Specific Reading Disability: Differences in Contrast Sensitivity as a Function of Spatial Frequency

Abstract

Contrast thresholds for sine-wave gratings of spatial frequencies of 2, 4, 12, and 16 cycles per degree were determined for normal and disabled readers at a range of stimulus durations. Normal readers demonstrated monotonically decreasing sensitivity with increasing spatial frequency at exposure durations between 40 and 100 milliseconds. At exposure durations of 150 to 1000 milliseconds, they showed peak sensitivity at 4 cycles per degree. In comparison, disabled readers showed monotonically decreasing sensitivity with increasing spatial frequency at all stimulus durations. The difference in sensitivity pattern across spatial frequencies was greatest at stimulus durations approximately equal to fixation durations during reading.

Disruption of the neural response to rapid acoustic stimuli in dyslexia: Evidence from functional MRI

“…These theories, however, have not been supported by the evidence (1). Although dyslexic individuals do exhibit some abnormalities of visual processing (particularly for rapidly transient visual stimuli) (9)(10)(16)(17)(18), a strong consensus has developed that the central difficulty in dyslexia is related to the processing of speech sounds, known as phonological processing (1,2). Sensitivity to speech sounds (phonemes) normally develops in infancy and continues to be shaped by experience, especially in the first year of life (19).…”

Motion and Form Coherence Detection in Autistic Spectrum Disorder: Relationship to Motor Control and 2:4 Digit Ratio

“…It seems probable that several different biological and neurological factors may contribute to the autistic syndrome; that is, it may have a heterogeneous etiology. Additionally, sensori-motor deficits have been reported in dyslexia (Fawcett et al, 1996;Livingstone et al, 1991;Lovegrove, Bowling, Badcock, & Blackwood, 1980;Tallal, 1980), and motion detection impairments have been reported in Williams syndrome (Atkinson et al, 1997). Ramus (2002) has proposed that sensori-motor impairments are not a core feature of dyslexia, but rather secondary features arising only in cases with excessive foetal testosterone.…”

Visual information processing in dyslexic children

“…An irregular magnocellular system could reduce the visual sensitivity for moving or flickering stimuli (Cornelissen et al, 1998a) and therefore to interfere with lexical decision tasks (Cornelissen et al, 1998b) or the detection of small letters (Stein and Walsh, 1997) for example. Since the earliest studies (Lovegrove et al, 1980(Lovegrove et al, , 1982(Lovegrove et al, , 1986) sinusgratings have been one of the most popular experimental means. Depending on the spatial frequency (cycles of the bright and dark bars per degree visual angle) dyslexics showed a reduced sensitivity (Evans et al, 1994;Kubová et al, 1995) for motion detection.…”