Duration Of Persistence Research Articles

Q fever in Plymouth, 1972–88: A review with particular reference to neurological manifestations

Between 1972 and 1988 we have serologically confirmed 103 Coxiella burnetii infections: 46 were acute, 5 were chronic, 52 represented past infections. Details of 61 cases are presented. Of acute cases 80% had respiratory involvement; at least 63% had pneumonias. The incidence (22%) of neurological complications was of particular interest; 40% of these patients had prolonged sequelae. One acutely ill patient died of fulminating hepatitis. Patients with pre-existing pathology or immunosuppression were especially susceptible to C. burnetii. In the absence of acute sera, the complement fixation test alone provided inadequate differentiation between recent and past Q fever: phase II titres persisted at greater than or equal to 80 for more than 1 year after the acute infection in 15 cases; maximum duration of persistence was 14 years. Three patients acquired high phase I titres. Only 5% of cases had chronic Q fever, but in view of the diverse sequelae observed in this series, we suggest that long-term serological and clinical follow-up of all cases of Q fever is fully justified.

On the relation between metacontrast masking and suppression of visible persistence.

Does the introduction of additional contours in a display sequence (an operation known to reduce the strength of suppression in metacontrast) also reduce suppression of visible persistence? In three experiments, duration of visible persistence was estimated by a method in which successful performance depends on the temporal integration of a pattern whose elements are displayed in two successive frames. In this procedure, the arrival of the trailing frame is known to exert a suppressive influence on the visible persistence of the leading frame. Embedding the elements of the leading frame within additional contours (a line grid) reduced the degree of suppression exerted by the trailing frame. This did not occur when the grid was part of the trailing display. We conclude that suppression of visible persistence and metacontrast masking belong to the same class of events.

The visible persistence of stimuli in stroboscopic motion

This paper reports an improved paradigm to measure visible persistence. The stimulus is a pair of lines stroboscopically displayed in successive positions moving in opposite directions. The subjects' judgement of simultaneous appearance of all the presented lines is used to estimate visible persistence. This paradigm permitted independent manipulation of spatial and temporal stimulus separations in linear motion. The resulting estimates of visible persistence increase with spatial separation up to 0.24 deg of visual angle and approaches a maximum value at larger spatial separations. The results are consistent with the existence of a hypothetical visual gain mechanism that operates over small retinal distances to effectively decrease persistence duration with decreasing spatial separation.

Spatial frequencies and the cerebral hemispheres: contrast sensitivity, visible persistence, and letter classification.

The hypothesis that the two cerebral hemispheres are specialized for processing different visual spatial frequencies was investigated in three experiments. No differences between the left and right visual fields were found for: (1) contrast-sensitivity functions measured binocularly with vertical gratings ranging from 0.5 to 12 cycles per degree (cpd); (2) visible persistence durations for 1- and 10-cpd gratings measured with a stimulus alternation method; and (3) accuracy (d') and reaction times to correctly identify digitally filtered letters as targets (L or H) or nontargets (T or F). One significant difference, however, was found: In Experiment 3, a higher decision criterion (beta) was used when filtered letters were identified in the right visual field than when they were identified in the left. The letters were filtered with annular, 1-octave band-pass filters with center spatial frequencies of 1, 2, 4, 8, and 16 cpd. Combining four center frequencies with three letter sizes (0.5 degrees, 1 degree, and 2 degrees high) made some stimuli equivalent in distal spatial frequency (cycles per object) and some equivalent in proximal spatial frequency (cycles per degree). The effective stimulus in the third experiment seemed to be proximal spatial frequency (cycles per degree) not distal (cycles per object). We conclude that each cerebral hemisphere processes visual spatial frequency information with equal accuracy but that different decision rules are used.

How Reliably Are Visual Differences Found in Dyslexics?

Duration of visible persistence was measured in 35 control and 35 dyslexic, subjects on 3 occasions to determine the reliability of previously reported , differences between the groups on this measure. Analyses of the data revealed significant differences between the two groups in the coefficient of regression of spatial frequency on visible persistence and the regression coefficient of individuals showed high consistency across occasions. These findings suggest that visual differences between dyslexic and control subjects are both robust and reliable.

