Turning the other cheek: the viewpoint dependence of facial expression after-effects.
How do we visually encode facial expressions? Is this done by viewpoint-dependent mechanisms representing facial expressions as two-dimensional templates or do we build more complex viewpoint independent three-dimensional representations? Recent facial adaptation techniques offer a powerful way to address these questions. Prolonged viewing of a stimulus (adaptation) changes the perception of subsequently viewed stimuli (an after-effect). Adaptation to a particular attribute is believed to target those neural mechanisms encoding that attribute. We gathered images of facial expressions taken simultaneously from five different viewpoints evenly spread from the three-quarter leftward to the three-quarter rightward facing view. We measured the strength of expression after-effects as a function of the difference between adaptation and test viewpoints. Our data show that, although there is a decrease in after-effect over test viewpoint, there remains a substantial after-effect when adapt and test are at differing three-quarter views. We take these results to indicate that neural systems encoding facial expressions contain a mixture of viewpoint-dependent and viewpoint-independent elements. This accords with evidence from single cell recording studies in macaque and is consonant with a view in which viewpoint-independent expression encoding arises from a combination of view-dependent expression-sensitive responses.
Benton
Christopher P
CP
Department of Experimental Psychology, University of Bristol, 12a Priory Road, Bristol BS8 1TU, UK.
Etchells
Peter J
PJ
Porter
Gillian
G
Clark
Andrew P
AP
Penton-Voak
Ian S
IS
Nikolov
Stavri G
SG
D000222:Adaptation, Physiological; D000360:Afterimage; D005149:Facial Expression; D005260:Female; D006801:Humans; D008297:Male