Abstract
Induced motion is an illusory percept, where a static object is seen moving in the opposite direction of a moving surround. The objective of our study was to establish the strength of this illusory motion for different spatial frequencies, contrasts, durations, and viewing conditions. Our stimuli consisted of a vertical grating of 1 c/deg in a circular window, surrounded by an annulus that contained another vertical grating with different frequencies (0.5-6 c/deg). In this kind of stimuli, moving the peripheral component induces the illusory motion on the static central grating. To estimate the strength of this illusion, we conducted two different experiments, where we measured the speed of the central grating, in the opposite direction of the illusion, that cancelled the induced motion (i.e. cancellation speed). In the first experiment, the cancellation speed as a function of the spatial frequency of the inducer revealed a band-pass tuning. Additionally, reducing the stimulus duration shifted the peak cancellation speed to a higher spatial frequency and increased the overall illusion strength. The second experiment showed that, when the central component had low contrast (0.1 and 0.3), cancellation speed increased up to a periphery’s contrast level, from which it stabilized despite further increases on the surround’s contrast. For a higher contrast level on the central component (0.6), the cancellation speed increased with the contrast of the periphery. In general, viewing the stimuli dichoptically (i.e., central and surrounding components in different eyes), compared to binocular presentations, produced less motion induction in both experiments, as shown by the slower cancellation speed on most of the conditions tested. These findings, using induced motion, show a strong interaction between high and low spatial frequencies in motion perception at short durations for binocular and dichoptic presentations, even when the spatial frequency components are located at different retinal positions.