Illusory rotation in the haptic perception of a moving bar

Haptic matching of the orientation of bars separated by a horizontal distance leads to large systematic deviations. This finding leads to the following intriguing question which we investigated in this study: How will a bar moving from left to right in a fixed orientation be perceived by blindfolded observers? Interestingly, this previous finding predicts that the translating bar will cause the illusory perception of a rotation. In our experiment, we used psychophysical methods to determine the rotation needed to perceive the bar as non-rotating, for both rightward and leftward translations. From our results, it can be estimated that, on average, a bar translating in parallel over 60 cm is perceived as rotating 18°, so we established that the predicted illusory rotation indeed exists. This implies that static and dynamic signals are processed in a similar way.