Exploring the Role of Verbal Mediation in Executive Functioning in Children with Autism

Background: Children with autism spectrum disorder (ASD) exhibit deficits in executive function (EF; Bennetto et al. 1993), including planning abilities (Hill, 2004). However, it is unclear what accounts for these deficits. One hypothesis is that language use influences EF (Zelazo et al., 1997). In typical development, EF performance is facilitated by verbal mediation (Diamond et al., 2002) and disrupted by articulatory suppression (Lidstone et al., 2010). In the autism literature, however, the link between EF and language is inconclusive (Joseph et al., 2005; Russell-Smith et al., 2014; Williams et al., 2012).

Objectives: The present study aimed: (1) to examine the role of verbal mediation in a complex EF task, the Tower of London, by comparing performance of typically developing (TD) children and children with ASD, and (2) to examine whether performance disruptions arise from suppression of verbal mediation or imposition of general dual-task demands.

Methods: Fourteen TD children and 14 children with ASD were matched on age and non-verbal IQ. The TD group had significantly better language skills than the ASD group (see Table 1). Children were administered a computerized Tower of London task under three conditions: no secondary task (NST), motor suppression task (MST), and articulatory suppression task (AST). Participants moved beads to match the model shown on the screen and were instructed to plan their moves prior to moving the first bead. Total number of moves, time to first move (planning time), and time to complete the trial after the first move (execution time) were recorded for each trial.

Results: ANOVAs (2x3) were conducted separately for each dependent variable with group (TD vs. ASD) as the between-groups variable and condition (NST vs. MST vs. AST) as the within-group variable. A main effect of condition was observed for total number of moves (p=0.004) and execution time (p<0.01), where MST and AST required significantly more moves and execution time than NST (all p<0.05). However, MST and AST did not differ significantly (ps>0.05), and groups did not differ significantly. For planning time, analyses revealed a main effect of condition (p=0.04), where MST took the longest time, and AST took the least (p=0.03), and a main effect of group (p=0.04) where children with ASD took significantly less time to plan than TD. There were no significant interaction effects.

Conclusions: The results revealed that the ASD group was impacted by verbal suppression in a planning task, similar to the TD children. This is contrary to previous work that suggested articulatory suppression does not impede EF performance in ASD (Russell-Smith et al., 2014) due to lack of verbal mediation. However, findings also indicated both groups of children were similarly disrupted by articulatory and motor suppression, suggesting that EF disruption in an articulatory suppression task is due to general dual-task processing demands, rather than verbal mediation.  Although children with ASD took significantly less time to plan than the TD children, these cognitively-matched groups performed similarly in total number of moves and execution time.