Does mental imagery of motion recruit populations of direction-selective neurons that also respond to perceptual motion? We show first that imagining a moving pattern while fixating a stationary target yielded a motion aftereffect (MAE), as measured by the response to directionally ambiguous perceptual test stimuli (dynamic dot displays). In a second experiment we replicated the effect and also observed the MAE when subjects' eyes were closed during imagery. In a further set of experiments, we asked whether photographs of objects frozen in motion (animals, people and vehicles) could also lead to motion adaptation. When a series of unrelated photographs was viewed, all with implied motion in the same direction, an MAE in the opposite direction was induced, again measured with dynamic dot test stimuli. The MAE was found both for right / left implied motion and for in / out implied motion, the latter created by using mirror-revered pairs of identical implied motion images either facing towards or away from each other. Similar to the perceptual MAE, the MAE to implied motion significantly declined if a delay (3 s) was introduced between adaptation and test. The MAEs to imagined and implied motion ranged from 20 – 35 % of the size of the MAE from perceived motion. The transfer of adaptation from imagined and implied motion to perception of real motion demonstrates that at least some of the same direction-selective neurons are involved in imagination and actual perception.
Both functional neuroimaging (fMRI) and electrocorticography (ECoG) research has revealed selective responses to faces, bodyparts, words and places, in human ventral temporal cortex (VTC). However, the precise spatial organization of ECoG selective responses in VTC, as well as the nature of the coupling between functional responses measured with ECoG and fMRI is poorly understood. To address these questions we measured category selectivity to faces, bodyparts, cars, and houses using ECoG and fMRI in six epileptic patients and precisely located ECoG and fMRI responses relative to each subject's cortical surface. Our data indicate a clear spatial organization of ECoG selectivity, where the mid-fusiform sulcus forms an anatomical boundary between regions showing preference to animate vs. inanimate categories. Specifically, ECoG broadband (30-160Hz) responses on the lateral fusiform gyrus and inferotemporal gyrus showed strong selectivity to faces, but responses in the mid fusiform gyrus, collateral suclus and parahippocampal gyrus showed a preference to houses and cars. Strikingly, an independent data set revealed that these preferential responses are reliable and are evident for individual images from these categories. We next compared the distributed pattern of ECoG selectivity with that measured with fMRI, finding significant correlations between the two measurements when the fMRI signal was extracted in the vicinity (3-5mm) of each electrode. The strength of this coupling varied with time and frequency band: early (100-350ms) ECoG responses across all frequency bands were positively coupled with fMRI, while later (>350ms) ECoG responses showed positive correlation with fMRI in the broadband range and negative correlation in low frequencies (4-12Hz). Our data thus reveal a clear spatial organization of ECoG category selectivity in VTC, which is evident even in responses to single images. Finally, the coupling between ECoG and fMRI selectivity in the human VTC depends on the timing and properties of neural response at different frequencies. Meeting abstract presented at VSS 2013
Human cortical area MT+ (hMT+) is known to respond to visual motion stimuli, but its causal role in the conscious experience of motion remains largely unexplored. Studies in non-human primates demonstrate that altering activity in area MT can influence motion perception judgments, but animal studies are inherently limited in assessing subjective conscious experience. In the current study, we use functional magnetic resonance imaging (fMRI), intracranial electrocorticography (ECoG), and electrical brain stimulation (EBS) in three patients implanted with intracranial electrodes to address the role of area hMT+ in conscious visual motion perception. We show that in conscious human subjects, reproducible illusory motion can be elicited by electrical stimulation of hMT+. These visual motion percepts only occurred when the site of stimulation overlapped directly with the region of the brain that had increased fMRI and electrophysiological activity during moving compared to static visual stimuli in the same individual subjects. Electrical stimulation in neighboring regions failed to produce illusory motion. Our study provides evidence for the sufficient causal link between the hMT+ network and the human conscious experience of visual motion. It also suggests a clear spatial relationship between fMRI signal and ECoG activity in the human brain.
