Interactions between form and motion perception are exciting to me, because they demonstrate that quite disparate domains of visual perception interact to produce our ongoing perception of the world. Moreover, motion and form is often thought of as being encoded by two separate processing streams, located in dorsal and ventral cortex, respectively, and form-motion-interactions indicate that this separation is far from complete. My work on form-motion interactions has demonstrated how perceptual grouping, an aspect of form processing, can influence perceived speed, an aspect of motion processing, to produce a dramatic reduction in perceived speed when multiple moving objects are grouped together as a coherent percept (Kohler et al., 2009). In a second paper we tested and rejected a number of plausible explanations for the effect (Kohler et al., 2014, but the question remains to be solved. See Demos 1-4 for demonstrations of this effect. In another set of experiments I have showed that perceived speed, subject to modulation by a different type of form-motion interaction, directly influences motion fading (Kohler et al., 2010). Finally, I have been involved in an fMRI project investigating robust form and motion percepts that arise due to spatiotemporal integration, in the absence of any true motion in the image (see Demo 5-6; McCarthy et al., 2015).
1: Original illusion by Stuart Anstis
2: Our basic slowdown effect
3: Slowdown effect control for rotational motion
4: Slowdown effect control for number of objects
5: Integration over space and time
6: Integration with positional updating