University of Sussex
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Effects of synaesthetic colour and space on cognition

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posted on 2023-06-07, 16:21 authored by Clare Jonas
A small proportion of the population experiences synaesthesia, in which a stimulus (the inducer) causes a percept (the concurrent) in its own sensory domain, and in another domain, or another sub-domain of the same sense. This thesis is concerned with synaesthesiae in which numbers and letters take on spatial locations or colours. In Paper 1, alphabet-form synaesthesia is investigated. The majority of alphabet forms belonging to native English speakers are straight, horizontal lines. Any breaks, gaps or direction changes tend to fall in line with the parsing of the Alphabet Song. Synaesthetes show greater inducer-concurrent consistency than controls; their spatial attention can also be cued by letters. In Paper 2, synaesthetes with alphabet forms and number forms took part in case or parity judgement tasks. Synaesthetes behave similarly to controls on the parity judgement tasks (i.e. both groups categorise small numbers more quickly with the left hand than the right hand). In the case judgement task neither group shows an equivalent effect for letters of the alphabet. Controls alone show a QWERTY effect, in which letters on the left of the keyboard are categorised more quickly with the left hand than the right hand. A large-scale study of letter-colour and number-colour synaesthesia in Paper 3 shows that correlations between letter frequency and saturation, alphabetical position and saturation, magnitude and luminance, magnitude and saturation are seen when luminance and saturation are considered as across-hue and within-hue variables. Papers 4 and 5 are concerned with synaesthetic bidirectionality, wherein concurrents can elicit implicit mental representations of their inducers. While no experiment in these papers shows evidence for bidirectionality, this may be due to the presentation of concurrent colours as graphemes instead of colour blocks. However, priming effects appear during a synaesthetic Stroop task when numbers are presented as digits, suggesting a stronger role for digits than other notations in number-colour synaesthesia.


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