Abstract
Background: It has been suggested that infants rely on low spatial frequency (SF) mechanisms for face processing. To investigate this, we asked whether infants' preference for upright vs. inverted faces was greater for “low” vs. “high” SF-filtered faces, using stimuli equated for detectability. Methods: Four-month-old infants (n = 11) were presented with an upright stimulus and its inverted image on the left and right side of a monitor, respectively (or vice versa). The stimulus was either a face or an object (the latter being a stroller). Using forced-choice preferential looking, we determined the percentage of trials an infant preferred the upright stimulus (>50% indicates an upright preference). Four conditions were presented: 2 stimulus types (faces vs. objects) x 2 SF filters (low: <0.3 c/deg vs. high: > 0.5 c/deg). Stimuli were presented at 3.3x contrast threshold, with threshold for the four conditions obtained in a separate group of infants prior to the upright preference study. Results: For face stimuli, infants showed an upright preference for high SF faces (64.1%, p=0.0035, 1-tailed t-test), but not low SF faces (52.7%, p=NS). Likewise, for objects, infants showed an upright preference for high SF objects (56.5%, p=0.002, 1-tailed t-test), but not low SF objects (49.9%, p=NS). However, the effect for high SF faces was greater than that for high SF objects (p=0.06, MS). Conclusions: The mechanisms underlying upright face preferences in infants appear to be selective for high SFs. The discrepancy with previous findings (de Heering et al. 2007) may be explained by proposing that: 1) previous studies did not control for detectability of low vs. high SFs (i.e., the low SF faces may have been more detectable), or 2) reliance on low vs. high SFs depends on the nature of the face processing measure, which differs between studies.
NIH/NEI R01-EY12153-06 (KRD).