Abstract
The last few years have seen the publication of a number of studies by researchers claiming to have induced “synaesthesia,” “pseudo-synaesthesia,” or “synaesthesia-like” phenomena in non-synaesthetic participants. Although the intention of these studies has been to try and shed light on the way in which synaesthesia might have been acquired in developmental synaesthestes, we argue that they may only have documented a phenomenon that has elsewhere been accounted for in terms of the acquisition of sensory associations and is not evidently linked to synaesthesia. As synaesthesia remains largely defined in terms of the involuntary elicitation of conscious concurrents, we suggest that the theoretical rapprochement with synaesthesia (in any of its guises) is unnecessary, and potentially distracting. It might therefore, be less confusing if researchers were to avoid referring to synaesthesia when characterizing cases that lack robust evidence of a conscious manifestation. Even in the case of those other conditions for which conscious experiences are better evidenced, when training has been occurred during hypnotic suggestion, or when it has been combined with drugs, we argue that not every conscious manifestation should necessarily be counted as synaesthetic. Finally, we stress that cases of associative learning are unlikely to shed light on two highly specific characteristic of the majority of cases of developmental synaesthesia in terms of learning patterns: First, their resistance to change through exposure once the synaesthetic repertoire has been fixed; Second, the transfer of conditioned responses between concurrents and inducers after training. We conclude by questioning whether, in adulthood, it is ever possible to acquire the kind of synaesthesia that is typically documented in the developmental form of the condition. The available evidence instead seems to point to there being a critical period for the development of synaesthesia, probably only in those with a genetic predisposition to develop the condition.
Highlights
In Prometheus, Poem of Fire (1910), Scriabin attempted to communicate to the audience the synaesthetic experience of colored musical keys that he claimed to have enjoyed for most of his life
As the innate character of synaesthesia is itself controversial, the label “acquired synaesthesia” is potentially misleading: After all, all synaesthesia might be acquired. This is why here we consider that the real question is that of artificially induced synaesthesia—a label which maintains the contrast with the spontaneous forms of synaesthesia that have been documented to develop in children, and encompass cases of training, including following the use of certain conversion devices, as well as drugs or hypnosis
In contrast to Kelly’s (1934) earlier study, we find subjective reports suggestive of what Howells (1944, p. 101) tentatively calls pseudo-synaesthesia: “The same S volunteered that he saw a clear image of the screen of the chromatoscope, and of the color normally associated with a given tone, when this tone was sounded while the eyes were closed or in the darkened room.”
Summary
In Prometheus, Poem of Fire (1910), Scriabin attempted to communicate to the audience the synaesthetic experience of colored musical keys that he claimed to have enjoyed for most of his life. Synaesthetes have been shown to exhibit significantly different performance, as a group, in a series of behavioral tests, such as the speeded congruency test presented by Eagleman et al (2007), designed to capture the involuntary and robust elicitation of conscious concurrents by specific inducers. The repertoire of inducer-concurrent pairings—for instance, the precise shade of color elicited by different musical notes—is usually not determined before an individual reaches the age of 9 years of age, after which time it appears to remain surprisingly consistent over the rest of the individual’s lifetime (e.g., Simner et al, 2009; Niccolai et al, 2012a). Some individuals claim to have lost their synaesthesia after their teenage years, but, of all the adult synaesthetes who have been tested in contemporary research, most remember having it since www.frontiersin.org
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