Abstract
Introduction: Previous studies using habituation techniques have shown infants as young as three months can discriminate between different faces (Slater et al., 1998; Sangrigoli & De Schonen, 2004; Kelly et al., 2008; Slater et al., 2010). The current study expands upon this literature by tracking the development of face discrimination using an oddball visual stimuli method in conjunction with eye-tracking methods. Unlike previous studies, the current investigation contrasts the development of face discrimination with that of a comparable shape discrimination task using scrambled faces. Methods: Twenty-eight infants (M = 8.5m (±1.6); age-range (5.8–11m); 14 females) provided gaze metrics recorded with eye-tracking. The dependent measure was first-fixation latency (msec) toward an oddball target presented amongst three distractors. Each target, per stimuli type, were randomly positioned in one of the four corners of the monitor and each trial lasted five seconds. For the Face condition, the target was a different face than the distractors, and for the Shape condition, the oval target differed in aspect ratio from the distractors. To check for infant engagement, a high contrast circle was interleaved across trials, and only infants who reliably fixated this stimulus were retained for analysis. For both Face and Shape conditions, effects of age were examined using exploratory correlational analyses. Results: For Faces, a significant negative correlation was observed between first-fixation latency and age (r(24) = −0.465, p = 0.016). By contrast, for Shapes, there was no significant effect of age (r(12) = 0.438, p = 0.154). The correlation between first-fixation to Faces and age remained significant after Bonferroni correcting for multiple comparisons (p’s < .025). Conclusion: Using eye-tracking methods, developmental changes in face discrimination can be observed in the first year of life. The fact that this age-related effect was seen for faces, and not shapes, suggest different underlying mechanisms for face vs. non-face objects.