The Tale is in the Tail: An Alternative Hypothesis for Psychophysical Performance Variability in Dyslexia

Abstract

Dyslexic groups have been reported to display poorer mean performance than groups of normal readers on a variety of psychophysical tasks. However, inspection of the distribution of individual scores for each group typically reveals that the majority of dyslexic observers actually perform within the normal range. Differences between group means often reflect the influence of a small number of dyslexic individuals who perform very poorly. While such findings are typically interpreted as evidence for specific perceptual deficiencies in dyslexia, caution in this approach is necessary. In this study we examined how general difficulties with task completion might manifest themselves in group psychophysical studies. Simulations of the effect of errant or inattentive trials on performance produced patterns of variability similar to those seen in dyslexic groups. Additionally, predicted relationships between the relative variability in dyslexic and control groups, and the magnitude of group differences bore close resemblance to the outcomes of a meta-analysis of empirical studies. These results suggest that general, nonsensory difficulties may underlie the poor performance of dyslexic groups on many psychophysical tasks. Implications and recommendations for future research are discussed.

Speech Perception Abilities of Adults With Dyslexia: Is There Any Evidence for a True Deficit?

“…Simulations of performance on adaptive discrimination tasks and categorical tasks that included errant trials yield patterns of group results that concur with those seen in studies of perceptual abilities in individuals with dyslexia (Roach et al, 2004;Davis, Castles, McAnally & Gray, 2001) although Breier et al (2001) found a deficit in phoneme categorization in a group of dyslexic children whether or not they were diagnosed with ADHD. Roach et al (2004) argue that in order to distinguish poor performance that is due to nonsensory factors from poor performance linked to a specific perceptual deficit, it is necessary to determine whether a task has construct validity, i.e. that it is tapping the dimension that is being investigated.…”

“…It is therefore important to examine the performance of individual participants in both the DYS and AR groups to get a better sense of the proportion of individuals showing poor performance on speech perception tasks, even when group effects are not significant. A further rationale for this kind of analysis is to ascertain whether any participants are consistently poor at subtasks that are assessing a given processing ability, or whether poor performance appears to be more random, and therefore more likely to be due to reasons other than a perceptual deficit (Roach et al, 2004;Heath et al, 2006). Also, if poor categorization ability is likely to result in further perceptual difficulties when the speech signal is degraded, we expect to see that individuals showing poor performance on categorization tasks also show higher thresholds in the words in noise tasks.…”

“…One alternative explanation of the heterogeneity seen in studies of the speech perception abilities of children and adults with dyslexia is that it is does not reflect a specific deficit in auditory or perceptual abilities but rather 'errant task performance', as caused by lapses in attention or confusion about the task procedure (Roach, Edwards & Hogben, 2004;Heath, Bishop, Hogben & Roach, 2006). Simulations of performance on adaptive discrimination tasks and categorical tasks that included errant trials yield patterns of group results that concur with those seen in studies of perceptual abilities in individuals with dyslexia (Roach et al, 2004;Davis, Castles, McAnally & Gray, 2001) although Breier et al (2001) found a deficit in phoneme categorization in a group of dyslexic children whether or not they were diagnosed with ADHD.…”

From temporal processing to developmental language disorders: mind the gap

“…The repetition task is particularly vulnerable to this type of criticism as it involves several cognitive components. Most psychoacoustic tasks are also laden with task demands other than sensory registration [101][102][103] (see Ramus & Ahissar [40] for a similar argument). For example, the requirement for explicit judgements introduces potential interference from auditory memory or even verbal processes that may be recruited to label the stimuli.…”

Perceptual deficits and inattention in schizophrenia

“…This is important since deficits in attention have the potential to affect performance on sensory tests (Peli and Marcia-Perez 1997;Stuart et al 2001;Davis et al 2001;Roach et al 2004). This, therefore, raises the question of if, or to what extent, the observed sensory deficits might reflect underlying attentional problems 1, 2 .…”