Relationships Among Lexical Processing Speed, Autistic Symptomology, and Linguistic Competence

Background:  Eye movements are closely time-locked to the occurrence of spoken words that refer to contextual objects (Cooper, 1974; Tanenhaus, Spivey-Knowlton, Eberhard, & Sedivy, 1995), implicating saccade speed as an index of spoken lexical information processing speed.  Processing speed can be conceptualized as a measure of efficiency in performing basic cognitive operations.  When processing is slow, information may be lost, affecting both success on tasks and the amount of information that can be successfully encoded. Several researchers have associated autism with specific disruption in rapid auditory listening and/or processing of spoken language with automaticity (Welsh, Rodrigues & Edgar, 2010; Kuhl et al., 2005).  A possible implication of this deficit may be abnormal language development.

Objectives:  We utilize a new Lexical Processing Eye-tracking Task (LPET), to test response time to verbally referenced targets, as measured by eye movements.  Target words are presented in several conditions (with and without linguistic competitors or Phonemic Cohorts) x 3 environmental Noise conditions, in order to examine individual differences in lexical processing and the relationship between speed, autistic symptomology, and linguistic competence.  

Methods:  Thirty-five children (mean age = 10.1, range 7.0-11.8) and 34 adult native speakers of English with no history of autism, developmental disorders or sensory impairments were assessed on the LPET as well as standardized language, IQ and social measures.  The LPET was conducted using a monitor based eye-tracking system.  Participants were asked to find images that map to prerecorded spoken words.  Target images were presented on a 2x2 array of photographic images, randomized for position on the screen and controlled for lexical frequency.  Saccades to targets were reinforced by animations that were triggered by fixation on the Target.  Saccade time to Target was compared to performance on subtests from the Comprehensive Assessment of Spoken Language (CASL), and the child Social Responsiveness Scale, a measure that may be used to assess the continuum of social impairment in the general population.(Constantino & Todd, 2003).  

Results:  Children and adults showed sensitivity to the cohort conditions, suggesting the LPET is a valid measure of online processing.  Results indicate a relationship between response time on the LPET and autistic symptomology, as reflected by children with slower reaction times exhibiting significantly higher parent rated SRS scores. Children, but not adults, showed a relationship between receptive and productive language skills (Synonyms, Grammatical Morphemes and Sentence Completion) and LPET performance, indicating that online lexical processing speed relates to higher level language skills during development.  

Conclusions:  We introduce a language based processing speed assessment which is an ecologically valid method to determine individual differences in lexical processing.  Since referents are fixated on in close temporal proximity to when they are heard, the LPET is a natural task, not confounded by motor or reading skills or compliance with complex task requirements.  These LPET results demonstrate the sensitivity of the assessment to autistic traits and linguistic competence in children, consistent with theories that suggest disturbances in auditory attention and speech parsing for children with autism (Constantino et al, 2007; Welsh et al, 2010).