Simple reaction time as a measure of the temporal response properties of transient and sustained channels

Temporal facilitation and stroboscopic motion

Luminance of extended-duration adapting field was varied from zero to a level sufficient to reduce brightness of a 5 ms test stimulus to a level just above increment threshold. Increasing the luminance of surrounds or solid adapting fields resulted in increased reaction time. With the perceived-order method, reduction of latency with increasing surround luminance (temporal facilitation) was obtained with a visual comparison stimulus but not with an auditory comparison. It was concluded that perceived motion is a necessary condition for temporal facilitation. This study and earlier studies using moving test stimuli may be explained by a shift from sustained to transient units with increasing adapting luminance.

Possible role of transient and sustained visual mechanisms in the determination of similarity judgments

Two studies examined the role played by transient and sustained visual mechanisms in the determination of similarity judgments produced in response to pairs of geometrical stimuli. In two experiments, subjects were trained to attend to two dimensions of a set of stimuli and to assign similarity ratings with respect to those two dimensions only. An INDSCAL multidimensional scaling analysis of the subsequent similarity ratings showed that subjects emphasized global blob, or low spatial frequency-dependent, dimensions of the stimuli when they were presented for brief durations (20 msec.), irrespective of the dimensions to which the subjects and had been trained to attend. This finding suggested that low spatial frequency selective transient mechanisms dominated the perceptual processes which underlie the similarity judgments. When the stimulus duration was raised to 50 msec. so that sustained mechanisms could also make a signficicant contribution to the perceptual processes underlying the similarity judgments, subjects emphasized only those dimensions on which they had been trained. The implications of the present findings for the concepts of selective attention and automatic activation were discussed.

The unspecified role of cones and rods in grating detection: a theoretical note

Detection and resolution thresholds for two 50 ms square-wave gratings (1.5 and 6.7 cps) were determined as a function of background luminance. Results indicated differential cone and rod involvement in resolution of the two targets at low background levels. Implications for other studies employing similar stimuli in terms of retinal inhomogeneity were suggested.

The spatial selectivity of early and late waves within the human visual evoked response

Two studies on the amplitude, latency, and waveform of human visual evoked responses to the onset of sine-wave grating patterns were made. Results indicated that the peak latencies of both early and late waves were a function of the spatial frequency of the stimulus. The amplitude of the early wave (N1-P1) was consistently greatest at low spatial frequenciies while the late wave (N2-P2) showed consistent attenuation at low spatial frequencies. In addition the location of the peak amplitude response of the late, but not the early, wave depended on the location (macular versus extramacular) and area(small versus large stimulus field) of retina stimulated. These findings are discussed in the light of evidence for separate transient and sustained systems within the human visual system.

A multistable movement display: evidence for two separate motion systems in human vision

Two competing sensations of apparent movement were produced by the rapid alternation of two multielement stimulus frames. Either sensation could be made dominant by, appropriate manipulations of the stimulus display. The results suggest that there are two systems capable of generating movement signals in man. One system depends on preliminary processing of form, and the second system does not.