Saccadic eye movements made to remembered locations in the dark show a distinct up-shift in macaque monkey, and slight upward bias in humans (Gnadt et al. 1991). This upward bias created in the visual spatial mapping of a saccade may be translated downstream in a hand/touch movement. This error could possibly reveal (a) information about the frames of reference used in each scenario and (b) the sources of this error within the brain. This would suggest an early planning stage if they are shared, or a later stage if the errors are distinct.
Methods: Eight human subjects performed touch responses to a touch screen monitor to both visual and remembered target locations. The subjects used a high-resolution touch-screen monitor, a bite bar and chin-rest for restricting head movements during responses. All target locations were 20 degrees vectors from the central starting position in horizontal, vertical and oblique planes of motion.
Results: Subjects were accurate to both visual and remembered target locations with little variance. Subject means showed no significant differences between control and memory trials; however, a distinct asymmetry was observed between cardinal and oblique planes during memory trials. Subjects consistently made errors to oblique locations during touches made to the remembered location that was not evident in control conditions. This error pattern revealed a strong hypermetric tendency for oblique planes of touches made to a remembered location.