Abstract
Previous studies of the dynamics of light adaptation have used a probe-sinewave paradigm, where the threshold for detecting a probe flash is measured at various phases with respect to a sinusoidally modulated background. Our interest is in the temporal changes in visual adaptation that occur during exposure to a train of brief, high intensity flashes. To investigate this we have used a flash-probe paradigm, where the sinusoidally modulated background is replaced with a flashing background. By varying the parameters (frequency, onset time, intensity, duration) of both the flash and the probe stimulus the adaptive state of the visual system has been explored. This technique has the potential for extremely elegant determination of the adaptive state of the visual system, including the investigation of temporal adaptation mechanisms to flashed stimuli.
In contrast to most other studies, the intensity of the flashing background we used was very high - up to seven log-trolands. For our initial investigations, although we have used temporal frequencies up to the threshold for fusion (around 50 Hz), most of our measurements have been at 3 Hz and 10 Hz. We have demonstrated forward and backward masking, and have observed very rapid adaptation within 50 ms of the flickering background. At these intensities and frequencies there is a shift in adaptation and the probe threshold is elevated at all phases relative to that on a steady background (of the same mean luminance). The detailed shape of the probe-threshold-versus-phase curve is being investigated, and will be used as test data for computational models of light adaptation dynamics.
This work was sponsored by the Air Force Office of Scientific Research and the Air Force Research Laboratory under contract number number F41624-02-D-7003.