Horizontal tuning for faces originates in high-level Fusiform Face Area.

in Neuropsychologia (2015), 81

Recent work indicates that the specialization of face visual perception relies on the privileged processing of horizontal angles of facial information. This suggests that stimulus properties assumed to be ... [more ▼]

Recent work indicates that the specialization of face visual perception relies on the privileged processing of horizontal angles of facial information. This suggests that stimulus properties assumed to be fully resolved in primary visual cortex (V1; e.g., orientation) in fact determine human vision until high-level stages of processing. To address this hypothesis, the present fMRI study explored the orientation sensitivity of V1 and high-level face-specialized ventral regions such as the Occipital Face Area (OFA) and Fusiform Face Area (FFA) to different angles of face information. Participants viewed face images filtered to retain information at horizontal, vertical or oblique angles. Filtered images were viewed upright, inverted and (phase-)scrambled. FFA responded most strongly to the horizontal range of upright face information; its activation pattern reliably separated horizontal from oblique ranges, but only when faces were upright. Moreover, activation patterns induced in the right FFA and the OFA by upright and inverted faces could only be separated based on horizontal information. This indicates that the specialized processing of upright face information in the OFA and FFA essentially relies on the encoding of horizontal facial cues. This pattern was not passively inherited from V1, which was found to respond less strongly to horizontal than other orientations likely due to adaptive whitening. Moreover, we found that orientation decoding accuracy in V1 was impaired for stimuli containing no meaningful shape. By showing that primary coding in V1 is influenced by high-order stimulus structure and that high-level processing is tuned to selective ranges of primary information, the present work suggests that primary and high-level levels of the visual system interact in order to modulate the processing of certain ranges of primary information depending on their relevance with respect to the stimulus and task at hand. [less ▲]

Attentional shifts induced by uninformative number symbols modulate neural activity in human occipital cortex

in Neuropsychologia (2012), 50

Number processing interacts with space encoding in a wide variety of experimental paradigms. Most intriguingly, the passive viewing of uninformative number symbols can shift visuo-spatial attention to ... [more ▼]

Number processing interacts with space encoding in a wide variety of experimental paradigms. Most intriguingly, the passive viewing of uninformative number symbols can shift visuo-spatial attention to different target locations according to the number magnitude, i.e., small/large numbers facilitate processing of left/right targets, respectively. The brain architecture dedicated to these attention shifts associated with numbers remains unknown. Evoked potential recordings indicate that both early and late stages are involved in this spatio-numerical interaction, but the neuro-functional anatomy needs to be specified. Here we use, for the first time, functional magnetic resonance imaging (fMRI) to investigate attentional orienting following uninformative Arabic digits. We show that BOLD response in occipital visual regions is modulated by the congruency between digit magnitude (small/large) and target side (left/right). Additionally, we report higher BOLD responses following large (8, 9) compared to small (1, 2) digits in two bilateral parietal regions, yielding a significant effect of digit magnitude. We propose and discuss the view that encoding of semantic representations related to number symbols in parietal cortex leads to shifts in visuo-spatial attention and enhances visual processing in the occipital cortex according to number-space congruency rules. [less ▲]

Orientation tuning for faces in the Fusiform Face Area and Primary Visual Cortex

Scientific Conference (2012, September)

From coarse to fine? Spatial and temporal dynamics of cortical face processing

in Cerebral Cortex (2011), 21(2), 467-476

Primary vision segregates information along 2 main dimensions: orientation and spatial frequency (SF). An important question is how this primary visual information is integrated to support high level ... [more ▼]

Primary vision segregates information along 2 main dimensions: orientation and spatial frequency (SF). An important question is how this primary visual information is integrated to support high level representations. It is generally assumed that the information carried by different SF is combined following a coarse-to-fine sequence. We directly addressed this assumption by investigating how the network of face-preferring cortical regions processes distinct SF over time. Face stimuli were flashed during 75, 150, or 300 ms and masked. They were filtered to preserve low SF (LSF), middle SF (MSF), or high SF (HSF). Most face-preferring regions robustly responded to coarse LSF, face information in early stages of visual processing (i.e., until 75 ms of exposure duration). LSF processing decayed as a function of exposure duration (mostly until 150 ms). In contrast, the processing of fine HSF, face information became more robust over time in the bilateral fusiform face regions and in the right occipital face area. The present evidence suggests the coarse-to-fine strategy as a plausible modus operandi in high level visual cortex. [less ▲]

Temporal dynamics of face spatial frequency processing: An fmri masking experiment

Poster (2009, May)

When processing a face stimulus, the human visual system tends to strongly integrate its constituent features (eyes, nose, mouth, etc) in a so-called holistic representation. Such feature integration ... [more ▼]

