Adaptation
to facesAdaptation
to faces
The phenomena of adaptation to the mean and adaptation and to variation have been demonstrated using low-level visual attributes such as luminance, colour, orientation and motion. Recently, Michael Webster and colleagues have been investigating these phenomena at a higher level of the visual system using a paradigm of adaptation to distorted faces (Webster & MacLin, 1999). They showed that, after adapting to a distorted face, normal faces look distorted in the opposite direction while faces distorted to a lesser degree in the same direction look normal. The aftereffect was found when adapting and testing faces were both upright or both inverted, but was reduced when adapting and test images had opposite orientations. It is thought that configurational information plays a greater role in the processing of upright than inverted faces. The existence of a distortion aftereffect for inverted faces thus suggests that the effect may be based on local image statistics and mediated at a level of the visual system prior to face processing. To test this hypothesis, the original experiment was replicated and extended. In Experiment 1, subjects were adapted to a horizontally distorted face, either upright or inverted, and were tested by judging the distortion of a face of the same or opposite orientation. In Experiment 2, adapting faces were horizontally distorted and tilted 45° to the left, and test faces were either horizontally or vertically distorted and tilted 45° to the right. In Experiment 1 it was found that, while all conditions produced an aftereffect, there was a significant interaction between adapting and test orientation. In Experiment 2, an after effect was found when subjects were adapted to a horizontally distorted face tilted 45° to the left then tested with horizontally distorted faces tilted 45° to the right, but not when tested with faces distorted vertically and tilted 45° to the right. The results of Experiment 1 show that significant aftereffects occur when adapting and test stimuli share a common axis, and that the effect is strongest when they have the same orientation. Experiment 2 shows that the axis of distortion moves with the face. These results show that the face distortion aftereffect is principally object-centred, suggesting that adaptation is occurring at a stage of object processing and not simply on the basis of local image statistics.
References
Calder, A.J., Jenkins, R., Cassel, A. & Clifford, C.W.G. (in press) Adaptation reveals that the visual representation of eye gaze is coded by a non-opponent multichannel system, JEP General.
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Rhodes, G., Robbins, R., Jaquet, E., McKone, E., Jeffery, L. & Clifford, C.W.G. (2005). Adaptation and face perception – how aftereffects implicate norm based coding of faces, in Fitting the Mind to the World: Aftereffects in High-Level Vision, C.W.G. Clifford & G. Rhodes (eds.), Oxford University Press, pp. 213-240.
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Watson, T.L. & Clifford, C.W.G. (2006). Orientation dependence of the orientation contingent face after effect, Vision Research, 46, 3422-3429.