Sensory Competition in the Face Processing Areas of the Human Brain

The concurrent presentation of multiple stimuli in the visual field may trigger mutually suppressive interactions throughout the ventral visual stream. While several studies have been performed on sensory competition effects among non-face stimuli relatively little is known about the interactions in the human brain for multiple face stimuli. In the present study we analyzed the neuronal basis of sensory competition in an event-related functional magnetic resonance imaging (fMRI) study using multiple face stimuli. We varied the ratio of faces and phase-noise images within a composite display with a constant number of peripheral stimuli, thereby manipulating the competitive interactions between faces. For contralaterally presented stimuli we observed strong competition effects in the fusiform face area (FFA) bilaterally and in the right lateral occipital area (LOC), but not in the occipital face area (OFA), suggesting their different roles in sensory competition. When we increased the spatial distance among pairs of faces the magnitude of suppressive interactions was reduced in the FFA. Surprisingly, the magnitude of competition depended on the visual hemifield of the stimuli: ipsilateral stimulation reduced the competition effects somewhat in the right LOC while it increased them in the left LOC. This suggests a left hemifield dominance of sensory competition. Our results support the sensory competition theory in the processing of multiple faces and suggests that sensory competition occurs in several cortical areas in both cerebral hemispheres

Process and Domain Specificity in Regions Engaged for Face Processing: An fMRI Study of Perceptual Differentiation

The degree to which face-specific brain regions are specialized for different kinds of perceptual processing is debated. This study parametrically varied demands on featural, first-order configural, or second-order configural processing of faces and houses in a perceptual matching task to determine the extent to which the process of perceptual differentiation was selective for faces regardless of processing type (domain-specific account), specialized for specific types of perceptual processing regardless of category (process-specific account), engaged in category-optimized processing (i.e., configural face processing or featural house processing), or reflected generalized perceptual differentiation (i.e., differentiation that crosses category and processing type boundaries). ROIs were identified in a separate localizer run or with a similarity regressor in the face-matching runs. The predominant principle accounting for fMRI signal modulation in most regions was generalized perceptual differentiation. Nearly all regions showed perceptual differentiation for both faces and houses for more than one processing type, even if the region was identified as face-preferential in the localizer run. Consistent with process specificity, some regions showed perceptual differentiation for first-order processing of faces and houses (right fusiform face area and occipito-temporal cortex and right lateral occipital complex), but not for featural or second-order processing. Somewhat consistent with domain specificity, the right inferior frontal gyrus showed perceptual differentiation only for faces in the featural matching task. The present findings demonstrate that the majority of regions involved in perceptual differentiation of faces are also involved in differentiation of other visually homogenous categories

Repetition probability effects for inverted faces

It has been shown, that the repetition related reduction of the blood-oxygen level dependent (BOLD) signal is modulated by the probability of repetitions (P(rep)) for faces (Summerfield et al., 2008), providing support for the predictive coding (PC) model of visual perception (Rao and Ballard, 1999). However, the stage of face processing where repetition suppression (RS) is modulated by P(rep) is still unclear. Face inversion is known to interrupt higher level configural/holistic face processing steps and if modulation of RS by P(rep) takes place at these stages of face processing, P(rep) effects are expected to be reduced for inverted when compared to upright faces. Therefore, here we aimed at investigating whether P(rep) effects on RS observed for face stimuli originate at the higher-level configural/holistic stages of face processing by comparing these effects for upright and inverted faces. Similarly to previous studies, we manipulated P(rep) for pairs of stimuli in individual blocks of fMRI recordings. This manipulation significantly influenced repetition suppression in the posterior FFA, the OFA and the LO, independently of stimulus orientation. Our results thus reveal that RS in the ventral visual stream is modulated by P(rep) even in the case of face inversion and hence strongly compromised configural/holistic face processing. An additional whole-brain analysis could not identify any areas where the modulatory effect of probability was orientation specific either. These findings imply that P(rep) effects on RS might originate from the earlier stages of face processing. © 2014 Elsevier Inc

Conscious awareness is required for holistic face processing.

Investigating the limits of unconscious processing is essential to understand the function of consciousness. Here, we explored whether holistic face processing, a mechanism believed to be important for face processing in general, can be accomplished unconsciously. Using a novel "eyes-face" stimulus we tested whether discrimination of pairs of eyes was influenced by the surrounding face context. While the eyes were fully visible, the faces that provided context could be rendered invisible through continuous flash suppression. Two experiments with three different sets of face stimuli and a subliminal learning procedure converged to show that invisible faces did not influence perception of visible eyes. In contrast, surrounding faces, when they were clearly visible, strongly influenced perception of the eyes. Thus, we conclude that conscious awareness might be a prerequisite for holistic face processing

