International Meeting for Autism Research: Bottom-up or Top-Down? : An Investigation of Perceptual Processing In ASD Using Dichotic Pitch

Bottom-up or Top-Down? : An Investigation of Perceptual Processing In ASD Using Dichotic Pitch

Saturday, May 14, 2011: 2:45 PM
Elizabeth Ballroom D (Manchester Grand Hyatt)
1:15 PM
V. Lodhia1, C. Nelumdeniya1, J. P. Hamm1, B. W. Johnson2, J. Brock2 and M. J. Hautus1, (1)Research Centre for Cognitive Neuroscience, Department of Psychology, University of Auckland, Auckland, New Zealand, (2)Macquarie Centre for Cognitive Science, Macquarie University, Sydney, Australia
Background: Various visual studies have indicated bottom-up and top-down processing difficulties in Autistic Spectrum Disorder (ASD). If the auditory system is analogous to the visual system, then we would expect to see similar impairments in the auditory domain in bottom-up and top-down tasks. Time-shifted Dichotic Pitch (DP) (Dougherty et al., 1998) is an effective way to measure bottom-up and top-down mechanisms. Our previous research using DP demonstrated the presence of Object Related Negativity (ORN) and Positive 400 (P400) components in the auditory event related potential (AERP) (Hautus & Johnson, 2005). An ORN is elicited when two auditory objects are concurrently perceived – indexing perceptual segregation of concurrent sounds (Alain, Arnott & Picton, 2001; Hautus & Johnson, 2005; Johnson, Hautus, Duff & Clapp, 2007). The ORN occurs irrespective of attention and is driven by the sequence of the incoming auditory information (i.e. bottom-up) (Alain et al., 2001; Hautus & Johnson, 2005; Johnson, et al., 2007).The P400 component is indexed when participants are actively attending to stimuli and is thought to reflect decision-making processes about the sound heard in concurrent stream-segregation tasks. The P400 is a controlled process that uses prior knowledge about the auditory information to extract meaning about incoming auditory data (i.e. top-down) (Alain et al., 2001; Hautus & Johnson, 2005; Johnson, et al., 2007).

Objectives: To see whether components of interest (ORN & P400) are indexed in the auditory AERP of ASD individuals using DP stimuli, and to determine whether or not there are differences in amplitude and/ or latency for these components between ASD and control individuals.

Methods: AERPs were determined for 32 adult participants (16 ASD, 16 matched controls), listening to DP stimuli. A mixture of lateralized DP, centralized DP, target (two objects), and control (one object) stimulus types were presented. Participants indicated via button press whether one or two auditory objects were heard in each trial.

Results: Only the control group obtained an ORN, which occurred at a latency of 150 – 250 ms. The P400 component was indexed at a latency of 400 – 500 ms for both groups (p < 0.0005). Both groups showed significant differences in amplitude between target and control conditions for the P400 (p < 0.0005).

Conclusions: The lack of ORN for the ASD group suggests difficulty in bottom-up processing, related to segregating concurrent sound objects using time-based cues. The presence of the P400 component indicates no deficits in top-down processing for the ASD group. The findings from this study will expand our knowledge on how the brain systematically organises simultaneous incoming auditory information and allow for greater understanding about perceptual processing in ASD.

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