Temporal facilitation and stroboscopic motion

Reaction time measures of backward masking

We employed both simple and choice reaction time (RT) paradigms in which the subjects were required to respond to 3.0 cycles per degree (c/d) square-wave gratings presented to one eye, while checkerboard masks were presented at various stimulus-onset asynchronies to the other eye. No masking was evident using the simple RT paradigm, but with the choice RT task, checkerboard masks presented to the contralateral eye of three subjects resulted in substantial decreases in response speed when the test preceded the mask by stimulus-onset asynchronies of 25 to 75 ms. Masks that contained lower fundamental spatial frequencies (1.0 c/d) than the target were more effective than masks containing fundamental spatial frequencies (6.0 c/d) higher than the target, while masks that contained fundamental components identical to those in the target (3.0 c/d) produced maximum masking. The results offer support for the sustained-transient theory of visual processing and validate RT as a technique for examining spatio-temporal factors in masking.

Effects of photopic annulus luminance level on reaction time and on the latency of evoked cortical potential responses to target flashes

Correlated experiments on visual reaction time (RT) and visual evoked cortical potentials (VECP's) were performed to assess the effects of illumination level of steady annulus surrounds on the latency of response to centrally presented target flashes (1 and 3 degrees in diameter) over a wide range of retinal illuminances. The latencies of the electrophysiological (VECP) responses are more variable than those of the psychophysical RT responses. For both classes of response, the visual latency for a given target flash luminance is systematically increased (inhibited) by a spatially contiguous annulus with a retinal illuminance that equals or exceeds that of the target. The inhibitory effect of a given annulus increases progressively as the target retinal illuminance is lowered below that of the annulus. The corresponding RT and VECP curves have the same shape, thus suggesting that the motor component of the RT responses is not differentially influenced by variations in target illumination. The inhibitory effects are characteristically greater for the 3 degrees target than for the 1 degree target. Lateral neural inhibition and stray-light models for these data are considered.

Distortions of vision and pain: two functional facets of D-lysergic acid diethylamide

D-lysergic acid diethylamide (LSD) produces distortions of visual perception and analgesia. Evidence is advanced from a functional standpoint that the observed visual effects result from an attenuation of light-evoked input to the dorsal lateral geniculate nucleus (LGN) from the purely centripetal pathways of the retina. More slowly responding visual afferents or those with more complex receptive fields seem to be affected most. LSD analgesia, accompanied by severe psychotic symptoms, appears to result from drug actions on a centrifugally controlled pain system involving neurons of the midbrain raphe.