Influence of Motor Function on a Continuous Performance Test with Suspected Attention Deficit/Hyperactivity Disorder

Clinicians and researchers have expressed concern about the potential confound of psychomotor skills on Continuous Performance Test variables commonly used in AD/HD assessments. Several studies have addressed this relationship but with limitations. Evidence for this potential influence as well as evidence of slow processing and motor speed in samples of children with known attention and motor deficits are demonstrated in the research. Due to the increasing rate of referrals for AD/HD diagnoses, the increasing use of CPTs, and the lack of knowledge about the influence of psychomotor functioning on these measures, an examination of this relationship is considered necessary to address the use of CPTs in AD/HD evaluations. The sample consisted of 99 children with suspected attention deficits between the ages of 6 and 16 years. Psychomotor functioning was assessed by the WISC-IV Processing Speed Index and the Beery VMI. Attention was measured with the WISC-IV Working Memory Index and subscales of the parent-rated BASC-2. Results of this study revealed that psychomotor and attention measures on the WISC-IV related to and accounted for variance in T.O.V.A. variables to a moderate degree. Stepwise regressions indicated the WISC-IV Processing Speed Index predicted both Response Time and Response Time Variability. In contrast, another measure of psychomotor skills, the Beery VMI, did not predict T.O.V.A. Variables. Interestingly, the Working Memory Index accounted for variance in Commission Errors, a measure of impulsivity, but not Omission Errors, a measure of sustained attention. Also, unexpected, differences among primary T.O.V.A. variables were not found across sub-samples when grouped by BASC-2 scores.
These significant but modest results suggest that when evaluating a child for AD/HD, clinical consideration of the influence of psychomotor skills, as measured by the WISC-IV, on T.O.V.A. Response Time and Response Time Variability is warranted. Furthermore, the use of both the WISC-IV Working Memory Index and the T.O.V.A. is useful for assessing varying components of attention, such as focused and sustained attention.