Individual differences in the tuning of the face adaptation aftereffect to the preferred fixation location on the face

Several studies have shown that humans make their first eye movement to a consistent preferred fixation location (PFL) that varies moderately across individuals (Peterson & Eckstein, 2012, 2013). While the transfer of the face aftereffect (FAE) across spatial locations is an active area of research, not much is known about the variation of the FAE across fixation locations on the face. Here, we investigate how individual differences in the PFL modulate the variation of the FAE with fixation position. Methods: Seven upper and five lower lookers screened by a free eye-movements face identification task participated in a gaze-contingent FAE task. On each trial, observers adapted to a face for 4 seconds while fixating the adapter face at either their own group’s mean PFL or that of the other group (3.6° away along the vertical midline). The test stimulus, a morph between the adapter and another face, was flashed either at the same position as the adapter or at the alternate position. We calculated the strength of the FAE as the shift in the point of subjective equality following adaptation compared to a baseline condition with no adaptation. Results: A 3-way mixed ANOVA on the strength of the FAE with adapter position, test position, and looker type as factors revealed two significant interaction effects: adapter position x test position (F (1, 10) = 58.0, p << 0.05), and adaptation position x looker type (F (1,10) = 6.75, p = 0.026). The former indicated that the FAE was stronger when the adaptation and testing occurred at the same fixation location. Critically, the latter indicated that the FAE in upper lookers is more PFL-specific than the lower lookers. Conclusion: Our findings demonstrate the importance of considering PFL and the actual fixation position on the face in assessing the position-specificity of the FAE.