Mohamed Rebaï

Familiarity and Emotional Expression Influence an Early Stage of Face Processing: An Electrophysiological Study.

Recent data indicate that the familiarity and the emotional expression of faces occur at an early stage of information processing. The goal of the present study was to determine whether these two aspects interact at the structural encoding stage as reflected by the N170 component of event-related potentials in tasks requiring the subjects either to identify whether the faces were familiar or the nature of the emotional expression. The results indicate that the neural responses to level of familiarity and emotional expression were observable at this early processing stage but without interacting. In particular, faces of personal importance to the subjects differed from those of less personal importance. Because familiarity did not interact with emotional expression at behavioral and electrophysiologic levels, our results support the contention of parallel and independent processing of faces.

ERPs associated with familiarity and degree of familiarity during face recognition.

Event-related potentials (ERPs) triggered by three different faces (unfamiliar, famous, and the subjects own) were analyzed during passive viewing. A familiarity effect was defined as a significant difference between the two familiar faces as opposed to the unfamiliar face. A degree of familiarity effect was defined as a significant difference between all three conditions. The results show a familiarity effect 170 ms after stimulus onset (NI70), with larger amplitudes seen for both familiar faces. Conversely, a degree of familiarity effect arose approximately 250 ms after stimulus onset (P2) in the form of progressively smaller amplitudes as a function of familiarity (subject s face < famous face < unfamiliar). These results demonstrate that the structural encoding of faces, as reflected by N170 activities, can be modulated by familiarity and that facial representations acquire specific properties as a result of experience. Moreover, these results confirm the hypothesis that N170 is sensitive to face versus. object discriminations and to the discrimination among faces.

The Stroop's Test Evokes A Negative Brain Potential, the N400

The Event Related Potential (ERP) of 8 french right handed subjects were recorded with 5 active electrodes located in frontal (Fz), central (Cz), occipital (Oz) and right/left parietal (RH, LH) sites while they were performing a modified version of the test of Stroop. They had either to read the names of basic colors (yellow, green, blue, red) written in the same colors (red written in red: concordant stimuli) or in a different color (red written in blue: discordant stimuli) or to name mentally the color in which was written the name of a color, both colors being concordant or discordant. The ERPs for reading were similar for concordant and discordant stimuli and showed no sign of a N400 wave, this was also the case for the mental naming of a color associated to the written name of the same color. A N400 wave with a Cz location was evident for the mental naming of a color when it was associated to the written name of another color. In this last case, the automatic reading of the name of a color would correspond to a priming which interferes with the access to the target word: the name of another color that the subject is required to evoke mentally.

CHRONOMETRY OF VISUAL WORD RECOGNITION DURING PASSIVE AND LEXICAL DECISION TASKS: AN ERP INVESTIGATION

In order to investigate the neuroanatomical chronometry of word processing, two experiments using: Event Related Potentials (ERPs) have been performed. The first one was designed to test the effects of orthographic, phonologic, and lexical properties of linguistic items on the presemantic components of ERPs during a passive reading task and massive repetition used to reduce familiarity effect between words and nonwords. In a second study, the level of familiarity was investigated by varying stimulus repetition and frequency in a lexical decision task. Overall results suggest a functional discrimination between orthographic and nonorthographic stimuli begun as early as 170 ms (N170 component) whereas the next components (N230 and N320) were sensitive to the orthographic nature of the stimuli, but also to their lexical/phonologic proprieties. The N320 associated to phonological processing (Bentin et al., 1999) was modulated by word frequency and massive repetition caused its disappearance. This suggests that this component may reflect a nonobligatory phonologic stage of graphemephoneme conversion postulated by the DRC model (Coltheart et al., 2001) or semantic phonologically mediated pathway (Harm and Seidenberg, in press).

The effects of familiarity and emotional expression on face processing examined by ERPs in patients with schizophrenia

BACKGROUND The main objective of the study was to determine whether patients with schizophrenia are deficient relative to controls in the processing of faces at different levels of familiarity and types of emotion and the stage where such differences may occur. METHODS ERPs based on 18 patients with schizophrenia and 18 controls were compared in a face identification task at three levels of familiarity (unknown, familiar, subjects own) and for three types of emotion (disgust, smiling, neutral). RESULTS The schizophrenic group was less accurate than controls in the face processing, especially for unknown faces and those expressing negative emotions such as disgust. P1 and N170 amplitudes were lower and P1, N170, P250 amplitudes were of slower onset in patients with schizophrenia. N170 and P250 amplitudes were modulated by familiarity and face expression in a different manner in patients than controls. CONCLUSIONS Schizophrenia is associated with a genelarized defect of face processing, both in terms of familiarity and emotional expression, attributable to deficient processing at sensory (P1) and perceptual (N170) stages. These patients appear to have difficulty in encoding the structure of a face and thereby do not evaluate correctly familiarity and emotion.

Event-related potentials for category-specific information during passive viewing of faces and objects.

