Identification of Differential Predictors of ADHD Subtypes Using Laboratory Procedures
Grip, Dana Richardson
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A laboratory task shown to differentiate the behavior of hyperactive (Spontaneously Hypertensive rats) and non-hyperactive rats (Wistar-Kyoto rats) was adapted for use with humans. The task allowed for exploring a Dynamic Developmental Theory (DDT) hypothesis (Sagvolden, Johansen, Aase, & Russell, 2005) that responding to fixed interval (FI) reinforcement schedules should differ as a function of ADHD symptomatology (Johansen, Killeen, & Sagvolden, 2007). The translation of the paradigm to humans utilized a computer task that generated reinforcement conditions specified by the DDT and similar to those used with rats. The participants were 152 undergraduates above the age of 18 who completed the computer task, a screening questionnaire, and a widely used ADHD self-report form. Hypotheses were formulated from the DDT concerning differential responding on the computer task as a function of ADHD symptomatology and were tested with respect to mean comparisons between a Hyperactive Impulsive (HI) group, an Inattentive (I) group, and a control group characterized by low HI and I scores. In addition, correlational procedures were used to assess how the two primary symptom dimensions of ADHD (hyperactive-impulsive and inattentive) related to computer task performance. The dependent variables, derived from behavior on the computer task, included button sampling (i.e., frequency of response and total clicks per trial), response variability (i.e., entropy), and rate of learning (i.e., beta). The results of correlational analyses showed a significant association between ADHD-I symptomatology and button sampling behavior, and no other significant findings. The results of a chi-square analysis revealed a significant difference for button sampling for both ADHD-I and for ADHD-HI compared to control participants. ANOVA and t-test results revealed no differences across groups for any of the dependent variables. The results are discussed with respect to (a) the usefulness of the computer task as a diagnostic tool, and (b) the fact that the FI schedule performance of humans may relate more strongly to Inattentive symptoms than it does to Hyperactive/Impulsive symptoms.