing blocks of expanding and contracting concentric gratings compared
with the blocks of stationary concentric gratings (supplemental Fig. 1,
available at www.jneurosci.org as supplemental material).
1997) and were shown on a linearized monitor (wide-screen 24 inch
Sony GDM-FW900 CRT, 1024 ? 640 resolution, 120 Hz). Viewing was
and background illumination were 0.01 and 31 cd/m2.
Psychophysical thresholds were measured by adaptive QUEST staircases
uli were drifting gratings (horizontal orientation, 1 cycle/degree, 4°/s, 99%
cosine envelope, whose radius defined the stimulus size (Fig. 1A). For very
brief stimuli (? ? 15 ms), the temporal contrast envelope was Gaussian.
Longer temporal envelopes were trapezoid-like, where flanks were half-
Gaussians and the central portion was set to the maximum contrast. Fine
temporal Gaussians. Stimulus duration was defined as the width at half-
Four stimulus conditions were used (Fig. 1A): two sizes (small, 1.2°
radius, or large, 8° radius) at two stimulus locations (?9° horizontal
eccentricity). The small stimulus size was chosen based on pilot experi-
Lappin, 2005b). The large stimulus was selected to be large enough to
mone, 1987; Raiguel et al., 1995), but small enough not to cross the
location, with its size and location chosen pseudorandomly. Subjects
indicated the perceived direction (up or down) by a key press. Feedback
was provided. The next trial started 800 ms after subjects’ responses.
10 s break. Each block contained 8 interleaved staircases, yielding 2
thresholds estimates for each of 4 conditions. Over 3 blocks, this yielded
which ensured that all trials were completed while the effects of TMS
lasted (see above). Brief stimulus durations (?100 ms) and their unpre-
dictable peripheral location precluded both saccadic and pursuit eye
Each subject completed five sessions (Fig. 1B). The first session was
conducted a day before TMS, and was used as a practice session and to
generate staircase starting points for following sessions. The second ses-
sion was a pre-TMS baseline. The third and fourth sessions were con-
ducted immediately following MT/V5 and EVA TMS (order of
a post-TMS baseline. To prevent carryover effects, there was at least a 90
min break between sessions.
2 • J.Neurosci.,Month??,2011 • 31(xx):xxx-xxxTadinetal.•CausalRoleofAreaMT/V5inSpatialSuppression
To measure spatial suppression strength, we used a simple task
where observers discriminated motion direction of brief stimuli.
Thresholds were measured for small (1.2° radius) and large (8°
radius) high-contrast stimuli that were moving either upward or
downward, and presented in either the right or the left visual
field (Fig. 1A). Typically, observers’ direction discrimination
thresholds are considerably higher for large than for small,
moving stimuli—a psychophysical finding described as spatial
suppression (Tadin et al., 2003). To quantify spatial suppres-
sion strength, we introduced the suppression index (SI), de-
fined as the difference of log10thresholds for large and small
stimuli (Tadin et al., 2003, 2006) with higher numbers indi-
cating stronger spatial suppression.
Results from pre-TMS baseline sessions demonstrated strong
spatial suppression (left field SI ? 0.41 ? 0.04, right field SI ?
0.46 ? 0.05), with motion discrimination thresholds for large
(20 ? 3 ms). These results are consistent with previous studies
(Tadin et al., 2003, 2006). As no SI differences were found be-
right field: t5? 0.60, p ? 0.58), these results were averaged to
this no TMS condition (the raw data are shown in the supple-
mental Fig. 2, available at www.jneurosci.org as supplemental
During TMS sessions, we applied 15 min of 1 Hz TMS to
either the scalp location corresponding to left MT/V5 (supple-
mental Fig. 1, available at www.jneurosci.org as supplemental
material) or the left occipital location where single-pulse TMS
was found to elicit peripheral phosphenes (EVA TMS). Our first
had an effect on spatial suppression strength. A repeated-
measures ANOVA, with stimulus location (contralateral and
ipsilateral to the stimulation) and TMS condition (no TMS,
MT/V5 TMS, EVA TMS) as main factors, revealed a significant
interaction (F(2,10)? 4.0, p ? 0.05). Planned pairwise compari-
sons showed that, for contralaterally presented stimuli, spatial
suppression strength was reduced following MT/V5 TMS (Fig.
2A; t5? 3.72, p ? 0.01) but not after EVA TMS (t5? 0.68, p ?
0.53). Demonstrating such specificity for the stimulated cortical
suggests that the measurable effects of TMS are largely confined
to the stimulated area. For ipsilaterally presented stimuli, no SI
changes were observed following MT/V5 TMS (t5? 0.32, p ?
0.76), demonstrating that the underlying mechanisms exhibit at
least a gross retinotopy.
The observed weakening of spatial suppression could be due
to (1) increased thresholds for discriminating small, moving
stimuli, (2) improved motion discriminations of large stimuli or
(3) a combination of both effects. Examination of post-TMS
threshold changes (Fig. 2B) showed that MT/V5 TMS had no
effect on direction discriminations of small grating stimuli (t5?
