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Establishing consistent relationships between neural activity and behavior is a challenge in human cognitive neuroscience research. We addressed this issue using variable time constraints in an oddball frequency-sweep design for visual discrimination of complex images (face exemplars). Sixteen participants viewed sequences of ascending presentation durations, from 25 to 333 ms (40–3 Hz stimulation rate) while their electroencephalogram (EEG) was recorded. Throughout each sequence, the same unfamiliar face picture was repeated with variable size and luminance changes while different unfamiliar facial identities appeared every 1 s (1 Hz). A neural face individuation response, tagged at 1 Hz and its unique harmonics, emerged over the occipito-temporal cortex at 50 ms stimulus duration (25–100 ms across individuals), with an optimal response reached at 170 ms stimulus duration. In a subsequent experiment, identity changes appeared non-periodically within fixed-frequency sequences while the same participants performed an explicit face individuation task. The behavioral face individuation response also emerged at 50 ms presentation time, and behavioral accuracy correlated with individual participants’ neural response amplitude in a weighted middle stimulus duration range (50–125 ms). Moreover, the latency of the neural response peaking between 180 and 200 ms correlated strongly with individuals’ behavioral accuracy in this middle duration range, as measured independently. These observations point to the minimal (50 ms) and optimal (170 ms) stimulus durations for human face individuation and provide novel evidence that inter-individual differences in the magnitude and latency of early, high-level neural responses are predictive of behavioral differences in performance at this function.

The N170 is a large deflection of the human electroencephalogram (EEG), peaking at about 170 milliseconds over the occipito-temporal cortex after the sudden onset of a face stimulus. The N170 reflects perceptual awareness of a face and its onset corresponds to the emergence of reliable face-selectivity in the human brain. However, whether sensitivity to the long-term familiarity of a face identity emerges already at this early time-point remains debated. Here we provide a brief survey of the 45 published studies comparing the N170 response to unfamiliar and familiar (famous, experimentally familiarized, personally familiar and own) faces. Even though effects of familiarity on the N170 are relatively small and inconsistent across studies, this overview indicates that face familiarity significantly increases the N170 amplitude. This effect is especially present for personally familiar faces, learned in natural conditions. In the human brain, effects linked to familiarity with specific facial identities therefore appear to emerge between 150 and 200 ms in occipito-temporal brain regions, i.e., shortly after the onset of face-selectivity but at the same time as the earliest high-level effects of immediate unfamiliar face identity repetition. This observation challenges standard neurocognitive models with a clear-cut distinction between perceptual and memory stages in human face recognition.

International audience; Sex categorization is essential for mate choice and social interactions in many animal species. In humans, sex categorization is readily performed from the face. However, clear neural markers of face-sex categorization, i.e., common responses to widely variable individuals from one sex, have not been identified so far in humans. To isolate a direct signature of rapid and automatic face-sex categorization generalized across a wide range of variable exemplars, we recorded scalp electroencephalogram (EEG) from 32 participants (16 females) while they were exposed to variable natural face images from one sex alternating at a rapid rate of 6 Hz (i.e., 6 images per second). Images from the other sex were inserted every 6th stimulus (i.e., at a 1-Hz rate). A robust categorization response to both sex contrasts emerged at 1 Hz and harmonics in the EEG frequency spectrum over the occipito-temporal cortex of most participants. The response was larger for female faces presented among male faces than the reverse, suggesting that the two sex categories are not equally homogenous. This asymmetrical response pattern disappeared for upside-down faces, ruling out the contribution of low-level physical variability across images. Overall, these observations demonstrate that sex categorization occurs automatically after a single glance at natural face images and can be objectively isolated and quantified in the human brain within a few minutes.

International audience; Conceptual knowledge allows the categorisation of items according to their meaning beyond their physical similarities. This ability to respond to different stimuli (e.g., a leek, a cabbage, etc.) based on similar semantic representations (e.g., belonging to the vegetable category) is particularly important for language processing, because word meaning and the stimulus form are unrelated. The neural basis of this core human ability is debated and is complicated by the strong reliance of most neural measures on explicit tasks, involving many non-semantic processes. Here we establish an implicit method, i.e., fast periodic visual stimulation (FPVS) coupled with electroencephalography (EEG), to study neural conceptual categorisation processes with written word stimuli. Fourteen neurotypical participants were presented with different written words belonging to the same semantic category (e.g., different animals) alternating at 4 Hz rate. Words from a different semantic category (e.g., different cities) appeared every 4 stimuli (i.e., at 1 Hz). Following a few minutes of recording, objective electrophysiological responses at 1 Hz, highlighting the human brain's ability to implicitly categorize stimuli belonging to distinct conceptual categories, were found over the left occipito-temporal region. Topographic differences were observed depending on whether the periodic change involved living items, associated with relatively more ventro-temporal activity as compared to non-living items associated with relatively more dorsal posterior activity. Overall, this study demonstrates the validity and high sensitivity of an implicit frequency-tagged marker of word-based semantic memory abilities.

International audience; Following brain damage, the patient PS suffers from selective impairment in recognizing individuals by their faces, i.e., prosopagnosia. Her case has been documented in more than 30 publications to date, informing about the nature of individual face recognition and its neural basis. Here we report new functional neuroimaging data obtained on PS with a recently developed fast periodic stimulation functional imaging (FPS-fMRI) paradigm combining high sensitivity, specificity and reliability in identifying the cortical face-selective network (Gao et al., 2018). We define the extent of the large and reliable face-selective activation in the lateral section of the right middle fusiform gyrus, i.e., right FFA, which forms a single cluster of activation lying at the anterior border of the patient's main lesion in the inferior occipital gyrus. The contribution of posterior face-selective responses in the right or left inferior occipital gyrus is ruled out, strongly supporting the view that face-selective activity emerges in the right middle fusiform gyrus of the patient's brain from non-face-selective inputs from early visual areas. Despite this, low-level visual cues, i.e., amplitude spectrum of images, do not contribute to neural face-selective responses anywhere in the patient's cortical face network. This sensitive face-localizer approach also reveals an intact face-selective network anterior to the fusiform gyrus, including clusters in the ventral anterior temporal lobe (occipito-temporal sulcus and temporal pole) and the inferior frontal gyrus, with a right hemispheric dominance. Overall, with the exception of the left inferior occipital gyrus, the cortical face network of the prosopagnosic patient PS appears remarkably similar to typical individuals in non-brain damaged regions. However, unlike in neurotypical adults tested in the present study, including age-matched controls, a novel paradigm based on FPS-FMRI confirms that the patient's face network is insensitive to differences between rapidly presented pictures of unfamiliar individual faces, in line with her prosopagnosia.

