Associations between rapid auditory processing of speech sounds and specific verbal communication skills in autism

Abstract

Introduction: The ability to rapidly process speech sounds is integral not only for processing other's speech, but also for auditory processing of one's own speech, which allows for maintenance of speech accuracy. Deficits in rapid auditory processing have been demonstrated in autistic individuals, particularly those with language impairment. We examined rapid auditory processing for speech sounds in relation to performance on a battery of verbal communication measures to determine which aspects of verbal communication were associated with cortical auditory processing in a sample of individuals with autism.

Methods: Participants were 57 children and adolescents (40 male and 17 female) ages 5-18 who were diagnosed with an Autism Spectrum Disorder (ASD). Rapid auditory processing of speech sounds was measured via a magnetoencephalographic (MEG) index of the quality of the auditory evoked response to the second of two differing speech sounds ("Ga" / "Da") presented in rapid succession. Verbal communication abilities were assessed on standardized clinical measures of overall expressive and receptive language, vocabulary, articulation, and phonological processing. Associations between cortical measures of left- and right-hemisphere rapid auditory processing and verbal communication measures were examined.

Results: Rapid auditory processing of speech sounds was significantly associated with speech articulation bilaterally (r = 0.463, p = 0.001 for left hemisphere and r = 0.328, p = 0.020 for right hemisphere). In addition, rapid auditory processing in the left hemisphere was significantly associated with overall expressive language abilities (r = 0.354, p = 0.013); expressive (r = 0.384, p = 0.005) vocabulary; and phonological memory (r = 0.325, p = 0.024). Phonological memory was found to mediate the relationship between rapid cortical processing and receptive language.

Discussion: These results demonstrate that impaired rapid auditory processing for speech sounds is associated with dysfunction in verbal communication in ASD. The data also indicate that intact rapid auditory processing may be necessary for even basic communication skills that support speech production, such as phonological memory and articulatory control.

Keywords: auditory processing; autism spectrum disorder; communication; language; magnetoencephalography; speech.

Figure 1

Schematic of rapid speech sound processing measurement. Individual participant responses to single speech sounds (“ga” or “da”) at 0–300 ms were projected onto the 300–600 ms time window to generate an interpolated waveform (dotted lines). This dotted line represents a predicted response to two different speech sounds presented 300 ms apart by assuming identical responses to each sound. These predicted waveforms were generated for each participant as a standard of comparison for their intact rapid processing response. For the 300–600 ms window, each participant’s predicted response to the second sound was compared to their actual response (solid lines) to the second sound by computing cross correlations. The clear response to both sounds (top drawing) demonstrates intact rapid processing and is characterized by high agreement between predicted and actual responses. The impaired rapid processing response (bottom drawing), illustrated by an absent response to the second sound, results in low agreement.

Figure 2

Examples of waveforms demonstrating intact (Top) and impaired (Bottom) rapid speech sound processing. The waveform on the top demonstrates a clear, timely response to both speech sounds (100 ms after stimulus presentation) in a participant with intact rapid processing. In contrast, the bottom waveform demonstrates impaired rapid processing. This participant’s initial response is present and clear at approximately 100 ms; however, the response to the second speech sound is delayed, prolonged, and poorly defined. This impaired response to the second speech sound corresponds to a low z-transformed CC value (z = 0.02) relative to the higher value (z = 0.67) for the intact waveform (top).

Figure 3

Scatterplots of rapid speech sound processing and verbal communication performance. Significant associations were identified between bilateral rapid processing and articulation, whereas associations between rapid processing and phonological memory and expressive vocabulary and language were limited to the left hemisphere.