Abstract
Learning and synesthesia are profoundly interconnected. On the one hand, the development of synesthesia is clearly influenced by learning. Synesthetic inducers – the stimuli that evoke these unusual experiences – often involve the perception of complex properties learned in early childhood, e.g., letters, musical notes, numbers, months of the year, and even swimming strokes. Further, recent research has shown that the associations individual synesthetes make with these learned inducers are not arbitrary, but are strongly influenced by the structure of the learned domain. For instance, the synesthetic colors of letters are partially determined by letter frequency and the relative positions of letters in the alphabet. On the other hand, there is also a small, but growing, body of literature which shows that synesthesia can influence or be helpful in learning. For instance, synesthetes appear to be able to use their unusual experiences as mnemonic devices and can even exploit them while learning novel abstract categories. Here we review these two directions of influence and argue that they are interconnected. We propose that synesthesia arises, at least in part, because of the cognitive demands of learning in childhood, and that it is used to aid perception and understanding of a variety of learned categories. Our thesis is that the structural similarities between synesthetic triggering stimuli and synesthetic experiences are the remnants, the fossilized traces, of past learning challenges for which synsethesia was helpful.
Highlights
When synesthesia first came under scientific scrutiny in the 1800s, a fairly common view was that synesthetic experiences were learned, and served to help synesthetes with tasks such as mathematics, remembering sequences, and many other learning challenges (e.g., Galton, 1881; Calkins, 1893; Jewanski et al, 2011)
We use the standard terminology of “inducer” to refer to the stimuli that trigger synesthetic experiences, and “concurrent” to refer to these experiences themselves, and we generally refer to types of synesthesia by the common formula inducer–concurrent
If synesthesia is the result of a hyperconnected brain, why do almost all the connections begin with objects of formal instruction? If grapheme–color synesthesia develops from an innate link between shapes and colors (Maurer et al, 2012), why do adult grapheme–color synesthetes not report colors for all shapes? At the very least, genetic and neurological accounts need to be able to answer these questions, and we see no way of doing so without a theory that places learning at the forefront of synesthetic development
Summary
When synesthesia first came under scientific scrutiny in the 1800s, a fairly common view was that synesthetic experiences were learned, and served to help synesthetes with tasks such as mathematics, remembering sequences, and many other learning challenges (e.g., Galton, 1881; Calkins, 1893; Jewanski et al, 2011). There has been a flurry of research on the profound impact of learning on synesthesia, and several prominent researchers argue that learning and conceptual factors are critical components of synesthetic development (cf Simner et al, 2009a; Jürgens and Nikolic, 2012; Deroy and Spence, 2013a; Witthoft and Winawer, 2013). Some of those who formerly denied the role of learning appear to have reversed their stance (cf., Cytowic and Eagleman, 2009). We use the standard terminology of “inducer” to refer to the stimuli that trigger synesthetic experiences, and “concurrent” to refer to these experiences themselves, and we generally refer to types of synesthesia by the common formula inducer–concurrent (e.g., time–space synesthesia refers to time being perceived by the synesthete in a spatial form)
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