Limitations of the Oriented Difference of Gaussian Filter in Special Cases of Brightness Perception Illusions

Abstract

The Oriented Difference of Gaussian (ODOG) filter of Blakeslee and McCourt has been successfully employed to explain several brightness perception illusions which include illusions of both brightness-contrast type, for example, Simultaneous Brightness Contrast and Grating Induction and the brightness-assimilation type, for example, the White effect and the shifted White effect. Here, we demonstrate some limitations of the ODOG filter in predicting perceived brightness by comparing the ODOG responses to various stimuli (generated by varying two parameters, namely, test patch length and spatial frequency) with experimental observations of the same.

A multi-scale Gaussian filtering model to explain the White’s illusion from the viewpoint of lightness assimilation for widely varying grating width and patch length

“…The perceived enhancement of lightness remains constant within the limit of the experimental error. The result is also similar to that obtained by Bakshi et. al.…”

“…Another very important evidence, that sets up a possible link of lightness assimilation with White's effect type of stimulus, comes from an old work of Arend et al (1971) who pointed out that for complex visual stimuli, contrast borders which are too far off to modulate local retinal mechanisms, may, affect the brightness sensation through long distance integrations. Although the Oriented Difference of Gaussians (ODOG) filter of McCourt (1999, 2004) have made a similar attempt achieving success to quite an extent, Bakshi & Ghosh (2012) and Bakshi et al (2015) have already shown the limitations of this model of lightness perception in explaining illusory effects at high frequency edges and beyond certain scales. Moreover, there is no known neural correlate of the contrast normalization step in Blakeslee and McCourt's algorithm.…”

Experimental Observations of the Visibility Threshold of Illusory effects in Hermann Grid, Sinusoidal and Square Gratings and their Possible Implications

“…But unlike the Grating Induction illusion with horizontal gray-strips, the vertical gray-strips in this case appear to have uniform brightness i.e. the illusory effect is not confined only to the boundaries but visible throughout the gray-strips, and this happens irrespective of the width or height of the strips [15]. In other words the illusory effect has infinite length scale as opposed to the finite length scale for the Square Grating Induction illusion above.…”

“…However, they too suffer from limitations. The White effect with a pretty long test patch demonstrates the failure of the ODOG type of models [15]. The White effect is a very interesting illusion, and it will not be a digression to discuss a little more about it context.…”

“…sigma values of Gaussians and the filter sizes) of their own and would not respond for stimuli much smaller or much larger than that typical length scale. This is actually the reason why the ODOG type of models, despite being highly successful in explaining many brightness perception phenomena, have completely failed to explain certain such situations involving larger length scales [15]. The design of perceptual models of visual illusions should therefore take such scaling behavior into consideration.…”