Abstract
In synaesthesia, stimuli such as sounds, words or letters trigger experiences of colors, shapes or tastes and the consistency of these experiences is a hallmark of this condition. In this study we investigate for the first time whether there are age-related changes in the consistency of synaesthetic experiences. We tested a sample of more than 400 grapheme-color synaesthetes who have color experiences when they see letters and/or digits with a well-established test of consistency. Our results showed a decline in the number of consistent grapheme-color associations across the adult lifespan. We also assessed age-related changes in the breadth of the color spectrum. The results showed that the appearance of primary colors (i.e., red, blue, and green) was mainly age-invariant. However, there was a decline in the occurrence of lurid colors while brown and achromatic tones occurred more often as concurrents in older age. These shifts in the color spectrum suggest that synaesthesia does not simply fade, but rather undergoes more comprehensive changes. We propose that these changes are the result of a combination of both age-related perceptual and memory processing shifts.
Highlights
Synaesthesia is a relative rare variation of human experience which involves the automatic activation of an unusual concurrent sensation in response to an inducing stimulus, for example a color experience in response to a letter printed in black
Using the method introduced by Simner et al (2006, 2009), Rothen and Meier (2010), and Simner and Bain (2013), we investigated in a sample of more than 400 grapheme-color synaesthetes whether the number of consistent grapheme-color associations changes across the adult lifespan
For letters, post hoc tests showed that the young group differed from both the middle and older groups, and no other effect. These findings suggest that rather than consistency per se, it is the bandwidth of synaesthesia that declines across the adult lifespan
Summary
Synaesthesia is a relative rare variation of human experience which involves the automatic activation of an unusual concurrent sensation in response to an inducing stimulus, for example a color experience in response to a letter printed in black. The consistency of the synaesthetic associations has been proposed as a defining characteristic of synaesthesia (Baron-Cohen et al, 1987; Cytowic and Eagleman, 2002; Rich et al, 2005; Asher et al, 2006; Simner et al, 2006). The question whether consistency may change across the lifespan is relevant for those types of synaesthesia which involve color as a concurrent, because there is clear evidence for a decrease of chromatic sensitivity in older age (Knoblauch et al, 2001; Kinnear and Sahraie, 2002; Paramei, 2012). As automatic retrieval from memory seems to be age-invariant (Meier et al, 2013) the consistency of synaesthetic perception may not be prone to age-related decline. There is evidence that late-blind synaesthetes maintain their synaesthetic visual percepts for years after blindness, synaesthesia can even persist with little or no natural sensory experience and independent from continuous associative learning (Steven and Blakemore, 2004)
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