Activity: Other activity types › Fellowship awarded competitively
The project will use the human saccadic eye movement response to investigate the more general problem of response time variability. Our previous work has established the importance of the visual stimulus and the nature of the response required in determining response time. Alongside this we have used mathematical models to explain changes in response time in terms of changes in threshold and accumulation rate of the decision variable to respond (c.f. Carpenter & Williams, 1995). The next step in this research is to use brain imaging (MEG and fMRI in this case) to investigate in more depth the neural basis of response time variability. A central first question for the development of models of choice and reaction time variability is understanding the origins of changes in response time when the stimulus and the response are held constant. The variability, which must be internally generated, cannot be investigated used standard behavioural methods which infer properties of the systems by changing either the stimulus or response. Equally the computational models in this area do not specify directly where this variability comes from and understanding the neural substrate of this variability will provide a significant constraint on these models. Pilot work, using MEG, collected in preparation for this application showed that the state of visual cortex in the pre-target period plays a major role in determining response latency. This leads to a set of questions that will be addressed in this application using MEG and fMRI: Why is there decreased Gamma activity for fast saccades in the pre target interval? Do the small changes in the visual response to target really reflect the differences between fast and slow saccades? Do the differences in visual response for fast saccades match responses to more visually salient targets?