Witton, C. & Talcott, J. B.
Aston Brain Centre, Aston University
Auditory processing disorders have been widely implicated in developmental dyslexia, based on a large body of psychophysical work. However psychophysical methods can be challenging to use with populations who may have cognitive difficulties, especially in working memory and attention, because they require the participant to attend to, and respond to, large numbers of trials. This study used simulated psychophysical observers to explore the sensitivity of some commonly-used staircase techniques to individual differences in attention, and to differences in psychometric function slope. The simulated observers had a psychometric function defined by a Weibull curve, of a specified slope and threshold. They could respond to a 2-AFC task either exactly as determined by this psychometric function (ideal observers), or with a specified 'lapse rate', whereby they responded randomly on a specified percentage of trials, to mimic the effects of inattention. For any given threshold and psychometric function, the staircase procedures yielded a distribution of threshold-estimates, which enabled the procedure to be assessed for suitability based on its skew and kurtosis. The data suggest that staircases are more likely to produce high threshold-estimates for psychophysical tasks (or observers) with shallower psychometric functions. An example of a task with a relatively shallow psychometric function is frequency discrimination, whereas an example of one with a steep function is gap detection. Furthermore, an attentional lapse-rate of 10% (i.e., a random response on perhaps 3 or 4 trials within one staircase) can result in threshold-estimates which differ significantly from the same data in a matched group of 30 ideal observers. The size of this effect depends on the staircase procedure chosen. Taken together, these data suggest that choice of staircase procedure is very important when measuring auditory processing in populations of children with dyslexia or other developmental disabilities, and provide some guidelines for design of measures.