Different integration of conflicting motion signals in perception and eye movements during object tracking

Abstract

The ability to accurately perceive and track moving objects is crucial for many everyday activities. In this study, we use a "double-drift stimulus" Lisi and Cavanagh (2015); Shapiro et al. (2010); Tse and Hsieh (2006) to explore the processing of visual motion signals that underlie perception, pursuit, and saccade responses to a moving object. Participants were presented with peripheral moving apertures filled with noise that either drifted orthogonally to the apertures direction or had no net motion. Participants were asked to saccade to and track these targets with their gaze as soon as they appeared, and then to report their direction. In the trials with internal motion, the target disappeared at saccade onset so that the first 100 ms of the post-saccadic pursuit response was driven uniquely by peripheral information gathered before saccade onset. This provided independent measures of perceptual, pursuit, and saccadic responses to the double-drift stimulus on a trial-by-trial basis. Our analysis revealed systematic differences between saccadic responses on one hand and perceptual and pursuit responses on the other. These differences are unlikely to be caused by differences in the processing of motion signals because saccade and pursuit appear to use a common motion processing mechanism (e.g., Erkelens, 2006; Fleuriet and Goffart, 2012). We conclude that our results are instead due to a difference in how the processing mechanisms underlying perception, pursuit, and saccades combine motor signals with target position. These findings advance our understanding of the mechanisms underlying dissociation in visual processing between perception and eye movements.