International audience; Typical human adults recognize numerous individuals from their faces accurately, rapidly and automatically, reaching a level of expertise at individual face recognition that is important for the quality of their social interactions. A non-human species of primates, the rhesus monkey, has been used for decades as a model of human face processing, in particular for understanding the neural basis of individual face recognition. However, despite responding specifically to faces behaviourally and neurally, this species, as well as other Old World and New World monkeys, is remarkably poor at individuating faces of conspecifics. Following extensive conditioning, monkeys only achieve moderate performance at individual face matching tasks where image-based cues are available. Contrary to humans, monkeys do not show a systematic inversion effect in such tasks, or an advantage for matching face pictures of familiar versus unfamiliar individuals, indicating that they do not rely on qualitatively similar individual face recognition processes as humans. These observations concur with the characteristics of the rhesus monkey cortical face processing system, which lacks two critical aspects for human expertise at individual face recognition: a distinct ventral face-selective pathway and a right hemispheric specialization. While the rhesus monkey brain is undoubtedly an informative non-human model for studying the neural basis of social behaviour and visual cognition, it does not provide an adequate model of human individual face recognition. More generally, this review urges for caution when drawing direct inferences across species without sufficient homologies in behaviour and anatomico-functional landmarks.

The developmental origins of human adults’ right hemispheric specialization for face perception remain unclear. On the one hand, infant studies have shown a right hemispheric advantage for face perception. On the other hand, it has been proposed that the adult right hemispheric lateralization for face perception slowly emerges during childhood due to reading acquisition, which increases left lateralized posterior responses to competing written material (e.g., visual letters and words). Since methodological approaches used in infant and children typically differ when their face capabilities are explored, resolving this issue has been difficult. Here we tested 5-year-old preschoolers varying in their level of visual letter knowledge with the same fast periodic visual stimulation (FPVS) paradigm leading to strongly right lateralized electrophysiological occipito-temporal face-selective responses in 4- to 6-month-old infants (de Heering and Rossion, 2015). Children's face-selective response was quantitatively larger and differed in scalp topography from infants’, but did not differ across hemispheres. There was a small positive correlation between preschoolers’ letter knowledge and a non-normalized index of right hemispheric specialization for faces. These observations show that previous discrepant results in the literature reflect a genuine nonlinear development of the neural processes underlying face perception and are not merely due to methodological differences across age groups. We discuss several factors that could contribute to the adult right hemispheric lateralization for faces, such as myelination of the corpus callosum and reading acquisition. Our findings point to the value of FPVS coupled with electroencephalography to assess specialized face perception processes throughout development with the same methodology.

The human brain rapidly and automatically categorizes faces vs. other visual objects. However, whether face-selective neural activity predicts the subjective experience of a face – perceptual awareness – is debated. To clarify this issue, here we use face pareidolia, i.e., the illusory perception of a face, as a proxy to relate the neural categorization of a variety of facelike objects to conscious face perception. In Experiment 1, scalp electroencephalogram (EEG) is recorded while pictures of human faces or facelike objects – in different stimulation sequences – are interleaved every second (i.e., at 1 Hz) in a rapid 6-Hz train of natural images of nonface objects. Participants do not perform any explicit face categorization task during stimulation, and report whether they perceived illusory faces post-stimulation. A robust categorization response to facelike objects is identified at 1 Hz and harmonics in the EEG frequency spectrum with a facelike occipito-temporal topography. Across all individuals, the facelike categorization response is of about 20% of the response to human faces, but more strongly right-lateralized. Critically, its amplitude is much larger in participants who report having perceived illusory faces. In Experiment 2, facelike or matched nonface objects from the same categories appear at 1 Hz in sequences of nonface objects presented at variable stimulation rates (60 Hz to 12 Hz) and participants explicitly report after each sequence whether they perceived illusory faces. The facelike categorization response already emerges at the shortest stimulus duration (i.e., 17 ms at 60 Hz) and predicts the behavioral report of conscious perception. Strikingly, neural facelike-selectivity emerges exclusively when participants report illusory faces. Collectively, these experiments characterize a neural signature of face pareidolia in the context of rapid categorization, supporting the view that face-selective brain activity reliably predicts the subjective experience of a face from a single glance at a variety of stimuli.Highlights- EEG frequency-tagging measures the rapid categorization of facelike objects- Facelike objects elicit a facelike neural categorization response- Neural face categorization predicts conscious face perception across variable inputs

The development of individual face recognition has been intensively studied and supports early expertise in childhood. However, how the differential use of holistic and analytical face processing modes contribute to the well-documented prolonged development of individual face recognition until adulthood remains poorly understood. We applied a gaze-contingency approach to study individual face recognition in 5-year-old children and young adults, allowing selective manipulation of processing modes and providing insights into facial information use through fixation patterns. Although both age groups relied on similar processing modes, children were less efficient in compensating for processing manipulations, in particular when analytical processing was emphasized. They were also less flexible in using facial information. Our findings suggest that efficiency in adaptively exploiting visual information contributes to still developing individual face recognition abilities in children.

In her Viewpoint paper, Meike Ramon proposes a stringent operational definition to identify people who excel at face identity recognition, i.e., super face identity recognizers (SFIR). Based on difficulties at defining cases of prosopagnosia and prosopdysgnosia, I suggest adding exclusion criteria and emphasizing domain-specificity of SFIR's performance. In future work to characterize this special population, implicit electrophysiological measures obtained during fast periodic visual stimulation may be particularly valuable, providing valid, objective, sensitive, and reliable indexes of face identity recognition.

Recording direct neural activity when periodically inserting exemplars of a particular category in a rapid visual stream of other objects offers an objective and efficient way to quantify perceptual categorization and characterize its spatiotemporal dynamics. However, since periodicity entails predictability, perceptual categorization processes identified within this framework may be partly generated or modulated by temporal expectations. Here we present a stringent test of the hypothesis that temporal predictability generates or modulates category-selective neural processes as measured in a rapid periodic visual stimulation stream. In Experiment 1, we compare neurophysiological responses to periodic and nonperiodic (i.e., unpredictable) variable face stimuli in a fast (12Hz) visual stream of nonface objects. In Experiment 2, we assess potential responses to rare (10%) omissions of periodic face events (i.e., violations of periodicity) in the same fast visual stream. Overall, our observations indicate that category(face)-selective processes elicited in a fast periodic stream of visual objects are immune to temporal predictability. These observations do not support a predictive coding framework interpretation of category-change detection in the human brain and have important implications for understanding automatic human perceptual categorization in a rapidly changing (i.e., dynamic) visual scene.

