Cortical dynamics of visual persistence and temporal integration

In a temporal integration experiment, subjects must integrate two visual stimuli, presented at separate times, to perform an identification task. Many researchers have assumed that the persistence of the leading stimulus determines the ability to integrate the leading and trailing stimuli. However, recent studies of temporal integration have challenged that hypothesis by demonstrating that several theories of persistence are incompatible with data on temporal integration. This paper shows that an account of visual persistence given by a neural network model of preattentive vision, called the boundary contour system, explains data on temporal integration. Computer simulations of the model explain why temporal integration becomes more difficult when the display elements are separated by longer interstimulus intervals or are of longer duration or of higher luminance, or are spatially closer together. The model suggests that different mechanisms underlie the inverse duration effects for leading and for trailing elements. The model further predicts interactions of spatial separation, duration, and luminance of the trailing display.     

Intensity dependence of perceived duration: data, theories, and neural integration

Evaluates 2 theoretical models suggested to explain studies of the effect of stimulus intensity on the perceived duration of brief light flashes. Some studies found a direct relationship between the 2 variables; others found an indirect relationship. Each model suggests that an additional variable interacts with stimulus intensity. Proposed variables have included the nature of the judgment and the absolute intensity. The present evaluation indicates that both of the proposed variables play a role and that a melding of the models could best account for this phenomenon. The melding incorporates known time- and intensity-dependent characteristics of neural integration into the behavioral performance. The evaluation also indicates that future experiments on this problem will be most informative if they (a) give particular attention to the role of instructions, (b) explore an adequate range of intensities, and (c) strictly control adaptive state.     

Effects of spatial-frequency specific adaptation and target duration on visual persistence

Two experiments investigated the properties of visual persistence as functions of spatial frequency, stimulus duration, and pattern-specific adaptation. In Experiment 1, increasing the duration of high spatial-frequency gratings from 50 to 500 msec decreased the duration of visual persistence produced by that grating to an asymptotic level. However, low-frequency gratings produced a constant estimate of visual persistence independent of presentation time. Also, spatial-frequency specific adaptation reduced the persistence of the high-frequency gratings to this asymptotic level, but the lower frequency persistence estimates already at this level were unaffected (Experiment 2). These findings are related to possible temporal properties of the sustained and transient visual systems.     

Perceived tachistoscopic duration and early visual processing in preschool children and adults

Two experiments further explored the Avant et al. (1975) finding that stimulus familiarity influences prerecognition processing to generate differences in the apparent duration of tachistoscopic flashes. The first experiment tested for developmental differences in the effects of upright versus 90°, 180°, and 270° rotations of a single letter or number upon the apparent duration of pre- and postmasked 30- and 50-msec flashes with adults and 4- and 5-year-old children. All age groups judged upright presentations to be of briefer duration. These differences in apparent duration were interpreted to index the automaticity of contacts between stimulus inputs and their memory representations. Failure of the children to recognize the letter and number in any orientation indicates that contact between stimulus inputs and memory representations precedes allocation of attention to the presented stimulus. The second experiment explored the influence of spatial structures which are not coded verbally by testing effects of good and poor dot pattern Gestalts on the apparent duration of tachistoscopic flashes. Adults discriminated between apparent durations of good and poor Gestalts but 4- and 5-year-olds did not. Apparent duration differences in the two experiments showed that spatial pattern structure and familiarity with verbal stimuli influence early visual processing in different ways.     

The contribution of visual persistence to the perceived duration of brief targets

Two experiments were conducted to examine the role of sensory persistence on tasks of perceived duration employing very brief visual stimuli. Using a standard temporal judgment task, the first experiment replicated both the “size effect” and “empty-filled” illusion reported by previous investigators. However, entirely comparable results were also found with a probematching task, which theoretically assesses the degree of persistence exhibited by a stimulus. The second experiment examined the effect of target luminance on perceived duration. Consistent with a sensory persistence interpretation, judgments of duration increased with increasing luminance. The results from the two experiments were discussed in terms of varying degrees of retinal persistence produced by different stimuli. This view was contrasted with currently dominant interpretations that postulate changes in perceived duration to reflect different information-processing requirements across stimulus conditions.     

