Infant face processing becomes more selective during the first year of life as a function of varying experience with distinct face categories defined by species, race, and age. Given that any individual face belongs to many such categories (e.g. A young Caucasian man's face) we asked how the neural selectivity for one aspect of facial appearance was affected by category membership along another dimension of variability. 6-month-old infants were shown upright and inverted pictures of either their own mother or a stranger while event-related potentials (ERPs) were recorded. We found that the amplitude of the P400 (a face-sensitive ERP component) was only sensitive to the orientation of the mother's face, suggesting that “tuning” of the neural response to faces is realized jointly across multiple dimensions of face appearance.

The current study provides evidence for the existence of an other-age effect (OAE), analogous to the well-documented other-race effect. Experiments 1 and 2 demonstrate that adults are better at recognizing adult faces compared with faces of newborns and children. Results from Experiment 3 indicate that the OAE obtained with child faces can be modulated by experience. Moreover, in each of the 3 experiments, differences in the magnitude of the observed face inversion effect for each age class of faces were taken to reflect a difference in the processing strategies used to recognize the faces of each age. Evidence from Experiment 3 indicates that these strategies can be tuned by experience. The data are discussed with reference to an experience-based framework for face recognition.

Whether the development of face recognition abilities truly reflects changes in how faces, specifically, are perceived, or rather can be attributed to more general perceptual or cognitive development, is debated. Event-related potential (ERP) recordings on the scalp offer promise for this issue because they allow brain responses to complex visual stimuli to be relatively well isolated from other sensory, cognitive and motor processes. ERP studies in 5- to 16-year-old children report large age-related changes in amplitude, latency (decreases) and topographical distribution of the early visual components, the P1 and the occipito-temporal N170. To test the face specificity of these effects, we recorded high-density ERPs to pictures of faces, cars, and their phase-scrambled versions from 72 children between the ages of 4 and 17, and a group of adults. We found that none of the previously reported age-dependent changes in amplitude, latency or topography of the P1 or N170 were specific to faces. Most importantly, when we controlled for age-related variations of the P1, the N170 appeared remarkably similar in amplitude and topography across development, with much smaller age-related decreases in latencies than previously reported. At all ages the N170 showed equivalent face-sensitivity: it had the same topography and right hemisphere dominance, it was absent for meaningless (scrambled) stimuli, and larger and earlier for faces than cars. The data also illustrate the large amount of inter-individual and inter-trial variance in young children's data, which causes the N170 to merge with a later component, the N250, in grand-averaged data. Based on our observations, we suggest that the previously reported “bi-fid” N170 of young children is in fact the N250. Overall, our data indicate that the electrophysiological markers of face-sensitive perceptual processes are present from 4 years of age and do not appear to change throughout development.

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Recent behavioural work suggests that newborn face preferences are derived from a general, nonspecific attentional bias toward patterns with more features in the upper versus lower half. In the current study we predicted that selectivity for the specific geometry of the face may emerge during the first 3 months of life as a product of perceptual narrowing, leading to the construction of the first broadly defined face category segregating faces from other visual objects which may share with faces one or more visual properties. This was investigated behaviourally, using a standard preferential looking paradigm, and electrophysiologically, using high-density ERPs. Behavioural results indicated that, at 3 months, the top-heavy property is no longer a crucial factor in determining face preferences. ERP results showed evidence of differentiation between the two stimuli only for the N700. No differentiation was found for earlier components that are thought to reflect the adult-like structural encoding stage of face processing in infants (N290 and P400). Together, ERP and behavioural results suggest that, by 3 months, the perceptual narrowing process has led to a behavioural response specific to the geometry of the human face, but that this response is not purely perceptual in nature. Rather, it seems related to the acquired salience of this stimulus category, which may reflect the high degree of familiarity and/or the social value faces have gained over the infants' first 3 months of life.