Perceptual categorization occurs rapidly under natural viewing conditions. Yet, the neural spatio-temporal dynamics of category-selective processes to single-glanced, natural (i.e., unsegmented) images in a rapidly changing presentation stream remain unknown. We presented human observers with natural images of objects at a fast periodic rate of 12.5 Hz, i.e., every 80 ms. Images of faces were inserted every 3, 5, 7, 9, or 11 stimuli, defining stimulus-onset-asynchronies (SOAs) between 240–880 ms, i.e., presentation frequencies (Fs) between 4.17–1.14 Hz. Robust face-selective responses were objectively identified and quantified at F and its harmonics (2F, 3F, etc.) for every condition in the electroencephalogram (EEG). The summed-harmonic face-selective response was significantly reduced by 25% at the lowest face SOA, i.e. 240 ms between two faces, but remained stable from 400 ms SOA onward. This high-level, right lateralized face-selective response emerged at about 100 ms post-stimulus onset and progressed spatially throughout four successive time-windows (i.e., P1-face, N1-face, P2-face, P3-face) from posterior to anterior occipito-temporal electrode sites. The total duration of a category-selective response to a briefly presented face stimulus in a rapid sequence of objects was estimated to be 420 ms. Uncovering the neural spatio-temporal dynamics of category-selectivity in a rapid stream of natural images goes well beyond previous evidence obtained from spatially and temporally isolated stimuli, opening an avenue for understanding human vision and its relationship to categorization behavior.

Although humans discriminate natural images of faces from other categories at a single glance, clarifying the neural specificity and spatio-temporal dynamics of this process without low-level visual confounds remains a challenge. We recorded high-density scalp electroencephalogram while presenting natural images of various objects at a fast periodic rate (5.88images/s). In different stimulation sequences, numerous variable exemplars of three categories associated with cortical specialization in neuroimaging - faces, body parts, or houses - appeared every five images (5.88Hz/5=1.18Hz). In these fast periodic visual stimulation (FPVS) sequences, common low- and high-level visual processes between these categories and other objects are captured at the 5.88Hz frequency, while high-level category-selective responses are objectively quantified at the 1.18Hz frequency and harmonics. Category-selective responses differed quantitatively and qualitatively between faces, body parts and houses. First, they were much larger (2-4 times) for faces over the whole scalp. Second, specific and reliable scalp topographical maps of category-selective responses pointed to distinct principle neural sources for faces (ventral occipito-temporal), body parts (lateral occipito-temporal) and houses (dorso-medial occipital). Category-selective EEG responses were found at multiple time-windows from 110 to 600ms post-stimulus onset. Faces elicited the most complex spatio-temporal profile with up to four selective responses, although body parts and houses also elicited selective responses more complex than previously described. These observations indicate that a single glance at natural face images inserted in a rapid stream of natural objects generates a quantitatively and qualitatively unique category-selective spatio-temporal signature in occipito-temporal cortical areas of the human brain.

Discrimination of facial identities is a fundamental function of the human brain that is challenging to examine with macroscopic measurements of neural activity, such as those obtained with functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). Although visual adaptation or repetition suppression (RS) stimulation paradigms have been successfully implemented to this end with such recording techniques, objective evidence of an identity-specific discrimination response due to adaptation at the level of the visual representation is lacking. Here, we addressed this issue with fast periodic visual stimulation (FPVS) and EEG recording combined with a symmetry/asymmetry adaptation paradigm. Adaptation to one facial identity is induced through repeated presentation of that identity at a rate of 6 images per second (6 Hz) over 10 sec. Subsequently, this identity is presented in alternation with another facial identity (i.e., its anti-face, both faces being equidistant from an average face), producing an identity repetition rate of 3 Hz over a 20 sec testing sequence. A clear EEG response at 3 Hz is observed over the right occipito-temporal (ROT) cortex, indexing discrimination between the two facial identities in the absence of an explicit behavioral discrimination measure. This face identity discrimination occurs immediately after adaptation and disappears rapidly within 20 sec. Importantly, this 3 Hz response is not observed in a control condition without the single-identity 10 sec adaptation period. These results indicate that visual adaptation to a given facial identity produces an objective (i.e., at a pre-defined stimulation frequency) electrophysiological index of visual discrimination between that identity and another, and provides a unique behavior-free quantification of the effect of visual adaptation.

One of the most striking pieces of evidence for a specialised face processing system in humans is acquired prosopagnosia, i.e. the inability to individualise faces following brain damage. However, a sensitive and objective non-behavioural marker for this deficit is difficult to provide with standard event-related potentials (ERPs), such as the well-known face-related N170 component reported and investigated in-depth by our late distinguished colleague Shlomo Bentin. Here we demonstrate that fast periodic visual stimulation (FPVS) in electrophysiology can quantify face individualisation impairment in acquired prosopagnosia. In Experiment 1 (Liu-Shuang et al., 2014), identical faces were presented at a rate of 5.88 Hz (i.e., ≈ 6 images/s, SOA=170 ms, 1 fixation per image), with different faces appearing every 5th face (5.88 Hz/5=1.18 Hz). Responses of interest were identified at these predetermined frequencies (i.e., objectively) in the EEG frequency-domain data. A well-studied case of acquired prosopagnosia (PS) and a group of age- and gender-matched controls completed only 4 × 1-min stimulation sequences, with an orthogonal fixation cross task. Contrarily to controls, PS did not show face individualisation responses at 1.18 Hz, in line with her prosopagnosia. However, her response at 5.88 Hz, reflecting general visual processing, was within the normal range. In Experiment 2 (Rossion et al., 2015), we presented natural (i.e., unsegmented) images of objects at 5.88 Hz, with face images shown every 5th image (1.18 Hz). In accordance with her preserved ability to categorise a face as a face, and despite extensive brain lesions potentially affecting the overall EEG signal-to-noise ratio, PS showed 1.18 Hz face-selective responses within the normal range. Collectively, these findings show that fast periodic visual stimulation provides objective and sensitive electrophysiological markers of preserved and impaired face processing abilities in the neuropsychological population.

