A longitudinal study of grapheme-color synesthesia in childhood:6/7 years to 10/11 years

Grapheme-colour synaesthesia is a condition characterised by enduring and consistent associations between letter/digits and colours. This study is the continuation of longitudinal research begun by Simner, Harrold, Creed, Monro and Foulkes (2009) which aimed to explore the development of this condition in real time within a childhood population. In that earlier study we randomly sampled over 600 children and tested them aged 6/7 years and 7/8 years. We identified the child synaesthetes within that cohort and measured their development over 1 year, in comparison to a group of nonsynaesthetic children with both average and superior memories. We were able to show the beginnings of a developmental progression in which synaesthetic associations (e.g. A = red) mature over time from relatively chaotic pairings into a system of fixed consistent associations. In the current study we return to this same population three years later when participants are now 10/11 years. We used the same paired-association memory task to determine the synaesthetic status of our participants and to also establish synaesthetes’ inventories of grapheme-colour associations. We compared their inventories to those from age 6/7 year and 7/8 years to examine how synaesthesia matures over time. Together with earlier findings, our study shows that grapheme-colour synaesthesia emerges with a protracted lineal trajectory, with 34% of letters/digits fixed at age 6/7 years, 48% fixed at 7/8 years and 71% fixed at 10/11 years. We also show several cases where synaesthesia is not developing in the same time-frame as peers, either because it has died out at an older age, or because it was slower to develop than other cases. Our study paints the first picture of the emergence of synaesthesia in real-time over four years within a randomly sampled population of child synaesthetes

Is synaesthesia an X-linked trait with lethality in males?

In previous research the inheritance patterns of synaesthesia (eg experiencing colours from graphemes) has been studied and it was concluded that synaesthesia is most likely to be the outcome of a single gene passed on the X chromosome in a dominant fashion. In addition, it has been reported that the female-male ratio of synaesthetes is as high as 6 : 1 and the families of synaesthetes contain more female than male members. This raises the possibility that the gene may be associated with lethality in males. In this study we replicate and extend previous research by investigating the female-male ratio and inheritance patterns in a large sample of synaesthetic families (N = 85). We were able to verify the authenticity of grapheme-colour associates in at least one proband from each family using internal consistency. As before, our results show a female-male bias and are broadly consistent with an X-linked dominant mode of inheritance. However, there was no evidence of male lethality (eg synaesthetes are just as likely to give birth to sons as to daughters). Moreover, our female-male ratio of synaesthetes within families was 2 : 1-considerably lower than previous estimates. We speculate that men may be more reluctant to disclose synaesthesia than women (indeed, our female -male ratio based on self-referral was 3.7 : 1). Finally, we discuss how the genotype may give rise to the phenotype in terms of changes in synaptogenesis or plasticity extending into childhood, to be subsequently shaped by the environment

Do children with grapheme-colour synaesthesia show cognitive benefits?

Grapheme-colour synaesthesia is characterized by conscious and consistent associations between letters and colours, or between numbers and colours (e.g., synaesthetes might see A as red, 7 as green). Our study explored the development of this condition in a group of randomly sampled child synaesthetes. Two previous studies (Simner & Bain, 2013, Frontiers in Human Neuroscience, 7, 603; Simner, Harrold, Creed, Monro, & Foulkes, 2009, Brain, 132, 57) had screened over 600 primary school children to find the first randomly sampled cohort of child synaesthetes. In this study, we evaluate this cohort to ask whether their synaesthesia is associated with a particular cognitive profile of strengths and/or weaknesses. We tested our child synaesthetes at age 10–11 years in a series of cognitive tests, in comparison with matched controls and baseline norms. One previous study (Green & Goswami, 2008, Cognition, 106, 463) had suggested that child synaesthetes might perform differently to non-synaesthetes in such tasks, although those participants may have been a special type of population independent of their synaesthesia. In our own study of randomly sampled child synaesthetes, we found no significant advantages or disadvantages in a receptive vocabulary test and a memory matrix task. However, we found that synaesthetes demonstrated above-average performance in a processing-speed task and a near-significant advantage in a letter-span task (i.e., memory/recall task of letters). Our findings point to advantages for synaesthetes that go beyond those expected from enhanced coding accounts and we present the first picture of the broader cognitive profile of a randomly sampled population of child synaesthetes

A is for apple: the role of letter-word associations in the development of grapheme-colour synaesthesia

This study investigates the origins of specific letter-colour associations experienced by people with grapheme-colour synaesthesia. We present novel evidence that frequently observed trends in synaesthesia (e.g. A is typically red) can be tied to orthographic associations between letters and words (e.g., “A is for apple”), which are typically formed during literacy acquisition. In our experiments, we first tested members of the general population to show that certain words are consistently associated with letters of the alphabet (e.g. A is for apple), which we named index words. Sampling from the same population, we then elicited the typical colour associations of these index words (e.g. apples are red) and used the letter → index word → colour connections to predict which colours and letters would be paired together based on these orthographic-semantic influences. We then looked at direct letter-colour associations (e.g., A → red, B → blue…) from both synaesthetes and non-synaesthetes. In both populations, we show statistically that the colour predicted by index words matches significantly with the letter-colour mappings: that is, A → red because A is for apple and apples are prototypically red. We therefore conclude that letter-colour associations in both synaesthetes and non-synaesthetes are tied to early-learned letter-word associations

