The peripheral drift illusion

The peripheral drift illusion

Illusions always seem to capture our attention, and they strike us as strange and interesting. However, we often do not think of these odd sensations as mere curiosities. In spite of this, a growing literature on illusions points to the fact that these sensations are not only interesting in themselves; they are potent sources for insight into normal vision.

There are numerous known and classic illusions, such as the Muller-Lyer illusion, the duck-bunny illusion, the Herman Grid illusion, and the Hering illusion. The illusions as such point to a general interpretation: the illusions are produced when the visual system uses a default mode in processing perception the ambiguous figures. Furthermore, the interpretations of the images are outside our immediate control, although some illusions can be controlled, at least partially.

Muller-Lyer Illusion

Duck-Bunny Illusion

Herman Grid Illusion

Hering Illusion

While a lot of illusions have been uncovered, not all have a strong effect on our perceptual system. In this regard, of the peripheral drift illusion is also considerably stronger than any similar attempts designing images that have stronger effects are desirable. One example of this can be found at the illusions page of Akiyoshi Kitaoka from the Department of Psychology, Ritsumeikan University, Kyoto, Japan. This site hosts a wide variety of illusions. One illusion that is particularly interesting, is the so-called ‘Peripheral Drift illusion, which can be displayed by clicking on the image below.

The thing that makes this illusion so interesting is the fact that you are experiencing movement in the periphery, although you soon come to realize that the moving objects are not moving at all. While the peripheral vision demonstrates movement over the entire field of the display, the focusing on one particular part of the display shows that it is stationary. Furthermore, this version of the peripheral drift illusion is also considerably stronger than any similar attempts, which makes it very suitable for experimental studies.However, Akiyoshi Kitaoka and Hiroshi Ashida, the designers of the illusion, have not yet performed any empirical studies of it. In an abstract from the 2003 summer meeting of the Vision Society of Japan, the researchers point out some vital characteristics of the illusion:

1. Illusory motion appears in the direction from a black region to the adjacent dark-gray region or in the direction from a white region to the adjacent light-gray region.
   They indicate directions of illusory motion, black to dark-gray or white to light-gray.
2. It occurs well in peripheral vision.
   The object we fixate at appears to be stationary.
   
3. It occurs well with stimuli of edges.
   Stimuli of smooth luminance profiles give weak illusions.
4. It occurs well with fragmented or curved edges.
   Stimuli made up of long edges give weak illusions.
5. It may be generated by involuntary eye movements.
   Retinal slips do not generate this illusion. Saccade may be necessary.

Thus, these gross phenomenal properties of the illusion invite considerably more research. these gross phenomenal properties of the illusion invite considerably more researchPrevious research with comparable but not identical stimuli has demonstrated that illusions of moving displays are correlated by an activation in the V5/MT area of the cortex, while previous areas, such as the striatum/V1 is not, as demonstrated by transcranial magnetic stimulation studies (Theoret et al, 2002) or by functional imaging techniques (Hauntzel et al. 2001; Tootell et al, 1995; Zeki et al. 1993).

However, these illusions are not nearly as powerful and vivid as the peripheral drift illusion made by Kitaoka and Ashida. It is therefore noteworthy that the development of these new and powerful illusions may contribute to the study of illusions by providing images that are likely to produce a stronger activation in areas that are responsible for the perception of movement.

© 2004 T.Z. Ramsøy

Author Info

Thomas Z. Ramsøy
Danish Research Centre for Magnetic Resonance
MR Department, Section 340
Copenhagen University Hospital, Hvidovre
Kettegaard Allé 30
DK-2650 Hvidovre
Denmark

Links

• The Peripheral Drift Illusion, or The Rotating Snake Illusion
• Akiyoshi Kitaoka’s illusions page

References

1. Theoret H, Kobayashi M, Ganis G, Di Capua P, Pascual-Leone A. Repetitive transcranial magnetic stimulation of human area MT/V5 disrupts perception and storage of the motion aftereffect. Neuropsychologia. 2002;40(13):2280-7.
2. Hautzel H, Taylor JG, Krause BJ, Schmitz N, Tellmann L, Ziemons K, Shah NJ, Herzog H, Muller-Gartner HW.The motion aftereffect: more than area V5/MT? Evidence from 15O-butanol PET studies. Brain Res. 2001 Feb 23;892(2):281-92.
3. Tootell RB, Reppas JB, Dale AM, Look RB, Sereno MI, Malach R, Brady TJ, Rosen BR. Visual motion aftereffect in human cortical area MT revealed by functional magnetic resonance imaging. Nature. 1995 May 11;375(6527):139-41. ]
4. Zeki S, Watson JD, Frackowiak RS. Going beyond the information given: the relation of illusory visual motion to brain activity. Proc R Soc Lond B Biol Sci. 1993 Jun 22;252(1335):215-22. ]