Ebbinghaus Illusion

For 25 years, the web has been used for psychological research ( Krantz et al., 1997 ; Reips, 1997 ). While many areas of psychology have benefitted from the increased access to participants and other benefits of web-based research, one area of psychology has rarely taken advantage of the online format, that is, sensation and perception. Largely, sensation and perception research has not used the web because of the need for carefully calibrated equipment to successfully run their experiments. However, there may be classes of phenomena in our sensory processes that might be studied online where the equipment and stimuli vary. Suppose the critical feature of the stimulus is an abstraction of the physical stimulus that does not vary with different displays. In that case, these features can be successfully studied online, meaning that results from online studies will match those from controlled laboratories. This study will examine the Ebbinghaus illusion to illustrate the successful use of the web for perceptual research. The implications and some discussion of types of perceptual studies conducted on the web will be discussed.

Most Findings Obtained With Untimed Visual Illusions Are Confounded

Visual illusions have been studied extensively, but their time course has not. Here we show, in a sample of more than 550 people, that unrestricted presentation times—as opposed to presentations lasting only a single second—weaken the Ebbinghaus illusion, strengthen lightness contrast with double increments, and do not alter lightness contrast with double decrements. When presentation time is unrestricted, these illusions are affected in the same way (decrease, increase, no change) by how long observers look at them. Our results imply that differences in illusion magnitude between individuals or groups are confounded with differences in inspection time, no matter whether stimuli are evaluated in matching, adjustment, or untimed comparison tasks. We offer an explanation for why these three illusions progress differently, and we spell out how our findings challenge theories of lightness, theories of global-local processing, and the interpretation of all research that has investigated visual illusions, or used them as tools, without considering inspection time.