Abstract
Fixational eye movements (FEMs) are not only crucial for enhancing visual acuity, but also for optimizing visually-guided behaviors. When FEMs fail its normal behavior (i.e., fixational instabilities), this results in visual impairments, suggesting a link between deficits in visual acuity and FEMs. Importantly, the frequency of FEMs increases significantly with increasing search demand tasks, indicating their important roles for both peripheral and foveal processing. Here, we set out to determine: 1) the influence of FEMs on visual search response times, and 2) the role of FEMs in saccadic latencies and subsequent oculomotor behaviors. Typically developing corrected-to-normal vision observers viewed naturalistic stimuli – a filtered version of “Where’s Waldo” – while performing a visual search task with varying crowding difficulties. Our results did not show a significant correlation between the FEMs and response times when subjects viewed with either dominant or non-dominant eye. However, subjects were slower to execute a saccade to the peripheral target when viewing with the non-dominant eye compared to the dominant eye. When the FEMs occurred near the peripheral target onset, saccade latencies were prolonged, suggesting a potential delay in the oculomotor system processes and the visual search. Furthermore, the first saccade landing was not affected by the preceding FEMs, but rather by the complexity of the upcoming target features. In contrast, mouse click positions at the targets demonstrated an inverse relationship with the widening distribution of saccade endpoints that depended on the target complexities, demonstrating a dissociation between the oculomotor system and the visually-guided behavior. Thus, FEMs play an important role on subsequent oculomotor system that ultimately affect both behavior and perception. In conclusion, our results show a promise in using the characteristics of eye movements to study the underlying mechanisms of visual perception.