Saccade-Contingent Spatial and Temporal Errors are Absent for Saccadic Head Movements

Psychophysical studies extending over a thirty-year period have repeatedly demonstrated that visual stimuli presented close to the onset of a saccadic eye movement are mislocalised both spatially and temporally. When post-saccadic visual references are available, this spatial distortion is best characterised by a compression of visual space toward the target of the saccadic eye movement. An important but unresolved issue, concerns the specificity of saccade-dependent visual mislocalisation phenomena. We investigated this by examining whether saccade-dependent spatial and temporal mislocalisation are observed in an individual (A.I.) who cannot make any form of eye movement (opthalamoplegia), but compensates when reading or scanning visual scenes by making saccadic head movements. We demonstrate that saccade- dependent spatial and temporal mislocalisation are absent in subject A.I. and suggest that spatiotemporal mislocalisation may be specific to rapid forms of movement, such as ocular saccades, that necessitate predictive re-mapping to maintain space constancy.