0.68, p ? 0.53) (see Discussion for more details). However, as
hypothesized, our results revealed improvements in motion dis-
criminations of large, moving stimuli presented contralateral to
stimulated MT/V5 (t5? 3.45, p ? 0.02). Specifically, the average
threshold for discriminating motion direction of large stimuli
decreased by 0.072 ? 0.02 log unit, which was, on average, a 10
ms threshold improvement. These paradoxical results mimic
Tadinetal.•CausalRoleofAreaMT/V5inSpatialSuppression J.Neurosci.,Month??,2011 • 31(xx):xxx-xxx • 3
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depression who exhibit better-than-normal motion perception
of large patterns coupled with normal perception of small, mov-
ing stimuli (Golomb et al., 2009).
rect effects of TMS associated with reductions in effective stimu-
tial suppression, reduction of stimulus speed yields increasing
duration thresholds for all sizes (Lappin et al., 2009), while a
for small, moving stimuli (Tadin et al., 2003).
Here, we report seemingly paradoxical TMS-induced improve-
ment in motion discriminations of large, moving stimuli—a re-
sult specific to MT/V5 stimulation and the stimuli presented in
the contralateral visual field. The weakening of spatial suppres-
sion during a TMS-induced period of reduced excitability of
MT/V5 suggests that the critical neural constraints limiting mo-
MT/V5. These findings are consistent with our hypothesis that
behaviorally observed spatial suppression is a direct perceptual
correlate of center–surround antagonism in area MT. Support
to elucidate functional roles of center–surround antagonism in
suppression of large, background-like motions facilitates rapid
figure-ground segregation of moving objects by suppressing
background motion signals (Born et al., 2000; Tadin and Blake,
Why does the disruption of MT/V5 attenuate behaviorally
measured spatial suppression? Center–surround neurons are
et al., 1995; Born, 2000), indicating that surround inhibition in
MT/V5 is not inherited from feedforward inputs. This, in turn,
indicates that a selective disruption of MT/V5 processing should
interfere with the development of center–surround antagonism,
in turn affecting perceptual correlates of MT/V5 surround inhi-
suppressive surround of MT/V5 neurons (see Materials and
significant changes in MT/V5 surround inhibition. Although
surround inhibition also occurs in a number of earlier visual
areas [V1 (Jones et al., 2001); V2 (Shushruth et al., 2009)], these
center–surround interactions occur at a smaller spatial scale and
likely play a lesser role in suppressing neural responses to 16°
diameter stimuli used here.
on duration thresholds and, consequentially, briefly presented
stimuli (?100 ms), likely facilitated detection of changes in sur-
round inhibition for three specific reasons: First, considerable
prior work on spatial suppression has documented the utility of
this strategy (Tadin et al., 2003, 2005b, 2006; Betts et al., 2005,
et al., 2008). Specifically, information about motion direction of
brief stimuli (?100 ms) in area MT/V5 is primarily carried by
neurons with antagonistic surrounds, and not by MT/V5 neu-
rons that lack suppressive surround and actually prefer large,
background-like motions. Third, spatial suppression results ob-
tained using this approach cannot be explained by size-
dependent changes in contrast sensitivity (Glasser and Tadin,
2010) as might be the case for longer, counterphasing stimuli
(Aaen-Stockdale et al., 2009).
yields improvements in motion perception of large stimuli cou-
pled with unchanged motion discriminations of small gratings
with a history of depression). This finding suggests that while
MT/V5 is critical for suppression of large, background-like mo-
tions, it is not solely responsible for the processing of small, first-
order moving stimuli. A similar conclusion arises from lesion
work, which revealed relatively unimpaired motion discrimina-
and Pasternak, 1999). The observed robustness to MT/V5 injury
is likely due to widely distributed mechanisms underlying per-
ception of first-order motion (Plant and Nakayama, 1993; Su-
naert et al., 1999).
Finally, we note that our results mimic spatial suppression
patients with schizophrenia (Tadin et al., 2006) and a history of
depression (Golomb et al., 2009). Specifically, our results closely
mimic Golomb et al. (2009), who also reported a weakening of
spatial suppression that was due to better-than-normal percep-
tion of large, moving stimuli paired with normal perception of
small, moving stimuli. It should be noted, however, that the out-
TMS is presumed to cause a gross impairment of MT/V5 func-
tioning, special population deficits are likely more specific and
probably involve a decrease in the efficacy of inhibitory mecha-
nisms (Betts et al., 2005; Tadin et al., 2006; Golomb et al., 2009).
Indeed, old age, schizophrenia, and depression have all been
2003; Yoon et al., 2010). In schizophrenia, abnormal reductions
of GABA concentration in visual cortex strongly correlate with
abnormally weak surround suppression in the orientation do-
main (Yoon et al., 2010).
In summary, our results show that disruption of MT/V5 pro-
cessing improves motion perception of large stimuli and, conse-
quently, reduces the strength of spatial suppression. While the
inhibitory processing within MT/V5 that normally impairs per-
ception of large background motions. In other words, normally
functioning MT/V5 is necessary for strong spatial suppression of
large moving stimuli. We speculate that this suppression of uni-
form background-like stimuli directly enhances saliency of
smaller moving objects—a hypothesis that is a topic of our cur-
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