Goal-directed pointing movements and perceived direction of multi-sensory cues

Sascha Serwe, University of Giessen, General and Experimental Psychology

Abstract
We studied multi-sensory integration of directional information during goal-directed pointing movements. Subjects pointed at a visual target without visual feedback during movement execution. Early in the movement directional information was presented orthogonal to the movement direction. We measured perceived direction of either a proprioceptive cue (force pulse, amplitude 1 N, duration 50 ms), a visual cue (set of radial lines) or a combination of both cues. Presentation time and spatial location of the cues were matched. In both-cue trials the direction of the visual cue was either consistent with the force pulse or differed by +/- 30°. Here we compared subjects’ responses to the predictions of an ideal observer model. For each single trial this model combines visual and proprioceptive direction estimates measured in single-cue conditions by weighted averaging. The weights depend on the reliability of each cue. A shift towards the more reliable cue and a higher reliability in combined trials is predicted. Whereas the mean shift prediction fits the observed data, we did not observe the gain in reliability. However, an alternative model describes the data quite well: it suggests that subjects choose between the cues with choice probability proportional to single cue reliability.

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