Integration of Visual Motion Signals in Reduced Visual Conditions.

Purpose: Neural sensory systems continuously tailor themselves to adapt to changes in the surrounding environment. In motion adaptation, a certain period of exposure to consistent motion in one direction (inducer) will alter the perceived direction of motion of the following stimulus. Depending on the timescale of the inducer, two opposite adaptation phenomena can be observed: motion priming for brief inducers, and motion aftereffect for longer inducers. The aim of this study was to investigate how the integration of motion signals during adaptation is affected by externally reduced visual conditions, such as luminance, contrast, and spatial frequency. We then considered how this would apply to the naturally impaired visual system in amblyopia.

Methods: We addressed this question by taking advantage of a visual illusion, the High-phi illusion. We measured the High-phi transition point when manipulating the visual conditions (contrast and luminance), the targeted subpopulations of neurons (by varying spatial frequency), and the integration properties of the visual system by changing the viewing conditions (monocular viewing, binocular viewing, and testing amblyopic participants).

Results: We found a larger transition point under high spatial frequency, low luminance, low contrast, and monocular viewing conditions. We then propose a model of temporal integration, for the motion signals, that accurately describes those effects.

Conclusions: Finally, we validated our model by testing amblyopic participants and demonstrating that the amblyopic visual system exhibits a larger High-phi transition point, thereby characterizing slower temporal integration. Overall, our results show that the integration of visual motion energy could switch adaptation from priming to aftereffect.