Short-term monocular deprivation induces an interocular delay

Is ocular dominance plasticity a special case of contrast adaptation?

The visual system can regulate its sensitivity depending on the prevailing contrast conditions. This is known as contrast adaptation and reflects contrast gain changes at different stages along the visual pathway. Recently, it has been shown that depriving an eye of visual stimulation for a short period of time can lead to neuroplastic changes in ocular dominance as the result of homeostatic changes in contrast gain. Here we examine, on the basis of previously published results, whether the neuroplastic ocular dominance changes are just manifestation of the mechanism responsible for contrast adaptation. The evidence suggests that these two visual processes are separate and do not have a common neural substrate.

A brief light reduction induces a significant delay in the previously dimmed eye

PURPOSE

We investigated how a short-term luminance reduction in one eye can influence temporal processing of that eye after luminance is restored by measuring the relative delay between the eyes.

METHODS

A paradigm based on the Pulfrich effect, which is a visual illusion of depth when no depth cue is present, was used to measure relative delay in visual processing between the eyes. We deprived the monocular luminance in adults with normal vision across different intensities. In the first experiment, the ratio of the light level between the eyes stayed constant, whereas the absolute value was allowed to vary. In the second experiment, both the ratio and the absolute light level stayed constant, by controlling the environmental light level. In both experiments, we measured the changes in relative delay before and after 60 min of light deprivation.

RESULTS

Our results indicated that short-term monocular deprivation of luminance slows the processing in the previously dimmed eye and that the magnitude of the delay is correlated with the degree of luminance reduction. In addition, we observed that the absolute luminance difference, rather than the absolute luminance levels seen by the dimmed eye, is important in determining the magnitude of delay in the previously dimmed eye. These findings differ from what has been reported previously for the monocular deprivation of contrast.

CONCLUSIONS

Taken together, these findings support the view that short-term deprivation of visual information could affect two distinct mechanisms (contrast gain and temporal dynamics) of neural plasticity.