The human brain is extremely efficient at detecting faces in complex visual scenes, but the spatio-temporal dynamics of this remarkable ability, and how it is influenced by category-search, remain largely unknown. In the present study, human subjects were shown gradually-emerging images of faces or cars in visual scenes, while neural activity was recorded using functional magnetic resonance imaging (fMRI). Category search was manipulated by the instruction to indicate the presence of either a face or a car, in different blocks, as soon as an exemplar of the target category was detected in the visual scene. The category selectivity of most face-selective areas was enhanced when participants were instructed to report the presence of faces in gradually decreasing noise stimuli. Conversely, the same regions showed much less selectivity when participants were instructed instead to detect cars. When “face” was the target category, the fusiform face area (FFA) showed consistently earlier differentiation of face versus car stimuli than did the “occipital face area” (OFA). When “car” was the target category, only the FFA showed differentiation of face versus car stimuli. These observations provide further challenges for hierarchical models of cortical face processing and show that during gradual revealing of information, selective category-search may decrease the required amount of information, enhancing and speeding up category-selective responses in the human brain.

Using a gaze-contingent morphing approach, we asked human observers to choose one of two faces that best matched the identity of a target face: one face corresponded to the reference face’s fixated part only (e.g., one eye), the other corresponded to the unfixated area of the reference face. The face corresponding to the fixated part was selected significantly more frequently in the inverted than in the upright orientation. This observation provides evidence that face inversion reduces an observer’s perceptual field of view, even when both upright and inverted faces are displayed at full view and there is no performance difference between these conditions. It rules out an account of the drop of performance for inverted faces – one of the most robust effects in experimental psychology – in terms of a mere difference in local processing efficiency. A brain-damaged patient with pure prosopagnosia, viewing only upright faces, systematically selected the face corresponding to the fixated part, as if her perceptual field was reduced relative to normal observers. Altogether, these observations indicate that the absence of visual knowledge reduces the perceptual field of view, supporting an indirect view of visual perception.

Neurotypical human adults have a high level of expertise in facial recognition, a key brain function for the quality of their social interactions. Studying cerebral mechanisms of facial recognition should help us understanding the most complex mechanisms of perception, memory, learning, as well as integration of semantic knowledge, emotion and attention in the brain. Neurophysiological studies performed in the macaque monkey brain are usually taken as providing evidence for the mechanisms of human face recognition but their relevance is limited by the weak capacities of this species in facial recognition compared to humans, and the absence of a human-like ventral occipito-temporal circuit selectively involved in face recognition. Functional magnetic resonance imaging studies in humans have identified a large network of occipito-temporal face-selective regions, dominant in the right hemisphere, but are limited in their temporal resolution and by important variations of signal in this region. By coupling electrophysiological recordings on large sample of human brain implanted with stereoelectroencephalography (SEEG) with fast periodic visual stimulation, this presentation will show how we can objectively and rapidly map human facial recognition in the human ventral temporal lobe, in order to make significant progress in our understanding of this function.

The sudden onset of a face image leads to a prominent face-selective response in human scalp electroencephalographic (EEG) recordings, peaking 170 ms after stimulus onset at occipito-temporal (OT) scalp sites: the N170 (or M170 in magnetoencephalography). According to a widely held view, the main cortical source of the N170 lies in the fusiform gyrus (FG), whereas the posteriorly located inferior occipital gyrus (IOG) would rather generate earlier face-selective responses. Here, we report neural responses to upright and inverted faces recorded in a unique patient using multicontact intracerebral electrodes implanted in the right IOG and in the OT sulcus above the right lateral FG (LFG). Simultaneous EEG recordings on the scalp identified the N170 over the right OT scalp region. The latency and amplitude of this scalp N170 were correlated at the single-trial level with the N170 recorded in the lateral IOG, close to the scalp lateral occipital surface. In addition, positive component maximal around the latency of the N170 (a P170) was prominent above the internal LFG, whereas this region typically generates an N170 (or “N200”) over its external/ventral surface. This suggests that electrophysiological responses in the LFG manifest as an equivalent dipole oriented mostly along the vertical axis with likely minimal projection to the lateral OT scalp region. Altogether, these observations provide evidence that the IOG is a major cortical generator of the face-selective scalp N170, qualifying the potential contribution of the FG and questioning a strict serial spatiotemporal organization of the human cortical face network.

What is the stimulus presentation rate at which the human brain can discriminate each exemplar of a familiar visual category? We presented faces at 14 frequency rates (1.0–16.66 Hz) to human observers while recording high-density electroencephalogram (EEG). Different face exemplars elicited a larger steady-state visual evoked (ssVEP) response than when the same face was repeated, but only for stimulation frequencies between 4 and 8.33 Hz, with a maximal difference at 5.88 Hz (170 ms cycle). The effect was confined to the exact stimulation frequency and localized over the right occipito-temporal cortex. At high frequency rates (>10 Hz), the response to different and identical exemplars did not differ, suggesting that the fine-grained analysis needed for individual face discrimination cannot be completed before the next face interrupts, or competes, with the processed face. At low rates (

Face perception is highly lateralized to the right hemisphere (RH) in humans, as supported originally by observations of face recognition impairment (prosopagnosia) following brain damage. Divided visual field presentations, neuroimaging and event-related potential studies have supported this view. While the latter studies are typically performed in right-handers, the few reported cases of prosopagnosia with unilateral left damage were left-handers, suggesting that handedness may shift or qualify the lateralization of face perception. We tested this hypothesis by recording the whole set of face-sensitive areas in 11 left-handers, using a face-localizer paradigm in functional magnetic resonance imaging (fMRI) (faces, cars, and their phase-scrambled versions). All face-sensitive areas identified (superior temporal sulcus, inferior occipital cortex, anterior infero-temporal cortex, amygdala) were strongly right-lateralized in left-handers, this right lateralization bias being as large as in a population of right-handers (40) tested with the same paradigm (Rossion et al., 2012). The notable exception was the so-called 'Fusiform face area' (FFA), an area that was slightly left lateralized in the population of left-handers. Since the left FFA is localized closely to an area sensitive to word form in the human brain ('Visual Word Form Area' - VWFA), the enhanced left lateralization of the FFA in left-handers may be due to a decreased competition with the representation of words. The implications for the neural basis of face perception, aetiology of brain lateralization in general, and prosopagnosia are also discussed.

