The Role of the Visual System During Synaesthesia

Swanandi Gawde, M. Optom

Assistant Professor, ITM Institute, Navi Mumbai, India

 

Synaesthesia is a voluntary experience from the human brain, and it originates from neurology. Synaesthesia is a rare condition where certain stimuli trigger unusual sensations, allowing the brain to process multiple senses at once. Individuals may see colours while listening to music or feel shapes when tasting foods showcasing the intricate interplay of sensory perception and how our brain can intertwine different senses. ⁽¹⁾

The human brain processes information through discovery, signalling, and understanding. Senses relay data to the brain, which interprets the surrounding world. However, individuals with synaesthesia process information differently, as their brains use multiple areas simultaneously. Visual tasks are significant in this condition, allowing them to associate colours with different frequencies and recognise object properties like colour, contrast, and size.

Types of Synaesthesia

There are different types involved during synaesthesia, such as word recognition, music recognition, colour recognition, and verbal intelligence. ⁽²⁾ Epidemiological data indicate that, among the five senses, vision plays a central part in synaesthesia. ⁽³⁾ 80% and 97% of synesthetes report colour-related synaesthesia on the visual sense of synaesthesia, like touch-smell, and audible and tactile. There are different types of visual synaesthesia present. Seeing colours when reading letters or figures is known as grapheme-colour synaesthesia and passing colours when hearing sounds is known as sound-colour synaesthesia. Seeing figures as specific shapes or spatial arrangements, nominated as figures, forms synaesthesia. ⁽⁴⁾

Most of the synesthetic phenomena are visual. Previous studies explain that vision is not important for the development of synaesthesia, but functional vision development from birth plays an important role in the experience of synaesthesia. Congenitally blind people fail to develop synaesthesia. People who get blind in the late-life stage can experience at least hallucinations. ⁽⁵⁾

The mortal brain continuously receives signals from different sensitive modalities. Synaesthesia has drawn much scientific attention in recent times due to both the interest in anomalous brain marvels and the perceptivity these marvels can give into normal mechanisms of perception and cognition.

Figure 1: Images Showing Different Types of Synaesthesia
(a) Grapheme-Colour Synaesthesia
(b) Cross-Path of the Scene
(c) Sound-Colour Synaesthesia

Hypothesis of Synaesthesia

There are two major hypotheses regarding the neural mechanisms that give rise to synaesthesia. The first view, generally termed the cross-activation hypothesis, suggests that excessive neural connections between adjacent cortical areas underline synesthetic experiences. Originally, this view postulated that grapheme-colour synaesthesia occurs because of excessive neural connections between colour-selective area V4 and the area of synaesthesia. Posterior temporal grapheme area, the second view, generally called the disinhibited-feedback hypothesis, suggests that synaesthesia results from a ‘malfunctioning’ mechanism that fails to inhibit the crosstalk between brain areas normally inhibited in non-synesthetic brains. ⁽⁶⁾

Earlier studies demonstrated that synaesthesia is a familial trait and suggested that it is more common in women than in men. ⁽⁷⁾ Subsequent large-scale studies have suggested that the prevalence of synaesthesia might be as high as 1 in 20 across all forms and 1 in 100 for grapheme-colour synaesthesia. ⁽⁸⁾

Conclusion

Synaesthesia plays a major role in the daily routine of human beings to perform various tasks. Visual attention plays a very important role during the process of Synaesthesia. The two or more tasks together while looking at some object, the person can perceive the colours, size, and shape at the same time. Synaesthesia also helps to understand the depth of aesthetic images with a short duration.

 

References

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