Luminance adaptation increased the contrast sensitivity of retinal ganglion cells.

In the present study, the activity changes of chicken retinal ganglion cells in response to light stimuli with defined contrast were investigated, in the presence of various levels of sustained background illumination. Following a step increase of light illumination, the firing rate of most retinal ganglion cells increased abruptly, and then decreased to a steady-state level with a much lower firing rate during the sustained application of light. However, when a test flash was applied, which superimposed the prolonged background illumination, an increased firing rate was observed. Moreover, the neuron firing rate was increased to a greater extent when the intensity of the background illumination was higher. This may suggest that the neuron sensitivity can be modified by the background illumination level, although the neuron firing rate was reduced during sustained illumination.