Computational modeling of collicular integration of perceptual responses and attention in microsaccades.

During visual fixation on a target object, our eyes are not motionless but generate slow fixational eye movements and microsaccades. Effects of visual attention have been observed in both microsaccade rates and spatial directions. Experimental results, however, range from early (<200 ms) to late (>600 ms) effects combined with cue-congruent as well as cue-incongruent microsaccade directions. On the basis of well characterized neural circuitry in superior colliculus, we construct a dynamical model of neural activation that is modulated by perceptual input and visual attention. Our results show that additive integration of low-level perceptual responses and visual attention can explain microsaccade rate and direction effects across a range of visual cueing tasks. These findings suggest that the patterns of microsaccade direction observed in experiments are compatible with a single dynamical mechanism. The basic principles of the model are highly relevant to the general problem of integration of low-level perception and top-down selective attention.