Normal subjects passively viewed an upright or inverted face or objects during recording of event-related potentials. Face inversion augmented N170 amplitude and latency in the temporal region, but on ly the latency in the parietal region. The same manipulation slowed down the on set of the P220 and caused disappearance of the N300, whereas none of these effects was seen after object inversion. Item-specific processing of objects was observed, namely disappearance of the N190 and the appearance of a P170 wave in the left posterior hemisphere to on e object but not the other. These results are concordant with the hypothesis of category-specific processing during the recognition of faces and objects.

Orthographic transparency and grapheme–phoneme conversion: An ERP study in Arabic and French readers

Numerous behavioral studies have suggested that orthographic transparency of a language is liable to influence the use of grapheme-phoneme conversion during reading. In order to test this hypothesis, the effect of orthographic transparency on event-related potentials was assessed by comparing French to Arab readers. Indeed, French language, contrary to Arabic one, was expected to favor the use of grapheme-phoneme rules during reading. Our results demonstrated that the N320, a component implicated in phonologic transcription, was modulated by orthographic transparency. Indeed, during reading in their mother tongue, only French subjects clearly elicited a N320. Moreover, the comparisons between activations elicited by Arabic words in Arab subjects and French monolingual people also confirm that the N170 component represents an important orthographic stage. The implications of these results on bilinguism and visual word recognition models are discussed.

Early holistic face-like processing of Arcimboldo paintings in the right occipito-temporal cortex: evidence from the N170 ERP component.

The properties of the face-sensitive N170 component of the event-related brain potential (ERP) were explored through an orientation discrimination task using natural faces, objects, and Arcimboldo paintings presented upright or inverted. Because Arcimboldo paintings are composed of non-face objects but have a global face configuration, they provide great control to disentangle high-level face-like or object-like visual processes at the level of the N170, and may help to examine the implication of each hemisphere in the global/holistic processing of face formats. For upright position, N170 amplitudes in the right occipito-temporal region did not differ between natural faces and Arcimboldo paintings but were larger for both of these categories than for objects, supporting the view that as early as the N170 time-window, the right hemisphere is involved in holistic perceptual processing of face-like configurations irrespective of their features. Conversely, in the left hemisphere, N170 amplitudes differed between Arcimboldo portraits and natural faces, suggesting that this hemisphere processes local facial features. For upside-down orientation in both hemispheres, N170 amplitudes did not differ between Arcimboldo paintings and objects, but were reduced for both categories compared to natural faces, indicating that the disruption of holistic processing with inversion leads to an object-like processing of Arcimboldo paintings due to the lack of local facial features. Overall, these results provide evidence that global/holistic perceptual processing of faces and face-like formats involves the right hemisphere as early as the N170 time-window, and that the local processing of face features is rather implemented in the left hemisphere.

Spatial frequency and right hemisphere: an electrophysiological investigation.

The influence of the spatial frequency of visual stimuli on hemispheric asymmetry has been studied with visual evoked potentials (VEP). Nineteen different sinusoidal gratings (19 SF from 1 to 10 cpd) were presented in an ON-OFF mode to five right-handed subjects. The amplitude of the VEPs and the latency of the first positive component (C1) were analyzed. The results show that in the low range of spatial frequencies, the latency and the amplitude of C1 are similar in both hemispheres. At medium to high spatial frequencies, the VEPs on the right hemisphere (RH) present shorter latencies and larger amplitudes than those on the left hemisphere (LH). These results, discussed in relation to the directional differences in the time of callosal interhemispheric transfer, strengthen the idea that the RH is relatively more sensitive than the LH to the spatial component of the visual stimuli.

Making decisions about time: event-related potentials and judgements about the equality of durations.

Participants were exposed to a temporal generalization task where the duration of a small visual stimulus was judged. People received a 600ms standard duration, then had to judge whether other durations (longer than, shorter than, or equal to the standard) were or were not the standard (making a YES or NO response). In different experimental conditions, the spacing of non-standard durations around the standard was 150ms (Easy condition), or 75ms (Difficult condition), so the two conditions involved some judgements made with the same stimuli (450, 600, and 750ms). The experiment thus compared judgements of the same physical stimuli, when the basis of the judgement was the same, thus avoiding some problems of control that have been present in earlier electrophysiological studies of time judgements. As in previous work, fewer YES responses occurred in the Difficult condition and the 450ms duration was less confused with the 600ms standard than the 750ms one was. Computer modelling suggested that this (fewer YES responses) was due to a decrease in the decision threshold for the YES judgement. The electrophysiological results showed a distinction between the Easy and Difficult conditions observable by a change in the LCPt (Late Positive Component of Timing) measured after the stimulus presentations and by a change in the P1, the CNV (Contingent Negative Variation), and its positive counterpart during the presentation of the stimulus, which were larger when the discrimination was difficult. Our results therefore suggest that the increase in the difficulty of the generalization task not only changes decision processes but also alters attentional mechanisms. They also reveal that the decision does not seem to involve a unitary mechanism but depends on a group of sub-processes, notably attentional mechanisms which are altered from the moment of presentation of the stimulus.