Emergence of Neural Face Selectivity in Infants Younger Than 4 Months Old.

Research on face-selectivity in infants under 4 months has shown mixed results, especially with rapid stimulus presentations. Here we tested whether increasing face saliency would promote face-selective responses even with brief presentation times in infants aged 4-to-6 months and younger. Using frequency-tagging EEG, we presented face and nonface stimuli at a rapid 6-Hz rate (i.e., 167 ms/stimulus), with faces appearing once per second as every 6th stimulus, therefore isolating face-selectivity at 1 Hz in the EEG spectrum. Two sets of images were presented in separate conditions: a "classic" set from previous studies and a "new" more salient set with increased luminance and size of the depicted items as well as a smoother background intending to facilitate figure-ground segregation. In Experiment 1, we validated the use of the new set to elicit high-level face-selectivity in adults (N = 19). Crucially, Experiment 2 demonstrated benefits from the new set for 2-to-6-month old infants (N = 46), with the youngest ones (2-to-4-month-olds) featuring face-selective responses only to this new set. Thus, adapting stimuli to the visual capabilities of infants uncovered earlier developmental emergence of face-selectivity to rapid visual stimulation than previously thought.