Deficits in visual-motor coordination and/or fine motor dexterity are often present in pediatric neurological and neurodevelopmental conditions and may adversely affect performance on tests with motor demands. This consideration is relevant when interpreting discrepant scores across Wechsler Intelligence Scale for Children, Fifth Edition (WISC-V) Processing Speed Index (PSI) subtests, specifically Symbol Search and the more motorically demanding Coding. Although test developers maintain that motor ability is unlikely to significantly impact Coding performances, clinicians often consider whether uneven WISC-V PSI subtest scores (Coding<Symbol Search) may in part be attributed to motor-related difficulties, when indicated. This has important clinical implications, as WISC-V Coding may then be omitted or substituted when calculating FSIQ. Thus, the present study aims to evaluate the role of motor task deficits in uneven PSI subtest scores in a sample of clinic-referred youth.

Participants were 238 children and adolescents (MAge=10.62 years; 65.5% male; 60.5% white) referred for neuropsychological assessment. All participants completed the Coding and Symbol Search subtests of the WISC-V and at least one of two motor tasks: the Beery-Buktenica Developmental Test of Visual-Motor Integration (VMI) and the Grooved Pegboard (GP). To evaluate patterns of functioning, we determined the frequencies of patients who demonstrated uneven PSI subtest performances (defined in this study as a Coding scaled score [ss] at least 3-points lower than that of Symbol Search) and/or normative weaknesses (i.e., Standard Score [SS] below 80, per recommendations from the American Academy of Clinical Neuropsychology) on motor tasks. A chi-square test of independence was used to evaluate associations between uneven PSI performance and the presence/absence of motor weaknesses. Among those with uneven PSI performance, a one-way ANOVA was used to examine whether PSI subtest difference scores varied as a function of motor performance group (No Weakness=0, VMI Weakness Only=1, GP Weakness Only=2, Weaknesses on Both=3).

Of the 238 participants, 28 (11.0%) displayed normative weaknesses on the VMI only, 43 (16.9%) displayed weaknesses on the dominant-GP only, and 18 (7.1%) displayed weaknesses on both tasks. On the WISC-V, 56 participants (23.5%) exhibited uneven PSI subtest performance (Coding<Symbol Search), with 21 (37.5%) of those participants displaying at least one normative motor weakness. Chi-square analyses indicated no significant association between the presence/absence of motor skill weakness and uneven PSI subtest performance, (X2 (3) = 5.79, p = .122). Among those with uneven PSI performance, Coding/Symbol Search difference scores were not significantly associated with motor performance group (F(3,55) = 1.26, p = .297).

These findings suggest that while patients with uneven WISC-V Coding and Symbol Search scores may also display motor task deficits, these deficits are not significantly associated with uneven performances overall. Additionally, of the participants with uneven PSI subtest scores, the majority did not exhibit normative weaknesses on motor tasks. Therefore, clinicians may be overcorrecting for a motoric cause of uneven performance and underappreciating the potential unevenness a child demonstrates in processing speed. Future studies should evaluate the role of other neurocognitive factors, such as working memory, in this score discrepancy pattern.