Rapid Categorization of Human and Ape Faces in 9-Month-Old Infants Revealed by Fast Periodic Visual Stimulation

Abstract

This study investigates categorization of human and ape faces in 9-month-olds using a Fast Periodic Visual Stimulation (FPVS) paradigm while measuring EEG. Categorization responses are elicited only if infants discriminate between different categories and generalize across exemplars within each category. In study 1, human or ape faces were presented as standard and deviant stimuli in upright and inverted trials. Upright ape faces presented among humans elicited strong categorization responses, whereas responses for upright human faces and for inverted ape faces were smaller. Deviant inverted human faces did not elicit categorization. Data were best explained by a model with main effects of species and orientation. However, variance of low-level image characteristics was higher for the ape than the human category. Variance was matched to replicate this finding in an independent sample (study 2). Both human and ape faces elicited categorization in upright and inverted conditions, but upright ape faces elicited the strongest responses. Again, data were best explained by a model of two main effects. These experiments demonstrate that 9-month-olds rapidly categorize faces, and unfamiliar faces presented among human faces elicit increased categorization responses. This likely reflects habituation for the familiar standard category, and stronger release for the unfamiliar category deviants.

Snakes elicit specific neural responses in the human infant brain

“…Frequency resolution (i.e., the interval between adjacent frequency bins) was of 1/20.83 s = 0.048 Hz. For each sequence, signal-to-noise (SNR) responses were computed as the ratio between the amplitude at each frequency bin and the average amplitude at the 12 surrounding frequency bins (6 on each side, excluding the immediately adjacent bins, see 37,39 ). SNR values significantly above 1 at oddball frequency would indicate specific discrimination of the oddball stimuli.…”

“…When oddball stimuli are tagged at a fraction of stimulus frequency, the ability of the brain to differentiate between base and oddball stimuli surfaces as periodic responses at oddball frequency. This methodology therefore provides an implicit, objective and predictive measure of stimulus discrimination, and has recently proven its sensitivity in infants exposed to complex visual stimuli [37][38][39] . Event-related potentials (ERPs) to oddball stimuli were also examined as to uncover the temporal course of the discrimination response.…”

Understanding human individuation of unfamiliar faces with oddball fast periodic visual stimulation and electroencephalography

“…To resolve these issues and shed light on the development of FI, the present paradigm may be easily extended for testing across age groups. Indeed, a similar FPVS‐EEG paradigm contrasting faces with objects at a fast 6 Hz stimulation frequency has been successfully used in 4‐ to 6‐month‐old infants, showing a specific neural response to highly variable natural images of faces as compared to equally variable images of objects (i.e., generic face categorization; de Heering & Rossion, 2015; Leleu et al., 2019; see also Peykarjou, Hoehl, Pauen, & Rossion, 2017 for human versus monkey face categorization in 9‐month‐olds). Yet, despite extensive testing, our group has so far been unable to find a reliable and significant FI response in 4‐ to 6‐month‐olds with the presently reviewed paradigm.…”

Maternal odor shapes rapid face categorization in the infant brain

“…To increase signal-to-noise ratio (SNR), two data-driven criteria were used for each infant to remove sequences with no general response of the visual system to the rapid stream of stimulation (Barry-Anwar, Hadley, Conte, Keil, & Scott, 2018;de Heering & Rossion, 2015;Peykarjou, Hoehl, Pauen, & Rossion, 2017), or with atypical scalp-wide power at the 1-Hz face-selective rate compared with the other sequences. A fast Fourier transform (FFT) was first applied to every epoch, and amplitude spectra were extracted for all electrodes with a frequency resolution of 1/32 = 0.03125 Hz.…”