When processing a face stimulus, the human visual system tends to strongly integrate its constituent features (eyes, nose, mouth, etc) in a so-called holistic representation. Such feature integration mainly occurs in face-sensitive regions located in bilateral fusiform gyrii. Behavioural studies showed that feature integration relies on the extraction of low spatial frequencies (LSF) while high SF (HSF) underlie more local aspects of feature analysis. Following coarse-to-fine models of vision, we propose that the LSF-driven feature integration is an early and fast stage of face perception, in contrast to the longer-lasting extraction of detailed feature cues in HSF. By means of an event-related fMRI design, the present study investigated the temporal dynamics of face LSF and HSF processing in the network of face-sensitive cortical regions. Faces were flashed at 75, 150, or 300 msec, followed by a Gaussian mask. They were band-pass filtered to preserve low or high SF. At short stimulus durations, face-sensitive regions located in bilateral fusiform gyrii and superior temporal sulci responded more strongly to LSF than HSF faces. At longer durations, the same regions were more active for HSF than LSF faces. This pattern did not replicate for phase-scrambled versions of the stimuli. Taken together our findings suggest that face perception proceeds following a coarse-to-fine scenario, with an early and fast LSF-driven feature integration being relayed by the slower accumulation of HSF local information. [less ▲]

The roles of "face" and "non-face" areas during individual face perception: Evidence by fmri adaptation in a brain-damaged prosopagnosic patient

in NeuroImage (2008), 40(1), 318-332

Two regions in the human occipito-temporal cortex respond preferentially to faces: 'the fusiform face area' ('FFA') and the 'occipital face area' ('OFA'). Whether these areas have a dominant or exclusive ... [more ▼]

Two regions in the human occipito-temporal cortex respond preferentially to faces: 'the fusiform face area' ('FFA') and the 'occipital face area' ('OFA'). Whether these areas have a dominant or exclusive role in face perception, or if sub-maximal responses in other visual areas such as the lateral occipital complex (LOC) are also involved, is currently debated. To shed light on this issue, we tested normal participants and PS, a well-known brain-damaged patient presenting a face-selective perception deficit (prosopagnosia) [Rossion, B., Caldara, R., Seghier, M., Schuller, A. M., Lazeyras, F., Mayer, E. (2003). A network of occipito-temporal face-sensitive areas besides the right middle fusiform gyrus is necessary for normal face processing. Brain 126 2381-2395.], with functional magnetic resonance imaging (fMRI). Of particular interest, the right hemisphere lesion of the patient PS encompasses the 'OFA' but preserves the 'FFA' and LOC [Sorger, B., Goebel, R., Schiltz, C., Rossion, B. (2007). Understanding the functional neuroanatomy of acquired prosopagnosia. NeuroImage 35, 836-852.]. Using fMRI-adaptation, we found a dissociation between the coding of individual exemplars in the structurally intact 'FFA', which was impaired for faces but preserved for objects in the patient PS's brain. Most importantly, a larger response to different faces than repeated faces was found in the ventral part of the LOC both for normals and the patient, next to the right hemisphere lesion. Thus, following prosopagnosia, areas that do not respond preferentially to faces such as the ventral part of the LOC (vLOC) may still be recruited for compensatory or residual individual face perception. Overall, these observations indicate that several high-level visual areas in the human brain contribute to individual face perception. However, a subset of these areas in the right hemisphere, those responding preferentially to faces ('FFA' and 'OFA'), appear to be critical for this function. [less ▲]

Investigation of featural versus configural processing of faces in the middle fusiform gyrus

Poster (2007, May)

Inverting a face affects the processing of the vertical relations between features (e.g. eye height) more than the processing of horizontal relations (e.g. interocular distance) and of local features (e.g ... [more ▼]

Inverting a face affects the processing of the vertical relations between features (e.g. eye height) more than the processing of horizontal relations (e.g. interocular distance) and of local features (e.g. eye shape and surface). Inversion also decreases hemodynamic responses (HR) in face-sensitive regions in the middle fusiform gyrus (MFG), presumably because it reduces face distinctiveness and leads to larger adaptation. Here we tested the hypothesis that inversion affects the perception of vertical metric distances between features in the MFG. In the present fMRI study, twelve subjects were presented with short blocks of upright and inverted pairs composed either of identical faces (‘same’ condition), or of faces that differed at the level of ‘vertical’ relations, ‘horizontal’ relations, the shape of all inner feature (‘different’), or the shape of one single ‘feature’. In rMFG, smaller HR were observed for ‘same’ as compared to ‘different’ condition when faces were presented upright; due to HR adaptation. ‘Vertical’, ‘horizontal’ and ‘featural’ conditions led to HR close to ‘same’ condition. Inversion decreased HR in all conditions except the ‘same’ condition, thus replicating previous findings. The largest inversion-related decrements measured in rMFG were observed for vertical relations. In the left MFG, all conditions led to larger HR than the ‘same’ condition at upright. Inversion decreased HR in vertical and horizontal conditions only. These results suggest different roles of the MFG across hemispheres. rMFG may code ecological face differences, since release from adaptation was only observed for completely different faces in this region. Moreover, rMFG may be sensitive to face configuration as suggested by the generalised inversion-related HR decrease. In contrast, lMFG may code any kind of physical difference between faces irrespective of orientation, except for relational differences. [less ▲]

