Auditory perception

Background

Individuals with Autism Spectrum Disorders (ASD) commonly report an increased awareness of environmental sounds, abnormal loudness perception, and difficulty in filtering or "hearing out" the important auditory information in background noise.

Auditory sensory phenomena have been associated with ASD since autism was first identified in 1943. Recent studies from a UK clinical database indicate that these phenomena may be present in over 60% of individuals with ASD. Difficulties with auditory perception are clinically prominent and can be disabling especially for children, who may become distressed and unable to understand speech in a noisy classroom environment, and therefore find themselves at an educational and social disadvantage to their peers.

Although individuals with ASD and their carers frequently report auditory perception problems, they have received relatively little attention by researchers recently, especially with a view to identifying the possible underlying mechanisms. This is especially true of studies on the perception of speech in adverse acoustic environments, such as classrooms or playgrounds.

Speech-in-noise perception

We recently compared the speech communication abilities of a group of individuals with ASD and age/IQ-matched control participants, who listened to sentences presented in different types of background noises. Specifically, the signal-to-noise ratio required for 50% speech intelligibility, known as the speech reception threshold (SRT), was measured for both groups in five background noise conditions and two noise level conditions. Individuals with ASD were found to be significantly poorer at identifying key words in the sentences than the control participants, especially for background noises that contained spectral and/or amplitude modulations (i.e. frequency or temporal "dips"). In other words, they were not as good as the control participants at selectively listening for the target speech in frequency and/or temporal dips present in the background noise, a process that is sometimes called "dip listening". The size of the SRT difference measured was between 2-4 dB, which though not numerically large, is perceptually significant and may result in as much as a 40-60% change in speech perception performance.

Frequency selectivity and temporal processing

Frequency selectivity refers to our ability to separate or "hear out" the frequency components in a complex sound, and to improve the speech-to-noise ratio (SNR). Temporal resolution refers to the ability to detect rapid changes in acoustic stimuli with time, and is a very important dimension in speech perception since speech sounds fluctuate over time, and much of the information is carried in the changes themselves. We are testing the idea that these two processes, that underlie dip listening ability, might be abnormal in ASD and might be the basis of the poorer-than-normal speech-in-noise perception abilities.

Significance

The studies underway will result in advances in the understanding of ASD by: (1) increasing the knowledge of the pathophysiology associated with autism, by specifying the mechanisms that underlie auditory processing disorders; (2) extending the current psychological theories that address the perceptual and attentional aspects of autism, by determining whether enhanced perceptual discrimination abilities underlie the local processing bias observed in ASD; and (3) establishing the importance of sensory processing in ASD, leading to a better understanding of the communication abilities of individuals with autism.

Related reading

Alcántara, J.I., Weisblatt, E.J., Moore, B.C.J., & Bolton, P.F. (2004). Speech-in-noise perception in high-functioning individuals with autism or Asperger's syndrome. Journal of Child Psychology and Psychiatry, 45, 1107-1114.

Plaisted, K.C., et al. (2003). Towards an understanding of the mechanisms of weak central coherence: experiments in configural learning and auditory perception. Philosophical Transactions of the Royal Society London, Biological Sciences, 358, pp.375-386.

Boatman, D., Alidoost, M., Gordon, B., Lipsky, F., & Zimmerman, W. (2001). Tests of auditory processing differentiate Asperger's syndrome from high-functioning autism, Annals of Neurology, 50, S95.

Khalfa, S., Bruneau, N., Rogé, B., Georgieff, N., Veuillet, E., Adrien, J.-L., et al. (2001). Peripheral auditory asymmetry in infantile autism. European Journal Of Neuroscience, 13, pp.628-632.