“Thinking in Speech” Amongst Individuals with Autism Spectrum Disorder (ASD): The Relations Between Inner Speech and Short-Term Memory, Executive Functioning, and Clinical Features

Background:

“Inner speech” is critical for flexible thinking and behaviour (Zelazo, 2004).  Yet, individuals with ASD sometimes report that their thoughts consist predominantly of visual images, rather than speech (Hurlburt, Happé, & Frith, 1996), which may contribute to their limitations in cognitive and behavioural flexibility (Russell, Jarrold, & Hood, 1999).  However, recent experimental studies of inner speech in ASD have produced mixed results, with some studies observing appropriate use (e.g., Williams, Happé, & Jarrold, 2008; Winsler et al., 2007) and others observing reduced use (e.g., Holland & Low, 2009; Wallace et al., 2009).

Objectives:

The present study combined techniques and tasks used across several of the above studies.  This allows us to clarify whether the discrepant results have been due to: a) the different techniques employed to measure inner speech use (“similarity effects” versus “articulatory-suppression”; see below), and/or; b) the different domains of cognition explored in each of the studies (e.g., memory versus executive functioning).  Also, the study is the first to explore the association between inner speech use and severity of ASD features. 

Methods:

Twenty high-functioning adults with ASD and 20 age- and ability-matched comparison participants (recruited as part of an on-going study in our laboratory) will complete two experimental tasks.  Data collection is ongoing.  Six participants with ASD and 4 (well-matched) comparison participants have been tested.

1) Inner speech in short-term memory: A serial recall task (similar to that used by Williams et al., 2008) was employed.  In one set of trials, pictorial items had similar sounding names (phonological trials) and in another set they did not (control trials).  If participants encode items using inner speech, rather than visual imagery, recall of phonological trials will be significantly poorer than recall of control trials [a “phonological similarity effect” (PSE)].

Participants completed each set of trials twice, once under baseline conditions and once under concurrent articulatory-suppression (repeating the word “Tuesday” throughout the presentation of stimuli).  Articulatory-suppression selectively disrupts inner speech.  If participants employ inner speech to mediate the experimental task, articulatory-suppression should reduce recall of control trials only (relative to baseline presentation), resulting in the disappearance of the PSE.  

2) Inner speech in planning: Participants will complete the Tower of London task with and without articulatory-suppression.  If participants employ inner speech to mediate their planning, performance will be significantly poorer under conditions of articulatory-suppression than under baseline conditions. 

Results:

On the serial recall task, both groups show a large PSE under baseline conditions (Cohen’s d = 2.31 amongst ASD participants; 2.10 amongst comparison participants), but not under articulatory-suppression (d = 0.13 amongst ASD participants; 0.18 amongst comparison participants).  Amongst ASD participants, size of the PSE was strongly (negatively) associated with severity of ASD features, as measured by the Autism-spectrum Quotient (r_s = -.70).  Tower of London data is yet to be collected.

Conclusions:

We will discuss the implications of the research results for a) our theoretical understanding of whether (or in what circumstances) people with ASD employ inner speech, and b) intervention strategies designed to remediate behavioural and cognitive inflexibility.