Chubb illusion
[2] This apparent variance in perception is influenced when it is viewed by different observers and when the background and central target patch are placed on "non-overlapping spatial frequency bands", as explained by Chubb et al.
[2] However, the lateral inhibition account is not consistent with phenomena such as the Benary cross and White's illusion as well as transparency and assimilation effects.
Lotto and Purves (2001) demonstrated that the Chubb illusion can be explained "by the degree to which imperfect transmittance is likely to have affected the light that reaches the eye.
[6] Chubb effect estimates that when an object is viewed through an imperfectly transmitting medium, it increases or decreases the apparent brightness or dullness of the target patch, even when luminance ratios and spatial frequencies remain the same.
Therefore, they chose to examine the Chubb illusion in 'wholly empirical' terms, as mainly a consequence of past experience, or in this case, the influence of transmittance on ambiguous stimuli.
[1] Imperfect transmittance causes observers to experience a reduced difference in spectral contrast or luminance from object surfaces.
For instance, transmittance varies when viewing objects from a distance, in smog or fog, or through fabric, glass or water.
This hypothesis was tested by altering the probable contributions of imperfect transmittance by manipulating motion, luminance and colour information.
In some cases, the relative luminance of two target surfaces can be reduced, as Lotto and Purves demonstrate, from a ratio of 8:3 to approximately 7:5.
"[1] Appropriate behavioural response depends on the evaluation of the relative contributions of illumination, reflectance and transmittance to the visual stimuli.
[1] The empirical findings also contradict the hypothesis that 'illusions of brightness' caused by contour junctions in the stimulus explain the Chubb illusion, as proposed by Anderson (1997).
[11] According to Eunice et al., "contextual illusions arise from vision's adaptive propensity to emphasize relative differences among features rather than their absolute characteristics.
[12] The schizophrenic group's immunity to contrast illusion was exceptional, with 12 out of 15 accurate judgements while healthy participants showed severe misperceptions of the centre stimuli.
Indeed, there has been a rapid growth in the use of contextual visual tasks (Chubb illusions) in clinical testing and NIH-supported studies of schizophrenia.
L. R. Betts et al. (2005) demonstrated that older people were able to distinguish the motion of high-contrast stimuli quicker than younger adults, and that inhibition was responsible for differences in spatial suppression.
The stimuli used for the experiments were based on the parameters used by Dakin, Carlin and Hemsley (2005), who used the Chubb illusion to check for reduced inhibition in people with schizophrenia.
