The purpose of this investigation is to find the neurophysiological basis of the distorted visual perception and of the visual illusions experienced by subjects under the influence of hallucinogenic drugs. The influence of hallucinogenic drugs upon the response properties of neurons in visual cortex and in lateral geniculate nucleus of cats will be studied. Both systemic and iontophoretic methods of drug administration will be used. Effects of hallucinogens on the receptive field characteristics and other physiological functions of single cells will be determined. Effects of responses to optical stimuli will be related to effects on responsiveness to pharmacological stimulation.