Perceived brightness as a function of flash duration in the peripheral visual field

Using a method of direct magnitude estimation, perceived brightness was measured in the dark-adapted eye with brief flashes of varying duration (1–1,000 msec), size (16’–116’), and retinal loci (0°–60°) for the lower photopic luminance levels covering the range between 8.60 and 86 cd/m² in steps of .5 log units. Perceived brightness increased as a function of flash duration as well as luminance up to approximately 100 msec, then remained constant above 100 msec. The enhancement of brightness at about a 50-msec flash duration has been observed not in the fovea but in the periphery. Target size also has been found to be effective on brightness.     

Temporal integration and perception duration

Abstract.— A mathematical model is proposed for the relationship between the intensity of a stimulus as function of time and the intensity of the corresponding respcnse in the form of a conscious experience. The model is based on the assumption that the psychophysical power law is valid for the energy contained in a sliding time-window. The width and shape of this time-window will determine both the region of temporal integration and the perception duration. The consequences of this model are compared with some measurements in hearing and vision, found in the literature.     

Perceived duration of expected and unexpected stimuli

Three experiments assessed whether perceived stimulus duration depends on whether participants process an expected or an unexpected visual stimulus. Participants compared the duration of a constant standard stimulus with a variable comparison stimulus. Changes in expectancy were induced by presenting one type of comparison more frequently than another type. Experiment 1 used standard durations of 100 and 400 ms, and Experiments 2 and 3 durations of 400 and 800 ms. Stimulus frequency did not affect perceived duration in Experiment 1. In Experiments 2 and 3, however, frequent comparisons were perceived as shorter than infrequent ones, and discrimination performance was better for infrequent comparisons. Overall, this study supports the notion that infrequent stimuli increase the speed of an internal pacemaker.     

Perceived duration decreases with increasing eccentricity

Previous studies examining the influence of stimulus location on temporal perception yield inhomogeneous and contradicting results. Therefore, the aim of the present study is to soundly examine the effect of stimulus eccentricity. In a series of five experiments, subjects compared the duration of foveal disks to disks presented at different retinal eccentricities on the horizontal meridian. The results show that the perceived duration of a visual stimulus declines with increasing eccentricity. The effect was replicated with various stimulus orders (Experiments 1–3), as well as with cortically magnified stimuli (Experiments 4–5), ruling out that the effect was merely caused by different cortical representation sizes. The apparent decreasing duration of stimuli with increasing eccentricity is discussed with respect to current models of time perception, the possible influence of visual attention and respective underlying physiological characteristics of the visual system.     

Display polarity, stimulus exposure duration, and visual lobe shape

This study investigated the effects of visual display polarity and stimulus exposure duration on visual lobe shape. Analysis showed that regardless of display polarity and exposure duration combinations tested here, visual lobe contours were slightly irregular and asymmetric, of medium roundness, with a moderately rough boundary, and horizontally elongated with a mean length-width ratio of 1.53. Visual lobes mapped with negative display polarity were significantly rounder, slightly more regular and more symmetric along the vertical axis, compared with those mapped with positive polarity. Under the different polarity conditions, there were no significant differences in visual lobe area, perimeter, boundary smoothness, and elongation. When stimulus exposure duration increased from 200 to 400 msec. and from 200 to 300 msec., there were significant increases in the visual lobe area, perimeter, roundness, boundary smoothness, and regularity. No such changes were found when duration increased from 300 to 400 msec. Exposure durations did not have a significant effect on the shape categories of elongation and horizontal symmetry for the different stimuli. There were no statistically significant interactions between polarity and stimulus exposure duration for any of the lobe shape indexes used here.     

Temporal integration between visual images and visual percepts

Using a temporal integration task, subjects in 5 experiments were expected to combine information from temporally separated visual presentations. Evidence from these experiments indicated that perceptual information can be integrated with previously generated and currently maintained visual images to form a representation that contains information from each source. Properties and limitations of this integration process were also explored, including the time required to generated the image, the speed at which percepts were integrated with images, and the capacity of the representation. Implications for theories of visual processing and memory are discussed.     

Hemispheric symmetry in duration of visible persistence

Nine right-handed subjects performed a visual task requiring perceptual integration of a pattern whose parts were displayed sequentially in time. Correct performance on the task depended critically on the simultaneous visibility of all parts of the pattern; duration of visible persistence could therefore be gauged by varying the duration of the temporal interval between successive portions of the display. The pattern was displayed either foveally or parafoveally in either visual field. Analysis of overall performance and of distribution of errors at each temporal interval revealed more accurate performance for foveal displays but no hemispheric asymmetries in duration of visible persistence. These and other results reported in the literature are interpreted in terms of Moscovitch’s (1979) information-processing model of hemispheric functioning.