The aftereffect of the ensemble average of facial expressions on subsequent facial expression recognition.

An ensemble or statistical summary can be extracted from facial expressions presented in different spatial locations simultaneously. However, how such complicated objects are represented in the mind is not clear. It is known that the aftereffect of facial expressions, in which prolonged viewing of facial expressions biases the perception of subsequent facial expressions of the same category, occurs only when a visual representation is formed. Using this methodology, we examined whether an ensemble can be represented with visualized information. Experiment 1 revealed that the presentation of multiple facial expressions biased the perception of subsequent facial expressions to less happy as much as the presentation of a single face did. Experiment 2 compared the presentation of faces comprising strong and weak intensities of emotional expressions with an individual face as the adaptation stimulus. The results indicated that the perceptual biases were found after the presentation of four faces and a strong single face, but not after the weak single face presentation. Experiment 3 employed angry expressions, a distinct category from the test expression used as an adaptation stimulus; no aftereffect was observed. Finally, Experiment 4 clearly demonstrated the perceptual bias with a higher number of faces. Altogether, these results indicate that an ensemble average extracted from multiple faces leads to the perceptual bias, and this effect is similar in terms of its properties to that of a single face. This supports the idea that an ensemble of faces is represented with visualized information as a single face.