Visible persistence in paranoid schizophrenics

A visual temporal integration (i.e., visible persistence) task was performed by normal controls and paranoid schizophrenics. The task evaluated the critical duration (CD), which approximates the duration of peripheral persistence duration and post-CD persistence, which is possibly more associated with central processes. Subjects were required to report when temporally modulated spatial frequency patterns, which are known to have characteristic temporal processing rates, were pulsing “on-off” with a distinct “off” period. The dependent measure was the duration of visible persistence. An analysis of groups X spatial frequency duration (50, 75, 150, 300 msec) X spatial frequency (high, medium, low), with repeated measures on the last two variables, revealed that the second-order interaction was significant ( p < 0.05). Schizophrenics had shorter visible persistence only for the 300-msec presentation for the high spatial frequency pattern. Also, the CD of schizophrenics did not conform to the duration of normals on the high spatial frequency. The results are discussed in terms of the role high spatial frequencies plays in visual information processing and how shorter visible persistence by paranoid schizophrenics may reflect a premature termination of information necessary for synthesis into accurate percepts.

The effect of field size and luminance on spatial-frequency-dependent visible persistence and specific reading disability

The duration of visible persistence for sine-wave gratings was measured in 13-year-old normal and specific-reading-disabled children as a function of stimulus duration, field size, and luminance level. The results show that in specific-reading-disabled children, visible persistence is less sensitive to the effect of field size, suggesting that the two groups may differ in terms of spatial-summation processes.

Persisting arguments about visual persistence: reply to Long.

In a recent paper we investigated the effect of stimulus duration on partial report performance (Yeomans & Irwin, 1985). Two experiments showed that variations in stimulus duration from 50 to 500 msec had little or no effect on partial report accuracy, decay, or error patterns. Our results contrasted with previous research demonstrating that increasing stimulus duration decreases visible persistence duration (e.g., Bowen, Pola, & Matin, 1974; Cohene, 1975; Di Lollo, 1977, 1980; Efron, 1970a, 1970b, 1970c; Haber & Standing, 1970). We concluded that our findings provided support for the argument (Coltheart, 1980) that informational persistence (knowledge about the visual properties of a stimulus, as accessed by partial report) is a phenomenon that is separate from visible persistence (the phenomenal persistence of a stimulus), and we suggested that the traditional view of iconic memory, which conflates these two forms of persistence, is incorrect. We proposed, as a replacement to the traditional view, a two-stage model in which a brief period of visible persistence initiated at stimulus onset and sensitive to stimulus energy is followed by a longer period of informational persistence which begins at stimulus offset and is relatively insensitive to stimulus energy. In a recent note, Long (l985a) took exception to the conclusions of our study. He made two specific criticisms-first, that it is dangerous to base a model on a null effect; and second, that we overlooked substantial empirical evidence that was inconsistent with the two-stage model we proposed. We address each of these criticisms below.

The effect of physical flicker on visible persistence in normal and specifically disabled readers

Abstract Howell, Smith, and Stanley (1981) found no significant differences between normal readers and specific reading-disabled children in spatial-frequency-dependent visible persistence durations as previously demonstrated by Lovegrove, Heddle, and Slaghuis (1980). Howell et al. (1981) argued that the difference between these two sets of results may have been due to their use of a flicker-free oscilloscope which reduced transient involvement whereas Lovegrove et al. (1980) used a tachistoscope which included some physical flicker. Four experiments are reported which investigate the role of physical flicker in visible persistence in controls and SRDs. The results indicate that the presence of stimulus flicker plays a role in determining visible persistence differences between the groups and are consistent with the proposal of a transient system deficit in the SRD group.

Temporal integration in amblyopic vision

Amblyopic subjects were tested on different visual tasks which required temporal integration of successively presented stimuli: (1) a figure had to be detected whose components were displayed successively and hidden in spatio-temporal noise. The time interval T over which the figure elements were dispersed was varied and the longest T value still compatible with figure detection was determined. In all subjects these T values were considerably longer for the normal than for the amblyopic eye. (2) A missing square had to be detected in a checker-board of 3 × 3 squares that was presented in two successive frames, each frame containing 4 squares. With the normal eye, identification of the missing square was possible over considerably longer interstimulus intervals (ISIs) than with the amblyopic eye. (3) Changes had to be detected in two patterns of randomly distributed squares that were presented successively with varying ISI whereby one square was added or subtracted in the second pattern. With the normal eye, detection of changes was possible over much longer ISIs than with the amblyopic eye. These experiments show a deficit of the amblyopic visual system to integrate temporally separated stimuli. We conclude that amblyopia is associated with a marked reduction of the duration of visual persistence and suggest that this is due to shortening of normally sustained neuronal responses.

