Dissociating early and late visual processing via the Ebbinghaus illusion

Abstract

Visual perception is not instantaneous; the perceptual representation of our environment builds up over time. This can strongly affect our responses to visual stimuli. Here, we study the temporal dynamics of visual processing by analyzing the time course of priming effects induced by the well-known Ebbinghaus illusion. In slower responses, Ebbinghaus primes produce effects in accordance with their perceptual appearance. However, in fast responses, these effects are reversed. We argue that this dissociation originates from the difference between early feedforward-mediated gist of the scene processing and later feedback-mediated more elaborate processing. Indeed, our findings are well explained by the differences between low-frequency representations mediated by the fast magnocellular pathway and high-frequency representations mediated by the slower parvocellular pathway. Our results demonstrate the potentially dramatic effect of response speed on the perception of visual illusions specifically and on our actions in response to objects in our visual environment generally.

Most Findings Obtained With Untimed Visual Illusions Are Confounded

“…1, middle). The Ebbinghaus illusion emerges after the other parts of the scene have been taken into account (Schmidt et al, 2016), but lightness contrast kicks in before it. Basic lightness contrast (e.g., a target on a plain background) peaks at the shortest possible duration, a flash of 10 ms, when only the luminance difference along the target’s edge has been processed.…”

“…These emerge very quickly—typically within a few tens of milliseconds—and some of them continue to develop over the next several hundred milliseconds, suggesting an increasingly sophisticated integration between the element that is being judged and its context (de Brouwer et al, 2014; Schmidt & Haberkamp, 2016; van Zoest & Hunt, 2011). Indeed, some size effects—such as the Ebbinghaus (Schmidt et al, 2016) and Delboeuf (Oyama & Morikawa, 1985) illusions—actually reverse when seen too briefly for contextual integration to take place.…”

Anodal Occipital Transcranial Direct Current Stimulation Enhances Perceived Visual Size Illusions

“…Converging evidence suggests that the processing of visual size illusions relies on both early feedforward processing in V1 (Chen, Qiao, Wang, & Jiang, 2018;Nakashima & Sugita, 2018;Sherman & Chouinard, 2016;Jaeger & Klahs, 2015;Jaeger, Klahs, & Newton, 2014) and late feedback projections from higher visual cortex to V1 (King, Hodgekins, Chouinard, Chouinard, & Sperandio, 2017;Schmidt, Weber, & Haberkamp, 2016;Schwarzkopf, 2015;Sperandio & Chouinard, 2015;Weidner et al, 2014;Schwarzkopf et al, 2011). Whether occipital tDCS affects the early or late processing stage remains to be determined.…”