Personal familiarity influences the processing of upright and inverted faces in infants

Abstract

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.

Keywords: ERPs; face recognition; familiarity; perceptual learning.

Figure 1

A Hierarchical ontology for face categories. A schematic view of multiple levels of face specificity. At the broadest level on top of this diagram, faces may only be differentiated from non-faces. Continuing downwards, faces are grouped by categories like race and species, ultimately grouped within those categories by individual identity. The goal of the current study is to determine how these varying levels of specificity affect one another in terms of the neural response to faces.

Figure 2

Responses to upright and inverted faces as a function of personal familiarity. (A) The P400 waveform depicted here represents averaged activity over 10 occipital electrodes included in the analysis. These 10 electrodes were grouped into three distinct regions for statistical analysis of regional effects. (B) Grand-averaged waveforms obtained for mother's face upright and mother's face inverted. (C) Grand-averaged waveforms obtained for a stranger's face upright and inverted. Note the absence of a differential response to upright and inverted faces in the “unfamiliar face” group.

Figure 3

Average P400 amplitudes by subject group and face orientation. At left, we present the between-subjects average of the P400 amplitude to the Mother's face in upright and inverted orientations for each of our three sensor groups. At right, the same results are presented for the Stranger's Face group. Error bars represent+/−1 sem. calculated over the subjects in each group.