The aim of the present study was to examine the time course and scalp distribution of electrophysiological manifestations of the visual word recognition mechanism. Event-related potentials (ERPs) elicited by visually presented lists of words were recorded while subjects were involved in a series of oddball tasks. The distinction between the designated target and nontarget stimuli was manipulated to induce a different level of processing in each session (visual, phonological/phonetic, phonological/lexical, and semantic). The ERPs of main interest in this study were those elicited by nontarget stimuli. In the visual task the targets were twice as big as the nontargets. Words, pseudowords, strings of consonants, strings of alphanumeric symbols, and strings of forms elicited a sharp negative peak at 170 msec (N170); their distribution was limited to the occipito-temporal sites. For the left hemisphere electrode sites, the N170 was larger for orthographic than for nonorthographic stimuli and vice versa for the right hemisphere. The ERPs elicited by all orthographic stimuli formed a clearly distinct cluster that was different from the ERPs elicited by nonorthographic stimuli. In the phonological/phonetic decision task the targets were words and pseudowords rhyming with the French word vitrail, whereas the nontargets were words, pseudowords, and strings of consonants that did not rhyme with vitrail. The most conspicuous potential was a negative peak at 320 msec, which was similarly elicited by pronounceable stimuli but not by nonpronounceable stimuli. The N320 was bilaterally distributed over the middle temporal lobe and was significantly larger over the left than over the right hemisphere. In the phonological/lexical processing task we compared the ERPs elicited by strings of consonants (among which words were selected), pseudowords (among which words were selected), and by words (among which pseudowords were selected). The most conspicuous potential in these tasks was a negative potential peaking at 350 msec (N350) elicited by phonologically legal but not by phonologically illegal stimuli. The distribution of the N350 was similar to that of the N320, but it was broader and including temporo-parietal areas that were not activated in the "rhyme" task. Finally, in the semantic task the targets were abstract words, and the nontargets were concrete words, pseudowords, and strings of consonants. The negative potential in this task peaked at 450 msec. Unlike the lexical decision, the negative peak in this task significantly distinguished not only between phonologically legal and illegal words but also between meaningful (words) and meaningless (pseudowords) phonologically legal structures. The distribution of the N450 included the areas activated in the lexical decision task but also areas in the fronto-central regions. The present data corroborated the functional neuroanatomy of word recognition systems suggested by other neuroimaging methods and described their timecourse, supporting a cascade-type process that involves di...

Event-related potentials (ERPs) were recorded while subjects were involved in three gender-processing tasks based on human faces and on human hands. In one condition all stimuli were only of one gender, preventing any gender discrimination. In a second condition, faces (or hands) of men and women were intermixed but the gender was irrelevant for the subject's task; hence gender discrimination was assumed to be incidental. In the third condition, the task required explicit gender discrimination; gender processing was therefore assumed to be intentional. Gender processing had no effect on the occipito-temporal negative potential at approximately 170 ms after stimulation (N170 component of the ERP), suggesting that the neural mechanisms involved in the structural encoding of faces are different from those involved in the extraction of gender-related facial features. In contrast, incidental and intentional processing of face (but not hand) gender affected the ERPs between 145 and 185 ms from stimulus onset at more anterior scalp locations. This effect was interpreted as evidence for the direct visual processing of faces as described in Bruce and Young's model [Bruce, V. & Young, A. (1986) Br. J. Psychol., 77, 305-327]. Additional gender discrimination effects were observed for both faces and hands at mid-parietal sites around 45-85 ms latency, in the incidental task only. This difference was tentatively assumed to reflect an early mechanism of coarse visual categorization. Finally, intentional (but not incidental) gender processing affected the ERPs during a later epoch starting from approximately 200 ms and ending at approximately 250 ms for faces, and approximately 350 ms for hands. This later effect might be related to attention-based gender categorization or to a more general categorization activity.

