On the rate of acquisition of visual information about space, time, and intensity

Abstract

The temporal course of acquisition of visual information was mapped by measuring the speed and accuracy with which Ss could discriminate the position, intensity, or duration of a stimulus that was varied independentiy on these three binary dimensions. The speed-accuracy tradeoff was different for each of the three discrimination tasks, with performance substantially superior in the position discrimination task. In the intensity and duration discrimination tasks, there were systematic changes with RT in the relative influences 'of the three stimulus variables over the two alternative responses, suggesting three phases of the corresponding perceptual processes: an initial dominance by position of the stimulus, a subsequent joint influence by both intensity and duration, and finally an exclusive control by the correct dimension. The results demonstrate that Ss can selectively attend to various dimensions of the same stimulus, with concommitantiy varying time constants. The perceptual processes being tapped by a discrimination task depend upon instructions and upon RT.One of the interesting characteristics of visual perception is the tendency to respond to stimulation integrated over relatively long periods of time. A reliable phenomenon, known as Bloch's law, is that visual detection thresholds are determined by the total energy occurring within a "critical duration" of roughly 100 msec, independent of the luminance at any point in time (see Graham, 1965). This temporal integration has also been obtained with above-threshold energy levels, in tasks requiring brightness discrimination (Graham & Kemp, 1938) and magnitude estimations of brightness (Stevens, 1966). Additionally, Eriksen (1966) has shown how the same principle can account for results in experiments on backward and forward masking.The pervasiveness of temporal summation phenomena misled many students ,of visual science to assume that the reciprocity of intensity and duration resulted from retinal processes, which supposedly produce equal neural responses for all stimulus presentations containing equal energy within a "critical duration." The clearest demonstration that this conclusion was unjustified was contributed by Zacks (1970), who asked the direct question: Can Ss discriminate between equally detectable flashes containing equal energy but differing in duration and intensity? Zacks showed that the discrimination between equal-energy stimuli of 4 and 81 msec was nearly as accurate as the detection of these flashes, rejecting the hypothesis that the peripheral visual system responds identically to such stimuli. *This research was supported in part by Public Health Service Grant MH 21105. We are grateful to Sylvan Kornblum, Alfred Kristofferson, and Ewart Thomas for their helpful comments on an earlier version of this paper.tRequests for reprints should be sent to Joseph S. Lappin, Department of Psychology. Vanderbilt University, Nashville. Tennessee 37240.Indeed, stimuli that produce identical behavior in one task need not do so in another task.Addit...

LOCAN: A general FORTRAN program for latency-operating characteristic (LOC) analysis

“…CAFs are computed by partitioning a latency distribution into equal-latency bands (not necessarily composed of equal numbers of trials) and computing accuracy within each time band. The second form of free-criterion analyses is the latency-operating characteristic (LOC), as employed in the work of Disch (1972a, 1973) and Lappin and Harm (1973;,1 LOCs are computed by partitioning a latency distribution into bands of equal numbers of trials and computing accuracy and latency measures for each band.…”