Motion coherence affects human perception and pursuit similarly

Pursuit and perception both require accurate information about the motion o f objects. Recovering the motion of objects by integrating the motion of th eir components is a difficult visual task. Successful integration produces coherent global object motion, while a failure to integrate leaves the inco herent local motions of the components unlinked. We compared the ability of perception and pursuit to perform motion integration by measuring directio n judgments and the concomitant eye-movement responses to line figure paral lelograms moving behind stationary rectangular apertures. The apertures wer e constructed such that only the line segments corresponding to the paralle logram's sides were visible; thus, recovering global motion required the in tegration of the local segment motion. We investigated several potential mo tion-integration rules by using stimuli with different object, vector-avera ge, and line-segment terminator-motion directions. We used an oculometric d ecision rule to directly compare direction discrimination for pursuit and p erception. For visible apertures, the percept was a coherent object, and bo th the pursuit and perceptual performance were close to the object-motion p rediction. For invisible apertures, the percept was incoherently moving seg ments, and both the pursuit and perceptual performance were close to the te rminator-motion prediction. Furthermore, both psychometric and oculometric direction thresholds were much higher for invisible apertures than for visi ble apertures. We constructed a model in which both perception and pursuit are driven by a shared motion-processing stage, with perception having an a dditional input from an independent static-processing stage. Model simulati ons were consistent with our perceptual and oculomotor data. Based on these results, we propose the use of pursuit as an objective and continuous meas ure of perceptual coherence. Our results support the view that pursuit and perception share a common motion-integration stage, perhaps within areas MT or MST.