The effect of temporal expectation on the co-variation between EEG activity and sensory-motor latency (KSBNS 2018 Abstract)

When a sprinter waits for the start signal, the reaction time depends on the sprinter’s internal prediction for the timing of the signal: if it coincides with the actual timing, the reaction will be fast, but if it does not, the reaction will be slow. It is important to understand the underlying neural mechanisms for how the subjective temporal expectation modulates the behavioral reaction time, but the attempts to identify the neural source in sensory-motor behavior have been scarce.

In this study, we sought to understand the neural mechanisms by studying trial-by-trial relationship between the pattern of multivariate EEG activity and the latency of smooth pursuit eye movements under two temporal expectation conditions. We asked the human subjects to track visual motion stimuli that randomly moved in one of five directions (pre-determined central direction d, d), and recorded eye position signals using an infrared eye tracking device (EyeLink 1000 Plus, SR Research Ltd.) and EEG activity using a 64-channel active electrode system (BrainAmp, Brain Products, GmbH). We found a significant trial-by-trial correlation between multivariate Alpha band EEG activity and latency of smooth pursuit eye movements, and the correlation was modulated by the subjective temporal expectation. Our result suggests that the temporal expectation modulates the behavioral reaction time through the Alpha band EEG activity.

 

The effect of combined directional and temporal expectations on the initiation of smooth pursuit eye movements (KSBNS 2018 Abstract)

When we interact with a dynamic environment, we use top-down expectations to improve our behavior. An earlier study showed that subjective expectations for the timing of the stimulus (temporal expectation) and the expectation for the spatial location (spatial expectation) can improve both the behavioral and neural responses (Doherty et al., 2005). However, the effect of the top-down expectations on motion induced sensory-motor behavior, such as smooth pursuit eye movements, has rarely been studied.

In this study, we investigated how the top-down expectations of visual motion direction and timing influence the initiation of smooth pursuit eye movements. We asked human subjects to hold the fixation at the central yellow point, while a 100% contrast grating stimulus moves across the screen in one of four directions (45 deg, -45 deg, 135 deg, -135 deg) from each corner of the screen to the fixation point at 12.5 deg/s of speed. The grating stimulus turned off when it reached an invisible circle around the fixation point (radius of 10 deg). After a while, it reappeared over the fixation point immediately after the extinction of the fixation point. The main task of the subjects was to track the grating that reappeared in the center of the screen. The target grating underwent a pattern motion (drift) without any window motion for 100 ms in one of the three directions (the same direction with the direction of the traversing grating, two orthogonal transverse directions). The speed of the target grating was 12.5 deg/s  and contrast was 25%. Then, it continued to move (window motion) in the same speed and direction with the pattern motion for 700 ~ 900 ms. We controlled the subjective temporal expectation by manipulating the duration of the disappearance of the grating. In one block, the duration of the disappearance can be calculated by the speed of the traversing grating, therefore, subjective temporal expectation of target will be high. In the other block, the subjective temporal expectation will be low because the hazard function of the disappearance duration   is flat (probability of the duration follows exponential distribution). Whether or not the motion direction of the tracking target matched the direction of traversing grating was used as an index of the top-down expectation for the direction of motion.

We found that 1) temporal expectation influences the reaction time only: reaction was faster when subjects could predict the timing of visual stimulus, and 2) directional expectation has effects both on the reaction time and direction of pursuit initiation. If the motion direction of the target does not match the direction of the traversing grating, latency of pursuit initiation was longer, and pursuit direction was biased towards the direction of the traversing grating. This result indicates that temporal and directional expectations interactively impact the sensory-motor transformation processes in smooth pursuit eye movements.