Phi phenomenon
The term phi phenomenon is used in a narrow sense for an apparent motion that is observed if two nearby optical stimuli are presented in alternation with a relatively high frequency.
[1] Max Wertheimer first described this form of apparent movement in his habilitation thesis, published 1912,[2] marking the birth of Gestalt psychology.
[3] In a broader sense, particularly if the plural form phi phenomena is used, it applies also to all apparent movements that can be seen if two nearby optical stimuli are presented in alternation.
The Magni-phi demonstration is robust to changes of parameters such as timing, size, intensity, number of disks, and viewing distance.
Gegeben sind sukzessiv zwei Objekte als Reize; diese werden empfunden; zuerst wird a gesehen, zuletzt b; zwischen ihnen war die ‚Bewegung von a nach b gesehen‘; ohne daß die entsprechende Bewegung resp.
die raum-zeit-kontinuierlichen Zwischenlagen zwischen a und b wirklich als Reize exponiert gewesen wären.
Der psychische Sachverhalt sei – ohne irgendeine Präjudiz – mit a φ b bezeichnet.
Sondern es war einfach Bewegung da; nicht auf ein Objekt bezüglich.
Edwin Boring's influential history of the psychology of sensation and perception, first published in 1942, contributed to this confusion.
However, Boring placed the phi phenomenon in the wrong position, namely as having a relatively long inter stimulus interval.
It is believed that reverse phi illusion is indeed brightness effects, that it occurs when brightness-reversing picture moving across our retina.
Third, the spatial summation by the receptive fields could be increased by the visual blurring of the reversed phi illusion projected on a screen with defocus lens.
Fourth, the amount of reversed phi illusion should be increasing with the decrease of displacement between positive and negative pictures.
[14] Phi phenomenon has long been confused with beta movement; however, the founder of Gestalt School of Psychology, Max Wertheimer, has distinguished the difference between them in 1912.
If an object is moving or changing position, it would be likely to stimulate both pathways and result in a percept of beta movement.
Whereas if the object changes position too rapidly, it might result in a percept of pure movement such as phi phenomenon.
[16] The Hassenstein–Reichardt detector model is considered to be the first mathematical model to propose that our visual system estimates motion by detecting a temporal cross-correlation of light intensities from two neighboring points, in short a theoretical neural circuit for how our visual system track motion.
