Later age or gender categorization processes

Longer-latency ERP effects were observed between about 215 and 265 msec poststimulation on the bilateral occipito-parietal regions when categorization according to age or gender was explicitly required. The patterns of effects showed large similarities for age and gender judgements, with highly significant values lasting up to about 400 msec for age processing. These effects are compatible with previous ERP results reporting enhanced activities beyond 200 msec post-stimulus at lateral posterior sites during explicit judgements of face gender (Eimer, 2000; Mouchetant-Rostaing et al., 2000a).

The fact that these effects were of larger amplitudes for age than for gender judgements may be explained by the ’higher difficulty’ of classifying faces according to age than gender, since the visual clues on which are based gender judgements are more isolated (eye and eyebrow regions) and more prominent than those (skin texture and colour) required for age judgements (Roberts and Bruce, 1988; Brown and Perrett, 1993; Burt and Perrett, 1995). This may be also due to the fact that age classification requires a distinction between two not well-delimited classes (young/old), whereas gender judgement is based on a qualitative distinction between two well-defined categories (male/female). In any case, these last effects were similar to those found in a control condition of hand classification (Mouchetant-Rostaing et al., 2000a). It seems therefore unlikely that these late activities are associated with any face-specific processing module, but rather with more general attention-based categorization processes.