Abstract
Prolonged visual exposure, or ‘adaptation’, to thin (wide) bodies causes a perceptual aftereffect such that subsequently seen bodies appear wider (thinner) than they actually are. Here, we conducted two experiments investigating the effect of rotating the orientation of the test stimuli by 90° from that of the adaptor. Aftereffects were maximal when adapting and test bodies had the same orientation. When they differed, the axis of the perceived distortion changed with the orientation of the body. Experiment 1 demonstrated a 58% transfer of the aftereffect across orientations. Experiment 2 demonstrated an even greater degree of aftereffect transfer when the influence of low-level mechanisms was reduced further by using adaptation and test stimuli with different sizes. These results indicate that the body aftereffect is mediated primarily by high-level object-based processes, with low-level retinotopic mechanisms playing only a minor role. The influence of these low-level processes is further reduced when test stimuli differ in size from adaptation stimuli.
Highlights
In estimating the size and shape of their own bodies, many humans make consistent errors
It has long been known 2 that prolonged viewing of a stimulus can lead to perceptual aftereffects, such that subsequently seen images have an appearance that is opposite to the original stimulus [7]
By assessing the properties of the aftereffects, previous research has used adaptation as a non-invasive method of probing the neural basis of perception, leading some to refer to it as the ‘psychophysicist’s microelectrode’ [10]. Some aftereffects, such as those arising from adaptation to motion, colour or the orientation of bars or edges, have been demonstrated to be ‘retinotopic’, i.e. their effects are restricted to the area of the retina that is exposed to the adaptation stimulus
Summary
In estimating the size and shape of their own bodies, many humans make consistent errors. By assessing the properties of the aftereffects, previous research has used adaptation as a non-invasive method of probing the neural basis of perception, leading some to refer to it as the ‘psychophysicist’s microelectrode’ [10] Some aftereffects, such as those arising from adaptation to motion, colour or the orientation of bars or edges, have been demonstrated to be ‘retinotopic’, i.e. their effects are restricted to the area of the retina that is exposed to the adaptation stimulus. The first report of body size aftereffects used adaptation images that were uniformly expanded or contracted horizontally, shifting the perceived width of subsequently seen bodies in the opposite direction [13] These image manipulations correspond to a decrease or an increase of the spatial frequency of vertical components of the image, and this result could reflect a simple low-level spatial frequency aftereffect [14,15]. The current study attempts to establish the relative contribution of high- and low-level processes in body adaptation in two experiments
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