Presentation of a face stimulus for several seconds at a periodic frequency rate leads to a right occipito-temporal evoked steady-state visual potential (SSVEP) confined to the stimulation frequency band. According to recent evidence (Rossion and Boremanse, 2011), this face-related SSVEP is largely reduced in amplitude when the exact same face is repeated at every stimulation cycle as compared to the presentation of different individual faces. Here this SSVEP individual face repetition effect was tested in 20 participants stimulated with faces at a 4 Hz rate for 84 s, in 4 conditions: faces upright or inverted, normal or contrast-reversed (2×2 design). To study the temporal dynamics of this effect, all stimulation sequences started with 15s of identical faces, after which, in half of the sequences, different faces were introduced. A larger response to different than identical faces at the fundamental (4 Hz) and second harmonic (8 Hz) components was observed for upright faces over the right occipito-temporal cortex. Weaker effects were found for inverted and contrast-reversed faces, two stimulus manipulations that are known to greatly affect the perception of facial identity. Addition of the two manipulations further decreased the effect. The phase of the fundamental frequency SSVEP response was delayed for inverted and contrast-reversed faces, to the same extent as the latency delay observed at the peak of the face-sensitive N170 component observed at stimulation sequence onset. Time-course analysis of the entire sequence of stimulation showed an immediate increase of 4Hz amplitude at the onset (16th second) of different face presentation, indicating a fast, large and frequency-specific release to individual face adaptation in the human brain. Altogether, these observations increase our understanding of the characteristics of the human steady-state face potential response and provide further support for the interest of this approach in the study of the neurofunctional mechanisms of face perception.

International audience; Face perception is subtended by a large set of areas in the human ventral occipito-temporal cortex. However, the role of these areas and their importance for face recognition remain largely unclear. Here we report a case of transient selective impairment in face recognition (prosopagnosia) induced by focal electrical intracerebral stimulation of the right inferior occipital gyrus. This area presents with typical face-sensitivity as evidenced by functional neuroimaging right occipital face area (OFA). A face-sensitive intracerebral N170 was also recorded in this area, supporting its contribution as a source of the well-known N170 component typically recorded on the scalp. Altogether, these observations indicate that face recognition can be selectively impaired by local disruption of a single face-sensitive area of the network subtending this function, the right OFA.

A number of human brain areas showing a larger response to faces than to objects from different categories, or to scrambled faces, have been identified in neuroimaging studies. Depending on the statistical criteria used, the set of areas can be overextended or minimized, both at the local (size of areas) and global (number of areas) levels. Here we analyzed a whole-brain factorial functional localizer obtained in a large sample of right-handed participants (40). Faces (F), objects (O; cars) and their phase-scrambled counterparts (SF, SO) were presented in a block design during a one-back task that was well matched for difficulty across conditions. A conjunction contrast at the group level {(F-SF) and (F-O)} identified six clusters: in the pulvinar, inferior occipital gyrus (so-called OFA), middle fusiform gyrus (so-called FFA), posterior superior temporal sulcus, amygdala, and anterior infero-temporal cortex, which were all strongly right lateralized. While the FFA showed the largest difference between faces and cars, it also showed the least face-selective response, responding more to cars than scrambled cars. Moreover, the FFA's larger response to scrambled faces than scrambled cars suggests that its face-sensitivity is partly due to low-level visual cues. In contrast, the pattern of activation in the OFA points to a higher degree of face-selectivity. A BOLD latency mapping analysis suggests that face-sensitivity emerges first in the right FFA, as compared to all other areas. Individual brain analyses support these observations, but also highlight the large amount of interindividual variability in terms of number, height, extent and localization of the areas responding preferentially to faces in the human ventral occipito-temporal cortex. This observation emphasizes the need to rely on different statistical thresholds across the whole brain and across individuals to define these areas, but also raises some concerns regarding any objective labeling of these areas to make them correspond across individual brains. This large-scale analysis helps understanding the set of face-sensitive areas in the human brain, and encourages in-depth single participant analyses in which the whole set of areas is considered in each individual brain.

Adults are experts at recognizing faces but there is controversy about how this ability develops with age. We assessed 6- to 12-year-olds and adults using a digitized version of the Benton Face Recognition Test, a sensitive tool for assessing face perception abilities. Children’s response times for correct responses did not decrease between ages 6 and 12, for either upright or inverted faces, but were significantly longer than those of adults for both face types. Accuracy improved between ages 6 and 12, ignificantly more for upright than inverted faces. Inverted face recognition improved slowly until late childhood, whereas there was a large improvement in upright face recognition between ages 6 and 8, with a further enhancement after age 12. These results provide further evidence that during childhood face processing undergoes protracted development and becomes increasingly tuned to upright faces.

How fast are visual stimuli categorized as faces by the human brain? Because of their high temporal resolution and the possibility to record simultaneously from the whole brain, electromagnetic scalp measurements should be the ideal method to clarify this issue. However, this question remains debated, with studies reporting face-sensitive responses varying from 50ms to 200ms following stimulus onset. Here we disentangle the contribution of the information associated with the phenomenological experience of a face (phase) from low-level visual cues (amplitude spectrum, color) in accounting for early face-sensitivity in the human brain. Pictures of faces and of a category of familiar objects (cars), as well as their phase-scrambled versions, were presented to fifteen human participants tested with high-density (128 channels) EEG. We replicated an early face-sensitivity – larger response to pictures of faces than cars – at the level of the occipital event-related potential (ERP) P1 (80–100ms). However, a similar larger P1 to phase-scrambled faces than phase-scrambled cars was also found. In contrast, the occipito-temporal N170 was much larger in amplitude for pictures of intact faces than cars, especially in the right hemisphere, while the small N170 elicited by phase-scrambled stimuli did not differ for faces and cars. These findings show that sensitivity to faces on the visual evoked potentials P1 and N1 (N170) is functionally dissociated: the P1 face-sensitivity is driven by low-level visual cues while the N1 (or N170) face-sensitivity reflects the perception of a face. Altogether, these observations indicate that the earliest access to a high-level face representation, that is, a face percept, does not precede the N170 onset in the human brain. Furthermore, they allow resolving apparent discrepancies between the timing of rapid human saccades towards faces and the early activation of high-level facial representations as shown by electrophysiological studies in the primate brain. More generally, they put strong constraints on the interpretation of early (before 100ms) face-sensitive effects in the human brain.

