Many studies have shown that autism is associated with atypical perceptual functioning, in vision as well as in audition. In the field of audition, these perceptual particularities include a hypo- or hyper-sensitivity to certain sounds, and also sensory capacities above average. It seems well established that the perception of simple sounds (pitch discrimination and categorization of pure tones) is finer in individuals with high functioning autism (HFA) than in typically developing (TD) persons. For more complex sounds, there is no consensus: some authors have claimed that temporal processing is altered while others failed to find differences between individuals with HFA and TD persons. Auditory sensory memory has been given less attention in the literature, but one study employing simple sounds suggests that it may be overdeveloped in individuals with HFA. To our knowledge, there are no studies on the sensory memory of complex sounds in autism.
The aim of this study is to determine if adults with HFA differ from TD adults with respect to the perception and memory of meaningless and physically complex auditory stimuli, consisting of wideband noise. Preliminary results are presented here.
The study currently includes 10 participants with HFA and 14 TD persons. The chronological ages range from 16 to 28 years for the participants with HFA, and from 18 to 27 years for the TD individuals. Two tasks are proposed to the participants.
In the "Perception" task, one has to detect, within white noise acting as a masker, a signal consisting of a repeating, brief segment of white noise (varied from trial to trial). The independent variable is the signal-to-masker (S/M) intensity ratio. An adaptive procedure is used to measure the S/M ratio for which the signal is just detectable.
In the "Memory" task, one has to judge whether a noise (varied from trial to trial) is periodic or not. An adaptive procedure similar to that employed in the Perception task is used to measure the longest period for which periodicity is still detectable.
In the Perception task, our current results show no significant difference in performance between participants with HFA and TD persons. In the Memory task, by contrast, performance is significantly worse in the participants with HFA than in the TD participants.
Our study suggests that autism has a stronger impact on auditory sensory memory than on auditory perception. However, further investigations are needed to clarify the characteristics of auditory memory in autism. We used here acoustic stimuli which were very complex both spectrally and temporally. Simpler stimuli and different tasks will have to be employed in the subsequent studies.
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