We examined the relationship between anatomy, category selectivity, and retinotopy in ventral visual cortex of 13 subjects using fMRI. Each subject participated in 3 experiments: 1) a functional localizer identifying face- and place-selective regions, 2) phase-encoded retinotopy to define retinotopic maps, & 3) an experiment where faces or houses were presented either foveally or peripherally to examine the relationship between category selectivity and eccentricity preference (Levy 2001). First, we replicate previous findings regarding the organization of ventral visual cortex including: 1) multiple face patches: IOG, mFus, pFus, and aFus (Weiner, 2010,Tsao 2008, Rajimehr, 2009), 2) hV4/VO organization (Brewer 2005), 3) overlap of parahippocampal (PHC) visual field maps with the PPA (Arcaro 2009), and 4) alignment of eccentricity preferences with category selectivity (Levy 2001). Second, we integrated these findings with anatomical constraints into a single organization extending that of Weiner 2010 by including: 1) Posterior posterior transverse collateral sulcus (COS) to guide the location of hV4/VO and face-selective IOG, 2) anterior transverse COS to distinguish between mFus and aFus, 3) posterior extent of the hippocampus as landmark for the anterior extent of retinotopy, a boundary between mFus and aFus patches, and marking where place selectivity spreads from the COS onto the PHC, and 4) alignment of face patches with distinct retinotopic clusters (hV4, VO, PHC).Third, we examined the eccentricity preferences of face and place regions finding 1) increased position tolerance from posterior to anterior with different preferences across IOG, pFus, mFus and aFus face patches and position invariance in place-selective regions appearing only anterior to visual field maps, and 2) different pattern of eccentricity bias for face and place-selective regions. The results bear directly on systematically defining commonly used functional regions (FFA, PPA), and suggest a hierarchical axis of visual processing from posterior to anterior in ventral cortex. Meeting abstract presented at VSS 2012
Abstract Skilled reading requires rapidly recognizing letters and word forms; people learn this skill best for words presented in the central visual field. Measurements over the last decade have shown that when children learn to read, responses within ventral occipito-temporal cortex (VOT) become increasingly selective to word forms. We call these regions the VOT reading circuitry (VOTRC). The portion of the visual field that evokes a response in the VOTRC is called the field of view (FOV) . We measured the FOV of the VOTRC and found that it is a small subset of the entire field of view available to the human visual system. For the typical subject, the FOV of the VOTRC in each hemisphere is contralaterally and foveally biased. The FOV of the left VOTRC extends ~9° into the right visual field and ~4° into the left visual field along the horizontal meridian. The FOV of the right VOTRC is roughly mirror symmetric to that of the left VOTRC. The size and shape of the FOV covers the region of the visual field that contains relevant information for reading English. It may be that the size and shape of the FOV, which varies between subjects, will prove useful in predicting behavioral aspects of reading.
Skilled reading requires rapidly recognizing letters and word forms; people learn this skill best for words presented in the central visual field. Measurements over the last decade have shown that when children learn to read, responses within ventral occipito-temporal cortex (VOT) become increasingly selective to word forms. We call these regions the VOT reading circuitry (VOTRC). The portion of the visual field that evokes a response in the VOTRC is called the field of view (FOV). We measured the FOV of the VOTRC and found that it is a small subset of the entire field of view available to the human visual system. For the typical subject, the FOV of the VOTRC in each hemisphere is contralaterally and foveally biased. The FOV of the left VOTRC extends ∼9° into the right visual field and ∼4° into the left visual field along the horizontal meridian. The FOV of the right VOTRC is roughly mirror symmetric to that of the left VOTRC. The size and shape of the FOV covers the region of the visual field that contains relevant information for reading English. It may be that the size and shape of the FOV, which varies between subjects, will prove useful in predicting behavioral aspects of reading.
Perceptual systems adapt to their inputs. As a result, prolonged exposure to particular stimuli alters judgments about subsequent stimuli. This phenomenon is commonly assumed to be sensory in origin. Changes in the decision-making process, however, may also be a component of adaptation. Here, we quantify sensory and decision-making contributions to adaptation in a facial expression paradigm. As expected, exposure to happy or sad expressions shifts the psychometric function toward the adaptor. More surprisingly, response times show both an overall decline and an asymmetry, with faster responses opposite the adapting category, implicating a substantial change in the decision-making process. Specifically, we infer that sensory changes from adaptation are accompanied by changes in how much sensory information is accumulated for the two choices. We speculate that adaptation influences implicit expectations about the stimuli one will encounter, causing modifications in the decision-making process as part of a normative response to a change in context.
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