Active control does not eliminate motion-induced illusory displacement

Abstract

When the sine-wave grating of a Gabor patch drifts to the left or right, the perceived position of the entire object is shifted in the direction of local motion. In the current paper, we explored whether active control of the physical position of the patch can overcome such motion induced illusory displacement. We created a simple computer game and asked participants to continuously guide a Gabor patch along a randomly curving path. When the grating inside the Gabor patch was stationary, participants could perform this task without error. When the grating drifted to either left or right, we observed systematic errors consistent with previous reports of motion-induced illusory displacement. Specifically, when the grating drifted to the right, participants adjusted the global position of the patch to the left of the target line, and when it drifted to the left, errors were to the right of the line. The magnitude of the errors was consistent with previously reported perceptual judgements for centrally presented items, and scaled systematically with the speed of local drift. Importantly, we found no evidence that participants could adapt or compensate for illusory displacement given active control of the target. The current findings could have important implications for interface design, suggesting that local dynamic components of a display could affect perception and action within the more global application environment

Action can amplify motion-induced illusory displacement

“…The adjustment error seen during the active task was of the same order of magnitude as that measured in our previous study (Caniard et al, 2011 ). Indeed, the current paradigm appears to give rise to slightly larger shifts.…”

“…First, when participants passively judged the alignment of drifting targets as they passed through the gates there was a clear shift in the perceived position, consistent with previous studies using this illusion (e.g., De Valois and De Valois, 1991 ). Second, as in our previous study (Caniard et al, 2011 ), we showed that providing direct, active control over the global position of the target object did not eliminate this illusory shift. Rather, participants consistently chose a path through the gates that was shifted in the direction opposite to the local drift.…”

“…Consistent with our previous paper (Caniard et al, 2011 ), estimates of illusion strength in the active task were calculated directly from the manual adjustments that participants made to control the patch as it passed through each gate. All negative values relate to positions to the left of gate center, positive values to the right of gate center.…”

“…Recently, we demonstrated that such illusory position shifts continue to affect performance even when participants are given direct, active control of the object’s global position (Caniard et al, 2011 ). That is, action does not eliminate this form of illusion (see also, Yamagishi et al, 2001 ).…”

“…The goal of the current paper was to directly compare the magnitude of the illusion that persists under active control to that obtained in more typical scenarios where the participant is a passive observer. Although the manual tracking used in Caniard et al ( 2011 ) provided a simple and intuitive way to measure action-related shifts, the continuous nature of the path was not amenable to creating a perceptual control task. Thus, although we were able to demonstrate that the illusion persisted in an active scenario, we could only calibrate the size of the illusion with reference to previous perceptual studies.…”