David G. Stork

Temporal impulse responses from flicker sensitivities

We derive visual temporal impulse response functions from the large-field sinusoidal flicker sensitivity measurements made at several luminances by Kelly [J. Opt. Soc. Am. 51, 422 (1961)]. To this end we recognize response function causality and use Kramers-Krönig relations to reconstruct the (unmeasured) temporal phase spectrum and hence also the impulse response functions. At high luminances our derived functions are triphasic, while at low luminances they are biphasic. These functions are model independent, rely on no free parameters, and are consistent with certain theoretical model-dependent functions as well as psychophysical measurements by others.

Receptive-field symmetry probed using converging gratings.

Contrast-sensitivity functions (CSFs) for converging and diverging gratings were obtained under voluntary fixation at several field widths and under retinal stabilization at one field width. In general, these types of gratings had similar CSFs at all temporal frequencies tested, a result that can be explained by plausible spatiotemporal receptive-field models possessing spatial antisymmetry but not by models possessing pure (even) spatial symmetry. Phase condition at the central line in converging and diverging gratings affected grating detectability at high spatial frequencies, as expected.