Face processing and prediction in schizophrenia: a functional MRI study on repetition probability modulation of repetition suppression

Abnormal processing of faces, a salient and social stimulus class, is a feature of cognitive dysfunction in schizophrenia. The major face processing areas are the fusiform face area (FFA), the occipital face area (OFA) and the dorsal-caudal region of the lateral occipital complex (LO). Hierarchical top-down prediction presumably from prefrontal areas to the occipitotemporal cortex relies on intact regional processing of faces. These feedback connections are thought to be disturbed in schizophrenia due to dorsolateral/medial prefrontal dysfunctions and/or prefronto-temporal disconnection. Recent studies in healthy subjects have suggested feedback connections between prefrontal and face-selective areas to be relevant in repetition probability (p(rep)) paradigms with predictive coding (PC) as underlying neural model. It is unclear, however, at which level of this processing hierarchy deficits in schizophrenia might emerge. In the present study, we tested hypotheses related to altered face perception in schizophrenia in a p(rep) paradigm. Our hypotheses were threefold: 1) Patients with schizophrenia (SZ) show altered BOLD (blood oxygenation level dependent contrast) responses to neutral faces in occipitotemporal face processing areas (FFA, OFA, LO) compared to healthy controls. 2) SZ show deficits in regional brain activation specific to the repetition suppression (RS) effect. 3) SZ show lower activation related to context modulation on RS as a correlate of impaired prediction.Die gestörte Verarbeitung von Gesichtern, als saliente und soziale Stimuli, ist ein Kernaspekt kognitiver Dysfunktion der Schizophrenie. Die für die Gesichter-Verarbeitung wichtigsten Areale sind das fusiforme (FFA), das okzipitale Gesichtsareal (OFA) und der dorso-kaudale Teil des lateral okzipitalen Komplexes (LO). Die hierarchische „top-down“ Vorhersage von (vermutlich präfrontalen) Arealen, hin zum okzipitotemporalen Kortex basiert auf intakter, regionaler Verarbeitung von Gesichtern. Diese Feedback-Verbindungen scheinen bei Schizophrenie gestört zu sein, basierend auf dorsolateral/medial präfrontalen Aktivierungsdefiziten und/oder gestörter präfrontotemporaler Konnektivität. Studien mit Gesunden teilen diesen Verbindungen in Paradigmen zur Wiederholungswahrscheinlichkeit (p(rep)), im Rahmen von Modellen des prädiktiven Kodierens (PC), eine wichtige Rolle zu. Es war bisher unklar, auf welcher Ebene der hierarchischen Verarbeitung die Defizite bei Schizophrenie auftreten. In dieser Studie wurden folgende Hypothesen in Bezug auf veränderte Gesichter-Wahrnehmung bei Schizophrenie im p(rep) Paradigma untersucht: 1) Patienten mit Schizophrenie (SZ) zeigen eine veränderte BOLD-Antwort (blood oxygenation level dependent contrast) auf neutrale Gesichter in okzipitotemporalen Arealen (FFA, OFA, LO). 2) SZ weisen Defizite in der wiederholungsbedingten Signalunterdrückung (repetition suppression, RS) auf, einem Charakteristikum regionaler Aktivität der Gesichtsareale. 3) SZ zeigen verminderte Aktivität hinsichtlich einer kontextuellen Modulation von RS als Ausdruck einer gestörten Vorhersage von Wiederholungen

Studying feature specific mechanisms of the human visual system

What are the current limits of our knowledge of brain activity underlying vision and can I further this knowledge? In this thesis, I explore this basic question. I focus on those aspects of visual input that can be described as basic features of visual perception. Examples include orientation, color, direction of motion and spatial frequency. However, understanding how humans visually perceive the external world is closely related with the study of attention. Attention, that is, the selection of some aspects of the environment over others, is one of the most intensively studied areas in experimental psychology, yet its neural mechanisms remain largely elusive. This thesis focuses on three distinct topics at the border of feature specific visual perception and feature-specific visual attention. First, in a series of studies, I explore the influence of heightened attentional demand to a central task to feature-specific neural processing in the ignored periphery. I discover that heightened attentional demand does not influence feature-specific representations in early visual cortices. Second, I investigate the influence of feature-based attention on neural processing of early visual cortices. At the same time, I also probe the influence of a behavioral decision to deploy feature-specific attention in the imminent future. I find that feature-based attention operates independent of other types of attention. Additionally, results indicate that a behavioral decision to deploy feature-based attention alone, without visual stimulation present, is able to modulate neural activity in early visual cortices. Third, I examine the more complex feature of facial gender and where in the brain gender discrimination might receive neural processing. I find that, in an established network of face-selective brain areas, facial gender is represented in nearly all areas of that network. Finally, I discuss all findings in the light of the current state of research, for their scientific significance and for future research opportunities