Visual-inertial coherence zone in the perception of heading

Knowledge of human motion perception can be applied in the optimization of motion cueing algorithms. In the past it has been shown that some discrepancies between the amplitude or phase of a visual and inertial cue go unnoticed. These acceptable discrepancies are referred to as coherence zones. In the present experiment we investigate whether a coherence zone applies to the direction of visual and inertial motion cues. More specifically, we investigated how much heading of an inertial stimulus may deviate from a visual stimulus suggesting ‘straight ahead’ motion, before the ‘straight ahead’ percept falls apart. Subjects were presented with congruent visual-inertial linear horizontal motion stimuli with varying heading and incongruent visual-inertial linear horizontal motion stimuli, in which a visual cue suggesting straight ahead motion was coupled with an inertial heading cue with varying heading. Subjects judged I) whether or not they moved straight ahead, and II) whether or not the visual and inertial stimulus were congruent. We fitted psychometric curves to the combined judgments and calculated detection thresholds for a violation of either criterion. The results show that the 50% detection thresholds are larger in the incongruent than in the congruent condition. We interpret the threshold for the incongruent condition as the size of the coherence zone. In conclusion: we provide evidence of a coherence zone for heading, as wella as a measure of the size of the heading coherence zone