Time course of discrimination of smiles: Saccade latency assessment.

Abstract

By means of saccade latency measures in a two-alternative-forced-choice task (2AFC), we investigated the time course of discrimination between (a) genuinely happy faces (a smile and happy eyes), (b) non-happy faces (neither a smile nor happy eyes), and (c) faces with blended expressions (a smile but not happy eyes). The time point at which the probability of correct saccades to the target face (happy) exceeded that to the distracter face (blended or non-happy) indicated the onset of the discrimination process. Results revealed: (a) an early discrimination (from 180 to 240 ms) between truly happy and non-happy faces; (b) a lack of discrimination between truly happy faces and blended expressions during the entire 600-ms saccade period; and (c) differences in discrimination were related to visual saliency of the mouth and the eye region. Being the smiling mouth highly salient in both the truly happy and the blended expressions, it probably overshadows their differences in the eye region, thus interfering with discrimination between genuine and fake smiles.