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Biomedical subjects

W Lovegrove

Publications and source records attributed to W Lovegrove.

13 recordsLinked to original sources
PubMed1987

Flicker contrast sensitivity in normal and specifically disabled readers.

Temporal contrast sensitivity for counterphase flicker was determined for specifically disabled and normal readers to investigate whether the two groups differ in the functioning of their transient systems. In experiment 1, temporal contrast sensitivity was measured over a range of temporal frequencies with a spatial frequency of 2 cycles deg-1. Disabled readers were less sensitive than the control subjects at all temporal frequencies. In experiment 2, temporal contrast sensitivity was measured at a temporal frequency of 20 Hz over a range of spatial frequencies. Disabled readers were less sensitive than the controls at all spatial frequencies, with the differences between the groups increasing as spatial frequency increased. Both these findings are interpreted as supporting the hypothesis of a transient-system deficit in the visual systems of disabled readers.

Adolescent↗
PubMed1986

Contrast and phase processing in amblyopia.

Contrast-coding was investigated in amblyopic, fellow non-amblyopic and control eyes. Using a contrast-matching paradigm similar to Georgeson and Sullivan [J. Physiol. 252, 627-656 (1975)], amblyopic eyes were found to have a high frequency contrast-coding deficit not only at threshold but also at suprathreshold levels up to at least 0.45 contrast. The results do not support the claim of Hess and Bradley [Nature 287, 463-464 (1980)] and Hess, Bradley and Piotrowski [Proc. R. Soc. Lond. B217, 309-330 (1983)] that amblyopes have normal or near-to-normal suprathreshold contrast-coding. By taking this contrast-coding deficit into account we demonstrate that previously reported poor phase discrimination [Lawden, Hess and Campbell, Vision Res. 22, 1005-1016 (1982); Pass and Levi, Invest. Ophthal. Visual Sci. 23, 780-786 (1984)] in amblyopia may, in part, reflect a more basic deficit in contrast-coding across spatial frequencies. The possible involvement of contrast processing mechanisms in phase discrimination is discussed.

Adult↗
PubMed1984

The effects of field size and luminance on contrast sensitivity differences between specifically reading disabled and normal children.

Contrast sensitivity functions were measured for normal and specifically disabled readers in experiments which varied either field size or luminance level. The nature of the differences between groups was unaffected by field size, implying that spatial summation in specifically disabled readers is normal. Increasing luminance, however, increased the range over which disabled readers are less sensitive than normal readers. The results are discussed in terms of possible differences in underlying mechanisms.

Animals↗
PubMed1984

The dependence of monocular rivalry on spatial frequency: some interaction variables.

The effect of spatial frequency upon the rate of monocular rivalry has been investigated on several occasions, with conflicting results. With increases in spatial frequency the rivalry rate has been variously reported as declining monotonically, increasing slightly and briefly before declining sharply, or showing a sharp increase before a sharp decrease. Experiments are reported which show that all three functions may be obtained depending on whether the number of cycles of the gratings is held constant across spatial frequency, or the field size is held constant (and, if the latter, what field size is used). The point at which any high-frequency decline occurs is also shown to increase with increasing luminance. All functions obtained correspond to visual sensitivity functions obtained under comparable conditions.

Dominance, Cerebral↗
PubMed1984

Flicker masking of spatial-frequency-dependent visible persistence and specific reading disability.

The effect of 6 Hz uniform-field flicker masking of visible persistence at a range of spatial frequencies was investigated in 12-year-old children with specific reading disabilities and a control group of average readers. This reduced differences in visible persistence between the two groups. The results suggest that children with specific reading disabilities experience a deficit in their transient system.

Child↗
PubMed1983

Instability in triangular-wave gratings: a role for perceptual inferences?

Recently it has been reported that a grating with a triangular-wave luminance profile may fluctuate between being perceived veridically , and as a percept which more closely resembles a square wave, and is itself bistable. Several additional percepts which may be experienced are reported. It is also noted that the relative dominance of two of these percepts can be altered by either physically present or inferred cues as to the probable direction of illumination. It is suggested that these observations implicate higher-level processes in this new form of perceptual instability.

Discrimination Learning↗
PubMed1979

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.

Afterimage↗
PubMed1978

Processing of visual contour orientation information in normal and disabled reading children.

Four experiments comparing the processing of contour orientation information in normal and specific reading disabled children were conducted. The first two experiments demonstrated that the reading disabled subjects had significantly longer visual information store durations than did the control subjects. In addition differences in visual information store durations for different orientations were found between the two groups. The final two experiments investigated processing of contour orientation information in the visual cortex. Results of Experiment IV suggested that the two groups differ in their processing of information in the visual cortex as well as in VIS. Because of the importance of feature detection in letter recognition, it is suggested that the present results may be important in understanding letter recognition is disabled readers.

Child↗
PubMed1978

Development of information processing in normal and disabled readers.

8- and 11-yr-old reading-disabled children were compared in two experiments with controls matched on intelligence and age. Exp. 1 measured duration of visual information store by means of a separation threshold technique. Exp. II determined the rate of transfer from visual information store to short-term memory using a backward masking technique. Results from Exp. I showed that at each age specific reading-disabled children had significantly longer durations of visual information store than controls. The difference between the reading ability groups decreased with increasing age. Exp. II demonstrated that rate of transfer of information was significantly slower for specific reading-disabled children than for controls at both age levels. In contrast to Exp. I, this difference increased with increasing age. The results are considered in terms of their possible relevance to developmental lag theories. The evidence indicates that the development of visual information processing in reading-disabled children is similar to that in controls but occurs at a slower rate.

Age Factors↗