Time perception: modality and duration effects in attention-deficit/hyperactivity disorder

Journal of Abnormal Child Psychology,  Oct, 2005  by Maggie E. Toplak,  Rosemary Tannock

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Presence of Reading Disorders

Approximately 24% (n = 11) of the adolescents with ADHD had a comorbid reading disorder. A definition of low achievement in both single-word reading and reading efficiency were used to classify reading disabilities, as both accuracy and fluency of single word decoding are important markers of reading problems in adolescents (Lovett & Barron, 2003; Pennington, Cardosa-Martins, Green, & Lefly, 2001). Reading disorders were identified by a standard score below the 25th percentile (SS 90) on the reading subtest of the WRAT-3 and on the Test of Word Reading Efficiency (TOWRE).

Experimental Tasks

Duration Discrimination Tasks

Based on the methodology of the auditory duration discrimination task used by Hetherington, Dennis, and Spiegler (2000) and by Toplak et al. (2003), four novel versions of this task were developed; these included visual and auditory tasks that both used two interval lengths (200 and 1000 ms). The 200 ms interval was chosen to represent those processes that are believed to be linked to an internal timing mechanism, and the 1000 ms interval was chosen to represent processes that may be associated with memory functions (Ivry, 1996).

Two control tasks (size and frequency discrimination) were included to test for more general deficits in perceptual processing that could confound the interpretation of performance on the duration discrimination tasks. For the visual control task, size of stimuli was used as the perceptual feature, and for the auditory control task, frequency of tone was used. In the visual control task, participants were presented with two squares (target square was 100 X 100 pixels, and the comparison square was smaller or larger) on the computer screen, and they were asked to determine which of the two squares was larger. In the auditory control task, participants were presented with two tones (target tone was 3000 Hz, and comparison tone was always higher) generated by the computer, and they were asked to determine which of the two tones sounded higher. Unfilled intervals were used to minimize any confound from the ongoing processing of stimuli that may occur when filled intervals are used (Ivry, 1996). Thus, in the auditory version of the duration discrimination task, participants were presented with two intervals defined by 50 ms, 1000 Hz boundary tones at the beginning and end of each interval, and separated by an inter-stimulus interval (ISI) of 500 ms. In the visual version of the duration discrimination task, participants were presented with two intervals defined by 50 ms, visual image of a 100 X 100 pixel square at the beginning and end of each interval, also separated by an ISI of 500 ms. The target interval refers to the consistently presented stimulus (either 200 or 1000 ms), while the comparison interval refers to the interval that was adapted to participants performance. The target interval (200 or 1000 ms) was randomly presented as the first or second duration. For the 200 ms target version, increments of the target duration changed by 5 ms (the first comparison duration was 230 ms), and for the 1000 ms target version, increments changed by 25 ms (the first comparison duration was 1200 ms). The comparison intervals and increment parameters were interpolated from those used by Hetherington et al. (2000). The inter-trial interval was 1000 ms.