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Contrast adaptation is little known complex process which occurs through all visual pathways started in retina and ended in higher cortex levels, mostly using the primary and secondary visual cortex, also it is closely related with aftereffects on retina.
There were findings in neuronal level using fMRI technology in august, 2005, but less is known about psychophysiological experiments

We used Gabor patch as stimulus in all our experiments, because they join with background without making borders.

Basically our experiments are divided in two parts; the first one is when subject adapts to stimulus of adaptation, called adaptation time. Other – starts, when test stimulus changes adaptation stimulus till subject percept this test stimulus. So we used term “contrast distinction” to describe the difference between adaptation stimulus contrast value and relaxation stimulus contrast value.

Firstly we determine if there any differences to affect different cone types in periphery [Fig 1.]. As we know, cones are divided by maximal response to wavelength, so we choose isoluminant stimulus in red, green and blue color. The test stimulus was similar phase as adaptation stimulus.

Figure 1: This graphic shows how contrast distinction depends from relaxation time using red, green and blue stimuli.

As we mentioned before, aftereffect is related with contrast adaptation, so we create model, which shows, how aftereffect impacts contrast adaptation and perception. We used reverse phased achromatic test stimulus in central area of retina. When test stimuli are reverse phased, aftereffect and stimuli summon, thus they amplify each other, and vice versa.

Te nāks bilde par modeli. Rītā.

Using the data we have we suggest that aftereffect depends only from adaptation stimuli, not test stimuli. As we can see from the graph, the time of disappearance of afterimage decreases when test contrast increases and it suggests that there is some contrast level, when subject will see test contrast without contrast adaptation.

Figure 3: Time when afterimage disappears and test stimuli appears. Used in four different contrast test stimuli levels.

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