Wl Slaghuis

A theoretical and experimental case for a visual deficit in specific reading disability

Abstract We present three lines of evidence indicating a low-level visual deficit in a large percentage of specifically-disabled readers. This research is presented within the theoretical framework of spatial frequency analysis, in particular, the framework of transient and sustained subsystems. a. Measures of visible-persistence duration as a function of spatial frequency in normal and specifically-disabled readers show that disabled readers have a different pattern of temporal processing across spatial frequencies. These differences disappear when transient system activity is reduced. b. On measures of pattern-contrast sensitivity specifically-disabled readers are less sensitive than controls at low spatial frequencies, but equal or more sensitive at high spatial frequencies. c. On measures of temporal-contrast sensitivity disabled readers are less sensitive than controls at all flicker rates with the greatest differences being at the higher temporal frequencies. These three sources of evidence indicate...

Reading disability: Spatial frequency specific deficits in visual information store.

Abstract Visual information store durations for sine-wave gratings were measured in normal and disabled readers. At low spatial frequencies, disabled readers have significantly longer store durations; at medium spatial frequencies, the two groups do not differ; and at high spatial frequencies, disabled readers have shorter store durations.

A novel pericentric inversion of chromosome 3 cosegregates with a developmental-behavioural phenotype

Current advances in genetic knowledge and analysis have facilitated the shift in emphasis from single gene disorders to complex traits such as cancer and atopic disorders where changes in more than one gene usually contribute to the disease phenotype. A challenging area of complex trait research is the determination of the genetic basis of behavioural phenotypes. Early studies in this area focused on classical linkage analysis in pedigrees which segregated the trait of interest and led to the identification of genes for intellectual disability, such as fraX(A).1,2 In this disorder, mutations in a single gene are sufficient to generate the disease phenotype. In contrast, with other neurodevelopmental disorders, results to date have been much more complex. With ADHD, for example, a large number of genes affecting neurotransmitter function, particularly dopamine, have been implicated. However, results from linkage or association studies have not been reliably replicated. Even the most promising gene candidates are implicated in only a small percentage of ADHD cases.3,4 Identification of the genes involved is a challenging task. Firstly, accurate phenotype definition is crucial to successful outcomes in these pooled studies. Secondly, neurodevelopmental disorders such as ADHD are multifactorial, with a number of different genes, likely to be of varying effect and interacting with environmental influences, presumably contributing to the development of the observed phenotypes. We have identified an extended family where the proband, a child with moderate intellectual disability as well as severe conduct disturbance, was found to have a pericentric inversion of chromosome 3. The inversion was found to cosegregate with developmental-behavioural problems in other members of the family. In order to describe the phenotype, a developmental-behavioural paediatrician undertook a standardised clinical evaluation of eight of the juvenile members of the extended family. The findings are presented in this paper. ### Participants The parents/guardians …

Spatio-temporal contrast sensitivity, coherent motion, and visible persistence in developmental dyslexia.

Three experiments measured spatio-temporal contrast sensitivity, coherent motion, and visible persistence in a single group of children with developmental dyslexia and a matched control group. The findings were consistent with a transient channel disorder in the dyslexic group which showed a reduction in contrast sensitivity at low spatial frequencies, a significant reduction in sensitivity for coherent motion, and a significantly longer duration of visible persistence. The results were also examined by classifying the dyslexic group into dyseidetic, dysphonetic, and mixed (dysphoneidetic) subgroups. There were no differences between the control and dyseidetic groups in contrast sensitivity, in coherent motion and in visible persistence. In comparison to the control group, the mixed (dysphoneidetic) dyslexic subgroup was found to have a significant reduction in contrast sensitivity at low spatial frequencies, a significant reduction in sensitivity for coherent motion, and a significantly longer duration of visible persistence. In comparison to the control group, the dysphonetic group only showed a reduction in contrast sensitivity at low spatial frequencies. Comparisons between the dyseidetic, dysphonetic and mixed dyslexic subgroups showed that there were no substantive differences in contrast sensitivity, coherent motion, and visible persistence. The results support the proposal and findings by Borsting et al. (Borsting E, Ridder WH, Dudeck K, Kelley C, Matsui L, Motoyama J. Vis Res 1996;36:1047-1053) that a transient channel disorder may only be present in a dysphoneidetic dyslexic subgroup. Psychometric assessment revealed that all the children with dyslexia appear to have a concurrent disorder in phonological coding, temporal order processing, and short-term memory.

Forward and backward visual masking of contour by light in positive- and negative-symptom schizophrenia.

Forward and backward masking of contour by light was investigated with stimulus onset asynchronies from 20 to 180 ms in a group of 22 schizophrenic patients and 22 matched normal controls. Individuals with schizophrenia were selected using American Psychiatric Association (1987) criteria and were also assessed using the Andreasen scales for the presence of positive and negative symptoms (N.C. Andreasen, 1981, 1983). The Andreasen scales were used to divide schizophrenic patients into 2 subgroups (positive and negative symptoms). Positive-symptom schizophrenic patients showed no differences in their target duration thresholds or in their backward masking functions. Negative-symptom schizophrenic patients showed significantly longer target duration thresholds and experienced significantly more backward masking. There was no difference between schizophrenic patients and controls in forward masking.

