Psychophysical indices of perceptual functioning in dyslexia: A psychometric analysis

Abstract

An influential causal theory attributes dyslexia to visual and/or auditory perceptual deficits. This theory derives from group differences between individuals with dyslexia and controls on a range of psychophysical tasks, but there is substantial variation, both between individuals within a group and from task to task. We addressed two questions. First, do psychophysical measures have sufficient reliability to assess perceptual deficits in individuals? Second, do different psychophysical tasks measure a common underlying construct? We studied 104 adults with a wide range of reading ability and two comparison groups of 49 dyslexic adults and 41 adults with normal reading, measuring performance on four auditory and two visual tasks. We observed moderate to high test–retest reliability for most tasks. While people with dyslexia were more likely to display poor task performance, we were unable to demonstrate either construct validity for any of the current theories of perceptual deficits or predictive validity for reading ability. We suggest that deficient perceptual task performance in dyslexia may be an associated (and inconsistent) marker of underlying neurological abnormality, rather than being causally implicated in reading difficulties.

Impairments in speech and nonspeech sound categorization in children with dyslexia are driven by temporal processing difficulties

“…We therefore conclude that the rapidly changing information of the sounds, rather than its speech character, constitutes the determining factor for observing group differences between dyslexic and normal readers. Other researchers (Roach, Edwards, & Hogben, 2004;Heath, Bishop, Hogben, & Roach, 2006;Hazan, Messaoud-Galusi, Rosen, Nouwens, & Shakespeare, 2009) have disagreed to attribute the observed problems on auditory tasks to a specific perceptual processing deficit of certain stimulus characteristics (e.g., temporal cues), but have explained the deficit by task demands. Most auditory processing tasks, like the ABX-identification task used in this study, also rely on non-sensory factors such as attention and verbal short-term memory, which have been shown to be impaired in persons with dyslexia (Ramus & Szenkovits, 2008;Fletcher, Shaywitz, & Shaywitz, 1999).…”

From temporal processing to developmental language disorders: mind the gap

“…Although both theories are supported by evidence of associations between language or reading and the signature task of the theory, there are also a host of findings that cannot fit within these frameworks. For example, there is evidence of impairments in other psychoacoustic tasks, such as duration, intensity or (especially) frequency discrimination, that do not require rapid processing or rise time perception [21,23,27,28,[30][31][32][33][43][44][45][46][47][48][49][50]. There are findings that fail to survive control for IQ [51] and failures to replicate (e.g.…”

“…Task reliability is rarely assessed (and may be too low, especially for the rise time tasks [53]). The resulting threshold is a measure of first impressions of naive participants [46,104] with different abilities in focusing on the task, identifying the critical acoustic elements and, crucially, adaptively tracking the progression of those elements towards threshold. It is unknown whether individual differences in concentration or perceptual learning ability contribute to the measured thresholds.…”

“…The two temporal theories considered here need not be competitors but may concern complementary aspects of speech processing, acting on different timescales, independently or in unison (see evidence in [115] and discussion in [116]). Alternatively, neural entrainment may only be incidentally and not causally associated with language or literacy difficulties [46], by virtue of some shared physiological substrate. It may turn out that impairments in speech processing are not consistently found in individuals with language or literacy disorders.…”

When words fail us: insights into language processing from developmental and acquired disorders

“…Mostly, this has been investigated with studies of auditory processing, which appears less important than was originally thought [91]. The evidence for visual perceptual deficits as a cause of developmental dyslexia is conflicting [92,93]. However, the kinds of perceptual task that have been used are different from those investigated in cases of acquired reading disorder, and it would be of considerable interest to see whether, for instance, dyslexics do poorly on sensitive tests of face perception-or whether children who are identified as having poor face perception skills are at risk of reading problems.…”