During the discussion on visual attention, it has been mentioned that autistic patients tend not to look at the salient stimuli in the environment, but instead at the background scene. In addition to visual inattention, Teder-Salejarvi, Pierce, Courchesne, & Hillyard (2005) discussed that people with autism have other sensory abnormalities and these include the auditory domain.
Parallel to the visual inattention, the hypothesized reason for this is their difficulty to attend to sound signals amidst noisy environment. They are either hyposensitive to acoustic cues to the point of completely ignoring sounds (Dawson, et.al., 1998: Kemper, et. al., 1998; cited in Teder-Salejarvi, et. al., 2005) or hypersensitive to such signals (Baranek, et. al., 1997; Bettison, 1996; cited in Teder-Salejarvi, et. al., 2005). Temple Grandin, a person with autism, pictured her experience of confusion when two people are talking at the same time. She described her ears as a microphone that picks up all sounds, all in equal intensity making it impossible to screen out the background noise and to understand the speech of other people in such noisy place. This failure to accurately tune spatial attention to a single sound, or in some cases, tuning too broadly, according to Teder-Salejarvi and colleagues, impedes orienting which then decreases accuracy of target detection and causes information to be missed. As a consequence, and as Courchesne, et.al. (1994; cited in Teder-Salejarvi, et. al., 2005) reports, autism is also related to the “developmental failure to engage in joint social attention” (p. 221).
Since no studies had tested the hypothesis that sound source attribution and selection may be involved in autism using neurofunctional techniques, Teder-Salejarvi, et. al. (2005) used event-related potential (ERP) measures to compare and characterize the tuning auditory spatial attention of adults with autism and those who are “healthy” (p.222), the latter as the control group. According to literature (i.e.Hansen, et. al., 1980; Hillyard, et. al., 1995; Teder, et. al., 1993; cited in Teder-Salejarvi, et. al., 2005), recorded ERP from normal subjects had revealed that enhanced negative wave in the auditory cortex (N1) is usually elicited when sounds are being attended to. As more attention is driven to the sound— thus in consequence the more its accuracy is improved— the more that the amplitude of the negative wave in the auditory cortex also increases. On the other hand, target detection involves a longer latency of ERP which is labeled P3 (Teder-Salejarvi, et. al., 2005) which according to Martineau, et.al. (1984) and Picton, et. al. (1999; cited in Teder-Salejarvi, et. al., 2005) is associated with the updating of working memory once target is being recognized.
To explore the mystery behind, that is whether the autistic patients would “display abnormalities in the selective tuning of attention to one sound source in the presence of multiple competing sources” (p.222), Teder-Salejarvi, et. al. (2005) had planned the research well and measured related factors in the experiment and employed necessary measures such as EEG recording, sensory discrimination testing specifically frequency and spatial discrimination tasks, topographical mapping, MRI anatomical measurements, and of course, the ERP analysis. Details of each of these are described in their paper, also each of these are essential to investigate where the problem, in case hypothesis is supported, comes from. For instance, through MRI anatomical measurements, this study has revealed that participants with autism had 7% less temporal gray matter compared to normal (Teder-Salejarvi, et. al., 2005); in some studies reduced volume of the left planum temporal (Rojas, et. al., 2001; cited in Teder-Salejarvi, et. al., 2005), and an abnormality in the white matter of the temporal lobes (Bamea-Goraly, et. al., 2004; cited in Teder-Salejarvi, et. al., 2005).
Before discussing the results further, just to describe the method of the study, there were 8 speakers that produce sounds altogether. The first one is place in the front center (0
) of the participant and the three succeeding speakers are placed one after another, 6 apart from each other. While the rest of the speakers at the right periphery of the listener (72
78
84 and 90). Noise burst were present with an intensity level of 76 dB. The onset asynchronies of stimulus were varied between 90 and 270ms (Teder-Salejarvi, et. al., 2005). As for the procedure, the participants were asked to attend, either to the central speaker or to the rightmost one; they have to ignore stimuli coming from other speakers and press a button to an infrequent high-pitched burst of noise, which is the target stimulus. Ten rounds of 1092 stimuli were presented in each condition! Teder-Salejarvi, et. al. (2005) did not also forget the architectural design’s influence to perceiving sound and conducted the experiment in an “acoustically shielded room” (p.223).
Supporting the hypothesis, the results of the study showed that adults with autism disorder have diminished ability to attend to a significant stimulus from its sound source among the many outer sources of sound in the environment. It has also been found that autistic adults have small “fronto-centrally distributed N1” (p.226) while P3 wave were broadly distributed compared to the control group who had negative enhancement of the N1 and a widely distributed P3 (Teder-Salejarvi, et. al., 2005). The amplitude of the N1 waves produced either by the center or periphery of the listener, did not differ significanlty ( y[6]= 1.19). The P3’s amplitude, based on the locations of the stimulus, whether it was placed on the S1 or S8, have no significant difference.
The study shows that auditory-related abnormalities in autism might be due to the impairment in sound source attribution (Teder-Salejarvi, et. al., 2005). These abnormalities related to auditory, aside from hypersensitivity and hyposensitivity to sounds, may also include confusion, aversive reactions to sounds, and abnormality in orienting and shifting one's attention as a response to sound signals. Finally, the results of the study implies that difficulty of sound localization might be a factor as to how autistic infants react to and learn, both from the social and non-social sounds. Also if this difficulty of autistic patients may have is apparent in a noisy environment, a simplifier and less noisy setting may lessen such difficulty.
Teder-Salejarvi, W. A, Pierce, K. L., Courchesne, E., & Hillyard, A. A. et. al. (2005). Auditory spatial localization and attention deficits in autistic adults. Cognitive Brain Research. 23. 221-234. Retrieved from Microsoft Academic Research.
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