Flicker Masking of Spatial-Frequency-Dependent Visible Persistence and Specific Reading Disability

Perception ◽  
1984 ◽  
Vol 13 (5) ◽  
pp. 527-534 ◽  
Author(s):  
Walter L Slaghuis ◽  
William Lovegrove
Keyword(s):  
Spatial Frequency ◽  
Reading Disabilities ◽  
Visible Persistence ◽  
Control Group ◽  
Uniform Field ◽  
Specific Reading Disability ◽  
Specific Reading ◽  
Spatial Frequencies ◽  
Transient System ◽  
Average Readers

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.

Uniform-Field Flicker Masking in Control and Specifically-Disabled Readers

Perception ◽  
1988 ◽  
Vol 17 (2) ◽  
pp. 203-214 ◽  
Author(s):  
Frances Martin ◽  
William J Lovegrove
Keyword(s):  
Test Stimulus ◽  
Contrast Sensitivity ◽  
Temporal Frequency ◽  
Control Group ◽  
Uniform Field ◽  
Complex Situation ◽  
Spatial Frequencies ◽  
Stationary Test ◽  
Disabled Readers ◽  
Transient System

Possible transient-system deficiencies in subjects with specific reading disabilities (SRDs) were investigated in groups of 13-year-old SRDs and control normal readers. In experiment 1, in which a 6 Hz uniform-field flicker (UFF) mask and a stationary test stimulus were used, it was found that the overall effect of UFF masking was to reduce differences in contrast sensitivity between SRDs and normal readers. In experiments 2a and 2b, with UFF masks of 6 and 20 Hz and a 6 Hz moving (experiment 2a) or flickering (experiment 2b) test stimulus, contrast sensitivity in both groups was decreased in the presence of the 6 Hz UFF mask. Only the control group, however, showed a further decrease in sensitivity with the 20 Hz UFF mask. This indicates that the groups differ in terms of a mechanism sensitive to high temporal frequencies. A 20 Hz counterphase flickering test stimulus was used in experiment 3 in the presence of 6 Hz UFF, and it was found that SRDs are less sensitive than controls to 20 Hz flicker across all spatial frequencies used. The 6 Hz mask, however, did not differentially affect the two groups. These findings provide further evidence for a transient-system deficit in the visual systems of SRDs, but also suggest a more complex situation by showing that the two groups differ in a high-temporal-frequency mechanism.

Specific reading disability: differences in contrast sensitivity as a function of spatial frequency

Science ◽  
1980 ◽  
Vol 210 (4468) ◽  
pp. 439-440 ◽  
Author(s):  
W. Lovegrove ◽  
A Bowling ◽  
D Badcock ◽  
M Blackwood
Keyword(s):  
Spatial Frequency ◽  
Reading Disability ◽  
Contrast Sensitivity ◽  
Specific Reading Disability ◽  
Specific Reading

Role of suppression in shaping orientation and direction selectivity of complex neurons in cat striate cortex

1996 ◽  
Vol 75 (3) ◽  
pp. 1163-1176 ◽  
Author(s):  
P. Hammond ◽  
J. N. Kim
Keyword(s):  
Spatial Frequency ◽  
Striate Cortex ◽  
Cutoff Frequency ◽  
Direction Selectivity ◽  
Uniform Field ◽  
Directional Tuning ◽  
Tuning Curves ◽  
Spatial Frequencies ◽  
Dominant Eye ◽  
Cat Striate Cortex

