White's illusion

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Figure 1. Rectangles A, on the left, look much darker than the rectangles B, on the right. However, rectangles A and B reflect the same amount of light.

White's illusion is a brightness illusion where certain stripes of a black and white grating is partially replaced by a gray rectangle (Fig. 1). Both of the gray bars of A and B are the same color and opacity. The brightness of the gray pieces appear to shift toward the brightness of the top and bottom bordering stripes. This is interesting because lateral inhibition cannot explain this occurrence. This occurs even when the gray patches in the black stripes are bordered by more white than black (and conversely for the gray patches in the white stripes).[1]

Lateral inhibition[edit]

Main article: Lateral inhibition

The amount of each bipolar cell response depends on the amount of the stimulation it receives from the receptor and the amount that this response is decreased by the lateral inhibition it receives from its neighboring cells.[2]

Lateral inhibition can't explain White's illusion. In Figure 2.1 lateral inhibition sent by black cells A and C should make cell O lighter; in Figure 2.2 lateral inhibition sent by white cells A and C should make cell O darker. It is suggested that brightness induction follows the brightness contrast in the direction of the bar not the surrounding area.

Lateral inhibition explained[edit]

Figure 2.

In Figure 2.1 we assume that light dropping on cells B and D generates a response of 100 units. Since the points A and C are darker we assume that only 20 units are generated from these points. Another assumption is that the lateral inhibition sent by each cell is 10% of its response; cells B and D send an inhibition of 10 units each and cells A and C send an inhibition of 2 units each. The inhibition sent by cells A and C is larger since their size is bigger than the size of cells B and D (let's say 2 times). This concludes that cell O receives an inhibition I = 10 + 10 + 2 × 2 + 2 × 2 = 28.

In Figure 2.2 with the same assumptions as above stated, cell O receives an inhibition of I = 10 × 2 + 10 × 2 + 2 + 2 = 44.

Because point O in Figure 2.1 receives an inhibition smaller than the point O in Figure 2.2 the gray cell should be lighter.

Experiments on lateral inhibition[edit]

White and White (1985) concluded that at a higher spatial frequency the grating of White's illusion could be described by brightness assimilation. They also concluded that at lower spatial frequencies White's illusion is still present.[3]

Blakeslee and McCourt (2004) suggested that patterns whose scales are larger compared to the encoding filters (low spatial frequency are represented with a loss of low frequency information exhibiting brightness contrast); patterns whose scales are smaller compared to encoding filters (high spatial frequency), are represented with a loss of high frequency information exhibiting brightness assimilation.[4]

Belongingness[edit]

Our perception of an area's lightness is influenced by the part of the surroundings to which the area appears to belong.

In the disc example (Fig. 3), the four discs on the left are identical to the four discs on the right in terms of how much light is reflected from the discs, that is to say, they are physically identical. The theory to explain the different psychological experiences is called belongingness.

The discs on the left appear dark and the ones on the right appear light, this is because of the two displays. In the display on the left, the dark area on the left seemingly belongs to the discs, and the discs are obscured by the light mist. On the right side, the same dark areas are interpreted as belonging to the dark mist. In the meanwhile, the white parts are seen as the color of the discs. Therefore, our perception of the lightness of the discs is significantly influenced by the display, which is the mist in this case (Anderson & Winawer, 2005).

We can use the belongingness theory to explain White's illusion. According to belongingness theory, the lightness of rectangle A is influenced by the white display, which should be the white bars that surround it. Similarly, the rectangle B on the right side is surrounded by the dark bars, and the lightness of rectangle B is affected by the dark background. As a result, area A which rests on the white background appears darker than area B which rests on the dark background.(Alan Gilchrist et al. 1999)

However, the limitation of belongingness theory is that, firstly, it only explains why rectangle A looks darker than rectangle B, but what we want to know is why the gray areas on rectangle A look darker than in rectangle B; secondly, when talking about the background, Belongingness theory appears quite the same as simultaneous contrast theory, they just use different names.

Other experiments/articles involving White's illusion[edit]

  • Anderson 2003[1]
  • Cornsweet and Teller 1965
  • White 1979, 1981
  • Shapley and Enroth-Cugell 1984
  • Foley and McCourt 1985
  • Grossberg and Todorovic 1988
  • Moulden and Kingdom 1989
  • Paradiso and Nakayama 1991
  • Kingdom and Moulden 1991
  • Taya et al 1995
  • Anderson 1997
  • Todorovic 1997
  • Zaidi et al 1997
  • Blakeslee and McCourt 1999
  • Gilchrist et al 1999
  • Kelly and Grossberg 2000
  • Ripamonti and Gerbino 2001

References[edit]

  1. ^ a b Anderson, L Barton. Perceptual organization and White's Illusion. Scholarly Journal. 2003. 269-271. URL http://www.psych.usyd.edu.au/staff/barta/TexturedWhites.pdf.
  2. ^ Sensation and perception, E. Bruce Goldstein, Edition 8, illustrated,Publisher Cengage Learning, 2009
  3. ^ Bhaumik, Kamales, and Kuntal Ghosh. "Complexity in human perception of brightness: a historical review on the evolution of the philosophy of visual perception." OnLine Journal of Biological Sciences 10.1 (2010): 17+. Academic OneFile. Web. 2 Apr. 2012. Document URL http://go.galegroup.com.ezproxy.ltu.edu:8080/ps/i.do?id=GALE%7CA237135562&v=2.1&u=lom_lawrencetu&it=r&p=AONE&sw=w
  4. ^ Bhaumik, Kamales, and Kuntal Ghosh. "Complexity in human perception of brightness: a historical review on the evolution of the philosophy of visual perception." OnLine Journal of Biological Sciences 10.1 (2010): 17+. Academic OneFile. Web. 2 Apr. 2012. Document URL http://go.galegroup.com.ezproxy.ltu.edu:8080/ps/i.do?id=GALE%7CA237135562&v=2.1&u=lom_lawrencetu&it=r&p=AONE&sw=w