Behavioural and Neuroimaging Investigation of Two Stages of Metaphor Comprehension Using the Metaphor Interference Effect in Individuals with Autism Spectrum Disorder

  • Author / Creator
    Chouinard, Brea D
  • Background Individuals with autism spectrum disorder (ASD) are reported to have difficulty understanding figurative language, such as metaphors, but emerging evidence suggests that such problems are associated with structural language impairments and not an ASD diagnosis. However, even when figurative meaning is successfully generated, accuracy and response time (RT) differences persist. Examining the individual stages of metaphor comprehension may help explain these differences. The metaphor interference effect (MIE), when metaphors require longer than control sentences to be judged as literally true or false, indicates interference resulting from co-existence of the metaphorical and literal meanings at the integration stage. Thus, the metaphorical meaning must be suppressed (selection stage) before the literal meaning can be isolated and judged. MIE tasks can therefore be used to evaluate integration and selection stages. Neuroimaging can also elucidate possible origins of behavioural differences, with recent advances focusing on the contribution of networks and network coordination to cognitive skills. Objective This doctoral dissertation had four specific objectives: 1) to establish the presence of the MIE in response to spoken metaphors; 2) to determine whether the integration stage of metaphor comprehension occurred via simultaneous or serial processing in individuals with ASD; 3) to investigate the selection stage by comparing the size of the MIE between individuals with and without ASD; and 4) to compare the functional neural underpinnings of the MIE between individuals with and without ASD. Methods For the first objective, participants without ASD completed either the spoken (n = 30) or written (n = 29) MIE task and the presence of the MIE was evaluated within each condition. For the next two objectives, groups of individuals with (n = 12) and without ASD (n = 12) completed the spoken MIE task. Within each group, the presence of the MIE was evaluated and, between groups, the size of the MIE was assessed. For the fourth objective, data from the spoken MIE task were collected in a 1.5T MRI scanner. Data were analyzed using three converging approaches to assess group differences in brain activation during the task: i) group level activation maps were created to compare areas and amount of activation; ii) within (metaphors>scrambled metaphors) and between (ASD>controls and controls>ASD) groups contrast maps were created to evaluate activation during the selection/suppression stage; and iii) graphical modeling (Cribben et al., 2012) was applied to quantify functional connectivity during the task for each group. Results The first objective was met, whereby the MIE was found in both written and spoken conditions (α = .05). With respect to the second and third objectives, simultaneous processing characterized the integration stage of metaphor comprehension in both individuals with and without ASD (α = .05). However, the ASD group had more difficulty with selection/suppression than controls as reflected in more errors in judging metaphors than other false sentences (α = .05). Finally, the fourth objective was achieved, such that individuals with ASD exhibited more activation than controls in similar regions of interest, which coincided with reduced functional connectivity. The graphical analysis differentiated the groups for the metaphor condition, despite between group similarities for control sentences. Specifically, in the selection stage condition and specific to individuals with ASD, there were fewer overall connections than the control group, reduced cortical-subcortical connectivity, and persistent subcortical-subcortical connectivity even when connections involving a cortical node were reduced. Conclusion These findings support the notion that individuals with ASD and intact structural language generate figurative meanings during metaphor comprehension, although difficulties arise in the selection/suppression stage (i.e., suppression). The neuroanatomical evidence demonstrates that, compared to controls, individuals with ASD have greater activation in regions related to verbal memory (thalamus), semantic associations (medial temporal gyrus), and basic visual processing (middle occipital gyrus) for the MIE task. Functional connectivity analysis using graphical modeling further differentiated the groups, for the metaphorical sentences only, on three metrics: overall connectivity, cortical-subcortical connectivity, and persistence of subcortical-subcortical connectivity. These findings support the notion that individuals with ASD and intact structural language understand metaphors, but that there are differences in processing with respect to suppression of unintended meanings and coordination of cortical and subcortical brain activity. The reduced cortical-subcortical interconnectedness in the ASD group compared to controls may reflect global differences in cognitive control pathways.

  • Subjects / Keywords
  • Graduation date
    2016-06:Fall 2016
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Faculty of Rehabilitation Medicine
  • Specialization
    • Rehabilitation Science
  • Supervisor / co-supervisor and their department(s)
    • Cummine, Jacqueline (Communication Sciences and Disorders)
    • Volden, Joanne (Communication Sciences and Disorders)
  • Examining committee members and their departments
    • Williams, Diane (External)
    • Fouad, Karim (Physiotherapy)
    • Kim, Ester (Communication Sciences and Disorders)
    • Westbury, Chris (Psychology)