Transitive Inference in Children with Autism Spectrum Disorder and Limited Verbal Ability

Background: Memory functioning in Autism Spectrum Disorder (ASD) follows a characteristic pattern, including good rote memory (Kanner, 1943) and cued recall (Bowler, Matthews & Gardiner (1997).  Impairments have been demonstrated in the free recall of semantically related items (Tager-Flusberg, 1991), and the recognition of combinations of features (Bowler et al., 2008, 2014).  This suggests a difficulty with relational binding- the ability to encode items and events, and the relationships between them, to allow for adaptive use of the information (Opitz, 2010). 

Objectives: Studies of relational binding in ASD have mainly been carried out with verbally able adults, using verbalisable stimuli (e.g. words).  The current study aimed to extend these findings to lower-functioning individuals with ASD.  A non-verbal transitive inference paradigm (if A > B, and B > C, then A > C) was adapted (Maclean et al., 2008).  Typical adults tend to use a relational strategy during these tasks (Moses, Villate, and Ryan, 2006), whereas non-human animals tend to use an associative, pair-by-pair strategy (von Fersen et al, 1991), suggesting that language may be important in the construction of relational strategies. 

Methods: 24 children with ASD and limited verbal ability (AD), and 24 typically developing children (TD), matched on non-verbal IQ.  Pairs of stimuli were presented in hierarchical order; participants were required to find the “higher-ranked” of the two by touching it onscreen; feedback was given after each trial regarding their choice.  A test phase was then presented, comprising two trial types: adjacent pairs of stimuli already seen during the training phase, and re-pairings of the stimuli into novel combinations of non-adjacent stimuli (e.g. B-D).  Participants must use information from the adjacent training pairs to infer the higher-ranked stimulus of a non-adjacent pair, which requires the flexible processing of the relations between pairs.  The current study predicted no group differences during the test phase where adjacent stimuli were presented, whereas participants with ASD would be impaired in the non-adjacent pairs, because of the flexible relational binding required to solve those trials.  An additional task in which participants were shown all the stimuli on the screen and asked to “put them in order” was included to determine participants’ awareness of the hierarchy. 

Results: Performance during training in the transitive inference task was > 70% for all participants.  During the test phase no group differences in performance were found between the two trial types (adjacent and non-adjacent); indicating that the level of performance was comparable between the groups, regardless of trial type.  However, there was a significant group difference in the stimulus hierarchy awareness task, t(46) = -3.0, p = .004, with impaired performance in the AD group. 

Conclusions: Results indicate that children with ASD and limited verbal ability can solve a task requiring transitive inference.  However, these participants also appear to be less aware of the stimulus hierarchy, which may imply that they are using an associative rather than a relational strategy, and therefore support the idea of the importance of language in the construction of relational strategies.