The face inversion effect in infants is driven by high, and not low, spatial frequencies

To investigate the mechanisms underlying development of upright face preferences in infants, the current study measured inversion effects for faces that were spatial frequency (SF) filtered, into low SF and high SF, with the notion that different SFs are analyzed by different visual mechanisms. For comparison to faces, we used object stimuli that consisted of pictures of strollers. In 4 month olds, 8 month olds, and adults, we measured the strength of the selective face inversion effect (sFIE), operationally defined as an upright over inverted looking preference that is greater for faces than objects. In Study 1, we employed unfiltered stimuli, and found a clear sFIE in both infants and adults. To determine what drove this sFIE, in Study 2, the sFIE was measured for low-SF and high-SF stimuli, with all stimuli being equated for visibility. For adults, the sFIE was equally strong for low-SF and high-SF stimuli. A different pattern was seen for infants. Infants exhibited a significantly greater sFIE for high-SF, than for low-SF, stimuli (and only for high SF was the sFIE significant). In fact, the strength of infants' upright face preference for high-SF stimuli was indistinguishable from that observed for unfiltered faces, indicating that in natural (unfiltered) stimuli, high SFs are sufficient to account for infants' upright face preferences.