Dark adaptation and the Hermann grid illusion

Abstract

The latency of the perception of the dark spot at the intersection of a Hermann grid was measured before and after dark adaptation. It was found that dark adaptation significantly increased the latency of perception of the spot while light adaptation had no effect. This finding was predicted from the lung and Spillman account of the Hermann grid illusion and from the Kuffler et al. finding that inhibitory receptive fields of the cat's retinal ganglion cells are reduced in size and responsiveness after dark adaptation. The significance of this finding in relation to other simultaneous contrast phenomena is discussed. Wist (1974) found that the visibility of Mach bands is significantly reduced when a stepwise luminance gradient with successive luminance steps staggered in depth is viewed binocularly. When this gradient is monocularly viewed so that all steps appear in the frontoparallel plane, strong Mach bands are visible. Thus the Mach band visibility is dependent on the adjacency in stereoscopic depth of the successive luminance steps, with greater depth adjacency resulting in greater variability. This fmding suggests that the lateral inhibition postulated by Ratliff (1965) to be responsible for the Mach band phenomenon at the retinal level can be disinhibited at the cortical level. Furthermore, it is consistent with the findings of several other recent studies on the role of depth adjacency in mediating brightness of whiteness contrast. Gogel and Mershon (1969) found that the magnitude of the simultaneous whiteness contrast between a disk and surround annulus was directly related to the adjacency in perceived depth between these stimuli. Similarly, Mershon (1972) found that the perceived whiteness contrast between two luminous squares was a function of both their lateral and depth separation. Also, Wist and Susen (1973) found that the perceived brightness difference between the two halves of the annulus in the Koffka ring illusion was a function of the perceived stereoscopic depth interval between the line bisecting the annulus and the annulus itself.Given that depth adjacency has been clearly shown to affect several instances of brightness or whiteness contrast, the question arose as to whether further instances of brightness contrast are similarly affected. The present study was provoked by a failure to find such an effect on the Hermann

Footsteps and Inchworms: Illusions Show That Contrast Affects Apparent Speed

“…To test this possibility, I adopted an idea from Cormack et al (1992) and informally tested whether the footsteps illusion was still present under scotopic viewing conditions. The Hermann grid disappears at scotopic levels (Patel 1966;Wist 1976;Tros¨cianko 1982), and so does the induced grating (McCourt 1990). So if the footsteps illusion were somehow caused by brightness induction, the illusion should disappear in scotopic vision.…”

Characterizing the whiteness dependence of the Hermann and Scintillating Grid visual illusions

“…On the other hand, the receptive fields of off-center neurons are more activated at the intersection than elsewhere due to more light falling on the activating surround. This relative increment in lateral inhibition is responsible for the perception of dark, illusory spots at the intersections of the Hermann Grid [6,7]. These receptive field inputs may be further propagated by later neural processes, resulting in illusion perception.…”

Hermann Grid Optical Illusion and The Rebelling Dots of Reality

“…(3) Wist experimented with dark adaptation relating to HGI. In his experiment, when subjects observed the grid after dark adaptation, reaction time to experience the illusion increased [Wist, 1976]. Our photoreceptor cells have the ability to function over wide range of light intensity.…”