1. Single binocularly driven complex neurons in cat striate cortex were recorded extracellularly under nitrous oxide-oxygen-halothane anesthesia and muscle relaxant. Orientational/directional tuning was initially derived for each eye in turn, with sine wave gratings of optimal spatial frequency and velocity, while the other eye viewed a uniform field. 2. For the dominant eye, previously concealed suppression was revealed against elevated levels of firing induced with a conditioning grating, drifting continuously in the preferred direction, simultaneously presented to the nondominant eye. During steady-state binocular conditioning, orientational/directional tuning was reestablished for the dominant eye. In a subset of cells, tuning curves during conditioning were also derived for the reverse configuration, i.e., nondominant eye tuning, dominant eye conditioning: results were qualitatively identical to those for conditioning through the nondominant eye. 3. Neurons were initially segregated into five groups, according to the observed suppression profiles induced at nonoptimal orientations/directions during conditioning: Type 1, suppression centered on orthogonal directions; Type 2, suppression around null directions; Type 3, null suppression combined with orthogonal suppression; Type 4, lateral suppression, maximal for directions immediately flanking those inducing excitation; and Type 5, the residue of cells, totally lacking suppression or showing complex or variable suppression. 4. Sharpness of (excitatory) tuning was correlated with directionality and with class of suppression revealed during binocular conditioning. Direction-biased neurons were more sharply orientation tuned than direction-selective neurons; similarly, neurons exhibiting lateral or orthogonal suppression during conditioning were more sharply tuned than neurons with null suppression. 5. Application of suboptimal directions of conditioning weakened the induced suppression but altered none of its main characteristics. 6. The relationship between excitation, suppression, and spatial frequency was investigated by comparing tuning curves for the dominant eye at several spatial frequencies, without and during conditioning. End-stopped neurons preferred lower spatial frequencies and higher velocities of motion than non-end-stopped neurons. Confirming previous reports, suppression in some neurons was still present for spatial frequencies above the cutoff frequency for excitation, demonstrating the tendency for suppression to be more broadly spatial frequency tuned than excitation. 7. Scatterplots of strength of suppression, in directions orthogonal and opposite maximal excitation, partially segregated neurons of Types 1-3. Clearer segregation of Types 1-4 was obtained by curve-fitting to profiles of suppression, and correlating half-width of tuning for suppression with the angle between the directions of optimal suppression and optimal excitation in each neuron. 8. Two interpretations are advanced-the first, based on three discrete classes of inhibition, orthogonal, null and lateral; the second, based on only two classes, orthogonal and null/lateral--in which null and lateral suppression are manifestations of the same inhibitory mechanism operating, respectively, on broadly tuned direction-selective or on sharply tuned direction-biased neurons. Orthogonal suppression may be untuned for direction, whereas lateral and null suppression are broadly direction tuned. Within each class, suppression is more broadly spatial frequency tuned than excitation. 9. It is concluded that orientational/directional selectivity of complex cells at different spatial frequencies is determined by the balance between tuned excitation and varying combinations of relatively broadly distributed or untuned inhibition.

Flicker Contrast Sensitivity in Normal and Specifically Disabled Readers

Perception ◽  
1987 ◽  
Vol 16 (2) ◽  
pp. 215-221 ◽  
Author(s):  
Frances Martin ◽  
William Lovegrove
Keyword(s):  
Spatial Frequency ◽  
Contrast Sensitivity ◽  
Temporal Frequency ◽  
Temporal Contrast ◽  
Control Subjects ◽  
Visual Systems ◽  
Spatial Frequencies ◽  
Disabled Readers ◽  
Transient System

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.

The Perceived Spatial Frequency, Contrast, and Orientation of Illusory Gratings

Perception ◽  
1980 ◽  
Vol 9 (6) ◽  
pp. 695-712 ◽  
Author(s):  
Mark A Georgeson
Keyword(s):  
Spatial Frequency ◽  
Temporal Frequency ◽  
Interocular Transfer ◽  
Contrast Threshold ◽  
Supporting Evidence ◽  
Uniform Field ◽  
Apparent Contrast ◽  
Spatial Frequencies ◽  
The Matrix ◽  
Matching Techniques

