Masood, Salik
(2022)
An investigation of sensory integration across the autistic spectrum using multisensory illusions.
MPhil thesis, University of Nottingham.
Abstract
In order to have a comprehensible representation of scenes and events, the human brain must combine information from different sensory sources. Integration of visual, tactile, and proprioceptive information is considered vital to this process as it underpins the subjective sense of self and body ownership; which has been linked to the development of social processes such as empathy and imitation. This issue has been investigated using sensory illusions and suggests that individuals with autism are less prone to multimodal illusions due to atypical sensory integration, i.e. they tend to rely on a single sensory source more, rather than integrating concurrent sources of information (i.e. over-reliance on proprioception). Studies that have measured illusion susceptibility and ownership, especially in regards to body ownership have provided mixed results. Therefore, it is important to understand and advance our knowledge on illusion susceptibility using sensory illusions.
In order to conduct this research, it was first required to identify typically developing individuals who have high and low autism tendencies using the Autistic Spectrum Quotient (Baron-Cohen et al., 2001b). This was important because previous research has indicated behavioral similarities between individuals with high autism traits and those with high-functioning autism (HfA). The primary aim of this research was to investigate whether individuals with high autism traits and those with a diagnosis of autism perform in a similar way in terms of illusion susceptibility and illusion ownership, as previous research has stated differences in illusion susceptibility (Palmer et al., 2013; Paton et al., 2012).
Three different multisensory illusions were presented to all the participants using the MIRAGE mediated reality device. This device enables the experimenter to presentvarious illusions on the participants’ limbs, where manipulations can be applied over the hand. Illusion ownership and susceptibility statements were used to measure the subjective experience of the participants, whereas, finger localization tasks were used as an objective measure of susceptibility to the illusions.
Experiments One and Two investigated the effects of crawling skin illusion which is a visual illusion that can produce somatosensory sensations without any tactile input- as this illusory percept manipulates an individual’s existing knowledge regarding their own hand (McKenzie & Newport, 2015). The results indicated that individuals with high AQ scores (compared to low AQ, Experiment 1) and HfA (compared to typically developing adults, Experiment 2) showed less influence of visual context. They reported reduced effects of the illusion, which could be due to a higher reliance on top- down knowledge. However, all the participating groups showed high ownership of their hand as viewed through the MIRAGE.
Participants with high and low autism traits (Experiment 3) and adults with HfA as well as typically developing adults (Experiment 4) were presented with the finger stretching illusion (Newport et al., 2015) which involves an interplay of vision, touch and proprioception. The results obtained showed that participants across all groups had high ownership score, however, only the low AQ group and the control group were susceptible to the illusion. An estimation task was used to measure whether participants embodied the illusion, adults with high AQ scores and HfA showed superior performance during the estimation task, however, the control groups estimates were significantly further, hence, making them more susceptible to the visuo- tactile manipulation.
The third illusion measured visuo- proprioceptive integration in individuals with high and low AQ scores (Experiment 5) and adults with HfA as well as typically developing adults (Experiment 6). The task involved participants estimating the location of their hidden index finger under different conditions i.e. participants were able to view their hand or the view of their hand was hidden. Participants first took part in an adaptation procedure (Newport & Gilpin, 2011) which involved relocating the hand from where the participants last saw their hand. This was to test whether individuals with high autism traits and those with HfA showed superior proprioceptive performance in estimating their index finger location. The results indicated that the HfA and the high AQ groups were less affected by the visuo- proprioceptive misalignment caused during the adaptation procedure. Participants with low AQ scores and the typically developing group’s estimates were more influenced by the visual input.
In conclusion, none of the experiments found strong evidence of over-reliance on proprioception in individuals with high AQ or those with HfA, however, they showed superior estimation abilities than the control group. My findings suggest that there is a preference, but not over- reliance on, for proprioception as opposed to visual and tactile information in the high AQ scoring group and the HfA group. Over- relying on a single sensory source, while not integrating multisensory information could have a detrimental impact on sensory processing and social interactions, especially the visuo- tactile system as it enables an individual to experience the environment through touch and understand everyday sensations such as temperature, pressure, itching, pain, etc. For future research, this research highlights the importance of studying the visual-tactile domain. An individual’s ability to process tactile input is related to their ability to visually discriminate and to have appropriate body awareness, which in turn helps in developing emotional security, academic learning, and social skills that are some of the core issues often reported in individuals with autism (Corbett et al., 2009; Happé & Frith, 2006; Piek & Dyck, 2004; Tager-Flusberg, 2008). More so, research investigating such processes should involve the whole spectrum of autism rather than focusing on a smaller subset.
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