Suárez-Pinilla, M;
Seth, AK;
Roseboom, W;
(2017)
Sensory Mechanisms of Perceptual Uniformity.
Presented at: 40th European Conference of Visual Perception (ECVP 2017), Berlin, Germany.
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Abstract
BACKGROUND AND AIMS: Visual experience appears rich in detail despite the poor performance of the vast majority of the visual field, as a result of the integration of coarse peripheral signals with the information of the comparatively tiny fovea. We examined the mechanisms of this integration by employing the uniformity illusion, in which a pattern with different properties in fovea and periphery uniformly takes the appearance of the fovea. We developed an adaptation paradigm to investigate whether the direction of an after-effect in the visual periphery followed the local, physical stimulation or the perception that arose under the Uniformity Illusion. We employed two different perceptual dimensions (orientation and spatial density) to investigate the extent to which the uniformity illusion is associated with changes in sensory encoding. RESULTS AND CONCLUSIONS: Experiments performed on two visual domains indicate that the uniformity illusion is not associated with a change in the sensory encoding on a local basis. Specifically, in our orientation experiments, the (V1-based) tilt after-effect only ever followed the local, physically presented orientation rather than the global orientation perceived under the illusion of uniformity. This was not due to insufficient exposure to the global pattern to produce an after-effect as presentation of physical uniformity for the same durations as participant reports of the illusion did produce an after-effect to the global orientation. Results on spatial-density based experiments showed an intermediate level of adaptation between (physical) low and high density, which could be consistent with an adaptation exerted by the illusory pattern. Thus, we could not rule out that the Uniformity Illusion might directly modify more abstract dimensions (such as numerosity, akin to our formalization of spatial density). However, the time invariance of the effect makes alternative explanations more likely and therefore, suggests that the uniformity illusion arises from high-level perceptual processes.
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