Behavioral studies have shown that matching individual faces across depth rotation is easier and faster for familiar than unfamiliar faces. Here we used event-related potentials (ERPs) to clarify the locus of this behavioral facilitation, that is whether it reflects changes at the level of perceptual face encoding, or rather at later stages of processing. We used an identity adaptation paradigm in ERPs, during which a first (adapting) face (~3000 ms) rotated 30° in depth was followed by a second full front face (200 ms) which was either the same or a different identity as the first face. For unfamiliar faces, the early face-sensitive N170 component was reduced for immediately repeated as compared to different unfamiliar faces in the right hemisphere only. However, for personally familiar faces, the effect was absent at right hemisphere electrode sites and appeared instead over the left hemisphere at the same latency. Later effects of face identity adaptation were also present on the scalp, but from about 300 to 400 ms over fronto-central regions, and slightly later on occipito-temporal regions, there was a strong adaptation effect only for familiar faces. These observations suggest that the perceptual encoding of familiar and unfamiliar faces may be of different nature, as indicated by early (N170) hemispheric differences for identity adaptation effects depending on long-term familiarity. However, the behavioral advantage provided by familiarity to match faces across viewpoints might rather be related to processes that are closer in time to the behavioral response, such as semantic associations between the faces to match.

We present an extensive investigation (24 experiments) of a new case of prosopagnosia following right unilateral damage, GG, with the aim of addressing two classical issues: (1) Can a visual recognition impairment truly be specific to faces? (2) What is the nature of acquired prosopagnosia? We show that GG recognizes nonface objects perfectly and quickly, even when it requires fine-grained analysis to individualize these objects. He is also capable of perceiving objects and faces as integrated wholes, as indicated by normal Navon effect, 3D-figures perception and perception of Mooney and Arcimboldo face stimuli. However, the patient could not perceive individual faces holistically, showing no inversion, composite, or whole-part advantage effects for faces. We conclude that an occipito-temporal right hemisphere lesion may lead to a specific impairment of holistic perception of individual items, a function that appears critical for normal face recognition but not for object recognition.

When the bottom halves of two faces differ, people's behavioral judgment of the identical top halves of those faces is impaired: they report that the top halves are different, and/or take more time than usual to provide a response. This behavioral measure is known as the composite face effect (CFE) and has traditionally been taken as evidence that faces are perceived holistically. Recently, however, it has been claimed that this effect is driven almost entirely by decisional, rather than perceptual, factors (Richler, Gauthier, Wenger, & Palmeri, 2008). To disentangle the contribution of perceptual and decisional brain processes, we aimed to obtain an event-related potential (ERP) measure of the CFE at a stage of face encoding (Jacques & Rossion, 2009) in the absence of a behavioral CFE effect. Sixteen participants performed a go/no-go task in an oddball paradigm, lifting a finger of their right or left hand when the top half of a face changed identity. This change of identity of the top of the face was associated with an increased ERP signal on occipito-temporal electrode sites at the N170 face-sensitive component (∼160ms), the later decisional P3b component, and the lateralized readiness potential (LRP) starting at ∼350ms. The N170 effect was observed equally early when only the unattended bottom part of the face changed, indicating that an identity change was perceived across the whole face in this condition. Importantly, there was no behavioral response bias for the bottom change trials, and no evidence of decisional biases from electrophysiological data (no P3b and LRP deflection in no-go trials). These data show that an early CFE can be measured in ERPs in the absence of any decisional response bias, indicating that the CFE reflects primarily the visual perception of the whole face.

Face recognition is an important ability of the human brain, yet its underlying mechanisms are still poorly understood. Two opposite views have been proposed to account for human face recognition expertise: the ability to extract the most diagnostic local information, feature-by feature (analytical view), or the ability to process all features at once over the whole face (holistic view). To help clarifying this debate, we used an original gaze-contingent stimulus presentation method to compare normal observers and a brain-damaged patient specifically impaired at face recognition (prosopagnosia). When a single central facial feature was revealed at a time through a gaze-contingent window, normal observers' performance at an individual face matching task decreased to the patient level. However, when only the central feature was masked, forcing normal observers to rely on the whole face but the fixated feature, their performance was almost not affected. In contrast, the prosopagnosic patient's performance decreased dramatically in this latter condition. These results were independent of the absolute size of the face and window/mask. This dissociation indicates that expertise in face recognition does not rest on the ability to analyze diagnostic local detailed features sequentially but rather on the ability to see the individual features of a face all at once, a function that is critically impaired in acquired prosopagnosia. (C) 2010 Elsevier Ltd. All rights reserved.

Faces are recognized by means of both shape and surface reflectance information. However, it is unclear how these two types of diagnostic information are represented in the human brain. To clarify this issue, we tested 14 participants in an event-related functional magnetic resonance adaptation paradigm, with four conditions created by using a 3D morphable model: (1) repetition of the same adapting face; (2) variation in shape only; (3) variation in surface reflectance only; (4) variation in both shape and surface reflectance. Change in face shape alone was the dominant driving force of the adaptation release in functionally defined face-sensitive areas in the right hemisphere (fusiform face area [FFA], occipital face area [OFA]). In contrast, homologous areas of the left hemisphere showed comparable adaptation release to changes in face shape and surface reflectance. When both changes in shape and reflectance were combined, there was no further increased release from adaptation in face-sensitive areas. Overall, these observations indicate that the two main sources of information in individual faces, shape and reflectance, contribute to individual face sensitivity found in the cortical face network. Moreover, the sensitivity to shape cues is more dominant in the right hemisphere, possibly reflecting a privileged mode of global (holistic) face processing.

I published a critical review of the face inversion effect (Rossion, 2008) that triggered a few reactions and commentaries by colleagues in the field (Riesenhuber & Wolff, 2009; Yovel, in press). Here, I summarize my original paper and attempt to identify the source of both the agreements and disagreements with my colleagues, as well as other authors, regarding the nature of the face inversion effect. My view is that the major cause of the detrimental effect of inversion on an observer's performance at individual face recognition is the disruption of a perceptual process. This perceptual process is makes and observer see the multiple features of a whole individual upright face at once. It also makes the percept of a given facial feature highly dependent on the location and identity of the other features in the whole face. The perceptual process is holistic because it is driven by a holistic face representation, derived from visual experience. Hence, an inverted face cannot be perceived holistically: the perceptual field of the observer is constricted for inverted faces, each facial feature having to be processed sequentially, independently, i.e. over a smaller spatial window than the whole face. Consequently, it is particularly difficult to perceive diagnostic cues that involve several elements over a wide space on an inverted face, such as long-range relative distances between features (e.g., relative distance between eyes and mouth), or diagnostic cues that are located far away from usual gaze fixation (e.g., mouth-nose distance or mouth shape when fixating between the eyes). These difficulties are mere consequences of face inversion--the cause being a loss of holistic perception--, and it does not follow that relative distances between internal features are necessarily particularly important to recognize faces, that they should be labeled "configural", or should be given a specific status at the representational level. I argue that distinguishing the cause and consequence(s) of face inversion this way can provide a parsimonious and yet complete theoretical account of the face inversion effect.

