Synaesthesia and autism: Different developmental outcomes from overlapping mechanisms?

Abstract

Synaesthesia, a mixing of the senses, is more common in individuals with autism. Here, we review the evidence for the association between synaesthesia and autism with regard to their genetic background, brain connectivity, perception, cognitive mechanisms and their contribution to exceptional talents. Currently, the overlap between synaesthesia and autism is established most convincingly at the level of alterations in sensory sensitivity and perception, with synaesthetes showing autism-like profiles of sensory sensitivity and a bias towards details in perception. Shared features may include a predominance of local over global connectivity in the brain. When autism and synaesthesia co-occur in the same individual, the chance of developing heightened cognitive and memory abilities is increased. We discuss how the same theoretical models could potentially explain both conditions. Given the evidence, we believe the phenotypical overlap between autism and synaesthesia has been established clearly enough to invite future research to confirm overlapping mechanisms.

Language evolution: examining the link between cross-modality and aggression through the lens of disorders

“…With regards to the uncontrollable nature of synaesthetic experiences (i), it should be stressed that synaesthesia results in automatic, involuntary experiences in another sensory or cognitive domain. Concerning cross-modality (ii), as noted by Cuskley & Kirby [33, p. 871], ‘synesthetes should be viewed as super cross-modal associators, with unusually strong, stable, and specific cross-modal biases.’ Synaesthetes exhibit a variety of advantages when it comes to memory, including an enhancement of both visual and verbal memory [114,115], as well as much better performance on episodic memory ([116]; see also [117] for a recent review). These advantages seem to have a positive effect on their language abilities, too.…”

“…It is thus not surprising that synaesthetes would have superior understanding of unfamiliar sound-symbolic foreign words, as found in Bankieris & Simner's [128] experiment, suggesting that sound symbolism relies on the type of cross-modal integration that characterizes synaesthesia to an exaggerated degree. Overall, the enhanced cross-modality in synaesthesia has been ascribed to the hyper-connectivity of a synaesthete's brain ([114,115,117,129]; more on this in §5).…”

“…For instance, synaesthetic experiences have been linked to (and seemingly triggered by) stressful experiences, as in the association found between grapheme–colour synaesthesia and post-traumatic stress disorder (PTSD) [133,134], as well as an association found between synaesthesia and anxiety (e.g. [117,135]). 5…”

“…In other words, each of these conditions is complex, with comorbidities, and each grades into neurotypicity. Beginning with synaesthesia, it has been reported to be comorbid with ASD, with more than chance probability [117,137–139]. ASD shares with synaesthesia bias towards detail processing, as well as atypical sensory sensitivity, such as hyper- or hypo-sensitivity to certain sounds, textures or smells, visual stimuli, and pain and temperature [73,139].…”

Perceptual processing links autism and synesthesia: a twin study

“…A link between synesthesia and ASC is further supported by studies showing that synesthetes have elevated autistic traits, and, similar to individuals with ASC (Ben-Sasson et al, 2009), an altered sensory processing style (Van Leeuwen et al, 2020;Ward, et al, 2017a & b). The latter includes both altered sensory sensitivity (hyperor hypo-sensitivity) and an increased attention to details.…”