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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Participants were also asked about strategy use, and only the reported use of counting strategies was included in this analysis. Data on strategy use were only available for 72 of the 90 participants, and chi-square analyses were used to compare reported strategy use in the two groups. There were no group differences that reached significance in the counting strategies reported.

We obtained a significant effect of duration, F(1, 85) = 242.15, p = .001, indicating that duration thresholds were higher at the longer duration than at the shorter duration across both modalities. The significant duration effect across both modalities indicates that larger intervals were required to successfully discriminate longer durations, indicating that our manipulation of duration worked properly. There was no significant effect of modality.

There was a significant duration by group interaction, F(1, 85) = 11.41, p = .001, and a significant modality by group interaction, F(1, 85) = 5.47, p = .022, indicating that the effects of group and modality differentially varied by group status. There was also a significant three-way interaction, F(1, 85) = 4.08, p = .046, indicating that both the modality and duration experimental manipulations differentially affected group performance. In order to facilitate interpretation of the three-way interaction, Fig. 1 displays the means and standard errors in a visual format.

We proceeded to analyze the three-way interaction instead of the two two-way interactions to understand the combined effects of modality and duration on group status. Within-subjects post hoc contrasts indicated that the significant differences emerged with the 1000 ms interval, F(1, 85) = 5.17, p = 0.025, and in the visual modality, F(1, 85) = 11.44, p = 0.001. This pattern in the visual 1000 ms duration discrimination task can be observed in Fig. 1, and is consistent with the effect size calculations.

Controlling for Estimated Full-Scale IQ

We performed the same analysis, examining estimated full-scale IQ as a covariate of performance. All of the significant effects were maintained, and estimated full-scale IQ did not enter as a significant covariate. Effect sizes were re-calculated with the adjusted means after IQ was entered into the analysis, and these effect sizes are displayed in Table II. Overall, the effect sizes were slightly lower, but the small to moderate effect sizes were maintained on the duration discrimination tasks, particularly on the visual tasks.

Control Tasks

To examine group differences on the visual and auditory threshold measures of the control tasks, two separate one-way ANOVAs were conducted. These means and standard deviations are also presented in Table II. No significant group differences were observed on discrimination thresholds for the visual or auditory control tasks. Effect sizes were small to moderate on the control tasks. The lack of group differences obtained on the control tasks suggest that group differences on the duration discrimination tasks are not attributable to general perceptual skills (e.g., size or tone discrimination), or problems with the response demands (forced choice), but to time perception difficulties. In addition, we re-examined duration discrimination performance by entering the visual and auditory control tasks as covariates of performance. Both the visual, F(1, 83) = 18.19, p = .0001, and the auditory, F(1, 83) = 19.71, p = .0001, control tasks entered as significant covariates. All of the significant effects were maintained, except the three-way interaction, which became marginally significant, F(1, 83) = 3.0, p = .087.