The role of eye movements in a contour detection task

Vision combines local feature integration with active
viewing processes, such as eye movements, to perceive
complex visual scenes. However, it is still unclear how
these processes interact and support each other. Here,
we investigated how the dynamics of saccadic eye
movements interact with contour integration, focusing
on situations in which contours are difficult to find or
even absent. We recorded observers’ eye movements
while they searched for a contour embedded in a
background of randomly oriented elements. Task
difficulty was manipulated by varying the contour’s
path angle. An association field model of contour
integration was employed to predict potential saccade
targets by identifying stimulus locations with high
contour salience. We found that the number and
duration of fixations increased with the increasing path
angle of the contour. In addition, fixation duration
increased over the course of a trial, and the time course
of saccade amplitude depended on the percept of
observers. Model fitting revealed that saccades fully
compensate for the reduced saliency of peripheral
contour targets. Importantly, our model predicted
fixation locations to a considerable degree, indicating
that observers fixated collinear elements. These results
show that contour integration actively guides eye
movements and determines their spatial and temporal
parameters.