Understanding the Visual Phantom Illusion Across the Visual and Motion Processing Systems

Abstract

Illusory visual phantoms are a form of perceptual completion that occurs when two low-contrast collinear drifting gratings are separated by a homogeneous region, leading to the ghostly impression of stripes extending across the gap. Here, we investigated whether visual phantoms elicit both a static motion aftereffect and a dynamic motion aftereffect. Each observer was adapted with two drifting collinear vertical gratings separated by a horizontal gap and tested with a grating in the blank gap. Participants were instructed to report whether the test grating moved in either direction. Both static and dynamic motion aftereffects could be induced by the visual phantom illusion, suggesting that moving visual phantoms are likely represented at multiple stages of visual processing. Rivalry suppression occurs when different stimuli presented to the two eyes compete for perceptual dominance and is thought to originate in the early visual system. In this second project, we asked whether rivalry suppression can be induced by the visual phantom illusion over a competing stimulus. Our display consisted of a pair of grating inducers oscillating sinusoidally displayed to one eye, and a low contrast grating patch displayed to the other eye. Subjects were instructed to report the level of visibility of the competing grating patch. The visual phantom illusion increased the proportion of fully faded percept switches, implying that the visual phantom illusion influences lower stages of visual processing. Finally, there is a debate as to whether perception and action are similarly influenced by visual illusions. Here, we investigated this question by measuring smooth pursuit eye movements (SPEMs) while observers tracked a moving visual phantom illusion. Our displays consisted of two collinear vertical gratings that oscillated sinusoidally, separated by a gap. Participants were instructed to follow, through horizontal SPEMs, the shifting position of a specific stripe above and below the gap along the gap region. SPEMs following visual phantom eliciting stripes were not improved compared to a no-phantom control condition. Thus, we report that moving visual phantoms appear to be represented at multiple levels across the visual system but do not seem to operate like real stimuli regarding the motor system.