In a previous experiment using scalp event-related potentials (ERPs), we have described the neuroelectric activities associated with the processing of gender information on human faces (Mouchetant-Rostaing, Giard, Bentin, Aguera, & Pernier, 2000). Here we extend this study by examining the processing of age on faces using a similar experimental paradigm, and we compare age and gender processing. In one session, faces were of the same gender (women) and of one age range (young or old), to reduce gender and age processing. In a second session, faces of young and old women were randomly intermixed but age was irrelevant for the task, hence, age discrimination, if any, was assumed to be incidental. In the third and fourth sessions, faces had to be explicitly categorized according to their age or gender, respectively (intentional discrimination). Neither age nor gender processing affected the occipito-temporal N170 component often associated with the detection of physiognomic features and global structural encoding of faces. Rather, the three age and gender discrimination conditions induced similar fronto-central activities around 145-185 msec. In our previous experiment, this ERP pattern was also found for implicit and explicit categorization of gender from faces but not in a control condition manipulating hand stimuli (Mouchetant-Rostaing, Giard, Bentin, et al., 2000). Whatever their exact nature, these 145-185 msec effects therefore suggest, first, that similar mechanisms could be engaged in age and gender perception, and second, that age and gender may be implicitly processed irrespective of their relevance to the task, through somewhat specialized mechanisms. Additional ERP effects were found at early latencies (45-90 msec) in all three discrimination conditions, and around 200-400 msec during explicit age and gender discrimination. These effects have been previously found in control conditions manipulating nonfacial stimuli and may therefore be related to more general categorization processes.

This chapter reviews the main data on the physiological substrates of auditory selective attention and their contribution to theoretical models of cognitive psychology.While event-related potentials, magnetoencephalography, and more recently neuroimaging techniques have provided fundamental information on the neural correlates of attention in the central cortical system, measurements of the frequency-following responses in the brainstem and evoked otoacoustic emissions at the cochlea strongly suggest attentional phenomena at the auditory periphery. We propose an adaptive filtering mechanism for selective auditory attention that can be flexibly and dynamically tuned depending on the attentional demand. INTRODUCTIONKnowledge of the psychophysiological mechanisms of modality-specific attention closely depends on knowledge of the corresponding sensory system. In spite of extensive research these last decades on audition and sound analysis, the neural basis of automatic and controlled processing in audition remains poorly understood compared to that in the visual system. We do not pretend here to make an exhaustive list of the studies of auditory attention, but rather give some landmarks of the hypotheses, orientations, and main findings that have contributed to the knowledge of the brain mechanisms of auditory selective attention in humans.Interestingly, the literature on this topic shows an evolution in the theoretical and experimental approaches, the questions raised, and of course the techniques used. Research in the 1960's has been characterized by the elaboration of theoretical models of attention based on behavioral measurements. Since the pilot experiment by Hillyard et al. in 1973 (1), the chronometric measures provided by event-related potentials (ERPs) and later by magnetoencephalographic recordings (MEG) have enriched the psychological theories and physiological models of selective attention. These models, in turn, have been improved with the development of ERP mapping systems and electrical source analysis methods. Likewise promising is the recent use of neuroimaging techniques such as functional magnetic resonance imaging (fMRI) and positron emission tomogaphy (PET), which provide better spatial resolution for locating the brain structures activated. However, as will be discussed, the variety of experimental paradigms and the empirical approaches frequently used have often made it difficult to interpret the findings within the framework of theoretical models of attention. On the other hand, the recent discovery of active mechanical processes in the cochlea that are directly connected with the efferent auditory system has given a new impetus to the peripheral gating hypothesis.These various aspects of attentional research are illustrated below. PSYCHOLOGICAL MODELS OF AUDITORY SELECTIVE ATTENTIONAuditory selective attention refers to the mental ability to resist distractor stimuli and select relevant information from the surrounding acoustic events, as illustrated in the "cocktail party effect". ...

In a previous experiment aimed at studying gender processing from faces, we had found unexpected early ERP differences (45-85 ms) in task-irrelevant stimuli between a condition in which the stimuli of each gender were delivered in separate runs, and a condition in which the stimuli of both genders were mixed. Similar effects were observed with hand stimuli. These early ERP differences were tentatively related to incidental categorization processes between male and female stimuli. The present study was designed to test the robustness of these early effects for faces, and to examine whether similar effects can also be generated between two classes of non-biological stimuli. We replicated the previous findings for faces, and found similar early differential effects (50-65 ms) for non-biological stimuli (grey and hatched geometrical shapes) only, however, when the two shape categories were separated by conspicuous visual characteristics. While these results can partly be explained by phenomena related to neuronal habituation in the visual cortex, they may also suggest the existence of coarse and automatic categorization processes for rapid distinction between two wide classes of stimuli with strong psychosocial significance for humans.