The human brain recognizes faces by means of two main diagnostic sources of information: three-dimensional (3D) shape and two-dimensional (2D) surface reflectance. Here we used event-related potentials (ERPs) in a face adaptation paradigm to examine the time-course of processing for these two types of information. With a 3D morphable model, we generated pairs of faces that were either identical, varied in 3D shape only, in 2D surface reflectance only, or in both. Sixteen human observers discriminated individual faces in these 4 types of pairs, in which a first (adapting) face was followed shortly by a second (test) face. Behaviorally, observers were as accurate and as fast for discriminating individual faces based on either 3D shape or 2D surface reflectance alone, but were faster when both sources of information were present. As early as the face-sensitive N170 component (approximately 160 ms following the test face), there was larger amplitude for changes in 3D shape relative to the repetition of the same face, especially over the right occipito-temporal electrodes. However, changes in 2D reflectance between the adapter and target face did not increase the N170 amplitude. At about 250 ms, both 3D shape and 2D reflectance contributed equally, and the largest difference in amplitude compared to the repetition of the same face was found when both 3D shape and 2D reflectance were combined, in line with observers' behavior. These observations indicate that evidence to recognize individual faces accumulate faster in the right hemisphere human visual cortex from diagnostic 3D shape information than from 2D surface reflectance information.

Event-related potential (ERP) studies have shown that sensitivity to individual faces emerges as early as approximately 160ms in the human occipitotemporal cortex (N170). Here we tested whether this effect generalizes across changes in viewpoint. We recorded ERPs during an unfamiliar individual face adaptation paradigm. Participants were presented first with an adapting face ( approximately 3000ms) rotated 30 degrees in depth, followed by a second face (200ms) in a frontal view of either the same or a different identity. The N170 amplitude at right occipitotemporal sites to the second stimulus was reduced for repeated as compared to different faces. A bilateral adaptation effect emerged after 250ms following stimulus onset. These observations indicate that individual face representations activated as early as 160ms after stimulus onset in the right hemisphere show a substantial degree of generalization across viewpoints.

Presenting a face stimulus upside-down generally causes a larger deficit in perceiving metric distances between facial features ("configuration") than local properties of these features. This effect supports a qualitative account of face inversion: the same transformation affects the processing of different kinds of information differently. However, this view has been recently challenged by studies reporting equal inversion costs of performance for discriminating featural and configural manipulations on faces. In this paper I argue that these studies did not replicate previous results due to methodological factors rather than largely irrelevant parameters such as having equal performance for configural and featural conditions at upright orientation, or randomizing trials across conditions. I also argue that identifying similar diagnostic features (eyes and eyebrows) for discriminating individual faces at upright and inverted orientations by means of response classification methods does not dismiss at all the qualitative view of face inversion. Considering these elements as well as both behavioral and neuropsychological evidence, I propose that the generally larger effect of inversion for processing configural than featural cues is a mere consequence of the disruption of holistic face perception. That is, configural relations necessarily involve two or more distant features on the face, such that their perception is most dependent on the ability to perceive simultaneously multiple features of a face as a whole.

A recent event-related potential (ERP) study (Thierry G., Martin, C.D., Downing, P., Pegna, A.J. 2007. Controlling for interstimulus perceptual variance abolishes N170 face selectivity. Nature Neuroscience, 10, 505-11) claimed that the larger occipito-temporal N170 response to pictures of faces than other categories -- the N170 effect -- is due to a methodological artifact in stimulus selection, specifically, a greater interstimulus physical variance between pictures of objects than faces in previous ERP studies which, when controlled, eliminates this N170 effect. This statement casts doubts on the validity of the conclusions reached by a whole tradition of electrophysiological experiments published over the past 15 years and questions the very interest of using the N170 to probe the time course of face processes in the human brain. Here we claim that this physical variance factor is ill-defined by Thierry et al. and cannot account for previous observations of a smaller N170 amplitude to nonface objects than faces without latency increase and component "smearing". Most importantly, this factor was controlled in previous studies that reported robust N170 effects. We demonstrate that the absence of N170 effect in the study of Thierry et al. is due to methodological flaws in the reported experiments, most notably measuring the N170 at the wrong electrode sites. Moreover, the authors attributed a modulation of N170 amplitude in their study to a differential interstimulus physical variance while it probably reflects a biased comparison of different quality sets of individual images. Here, by taking Thierry et al.'s study as an exemplar case of what should not be done in ERP research of visual categorization processes, we provide clarifications on a number of methodological and theoretical issues about the N170 and its largest amplitude to faces. More generally, we discuss the potential role of differential visual homogeneity of object categories as well as low-level visual properties versus high-level visual processes in accounting for early face-preferential responses and the question of the speed at which visual stimuli are categorized as faces. This survey of the literature points to the N170 as a critical event in the time course of face processes in the human brain.

OBJECTIVE: Rhythm perception appears to be non-linear as human subjects are better at discriminating, categorizing and reproducing rhythms containing binary vs non-binary (e.a. 1:2 vs 1:3) as well as metrical vs non-metrical (e.a. 1:2 vs 1:2.5) interval ratios. This study examined the representation of binary and non-binary interval ratios within the sensory memory, thus yielding a truly sensory, pre-motor, attention-independent neural representation of rhythmical intervals. METHODS: Five interval ratios, one binary, flanked by four non-binary ones, were compared on the basis of the MMN they evoked when contrasted against a common standard interval. RESULTS: For all five intervals, the larger the contrast was, the larger the MMN amplitude was. The binary interval evoked a significantly much shorter (by at least 23 ms) MMN latency than the other intervals, whereas no latency difference was observed between the four non-binary intervals. CONCLUSIONS: These results show that the privileged perceptual status of binary rhythmical intervals is already present in the sensory representations found in echoic memory at an early, automatic, pre-perceptual and pre-motor level. SIGNIFICANCE: MMN latency can be used to study rhythm perception at a truly sensory level, without any contribution from the motor system.

