Alison C Bowling

Contrast sensitivity functions and specific reading disability

Contrast sensitivity functions for normal and specifically disabled readers were measured in two experiments. Each study showed that specifically disabled readers and controls differ in the pattern of relative sensitivity across spatial frequencies. Both studies provide evidence of differences between normal and disabled readers on measures of visual mechanisms fundamental to the reading process.

The effect of spatial frequency and contrast on visual persistence

The visual persistence of sinusoidal gratings of varying spatial frequency and contrast was measured. It was found that the persistence of low-contrast gratings was longer than that of high-contrast stimuli for all spatial frequencies investigated. At higher contrast levels of 1 and 4 cycles deg−1 gratings, a tendency for persistence to be independent of contrast was observed. For 12 cycles deg−1 gratings, however, persistence continued to decrease with increasing contrast. These results are compared with recently published data on other temporal responses, and are discussed in terms of the different properties of sustained and transient channels.

The effect of stimulus duration on the persistence of gratings

The persistence of gratings varying in spatial frequency and exposure duration was measured using a stimulus-blank alternation method. Persistence was found to lengthen with increasing spatial frequency and to shorten with increasing exposure duration. For each spatial frequency, persistence decreased linearly with a slope of approximately —.75 as duration increased for short stimulus durations. For longer stimulus durations, the rate of decline in persistence with increasing duration was reduced, the slope being approximately —.13. The stimulus duration at which the change in slope of the persistence-duration relationship occurred was shown to increase with increasing spatial frequency and was approximately equivalent to the critical duration for each spatial frequency. The data were consistent with an interpretation of persistence in terms of a temporal integration component and a second, possibly cortically located, component.

Two components to visible persistence: Effects of orientation and contrast

Abstract It has been hypothesised, that visible persistence consists of two components, one of which was identified with temporal integration and thought to occur at the peripheral level of the visual system. The second component may occur at later stages of visual processing. These hypotheses were investigated by examining the effect of orientation upon persistence across a range of spatial frequencies and exposure durations. Oblique gratings ranging from 2 to 12 c/deg were shown to persist longer than vertical stimuli at both 50 and 200 msec exposure durations. For a 4 c/deg stimulus, this “oblique effect” was relatively constant across stimulus durations from 50 to 300 msec. The relationship between persistence and stimulus duration was best fitted by two straight lines, which intersected at the approximate duration of temporal integration for a 4 c/deg grating. The stimulus durations of the intersection points were similar for oblique and vertical gratings, indicating that the duration of the hypothesised first persistence component was not affected by orientation. The data thus support the hypothesis that orientation influences the duration of only the second persistence component, indicating that this component may be due to cortical processes. A further study indicated that contrast predominantly affects the duration of the second persistence component.

Spatial frequency processing and the prediction of reading ability : a preliminary investigation

Measures of vocabulary, digit span, and pattern-contrast sensitivity for low- to medium-spatial-frequency gratings were collected from 123 representative prereaders. A multiple regression analysis showed that these were moderate predictors of reading ability 2 years later. The contrast-sensitivity measure made a significant unique contribution to the regression equation. The results are interpreted in terms of recent data that indicate a transient-system deficit in specifically disabled readers.

The relationship between speed of information processing and cognitive ability

Speed of information processing as measured by various reaction time and inspection tasks has been shown to correlate with psychometric intelligence, and it has been suggested that general intelligence (g) is determined to some degree by the speed that information is processed. If this is so, then various measures of speed of information processing should correlate substantially with each other, and each should also correlate with a wide range of psychometric tests that load on g. Alternatively, intelligence may be considered to be a multi-faceted complex of partially related abilities with specific abilities being dependent upon specific cognitive processes. If this is the case, it should be possible to discover independent cognitive processes, some of which correlate with one facet or broad ability and some with another. This paper presents three experiments in which the relationship between intellectual ability and four speed of information processing measures was examined. These were rate of memory scanning, rate of retrieval of information from long term memory, speed of stimulus-response mapping and inspection time (IT). Results showed that correlations between IT and most reaction time measures of speed of information processing were low, and that correlations between different versions of IT were negligible. In addition, some cognitive tasks with verbal material (memory scanning rate for digits and Posner letter matching IT) correlated most substantially with Verbal Reasoning whereas non-verbal (two-line) IT consistently correlated with tests loading on g. It was thus suggested that while non-verbal IT may be a measure of a perceptual speed attribute that contributes to mental functioning, other “speed of information processing” parameters may be more specific to a subset of abilities.

