<p>The cockroach visual system comprises compound eyes with photoreceptors of two spectral classes and ocelli – simple eyes consisting of green-sensitive photoreceptors. Using the method of non-invasive electroretinogram (ERG)recording from both compound eyes, it was shown that shielding of both ocelli leads to a significant alteration of ERG parameters, namely, an increase in the amplitude of responses to short-wavelength stimuli of saturating intensity and a slowing down of responses to both short-wavelength and long-wavelength light. Ocelli estimating the total light level modulate the functioning of photoreceptors of compound eyes at night, under low-light conditions, by increasing the summation time of light entering the eye to generate a response.</p>