Exemplar Selectivity Reflects Perceptual Similarities in the Human Fusiform Cortex

Abstract

While brain imaging studies emphasized the category selectivity of face-related areas, the underlying mechanisms of our remarkable ability to discriminate between different faces are less understood. Here, we recorded intracranial local field potentials from face-related areas in patients presented with images of faces and objects. A highly significant exemplar tuning within the category of faces was observed in high-Gamma (80-150 Hz) responses. The robustness of this effect was supported by single-trial decoding of face exemplars using a minimal (n = 5) training set. Importantly, exemplar tuning reflected the psychophysical distance between faces but not their low-level features. Our results reveal a neuronal substrate for the establishment of perceptual distance among faces in the human brain. They further imply that face neurons are anatomically grouped according to well-defined functional principles, such as perceptual similarity.

A face-selective ventral occipito-temporal map of the human brain with intracerebral potentials

“…These relatively rare (i.e., compared with neuroimaging) intracranial electroencephalographic (iEEG) recordings offer a unique opportunity to measure direct local neural activity with a very high SNR. iEEG studies comparing faces and nonface objects have recorded face-selective responses in widely distributed regions of the VOTC and made a number of important observations for understanding the neural basis of face categorization (26)(27)(28)(29)(30)(31)(32)(33)(34). However, even when large samples of participants are tested, face-selective responses are broadly distributed in the VOTC, without evidence of a clustered organization as found in fMRI (27,30,34).…”

“…For instance, increases of neural activity to faces compared with nonface objects can be found at various time scales, both in low-frequency responses time-locked and phase-locked to the stimulus [i.e., eventrelated potentials (ERPs), such as the N200/N170 component (27,31,36,40)] and in non-phase-locked high-frequency electrophysiological activity [high-frequency broadband, i.e., gamma activity (29,30,(33)(34)(35)40)]. In the latter case, relevant frequency bands vary substantially across recording sites, individual brains, and time windows, making it virtually impossible to objectively define, quantify, and compare face-selective responses across different brain regions.…”

Ignition’s glow: Ultra-fast spread of global cortical activity accompanying local “ignitions” in visual cortex during conscious visual perception

“…The comparison was based on the areas under the curves of these intervals' time courses (AUC, defined here as the mean of the interval's time point values). Electrodes were defined as responsive if their response AUCs were significantly larger compared to their baseline AUCs over trials (Davidesco et al, 2013b).…”

Brain activity correlates with emotional perception induced by dynamic avatars

“…Similar visual localizers have been used in recently published studies from our lab (Davidesco et al, 2013;Harmelech et al, 2015;Yellin et al, 2015).…”

“…The first four bilateral group-ROIs were defined as the activated voxels located within 30 mm of the multi subject activity center (p < 0.05 corrected). Three bilateral ROIs were defined using the visual localizer, and were based on contrasts used in previous published studies -EBA and FBA were defined using the contrast: Body > Texture (Harmelech et al, 2015), FFA was defined using the contrast Faces > Buildings (Davidesco et al, 2013;Kanwisher et al, 1997). STS was defined using the contrast emotional gait vs. neutral gait per subject according to the leave one out criteria (e.g.…”