Understanding the functional neuroanatomy of acquired prosopagnosia

in NeuroImage (2007), 35(2), 836-852

One of the most remarkable disorders following brain damage is prosopagnosia, the inability to recognize faces. While a number of cases of prosopagnosia have been described at the behavioral level, the ... [more ▼]

One of the most remarkable disorders following brain damage is prosopagnosia, the inability to recognize faces. While a number of cases of prosopagnosia have been described at the behavioral level, the functional neuroanatomy of this face recognition impairment, and thus the brain regions critically involved in normal face recognition, has never been specified in great detail. Here, we used anatomical and functional magnetic resonance imaging (fMRI) to present the detailed functional neuroanatomy of a single case of acquired prosopagnosia (PS; Rossion, B., Caldara, R., Seghier, M., Schuller, A.-M., Lazeyras, F., Mayer, E., 2003a. A network of occipito-temporal face-sensitive areas besides the right middle fusiform gyrus is necessary for normal face processing. Brain 126, 2381-95; Rossion, B., Joyce, C.A., Cottrell, G.W., Tarr, M.J., 2003b. Early lateralization and orientation tuning for face, word, and object processing in the visual cortex. Neuroimage 20, 1609-24) with normal object recognition. First, we clarify the exact anatomical location and extent of PS' lesions in relation to (a) retinotopic cortex, (b) face-preferring regions, and (c) other classical visual regions. PS' main lesion - most likely causing her prosopagnosia - is localized in the posterior part of the right ventral occipitotemporal cortex. This lesion causes a left superior paracentral scotoma, as frequently observed in cases of prosopagnosia. While the borders of the early visual areas in the left hemisphere could be delineated well, the extensive posterior right-sided lesion hampered a full specification of the cortical representation of the left visual field. Using multiple scanning runs, face-preferring activation was detected within the right middle fusiform gyrus (MFG) in the so-called 'fusiform face area' ('FFA'), but also in the left inferior occipital gyrus (left 'OFA'), and in the right posterior superior temporal sulcus (STS). The dorsal part of the lateral occipital complex (LOC) and the human middle temporal cortex (hMT+/V5) were localized bilaterally. The color-preferring region V4/V8 was localized only in the left hemisphere. In the right hemisphere, the posterior lesion spared the ventral part of LOC, a region that may be critical for the preserved object recognition abilities of the patient, and the restriction of her deficit to the category of faces. The presumptive functions of both structurally damaged and preserved regions are discussed and new hypotheses regarding the impaired and preserved abilities of the patient during face and non-face object processing are derived. Fine-grained neurofunctional analyses of brain-damaged single cases with isolated recognition deficits may considerably improve our knowledge of the brain regions critically involved in specific visual functions, such as face recognition. [less ▲]

Face-sensitive responses in the occipital inferior cortex of normal humans through feedback inputs from the fusiform gyrus? Evidence from neuroimaging studies of brain-damaged prosopagnosic patient

Poster (2004, August 13)

In humans, neuroimaging studies have identified two major visual extrastriate areas presenting face-sensitive responses: in the inferior occipital cortex (‘occipital face area’, OFA), and the middle ... [more ▼]

In humans, neuroimaging studies have identified two major visual extrastriate areas presenting face-sensitive responses: in the inferior occipital cortex (‘occipital face area’, OFA), and the middle fusiform gyrus (the ‘fusiform face area’, FFA), with a right hemispheric dominance. It has been proposed that the OFA, located anteriorly to foveal V4v (Halgren et al., 1999), has a critical role in the early perception of facial features and provides the feedforward outputs to later stages of face processing in both the FFA and the STS (Haxby et al., 2000). However, we have recently reported a normal activation of the right FFA despite a lesion encompassing the region of the right OFA in a brain-damaged prosopagnosic patient, PS (Rossion et al., 2003), suggesting that the face-sensitive responses observed at the level of the OFA in normals may rather arise from feedback connections from the FFA. Here we provide complementary fMRI evidence supporting this view. First, the normal differential activation for faces and objects in the right FFA of PS was observed only for left visual field presentations and is thus unlikely to originate from contralateral intact regions of the occipital cortex (e.g. left OFA). Second, the time-course in the right FFA and left OFA of PS for centrally presented items suggests an earlier differential activity between faces and objects in the most anterior region, the FFA. Finally, we imaged another (prosop)agnosic patient (NS, Delvenne et al., 2004) with a lesion encompassing the right FFA but sparing all posterior visual areas, and failed to disclose any face-sensitive response in his nonetheless structurally and functionnally intact occipital cortex. Together, these findings illustrate the necessary role of both the right FFA and OFA for accurate face perception, and reinforce the hypothesis that a dominant (feedback) connection from the FFA to the OFA subtends face-sensitive responses observed in the latter area when processing faces. [less ▲]

Neuroimaging studies of a brain-damaged prosopagnosic patient reveal a critical role of the right fusiform gyrus in individual face discrimination

Poster (2004, June)