Abstract
By using a Ternus-Pikler display, we show that features presented at one spatial location can be perceived at another one in violation of retinotopic relations but in accordance with perceptual grouping. The stimulus consisted of a first frame (70ms) containing three vertical lines, an ISI, and a second frame (70ms) containing three lines shifted to the right. The second and third line of the first frame overlapped spatially with the first and second line of the second frame, respectively. When the ISI was 0ms, observers perceived a single line in motion (element motion); when the ISI was 100ms, the three lines were perceived to move as a group (group motion). We inserted a vernier offset at the second element of the first frame only. Observers' task was to report the perceived direction of vernier offset for a pre-designated line in the second frame. Naïve observers had no knowledge that the lines in the second frame were not offset.
In the case of element motion, performance was high if observers attended to the first element of the second frame and close to chance for the other lines. This result is in good agreement with retinotopic relations: the vernier offset is perceived at the spatial position it was displayed. Surprisingly, when group motion was perceived, performance was high for the second element of the second frame - even though there was no vernier information at this retinotopic location neither in the first nor the second frame! This mislocalization of vernier offset is in accordance with element correspondences in group motion: the second element of the first frame corresponds to the second element of the second frame. Hence, the attribution of the vernier offset depends on perceptual grouping rather than on retinotopic relations. Our results suggest that motion and form systems interact in real-time to remap the retinotopic projection of the physical space to maintain object identities in the perceptual space.
Supported by Hanse-Wissenschaftskolleg, MH49892 (NIH).