How well do patients understand written instructions?: health literacy assessment in rural and urban rheumatology outpatients

Abstract The aim of this study was to assess health literacy (word recognition and comprehension) in patients at a rural rheumatology practice and to compare this to health literacy levels in patients from an urban rheumatology practice. Inclusion criteria for this cross-sectional study were as follows: ≥18-year-old patients at a rural rheumatology practice (Mid-North Coast Arthritis Clinic, Coffs Harbour, Australia) and an urban Sydney rheumatology practice (Combined Rheumatology Practice, Kogarah, Australia). Exclusion criteria were as follows: ill-health precluding participation; poor vision/hearing, non-English primary language. Word recognition was assessed using the Rapid Estimate of Adult Literacy in Medicine (REALM). Comprehension was assessed using the Test of Functional Health Literacy in Adults (TOFHLA). Practical comprehension and numeracy were assessed by asking patients to follow prescribing instructions for 5 common rheumatology medications. At the rural practice (Mid-North Coast Arthritis Clinic), 124/160 patients agreed to participate (F:M 83:41, mean age 60.3 ± 12.2) whereas the corresponding number at the urban practice (Combined Rheumatology Practice) was 99/119 (F:M 69:30, mean age 60.7 ± 17.5). Urban patients were more likely to be born overseas, speak another language at home, and be employed. There was no difference in REALM or TOFHLA scores between the 2 sites, and so data were pooled. REALM scores indicated 15% (33/223) of patients had a reading level ⩽Grade 8 whereas 8% (18/223) had marginal or inadequate functional health literacy as assessed by the TOFHLA. Dosing instructions for ibuprofen and methotrexate were incorrectly understood by 32% (72/223) and 21% (46/223) of patients, respectively. Up to 15% of rural and urban patients had low health literacy and <1/3 of patients incorrectly followed dosing instructions for common rheumatology drugs. There was no significant difference in word recognition, functional health literacy, and numeracy between rural and urban rheumatology patients.

Sleep after exercise of variable intensity in fit and unfit subjects

Abstract Bodily restorative theories of sleep predict that physical exercise results in elevated levels of slow wave sleep (SWS). However the evidence is contradictory. A number of hypotheses have been proposed to accomodate the negative results. Two of these proposals are tested in the present paper. The first argues that under various circumstances stress counteracts the facilitative effect of exercise on SWS. The second, that the facilitative effect is only observed in fit subjects given very intense exercise schedules. Two experiments were conducted in which exercise intensity was systematically varied and in which an attempt was made to minimize stress effects. Physically unfit subjects were used in the first study and fit subjects in the second. Exercise had no effect on SWS under any conditions in either experiment. In addition the failure to observe the effect could not be accounted for by stress. Thus the results of the two experiments offer no support for bodily restorative theories.

Physical fitness, exercise, age and human sleep

A number of studies have reported that physically fit individuals have more slow wave sleep (SWS) than unfit individuals on nights following non-exercise days. However these studies have failed to control for residual exercise effects from previous days. The present study was designed to replicate the original finding and to determine if the reported difference was due to a chronic fitness effect or to a residual exercise effect. In addition the fitness effect was tested in an older population than had previously been tested. The design consisted of two levels of fitness, two age groups (22–0 and 31–8 years of age) and 3 measurements occasions, the first following afternoon exercise and the second and third following 2 and 4 days of exercise deprivation for fit subjects and 3 non-exercise days for unfit subjects. The conditions were arranged in a 2×2×3 design. The results indicated a significant effect of physical fitness on SWS in the younger age group but not the older. As there was no immediate effect of exercise, the elevation of SWS in the younger fit group appears to represent a chronic difference between young fit and unfit populations. The results have implications for the nature of restorative processes occurring during sleep.

The effects of peripheral movement and flicker on the detection thresholds of sinusoidal gratings

Contrast sensitivity functions were obtained in the presence of temporally modulated surrounds. Sensitivity to low spatial frequencies was depressed below that found with a steady surround when the surround was either a sinusoidally flickering field or a drifting vertical square-wave grating. This effect was observed both with 1-sec presentations of 5- and 0.5-Hz counterphase flicker and with 60-msec pulsed gratings. In addition, reaction time histograms became more characteristic of sustained mechanisms in the presence of temporal modulation. The data were considered in terms of the activity of a nonlinear network of retinal subunits.