Visual and Language Processing Deficits are Concurrent in Dyslexia

Research has demonstrated that dyslexic subjects have language processing problems. More recent evidence indicates that dyslexic subjects also suffer a low-level visual information processing deficit. Little evidence is available to indicate the extent to which dyslexic subjects simultaneously show a visual and language processing dysfunction. In this study, 35 normal and 35 dyslexic subjects aged from 7.9 to 14 years of age were compared on three reading process variables, a visual processing score, a test of phonological coding and a test of language comprehension, each of which were shown to be related to reading performance. The visual processing score was the slope of the regression line predicting the duration of visible persistence as a function of spatial frequency. The language processing measures were a test of phonological coding of orthographically legal Non-Words and a test of language comprehension, the Token Test. The results showed that the visual processing score was significantly predictive of group membership with 91% of the dyslexic group and only 20% of the normal readers having low scores on this measure. The Non-Word test was found to be a perfect discriminator for dyslexia by indicating that every subject in this group had a major phonological coding deficit. An unexpected finding of the present results was that the Token Test did not discriminate between the groups. The results are interpreted as providing evidence for the concurrence of visual and language deficits in dyslexia.

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.

The effect of peripheral visual motion on focal contrast sensitivity in positive- and negative-symptom schizophrenia

The aim of the present research was to investigate the effect of peripheral (ambient) stimulation on focal visual processing using the far-out jerk effect in normal observers and subgroups with positive- and negative-symptoms in schizophrenia. The far-out jerk effect refers to a reduction in sensitivity of a briefly presented stimulus in central vision in the presence of a sudden movement or oscillation of a stimulus in peripheral vision. In order to measure the far-out jerk effect the focal contrast sensitivity of 5.0Hz modulated sinusoidal target gratings (0.5, 1.0, 2.0, 4.0, and 8.0 number of cycles per degree (c/degrees )) was measured in the presence of three kinds of peripheral surround: a blank field, a stationary 0.75 c/degrees grating, and a 5.0Hz drifting 0.75 c/degrees grating (far-out jerk effect). The findings showed that there were no significant differences in focal contrast sensitivity between the control and positive-symptom group with a blank field and stationary grating surround. However, a 5.0Hz drifting grating surround resulted in a significant reduction in contrast sensitivity at 0.5, 1.0 and 2.0 c/degrees in the positive-symptom group. In comparison with the control group the negative-symptom group showed a generalised reduction in focal contrast sensitivity, a significantly smaller far-out jerk effect, and a significant reduction in contrast sensitivity at 0.5 c/degrees with a stationary grating surround. The finding that both stationary and moving peripheral surrounds have an inhibitory effect on focal contrast sensitivity suggests that there is a dispersion in the visual demarcation between stationary and temporal events in the perception of visual motion in the negative-symptom group.

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.

Directional motion contrast sensitivity in developmental dyslexia

The present study compared the perception of visual motion in two dyslexia classification schemes; the [Boder, E. (1973). Developmental dyslexia: a diagnostic approach based on three atypical reading-spelling patterns. Developmental Medicine and Child Neurology, 15, 663-687.] dyseidetic, dysphonetic and mixed subgroups and [Williams, M. J., Stuart, G. W., Castles, A., & McAnally, K. I. (2003). Contrast sensitivity in subgroups of developmental dyslexia. Vision Research, 43, 467-477.] surface, phonological and mixed subgroups by measuring the contrast sensitivity for drifting gratings at three spatial frequencies (1.0, 4.0, and 8.0 c/deg) and five drift velocities (0.75, 3.0, 6.0, 12.0, and 18.0 cyc/s) in a sample of 32 children with dyslexia and 32 matched normal readers. The findings show that there were no differences in motion direction perception between normal readers and the group with dyslexia when dyslexia was taken as a homogeneous group. Motion direction perception was found to be intact in the dyseidetic and surface dyslexia subgroups and significantly lowered in both mixed dyslexia subgroups. The one inconsistency in the findings was that motion direction perception was significantly lowered in the [Boder, E. (1973). Developmental dyslexia: a diagnostic approach based on three atypical reading-spelling patterns. Developmental Medicine and Child Neurology, 15, 663-687.] dysphonetic subgroup and intact in the [Williams, M. J., Stuart, G. W., Castles, A., & McAnally, K. I. (2003). Contrast sensitivity in subgroups of developmental dyslexia. Vision Research, 43, 467-477.] phonological subgroup. The findings also provide evidence for the presence of a disorder in sequential and temporal order processing that appears to reflect a difficulty in retaining sequences of non-meaningful auditory and visual stimuli in short-term working memory in children with dyslexia.