Suppression of visible persistence.

Five experiments were conducted to examine duration of visible persistence in sequences of stimuli. The basic display consisted of a point that stepped around a circular path on the face of an oscilloscope. Observers estimated the number of points seen simultaneously. Results were compared with a control condition in which the points were plotted in random order rather than sequentially. It was found that visible persistence of a point is suppressed if other points are shown nearby and after an appropriate delay. The degree of suppression depended on the spatial proximity of successive points. It was also found that both duration of visible persistence and degree of suppression increase with eccentricity in the visual field. The results are discussed in terms of two independent processes, persistence and suppression, that operate in a hierarchically antithetical relation.

Spatial-frequency-dependent visible persistence and specific reading disability

Visible persistence duration for sine-wave gratings was measured in 9-year-old normal and specific-reading-disabled children. Experiment 1 investigated the influence of stimulus duration on visible persistence. The results demonstrated a Reading Group × Spatial Frequency interaction with disabled readers showing a smaller increase in persistence duration with increasing spatial frequency than controls. This interaction was greatest with stimulus durations longer than 80 msec. In Experiments 2a and 2b persistence was measured across a range of contrasts from .1 to .5. The stimulus durations employed were 100 msec in Experiment 2a and 300 msec in Experiment 2b. In both experiments, increasing contrast decreased persistence duration at 2 and 12 cycles per degree (c/deg) for the control group. In the specific-reading-disabled group, however, contrast had little effect on the persistence of 2-c/deg gratings in either experiment. In Experiment 2a the persistence of the 12-c/deg grating decreased with increasing contrast for both groups. In Experiment 2b contrast had significantly less effect on persistence duration in the specific-reading-disabled group than in the control group at 12 c/ deg. Consequently, contrast had less effect on persistence in specific-reading-disabled children than in normal readers, especially at durations longer than the “critical duration” for each spatial frequency. Experiment 3 extended this finding to gratings with spatial frequencies of 4 and 8 c/deg. These results indicate a difference between normal and specific-reading-disabled children in cortical visible persistence. Two scores of visual processing were derived from the above experiments. On these scores the reading-disabled children were divided into Visual Disabled Readers (approximately 70%—eight subjects) and Nonvisual Disabled Readers (approximately 30%—four subjects). The percentages of disabled readers in each category remained constant when the sample size was increased to 61 normal and disabled readers.

Duration and resolution effects on visual persistence (positive afterimages)

The effects of varying target duration and target size on the duration of visual persistence were assessed in a probe-matching task for both foveal and peripheral targets presented against scotopic, mesopic, and photopic background fields. Persistence was found to increase with increasing target duration and increasing target size under all conditions of retinal location and background field. Results are discussed in terms of an early sensory locus to the persistence assessed by the task employed. The possible bases for discrepancies with other work are proposed in terms of differing processes within the visual system that may be involved by the different persistence tasks favored by various investigators.

Stimulus duration and partial report performance.

This paper investigates the effect of stimulus duration on partial report performance. Two experiments showed that variations in stimulus duration from 50 to 500 msec had little or no effect on partial report accuracy, decay, or error patterns. These results contrast with previous research demonstrating that increasing stimulus duration decreases visible persistence duration. Our findings thus provide support for the argument (Coltheart, 1980) that informational persistence (knowledge about the visual properties of a stimulus) is a separate phenomenon from visible persistence (the phenomenal persistence of a stimulus), and suggest that the traditional view of iconic memory, which conflates these two forms of persistence, is incorrect. Furthermore, our results indicate that informational persistence is not merely a function of unnaturally brief stimulus exposures, but exists even after exposure durations as long as 500 msec. Possible mechanisms of informational persistence, as well as its potential role in everyday perception, are discussed.

In vivo and in vitro models of demyelinating disease. XI. Tropism and differentiation regulate the infectious process of coronaviruses in primary explants of the rat CNS.

