title: Turning the other cheek: the viewpoint dependence of facial expression after-effects.
abstract: 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.
authors.affiliation: Department of Experimental Psychology, University of Bristol, 12a Priory Road, Bristol BS8 1TU, UK.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Benton
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Etchells
authors.forename: Gillian
authors.initials: G
authors.lastname: Porter
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Clark
authors.forename: Ian S
authors.initials: IS
authors.lastname: Penton-Voak
authors.forename: Stavri G
authors.initials: SG
authors.lastname: Nikolov
mesh_terms: D000222:Adaptation, Physiological; D000360:Afterimage; D005149:Facial Expression; D005260:Female; D006801:Humans; D008297:Male