Abstract
ObjectiveIncreased levels of reaction time variability (RTV) are characteristics of sustained attention deficits. The clinical significance of RTV has been widely recognized. However, the reliability of RTV measurements has not been widely studied. The present study aimed to assess the test-retest reliability of RTV conventional measurements, e.g., the standard deviation (SD), the coefficient of variation (CV), and a new measurement called the amplitude of low frequency fluctuation (ALFF) of RT. In addition, we aimed to assess differences and similarities of these measurements between different tasks.MethodThirty-seven healthy college students participated in 2 tasks, i.e., an Eriksen flanker task (EFT) and a simple reaction task (SRT), twice over a mean interval of 56 days. Conventional measurements of RTV including RT-SD and RT-CV were assessed first. Then the RT time series were converted into frequency domains, and RT-ALFF was further calculated for the whole frequency band (0.0023–0.167 Hz) and for a few sub-frequency bands including Slow-6 (<0.01 Hz), Slow-5 (0.01–0.027 Hz), Slow-4 (0.027–0.073 Hz), and Slow-3 (0.073–0.167 Hz). The test-retest reliability of these measurements was evaluated through intra-class correlation (ICC) tests. Differences and correlations between each EFT and SRT measurement were further examined during both visits.Results1) The RT-ALFF of the Slow-5/4/3 and conventional measurements of RT-SD and RT-CV showed moderate to high levels of test-retest reliability. EFT RT-ALFF patterns generated slightly higher ICC values than SRT values in higher frequency bands (Slow-3), but SRT RT-ALFF values showed slightly higher ICC values than EFT values in lower frequency bands (Slow-5 and Slow-4). 2) RT-ALFF magnitudes in each sub-frequency band were greater for the SRT than those for the EFT. 3) The RT-ALFF in the Slow-4 of the EFT was found to be correlated with the RT-ALFF in the Slow-5 of the SRT for both two visits, but no consistently significant correlation was found between the same frequency bands.ConclusionsThese findings reveal good test-retest reliability for conventional measurements and for the RT-ALFF of RTV. The RT-ALFF presented frequency-dependent similarities across tasks. All of our results reveal the presence of different frequency structures between the two tasks, and thus the frequency-dependent characteristics of different tasks deserve more attention in future studies.
Highlights
Reaction time variability (RTV) refers to variations in an individual’s response speed across trials during engagement in a stimulus-response task
1) The RT-amplitude of low frequency fluctuation (ALFF) of the Slow-5/4/3 and conventional measurements of RT-standard deviation (SD) and RT-coefficient of variation (CV) showed moderate to high levels of test-retest reliability
2) RT-ALFF magnitudes in each sub-frequency band were greater for the simple reaction task (SRT) than those for the Eriksen flanker task (EFT). 3) The RT-ALFF in the Slow-4 of the EFT was found to be correlated with the RT-ALFF in the Slow-5 of the SRT for both two visits, but no consistently significant correlation was found between the same frequency bands. These findings reveal good test-retest reliability for conventional measurements and for the RT-ALFF of RTV
Summary
Reaction time variability (RTV) refers to variations in an individual’s response speed across trials during engagement in a stimulus-response task. Used measurements of individual RTV include the standard deviation (SD) and coefficient of variation (CV) [9] Neither of these can depict periodic fluctuations in RT over time. Castellanos and colleagues (2005) were the first to convert the time course of the RT of the Eriksen flanker task (EFT) into frequency domains and to identify periodic fluctuations in RT [10]. Their results indicate that RT fluctuations reach a peak amplitude of approximately 0.05 Hz and importantly that the peak amplitude of the RT of children with ADHD is significantly higher than that of controls [10]. RT-ALFF patterns of inattentive symptoms may be frequency-dependent [11]
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