Significance Experiments with rapid hand pointing demonstrate an extraretinal eye position signal (ERS) that is more accurate than intravisual comparison experiments and studies of visual stability once seemed to allow. Gaze pointing studies have drawn similar conclusions, but these experiments are seriously flawed and replication is long overdue. The motor system dependence and detailed time course of the ERS have not been studied in a well-controlled egocentric localization paradigm. The adaptability of saccadic eye movements raises the question of whether eye position can be decoupled from the ERS; the answer would have important implications for the locus of adaptive change and the source of the ERS. Finally, it has been suggested that slow or delayed motor movements might be programmed on a different basis, and therefore reflect errors not seen with rapid movements. Objectives and Methods Our objective is to address these questions with a within-subjects, factorial study. For each of several localization measures and states of saccadic gain adaptation, we will accurately determine the time course of localizations of dim and bright flashes presented in the dark, before, during, and after horizontal saccades. Normal human subjects will perform four different localization tasks: immediate or delayed pointing either with the eye or with unseen hand. Saccades will be: normal, gain-adapted early in training, and gain-adapted late in training. Saccades will be adapted with manipulated visual feedback, and eye position monitored by diffuse limbus-reflection. The proposed studies should help clarify the functional connectivity of the perceptual-motor system, particularly as it determines visually-based motor performance.
| Miller, J M (1996) Egocentric localization of a perisaccadic flash by manual pointing. Vision Res 36:837-51 |
