Abstract
Negative afterimages have traditionally been ascribed to retinal adaptation, but recent studies suggest that adaptation mediating afterimage formation occurs at multiple levels of visual processing. Here, we use an interocular suppression technique, called continuous flash suppression (Tsuchiya 05 NatNeuro), to dissociate microgenesis of retinal adaptation (which should be immune to suppression) from non-retinal adaptation (which is susceptible to suppression). We achieve this dissociation by holding retinal adaptation constant at 5 sec while manipulating the duration of suppression. Remarkably, presentation of five, brief flashes during the last 500 msec of adaptation was sufficient to reduce the magnitude of non-retinal adaptation by half. To quantify the strength of suppression, we used a forced-choice probe detection task and found that as few as five successive, brief flashes interfered with probe detection as much as continuous flash suppression. However, a single flash only exerted suppression within a narrow window of time between onset of the probe and onset of the suppression figure; moreover, the suppression from this single flash did not sum its effect when we paired flash suppression with conventional binocular rivalry suppression. This modified flash suppression technique provides a useful method for dissecting adaptation arising within mechanisms at multiple visual processing levels.
EY13358, NIMH, NSF, the Keck Foundation, the Moore Foundation