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

Abstract

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.

Visual and auditory processing and component reading skills in developmental dyslexia

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Visual and auditory processing and component reading skills in developmental dyslexia

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Flicker fusion thresholds as a clinical identifier of a magnocellular-deficit dyslexic subgroup

“…Our results indicate that the presence of temporal processing impairments are not necessarily related to the phonological, rapid naming, double-deficit, or no-deficit subtypes of dyslexia that are proposed by Wolf and Bowers’ Double-Deficit Hypothesis 6 and so provide evidence for the identification of a new subgroup of dyslexia characterised by visual temporal processing differences. Our results compliment the findings of several studies showing little association between tests of M functioning and specific subtypes of dyslexia 53 , 54 , however, others studies have reported a link between M functioning and phonological and double-deficit subtypes 55 – 58 , indicating a clear need for further research. Inclusion of orthographic processing tasks, for example, would enable future FFT research to further explore dyseidetic and surface subtypes 4 , 5 .…”

Speed discrimination predicts word but not pseudo-word reading rate in adults and children

“…Our sample included normal and poor readers but only a few diagnosed dyslexics. Consistent with previous work, we found that dyslexics largely reside at the lower end of the performance distributions for both reading and speed discrimination (Demb, Boynton, Best, et al, 1998; Talcott et al, 1998; Witton et al, 1998; Slaghuis & Ryan, 1999; Talcott, Hansen, Assoku, & Stein, 2000; Hansen, Stein, Orde, Winter, & Talcott, 2001; Ridder, Borsting, & Banton, 2001; Ramus et al, 2003; Kevan & Pammer, 2008). …”

Visual and auditory processing and component reading skills in developmental dyslexia

“……”

Flicker fusion thresholds as a clinical identifier of a magnocellular-deficit dyslexic subgroup

“…Our results indicate that the presence of temporal processing impairments are not necessarily related to the phonological, rapid naming, double-deficit, or no-deficit subtypes of dyslexia that are proposed by Wolf and Bowers’ Double-Deficit Hypothesis 6 and so provide evidence for the identification of a new subgroup of dyslexia characterised by visual temporal processing differences. Our results compliment the findings of several studies showing little association between tests of M functioning and specific subtypes of dyslexia 53 , 54 , however, others studies have reported a link between M functioning and phonological and double-deficit subtypes 55 – 58 , indicating a clear need for further research. Inclusion of orthographic processing tasks, for example, would enable future FFT research to further explore dyseidetic and surface subtypes 4 , 5 .…”

Speed discrimination predicts word but not pseudo-word reading rate in adults and children

“…Our sample included normal and poor readers but only a few diagnosed dyslexics. Consistent with previous work, we found that dyslexics largely reside at the lower end of the performance distributions for both reading and speed discrimination (Demb, Boynton, Best, et al, 1998; Talcott et al, 1998; Witton et al, 1998; Slaghuis & Ryan, 1999; Talcott, Hansen, Assoku, & Stein, 2000; Hansen, Stein, Orde, Winter, & Talcott, 2001; Ridder, Borsting, & Banton, 2001; Ramus et al, 2003; Kevan & Pammer, 2008). …”

Visual and auditory processing and component reading skills in developmental dyslexia

“……”

Flicker fusion thresholds as a clinical identifier of a magnocellular-deficit dyslexic subgroup

“…Our results indicate that the presence of temporal processing impairments are not necessarily related to the phonological, rapid naming, double-deficit, or no-deficit subtypes of dyslexia that are proposed by Wolf and Bowers’ Double-Deficit Hypothesis 6 and so provide evidence for the identification of a new subgroup of dyslexia characterised by visual temporal processing differences. Our results compliment the findings of several studies showing little association between tests of M functioning and specific subtypes of dyslexia 53 , 54 , however, others studies have reported a link between M functioning and phonological and double-deficit subtypes 55 – 58 , indicating a clear need for further research. Inclusion of orthographic processing tasks, for example, would enable future FFT research to further explore dyseidetic and surface subtypes 4 , 5 .…”

Speed discrimination predicts word but not pseudo-word reading rate in adults and children

“…Our sample included normal and poor readers but only a few diagnosed dyslexics. Consistent with previous work, we found that dyslexics largely reside at the lower end of the performance distributions for both reading and speed discrimination (Demb, Boynton, Best, et al, 1998; Talcott et al, 1998; Witton et al, 1998; Slaghuis & Ryan, 1999; Talcott, Hansen, Assoku, & Stein, 2000; Hansen, Stein, Orde, Winter, & Talcott, 2001; Ridder, Borsting, & Banton, 2001; Ramus et al, 2003; Kevan & Pammer, 2008). …”