Abstract
Face aftereffects (e.g., expression aftereffects) can be simultaneously induced in opposite directions for different face categories (e.g., male and female faces). Such aftereffects are typically interpreted as indicating that distinct neural populations code the categories on which adaptation is contingent, e.g., male and female faces. Moreover, they suggest that these distinct populations selectively respond to variations in the secondary stimulus dimension, e.g., emotional expression. However, contingent aftereffects have now been reported for so many different combinations of face characteristics, that one might question this interpretation. Instead, the selectivity might be generated during the adaptation procedure, for instance as a result of associative learning, and not indicate pre-existing response selectivity in the face perception system. To alleviate this concern, one would need to demonstrate some limit to contingent aftereffects. Here, we report a clear limit, showing that gaze direction aftereffects are not contingent on face sex. We tested 36 young Caucasian adults in a gaze adaptation paradigm. We initially established their ability to discriminate the gaze direction of male and female test faces in a pre-adaptation phase. Afterwards, half of the participants adapted to female faces looking left and male faces looking right, and half adapted to the reverse pairing. We established the effects of this adaptation on the perception of gaze direction in subsequently presented male and female test faces. We found that adaptation induced pronounced gaze direction aftereffects, i.e., participants were biased to perceive small gaze deviations to both the left and right as direct. Importantly, however, aftereffects were identical for male and female test faces, showing that the contingency of face sex and gaze direction participants experienced during the adaptation procedure had no effect.
Highlights
The human face provides us with cues about a person’s identity, age, sex, ethnicity, emotional expression, and current focus of attention (Calder et al, 2011)
Participants who adapted to male stimuli with left gaze and female stimuli with right gaze would be expected to show a selective increase in “direct” responses only to male test faces with left gaze and female test faces with right gaze, but not to male faces with right gaze and female faces with left gaze
We have shown that adaptation to alternating male and female faces with opposite gaze directions induces significant gaze direction aftereffects that are not contingent on face sex
Summary
The human face provides us with cues about a person’s identity, age, sex, ethnicity, emotional expression, and current focus of attention (Calder et al, 2011). The efficiency with which our visual system processes the various facial cues is partly owed to perceptual adaptation (for a review, see Webster and MacLeod, 2011). The response properties of Limits to Contingent Face Aftereffects face-sensitive neurons in the visual system constantly adjust to the specific characteristics of the faces surrounding us. Neural responses to frequently occurring stimulus characteristics are down-regulated, which frees up capacity to respond to novel stimuli and equips us with highly sensitive face discrimination abilities. Adaptation to faces with expanded features will bias participants to perceive a subsequently presented undistorted face as slightly compressed. After adaptation to compressed faces they will be biased to perceive the same undistorted face as expanded (face distortion aftereffect, Webster and MacLin, 1999)
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