The coronaviruses, ubiquitous in mammals, including man, manifest serotype-related predeliction for different tissues. This presentation deals with specificity of the murine viscerotropic MHV3 and neurotropic JHMV for explanted cells from the CNS of newborn, inbred, Wistar-Furth rats. An unambiguous tropism of MHV3 for astrocytes and JHMV for oligodendrocytes is demonstrated. With the latter cell-virus interaction, relatively small differences in spatial density of oligodendrocytes influence profoundly the duration of persistence and virus yield. The in vitro temporal program of oligodendrocyte differentiation, monitored by induction of a myelin-related enzyme, 2′:3′-cyclic nucleotide-3′-phosphohydrolase, corresponds to that occurring in vivo (F. A. McMorris, J. Neurochem.41, 506–515, 1983). It is complete within 15–21 days and is coincident with the onset of insusceptibility to disease caused by JHMV. Experimental elevation of intracellular cyclic-AMP levels, presumed to reflect oligodendrocyte differentiation, likewise suppresses JHMV replication without affecting that of MHV3 in astrocytes. On the basis of these data it is concluded that in vitro interaction of JHMV with oligodendrocytes reflects accurately the in vivo host control over the tropism and expression of this virus, thereby effecting the progressive, demyelinative disease, process.

Continuous measurement of visible persistence.

In the synchrony judgment paradigm, observers judge whether a click precedes or follows the onset of a light flash and, on other trials, whether or not a click precedes light termination. The interclick interval defines the duration of visible persistence. An elaboration of this method consists of two phases: In Phase 1, the luminance of a reference stimulus is psychophysically matched to the peak brightness of the test flash. Five luminance values between .1 and 1.0 of the reference stimulus are used subsequently. In Phase 2, a random one of the five reference stimuli, a test flash, and a click are presented; the observer judges whether the click occurred before or after the brightness of test flash reached the reference value (on onset trials) or decayed below it (on termination trials). This method was validated on 3 subjects with test stimuli whose luminance rises and decays slowly in time, and then was used to trace out the precise subjective rise and decay (temporal brightness response function) of brief flashes.

Visible Persistence as a Function of Viewing Condition and Eye-Handedness Relationship

Duration of visible persistence was investigated as a function of spatial frequency, orientation and viewing condition (binocular, dominant eye and non-dominant eye). Persistence increased with increasing spatial frequency and was longer for oblique than vertical gratings. Viewing condition also influenced visible persistence such that binocular persistence was significantly shorter than for either monocular condition. A post-hoc analysis indicated that this was only true with subjects who were right-handed and right-eyed. Subjects mixed on this relationship showed no differences in persistence across viewing conditions. A second experiment which selected subjects on the basis of this relationship confirmed the results of Experiment 1. The results for the right-right group broaden the generality of the rule showing an inverse relationship between response strength and persistence duration. The results for the Mixed group indicate a lack of binocular summation.

On the relationship between stimulus intensity and duration of visible persistence.

Stimulus intensity and duration of visible persistence have been found to vary directly in some studies but inversely in others. Hawkins and Shulman (1979) have proposed that this inconsistency can be resolved by separating the studies that employed a decrement-threshold measure of persistence (Type I measure) from those that measured the total duration of persistence (Type II measure). They suggested that Type I measures yield an inverse relationship, whereas Type II measures yield a direct relationship between intensity and persistence. Hawkins and Shulman's model is incomplete in ways that are easily remedied. However, the model is totally contradicted by the experimental evidence. A new resolution of the inconsistent results is proposed in terms of retinal afterimages.

Visible persistence as a function of spatial frequency, number of cycles and retinal area

Using a variety of measures it has been shown that processing time increases with increasing spatial frequency. Long and Sakitt (1981) [ Vision Res. 21, 1387–1393] investigated duration of visible persistence as a function of both spatial frequency and number of cycles present. They concluded that number of cycles and not spatial frequency is the crucial variable in determining duration of visible persistence. The present paper investigates this issue in three experiments. Experiments 1 and 2 determined duration of visible persistence with spatial frequencies of 2, 4, 8 and 10c/deg while holding both number of cycles and grating area constant in a dark surround and in a light surround. Stimulus durations of 50 and 300msec were used in Experiments 1 and 2 respectively. The results at each stimulus duration showed an increase in duration of visible persistence with increasing spatial frequency similar to that found in most previous reports. This increase was less with a 300 than with a 50 msec stimulus duration. Whether the gratings were presented in a light or a dark surround had no significant effect. Experiment 3 showed that at 2 c/deg duration of visible persistence increased with increasing size of the grating stimuli when all stimulus sizes fell within the area of spatial summation. This effect was greater in a dark than in a light surround. It is concluded that visible persistence does increase with spatial frequency. Previous results inconsistent with this conclusion are explained in terms of spatial summation.

On the relationship between stimulus intensity and duration of visible persistence.

On the relationship between stimulus intensity and duration of visible persistence.