Illusory vertical gratings (V) and diagonal gratings (D) can be seen on a uniform field after inspection of a vertical grating. When using simultaneous and successive matching techniques the spatial frequencies of the V effect were found to be about 2 octaves below and 1–2 octaves above the adapting spatial frequency, but to be invariant with temporal frequency. At high adapting frequencies the D effect dominated, and was about 0·8 octave below the adapting spatial frequency, oriented about ±35° from vertical. The apparent contrast of V was about twice the value of the contrast threshold at its apparent spatial frequency. D effects seen during adaptation were about 60° from vertical and 3 octaves below the adapting frequency. The results are interpreted in terms of inhibition and disinhibition in an organized matrix of tuned channels, and the dominant pattern of inhibition in the matrix is inferred. Supporting evidence from neurophysiology, neuroanatomy, and psychophysics is briefly reviewed. An appendix deals with the question of interocular transfer of the aftereffect.

The Perceived Duration of Gratings

Perception ◽  
1992 ◽  
Vol 21 (2) ◽  
pp. 161-166 ◽  
Author(s):  
John A Baro ◽  
Lynda J Brzezicki ◽  
Stephen Lehmkuhle ◽  
Howard C Hughes
Keyword(s):  
Spatial Frequency ◽  
Reaction Times ◽  
Visible Persistence ◽  
Subjective Duration ◽  
Spatial Frequencies ◽  
The Difference ◽  
Perceived Duration

Since visible persistence of grating patterns increases with spatial frequency, it is often inferred that the perceived duration of a grating is also longer at higher spatial frequencies. However, other work has demonstrated that the perceived onset of a grating is also delayed at higher spatial frequencies. Thus it is impossible to infer the subjective duration from the results of visible persistence studies alone. In order to estimate perceived duration in the present study, reaction times (RTs) to grating onsets and offsets were measured for a range of spatial frequencies. The results indicate that although the perceived duration (ie the difference between offset and onset RTs) was consistently longer than the physical duration, the estimates of perceived duration did not vary with changes in spatial frequency. Differences between the present results and earlier findings are interpreted in the context of the different methods used to measure perceived offset.

scholarly journals Are Contrast Sensitivity Functions Impaired in Insulin Dependent Diabetics Without Diabetic Retinopathy?

1999 ◽  
Vol 42 (4) ◽  
pp. 133-138 ◽  
Author(s):  
Vladimír Liška ◽  
Miroslav Dostálek
Keyword(s):  
Visual Acuity ◽  
Diabetic Retinopathy ◽  
Spatial Frequency ◽  
Contrast Sensitivity ◽  
Dependent Diabetes Mellitus ◽  
Control Group ◽  
Study Group ◽  
Sensitivity Functions ◽  
Spatial Frequencies ◽  
Insulin Dependent

Purpose: To confirm the influence of multilevel metabolic disturbance of insulin dependent diabetes mellitus (IDDM) on the vision even before the onset of the other changes routinely evaluated by ophthalmologists. Methods: Contrast sensitivity functions (CSFs) were estimated using the VCTS 6500 board. The standardised measurement procedure was performed. The value of the threshold contrast sensitivity was obtained for five spatial frequencies (1.5 - 3 - 6 - 12 - 18 c/deg). Other data was collected (duration of diabetes, BCVA, funduscopy, fluoresceine angiography, HbA1C). The study group consisted of 48 IDDM patients (94 eyes) without diabetic retinopathy and with Snellen BCVA > 1.0. The control group (56 normals, 98 eyes) was age and BCVA matched. Results: Highly statistically significant decrease of the CSFs in all spatial frequencies in the study group was obtained. Correlation between duration of the diabetes and impaired degree of CSFs was present in the middle spatial frequency. No significant changes in CSFs were found among patients with pathological value of glycated hemoglobin HbA1c (>7.8 %). Conclusions: If compared with routinely used Snellen visual acuity, the CSFs are more complex descriptors of the subjects vision abilities. IDDM has an influence on these sensitive functions, especially during examination in the middle spatial frequency of 6 and 12 c/deg, before disturbing visual acuity and before changes in the retinal morphology. Decrease of CSFs was influenced mainly by the patients’ age and partially (in the middle spatial frequency) by the IDDM duration.

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