Picture-plane inversion dramatically impairs face recognition. Behavioral and event-related potential (ERP) studies suggest that this effect takes place during perceptual encoding of the face stimulus. However, the relationship between early electrophysiological responses to upright and inverted faces and the behavioral face inversion effect remains unclear. To address this question, we recorded ERPs while presenting 10 subjects with face photographs at 12 different orientations around the clock (30 degrees steps) during an individual face matching task. Using the variability in the electrophysiological responses introduced by the multiple orientations of the target face, we found a correlation between the ERP signal at 130-170 ms on occipito-temporal channels, and the behavioral performance measured on the probe stimulus. Correlations between ERP signal and behavioral performance started about 10 ms earlier in the right hemisphere. Significant effects of orientation were observed already at the level of the visual P1 (peaking at 100 ms), but the ERP signal was not correlated with behavior until the face-sensitive N170 time window. Overall, these observations indicate that plane-inversion affects the perceptual encoding of faces as early as 130 ms in occipito-temporal regions, leading directly to an increase in error rates and RTs during individual face recognition.

Two identical top parts of a face photograph look different if their bottom parts differ. This perceptual illusion, the "face composite effect", is taken as strong evidence that faces are processed as a whole rather than as a collection of independent features. To test the hypothesis that areas responding preferentially to faces in the human brain represent faces holistically, we recorded functional magnetic resonance imaging (fMRI) during an adaptation paradigm with the composite face illusion. In both the middle fusiform gyrus (MFG) and the inferior occipital gyrus (IOG), we observed a significantly larger response to the same top face when it was aligned with different bottom parts than with the same bottom part, with a most robust effect in the right middle fusiform gyrus. This difference was not found when the top and the bottom face parts were spatially misaligned or when the faces were presented upside-down. These findings indicate that facial features are integrated into holistic face representations in areas of the human visual cortex responding preferentially to faces.

OBJECTIVE: (1) To investigate the hypothesis that the vertex positive potential (VPP) and the N170 ERP components reported in the face processing literature are two manifestations of the same brain processes whose relative amplitude in a given experiment is dependent on reference electrode; (2) to investigate whether differences in face/object results reported in studies looking at the VPP and N170 are attributable to the location of reference. METHODS: EEG was recorded from 53 scalp electrodes referenced online to the left mastoid while subjects viewed face, car and word stimuli. Off-line, the data were systematically re-referenced to the common average, averaged mastoids, averaged earlobes, non-cephalic, and nose. The correlation of timing, amplitude, and effects was investigated across reference electrodes. RESULTS: (1) The amplitude of the N170 and VPP components varies in a precisely inverse manner across reference; (2) the peaks of the N170 and VPP are temporally coincident for all reference electrodes, (3) both components can be accounted for by the same dipolar configuration, and (4) the components show identical functional properties. CONCLUSIONS: The VPP and N170 are two 'faces' of the same brain generators. SIGNIFICANCE: The differential N170/VPP effects observed in ERP studies can be accounted for by differences in reference methodology.

Perception results from ongoing interactions between stimulus-driven visual processes and cognitive context. These reciprocal relations are emphasized when a visual stimulus is degraded, forcing the perceiver to fill the missing information in, based on internal representations. The neural mechanisms by which internal representations facilitate visual perception are still unclear. Here we investigated the role of EEG oscillations in the gamma band, thought to reflect the elaboration of internal visual representations, in the experience-based perception of visual scenes. Twelve subjects were trained with degraded images of natural scenes. EEG was recorded while they performed a detection task on trained and untrained degraded stimuli. Non-phase-locked gamma band responses in a large frequency spectrum (55-85 Hz) were observed around 200 ms post-stimulus onset at posterior sites, and were larger when subjects reported an accurate perception based on previous experience. These results suggest that mid-latency gamma oscillations in the visual cortex underlie the experience-based perception of visual scenes.

Event-related potential (ERP) studies of the human brain have shown that object categories can be reliably distinguished as early as 130-170 ms on the surface of occipito-temporal cortex, peaking at the level of the N170 component. Consistent with this finding, neuropsychological and neuroimaging studies suggest major functional distinctions within the human object recognition system, particularly in hemispheric advantage, between the processing of words (left), faces (right), and objects (bilateral). Given these observations, our aim was to (1) characterize the differential response properties of the N170 to pictures of faces, objects, and words across hemispheres; and (2) test whether an effect of inversion for highly familiar and monooriented nonface stimuli such as printed words can be observed at the level of the N170. Scalp EEG (53 channels) was recorded in 15 subjects performing an orientation decision task with pictures of faces, words, and cars presented upright or inverted. All three categories elicited at the same latency a robust N170 component associated with a positive counterpart at centro-frontal sites (vertex-positive potential, VPP). While there were minor amplitude differences at the level of the occipital medial P1 between linguistic and nonlinguistic categories, scalp topographies and source analyses indicated strong hemispheric and orientation effects starting at the level of the N170, which was right lateralized for faces, smaller and bilateral for cars, and as large for printed words in the left hemisphere as for faces. The entire N170/VPP complex was accounted for by two dipolar sources located in the lateral inferior occipital cortex/posterior fusiform gyrus. These two locations were roughly equivalent across conditions but differed in strength and lateralization. Inversion delayed the N170 (and VPP) response for all categories, with an increasing delay for cars, words, and faces, respectively, as suggested by source modeling analysis. Such results show that early processes in object recognition respond to category-specific visual information, and are associated with strong lateralization and orientation bias.

In a highly dynamic visual environment the human brain needs to rapidly differentiate complex visual patterns, such as faces. Here, we defined the temporal frequency tuning of cortical face-sensitive areas for face discrimination. Six observers were tested with functional magnetic resonance imaging (fMRI) when the same or different faces were presented in blocks at 11 frequency rates (ranging from 1 to 12 Hz). We observed a larger fMRI response for different than same faces – the repetition suppression/adaptation effect – across all stimulation frequency rates. Most importantly, the magnitude of the repetition suppression effect showed a typical Gaussian-shaped tuning function, peaking on average at 6 Hz for all face-sensitive areas of the ventral occipito-temporal cortex, including the fusiform and occipital “face areas” (FFA and OFA), as well as the superior temporal sulcus. This effect was due both to a maximal response to different faces in a range of 3 to 6 Hz and to a sharp drop of the blood oxygen level dependent (BOLD) signal from 6 Hz onward when the same face was repeated during a block. These observations complement recent scalp EEG observations (Alonso-Prieto et al., 2013), indicating that the cortical face network can discriminate each individual face when these successive faces are presented every 160–170 ms. They also suggest that a relatively fast 6 Hz rate may be needed to isolate the contribution of high-level face perception processes during behavioral discrimination tasks. Finally, these findings carry important practical implications, allowing investigators to optimize the stimulation frequency rates for observing the largest repetition suppression effects to faces and other visual forms in the occipito-temporal cortex.