Early experiments by Brindley, Dobelle, and Pollen demonstrated that a field of individual phosphenes could be evoked by stimulating visual cortex with an array of electrodes implanted subdurally over its surface. Experiments by Schmidt using intracortical micro-stimulation demonstrated that phosphenes could be evoked in a human volunteer with currents that were orders of magnitude lower than those used with surface stimulation. Bradley and colleagues implanted a relatively large number of intracortical stimulating electrodes into the visual cortex of macaque monkeys and confirmed the findings of Schmidt, but with greater spatial resolution. These studies, however, have failed to answer the key question upon which a cortical approach to artificial vision must be based: Does patterned electrical stimulation via an electrode array evoke discriminable patterned percepts or simply nondiscriminable blobs of light? The first step in answering this question is to characterize the distribution of luminance threshold parameters across the visual field. To accomplish this, we have trained two nonhuman primates in a forced choice detection task, with a success rate of 80% and higher, to indicate whether or not they perceived photic stimuli presented at varying luminance levels. Using a modified version of the QUEST algorithm we have calculated luminesance thresholds at the fovea of our animals to be between 3-5% of the maximum screen intensity. These values are comparable to human obtained threshold values. These data will be used to map photic stimulation thresholds onto electrical stimulation thresholds evoked with Utah Electrode Arrays implanted in primary visual cortex. By utilizing this mapping and similar tasks in the nonhuman primate, we will determine if spatio-temporal patterns of micro-stimulation are able to evoke discriminable percepts.