The effect of smooth pursuit eye movements and contextual motion on the visibility of low-contrast drifting target gratings

Our sensory systems are constantly bombardedby sensory stimulation. It is the result of complex neural processes that signals reflected by these physical stimuli are processed andperceived  the brain. That we perceivecolours, for example,is the end product of light waves reflected by objects getting processed on the basis of incoming wavelenght information. Ormotion getting analysed with respect to the speed vector and motiondirection of objects and a 3-­dimensional internal representation getting reformed out of a 2-­dimensional retinal signal are all a few examples of how complex are the sensory computations involved in the visual system. All these complex computational processes during the transmission of signals coming from the outer world, though, take some time to create a conscious percept. Thus, there happens to be a delay in the millisecond range between the transduction of the energy into the electrochemical signallingand the formation of a conscious percept: This means that once the subject becomes aware of an object, its reality in the physical world would have already been changed. A growing number of  recent  studies  in  the  literature  report  prediction  mechanisms  in  the  sensory  and  sensory-­motor  systems  in  order  to compensate  these  temporal  delays  and  form  a  more  accurate  representation  of  the  motion  signals  in  the  environment. According to the implications of these studies, while playing a volleyball game, for example, the system is thought to compute/predict the near-­future position when the hands are going to hit a ball in the ball’s motion trajectory. In this context, the aim of this project is to investigate the prediction mechanisms involved in the visual motion computation during smooth pursuit eye movements and to make not only significant theoretical contributions, but also to introduce an original experimental paradigm to investigate predictive strategies the sensory-­motor systems employ. 

In a recent work published inCurrent Biology, Roach et al (2011) suggested that as well as analysing image velocity, cortical motion analysis might also use a predictive encoding strategy in relation to future patterns of sensory stimuli along the motion path. The results of their psychophysical experiments showed that locally drifting sinusoidal target patterns presented at the leading edge of a region containing phase-­congruent motion can be detected at even very low contrast levels, indicating a reduction in discrimination thresholds in comparison to those obtained in target-­phase-­incongruent motion conditions. In all experiments, Roach et al studied predictive sensory encoding mechanisms while eyes were fixated on a fixation. In daily life, however, our eyes are rarely steady. We rather make frequent eye movements. Predictive encoding strategies of sensorimotor systems  in  the  presence  of  eye  movements  (i.e.  smooth  pursuit  eye  movements),  therefore,  remains  to  be  an  important research question.Our main interest, here, is to investigate motion-­induced prediction of spatio-­temporal patterns in the presence of both object and smooth pursuit eye movements using psychophysical methodology. The suggested stimulus in the project, sinusoidally-­modulated counterphase gratings, are perceived as ambious with no net motion when eyes are steady. A recent study by Terao et al. (2015), however, has shown that when the counterphase stimulus is tracked by smooth pursuit eye movements on the periphery, they appear to be moving in the direction opposite to the pursuit direction. This  particular  feature  of  counterphase  grating  stimuli will  also  allow  us  to  study  a  critical  question  yet  to  be  investigated: “Whether visual awareness of motion direction is a necessity in order to generate motion-­induced predictive signals”.

Roach N. W., McGraw P. V., Johnston A. 2011. “Visual  motion induces a forward prediction of spatial pattern”. Current Biology, 21 (9):740–745.  

Terao, M., Murakami, I., & Nishida, S. Y. 2015. “Enhancement of motion perception in the direction opposite to smooth  pursuit eye movement”. Journal of Vision, 15(2).  

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https://visionlab.boun.edu.tr/sites/visionlab.boun.edu.tr/files/suppleme...