Proceedings of the Royal Society B: Biological Sciences
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Turning the other cheek: the viewpoint dependence of facial expression after-effects

Christopher P Benton

Christopher P Benton

Department of Experimental Psychology, University of Bristol12a Priory Road, Bristol BS8 1TU, UK

[email protected]

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,
Peter J Etchells

Peter J Etchells

Department of Experimental Psychology, University of Bristol12a Priory Road, Bristol BS8 1TU, UK

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,
Gillian Porter

Gillian Porter

Department of Experimental Psychology, University of Bristol12a Priory Road, Bristol BS8 1TU, UK

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,
Andrew P Clark

Andrew P Clark

Department of Experimental Psychology, University of Bristol12a Priory Road, Bristol BS8 1TU, UK

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Ian S Penton-Voak

Ian S Penton-Voak

Department of Experimental Psychology, University of Bristol12a Priory Road, Bristol BS8 1TU, UK

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and
Stavri G Nikolov

Stavri G Nikolov

Department of Electrical and Electronic Engineering, University of BristolMerchant Venturers Building, Woodland Road, Bristol BS8 1UB, UK

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    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.

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