Abstract
A large number of psychophysical and neurophysiological studies have demonstrated that smooth pursuit eye movements are tightly related to visual motion perception. This could be due to the fact that visual motion sensitive cortical areas such as meddle temporal (MT), medial superior temporal (MST) areas are involved in motion perception as well as pursuit initiation. Although the directional-discrimination and perceived target velocity tasks are used to evaluate visual motion perception, it is still uncertain whether the speed of visual motion perception, which is determined by visuomotor reaction time (RT) to a small target, is related to pursuit initiation. Therefore, we attempted to determine the relationship between pursuit latency/acceleration and the visual motion RT which was measured to the visual motion stimuli that moved leftward or rightward. The participants were instructed to fixate on a stationary target and press one of the buttons corresponding to the direction of target motion as soon as possible once the target starts to move. We applied five different visual motion stimuli including first- and second-order motion for smooth pursuit and visual motion RT tasks. It is well known that second-order motion induces lower retinal image motion, which elicits weaker responses in MT and MST compared to first-order motion stimuli. Our results showed that pursuit initiation including latency and initial eye acceleration were suppressed by second-order motion. In addition, second-order motion caused a delay in visual motion RT. The better performances in both pursuit initiation and visual motion RT were observed for first-order motion, whereas second-order (theta motion) induced remarkable deficits in both variables. Furthermore, significant Pearson’s correlation and within-subjects correlation coefficients were obtained between visual motion RT and pursuit latency/acceleration. Our findings support the suggestion that there is a common neuronal pathway involved in both pursuit initiation and the speed of visual motion perception.
Highlights
When we look at a moving target, smooth pursuit eye movements ensure to hold the image of a moving target on or near the fovea in order to obtain clear vision
No significant difference was observed between first-order+ motion, second-order static and dynamic motions, these visual motion tasks yielded longer pursuit latency compared to first-order motion (Fig 3A)
We attempted to determine the relevance between visual motion reaction time (RT) and pursuit initiation using five different visual motion stimuli including first- and second-order motion
Summary
When we look at a moving target, smooth pursuit eye movements ensure to hold the image of a moving target on or near the fovea in order to obtain clear vision. Several studies have revealed that the initial part of smooth pursuit is driven by visual motion related signals from cortical areas including the middle temporal (MT) and medial superior temporal (MST) areas [4, 5]. Osborne and colleagues have demonstrated that the variability of pursuit initiation is mostly due to sensory errors in estimating target motion in monkeys [6, 7]. They have reported that almost all available directional information can be extracted from the first few spikes of the response of MT neuron, which is comparable with the pursuit initiation in terms of time scale [8]
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