Non-Retinotopic Perception: Predictions and Empirical Tests of a Reference-Frame Metric Field Theory

摘要

Purpose: Retinotopic representations cannot explain perception under normal viewing conditions. Recent studies have shown that processing of shape, color, motion, search, attention, and perceptual learning can take place in non-retinotopic representations. The bases of non-retinotopic representations remain largely unknown. Here, we propose and empirically test a Reference-Frame Metric Field (RFMF) theory for non-retinotopic representations. Methods: According to the RFMF theory, motion groupings in the retinotopic space generate local motion vectors with an associated reference-frame field spreading in space. Fields of different motion vectors interact. Each region in the resulting field is mapped onto a non-retinotopic representation. In order to test RFMF, we used a Ternus-Pikler display consisting of three disks and a probe dot whose perceived motion served as the dependent variable (Boi et al., 2009). The probe dot was placed inside as well as outside of the Ternus-Pikler disks and the distance of the probe dot to the disks was the independent variable. In additional experiments, two Ternus-Pikler stimuli were used to study field interactions. Results: Ternus-Pikler stimuli act as non-retinotopic reference-frames outside of their inducing disks, supporting the field prediction. Multiple Ternus-Pikler stimuli generate interacting reference frames, as one would expect from interacting fields. In contrast, static Ternus-Pikler stimuli have no effect on a field created by a dynamic Ternus-Pikler stimulus. The size of the Ternus-Pikler disks has no effect on the field strength. These results indicate that fields are generated by motion, and not by static aspects of the stimuli. We also show a novel illusion wherein the field generated by a Ternus-Pikler stimulus can cause dynamic switches in the identities of stationary stimuli creating non-retinotopic motion and invisibility effects. Conclusions: Taken together our results support the theoretical view that a field organization in the retinotopic space leads to coordinate transforms that establish non-retinotopic spacetime representations.