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Kimberley Halen, Michael Webster; Contrast dependence of figural aftereffects for faces. Journal of Vision 2011;11(11):588. doi: 10.1167/11.11.588.
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© ARVO (1962-2015); The Authors (2016-present)
Neural responses to shapes and faces in higher visual areas show relatively little dependence on stimulus contrast. We examined whether the effects of physical contrast on adaptation to faces was consistent with sensitivity changes at these more contrast invariant sites. Stimuli were grayscale images of frontal-view faces cropped to remove the external features of the head. The faces were distorted by locally expanding or contracting the image relative to a midpoint on the nose. Observers adapted for 2 min to a distorted face and then judged the distortions of 1 sec test faces interleaved with 4 sec readaptation intervals, with the test distortion varied in a staircase to determine the image that appeared undistorted. Test faces were 1.5 times smaller than the adapt faces to reduce effects of low-level retinotopic adaptation. Luminance levels in the test and adapt images were scaled to span a wide range of contrasts, with scaling relative to the mean luminance level in the cropped face. Additional image sets flattened the contrast variations within the face to control for the large luminance differences within the eye region. Aftereffects to the distorted faces showed relatively weak but significant effects of stimulus contrast. Pronounced aftereffects were induced in a full contrast face even by adaptation to faces with contrasts 16× lower that were near the threshold for recognition. The contrast response for adaptation to the face distortions was thus similar to other high-level figural aftereffects in implicating a central site of the sensitivity change. The face aftereffects are also selective for the polarity of luminance contrast, and in further experiments we examine the effects of these polarity differences both in the full face or restricted (eye) regions.
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