The current theory of internal noise inside the brain being a key factor in autism spectrum disorder (ASD) has been challenged by theoretical and empirical studies. Other scholars argue that the problem is actually a person’s problem to filter out external noises. In a study conducted at the University of Rochester in New York, researchers used mathematical models in order to understand the presence of varying levels of external noise to see whether or not ASD patients would experience changes in internal noise and external noise filtering (Park et al., 2017). But first, it is important to understand what internal noise is and how we may distinguish internal and external noise.
Since the late 1980s, psychologists have shifted to understanding possible reasons why adults are able to perform better at complex auditory tasks than young children (Buss & Hall, 2006). Adults, although they seemed to be listening just as much as the children did, seemed to perform better by noticing speech in a commotion (Nábĕlek & Robinson, 1982), detecting a hidden tone while someone is speaking (Maxon & Hochberg, 1982), frequency discrimination (Jensen & Neff, 1993), and intensity discrimination (Jensen & Neff, 1993). Some suggested that adults were strategizing better than children do or that children simply have too short of attention spans to be motivated to actually focus. However, the plurality of research showed that these hypotheses do not explain the entire truth; when given short tasks, adults and children would be engaged similarly, using similar listening strategies.
It was only until psychologists such as Bruce Schneider when scientists began looking at the neurological basis of auditory filtering (Schneider et al., 1992). “Internal noise” describes generally any type of inaccuracies in the neural representations inside the brain of the outside environment. In contrast, “external” noise describes any obstacles in the outside environment of stimuli reaching a person before they are able to process it. From then on, scientists such Lynne Werner of the University of Washington, showed how children’s listening abilities are able to improve in age as the effects of internal noise on the listeners decreased.
As Park et al. explain, both external noise from the environment and internal noise from the nervous system may play different roles in a person’s experience of the world. Children, who are not as adapted to all the external noises in the world, are more stimulated by the noises of people passing by when going through a crowd. In contrast, adults have learned to pick out specific words from experience. The ability to filter out noise from their environment, and thus their internal responses to these stimuli, may be a clue to how autistic patients may react to different situations. In an fMRI study in 2011, children with ASD had more variability in how they reacted to the same stimuli outside. In comparison, children without ASD were able to get used to these situations once they were exposed a couple of times. This suggests that although they were exposed to the same circumstances over and over again, each situation was still freshly new to ASD patients. As a result, many ASD patients also exhibit rigid habits, such as only eating food that they recognize (Kinnaird et al., 2019).
However, as Kinnaird et al. note, adults with ASD are able to learn to overcome their challenges by practicing different habits to adapt to new situations. Currently, it is still unclear about how internal noise, how we process our external stimuli, affects making decisions. In a study by Coskun et al., the team targeted the cortical network which is important in sensory processing and memory making. They hypothesized that ASD patients may have different neural networks that do not inhibit or excite them as a normal person would. Using magnetoencephalography (MEG), they measured brain responses to magnetic taps on 17 ASD patients’ fingers. They then measured their responses in different parts of the brain and the variation between different responses. As a result, they found that the contralateral somatosensory cortex had the most stimulus response to the tactile stimuli, but there was no significant variability in the response to the stimulation.
Consequently, future research with behavioral therapy may be improved by focusing on how ASD patients process their reactions to stimulation, not just how they immediately react to just touch or small stimuli. Focusing on how ASD patients learn to process what stimuli are important and how they focus and adapt may provide clues for how ASD patients may be better included in classrooms and workplaces.
Citations
Buss, E., Hall, J. W., 3rd, & Grose, J. H. (2006). Development and the role of internal noise in detection and discrimination thresholds with narrow band stimuli. The Journal of the Acoustical Society of America, 120(5 Pt 1), 2777–2788. https://doi.org/10.1121/1.2354024
Coskun MA, Varghese L, Reddoch S, Castillo EM, Pearson DA, Loveland KA, Papanicolaou AC, Sheth BR. Increased response variability in autistic brains? Neuroreport. 2009 Nov 25; 20(17):1543-8.
Jensen JK, Neff DL. Development of basic auditory discrimination in preschool children. Psychol Sci. 1993;4:104–107.
Kinnaird, E., Norton, C., Pimblett, C., Stewart, C., & Tchanturia, K. (2019). Eating as an autistic adult: An exploratory qualitative study. PloS one, 14(8), e0221937. https://doi.org/10.1371/journal.pone.0221937
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Olsho LW, Koch EG, Carter EA, Halpin CF, Spetner NB. Pure-tone sensitivity of human infants. J Acoust Soc Am. 1988 Oct; 84(4):1316-24.
Schneider BA, Trehub SE. Sources of developmental change in auditory sensitivity. In: Werner LA, Rubel EW, editors. Developmental Psychoacoustics. American Psychological Association; Washington, DC: 1992. pp. 3–46.
