![\"illusion\"](\"https:\/\/www.blog-thebrain.org\/wp-content\/uploads\/illusion.jpg\" "\\"illusion\\"")
Science is not immune to historic errors that can be passed along for decades. One such error was the confusion of the phi effect with the beta effect, which persisted until Robert M. Steinman and his colleagues published their clarification in 2000.<\/p>\n
The phi effect was first described in Experimental Studies on the Seeing of Motion<\/em>, a book published in 1912 by Max Wertheimer, one of the fathers of Gestalt psychology. The problem was that in his book, Wertheimer did not describe the conditions for the appearance of the phi effect precisely. He said that this phenomenon occurs when two lines are projected on a screen in very close chronological succession, thus creating the impression (under certain observation conditions that he left undefined) that a fuzzily defined area the same colour as the background is moving between these two lines.<\/p>\n In his book, Wertheimer distinguishes this this \u201cpure apparent movement\u201d from another type of apparent movement called beta. The beta illusion of movement, like the phi, is caused by the presentation of fixed images in succession, but at a slower rate<\/span><\/a>, similar to the rate at which fixed images are displayed in a movie or a video to create the impression of continuous movement<\/span><\/a>.<\/p>\n However, most textbooks and web sites that discuss apparent movement in movies, whether from the standpoint of the cinema or from that of psychology (including the present web site, until now), still attribute this apparent movement to the phi effect and not to the beta effect. In his article, Steinman points out one possible source of this confusion.<\/p>\n The source in question is another book, Sensation and Perception in the History of Experimental Psychology<\/em>, published by E.G. Boring in 1942. Boring\u2019s descriptions of Wertheimer\u2019s observations of the phi and beta effects are correct, but Boring errs when he states that the phi effect is observed when the images succeed each other at a relatively slow rate. In reality, it is observed when they do so at a relatively fast rate, close to the one at which the two images are seen simultaneously. Because Boring\u2019s book was so influential in the years that followed, Steinman believes that it was this strange error on Boring\u2019s part, as well as the lack of clarity in Wertheimer\u2019s original description, that made subsequent generations of researchers mistake the beta effect for the phi effect.<\/p>\n Students reading this blog may be interested to learn that it was when Steinman was trying to reproduce the surprising phi effect in front of his students to convince them of its existence that he realized Boring\u2019s error. And it was when I was preparing to give a lecture about vision to a group of students that I came across Steinman\u2019s article. Thus we see that in the course of their jobs, teachers can sometimes uncover the errors of the past, and not just perpetuate them!<\/p>\n![\"a_lien\"](\"https:\/\/www.blog-thebrain.org\/wp-content\/uploads\/a_lien.gif\" "\\"a_lien\\"")
Phi is not beta, and why Wertheimer\u2019s discovery launched the Gestalt revolution <\/span><\/a>
\n Magni-phi and related phenomena<\/span><\/a>
\n![\"i_lien\"](\"https:\/\/www.blog-thebrain.org\/wp-content\/uploads\/i_lien.gif\" "\\"i_lien\\"")
Phi phenomenon<\/span><\/a>
\n Beta movement<\/span><\/a>
\noffered isn\u2019t psychoactive cannabinoid found in the fact that CBD was impervious to ease manifestations identified with pharmaceutical medications<\/p>\n