The MULTISENSE test of lexical-gustatory synaesthesia: an automated online diagnostic

Lexical–gustatory (LG) synesthesia is an intriguing neurological condition in which individuals experience phantom tastes when hearing, speaking, reading, or thinking about words. For example, the word “society” might flood the mouth of an LG synesthete with the flavor of fried onion. The condition is usually verified in individuals by obtaining verbal descriptions of their word–flavor associations on more than one occasion, separated by several months. Their flavor associations are significantly more consistent over time than are those of controls (who are asked to invent associations by intuition and to recall them from memory). Although this test reliably dissociates synesthetes from nonsynesthetes, it suffers from practical and methodological limitations. Here we present a novel, automated, online consistency test, which can be administered in just 30 min in order to instantly and objectively verify LG synesthesia. We present data from two versions of our diagnostic test, in which synesthetes report their synesthetic flavors either from a hierarchical set of food categories (Exp. 1) or by specifying their basic component tastes (sweet, salty, bitter, etc.). We tested the largest sample of self-declared LG synesthetes studied to date and used receiver operating characteristic analysis to assess the discriminant power of our tests. Although both our methods discriminated synesthetes from controls, our second test (Exp. 2) has greater discriminatory power with a threshold cutoff. We suggest that our novel diagnostic for LG synesthesia has unprecedented benefits in its automated and objective scoring, its ease of use for participants and researchers, its short testing time, and its online platform

Does synaesthesia protect against age-related memory loss?

Synaesthesia is known to be linked to enhanced episodic memory abilities, across a variety of stimuli and tests, but the evidence has tended to come from younger adults. This enhanced cognitive ability in early adult life, together with the known brain-related differences linked to synaesthesia (e.g., in both grey and white matter structure), makes it an ideal candidate for exploring the notion of ‘reserve’. That is, synaesthetes may be able to utilise additional cognitive and/or neural resources to mitigate against the effects of age-related decline. This was explored in a 2x2 design contrasting age (young, old) against presence/absence of synaesthesia in two different studies: recognition memory for digits, snowflakes and music; and visual associative learning. Synaesthesia and age had independent, non-interacting, effects on memory ability suggesting that, whilst synaesthetes show a memory advantage and maintain this advantage in later life, the presence of synaesthesia is not able to act as a reserve to protect against the effects of ageing. On our tasks, the benefit of having synaesthesia (enhancing memory) was of a similar magnitude to the effects of age (impairing memory); in other words, elderly synaesthetes present with ‘youthful’ memory abilities. It is important for future research on elderly cohorts to consider the presence of synaesthesia as an individual difference

Does synaesthesia age? Changes in the quality and consistency of synaesthetic associations

Developmental grapheme-colour synaesthesia is a rare condition in which colours become automatically paired with letters or digits in the minds of certain individuals during childhood, and remain paired into adulthood. Although synaesthesia is well understood in younger adults almost nothing is known about synaesthesia in aging. We present the first evidence that aging desaturates synaesthetic colours in the minds of older synaesthetes, and we show for the first time that aging affects the key diagnostic measure of synaesthesia (consistency of colours over time). We screened ~4000 members of the general population to identify grapheme-colour synaesthetes, targeting both younger and older adults. We found proportionally fewer older than younger synaesthetes, not only because fewer older people self-reported the condition, but because fewer also passed the objective diagnostic test. We examined the roots of this apparent decline in grapheme-colour synaesthesia, finding that the internal mental colours of synaesthetes become less saturated in older subjects, and importantly, that low-saturated colours are linked with test-failure. We discuss what these findings mean for a novel field of aging and synaesthesia research, in terms of the lifespan development of synaesthesia and how best to diagnose synaesthesia in later life

Vocal communication of simulated pain

While evidence suggests that pain cries produced by human babies and other mammal infants communicate acoustic cues to pain intensity, whether the pain vocalisations of human adults also encode pain intensity, and which acoustic characteristics influence listeners’ perceptions, remains unexplored. Here, we investigated how trained actors communicated pain by comparing the acoustic characteristics of nonverbal vocalisations expressing different levels of pain intensity (mild, moderate, and severe). We then performed playback experiments to examine whether vocalisers successfully communicated pain intensity to listeners, and which acoustic characteristics were responsible for variation in pain ratings. We found that the mean and range of voice fundamental frequency (F0, perceived as pitch), the amplitude of the vocalisation, the degree of periodicity of the vocalisation, and the proportion of the signal displaying nonlinear phenomena all increased with the level of simulated pain intensity. In turn, these parameters predicted increases in listeners’ ratings of pain intensity. We also found that while different voice features contributed to increases in pain ratings within each level of expressed pain, a combination of these features explained an impressive amount of the variance in listeners’ pain ratings, both across (76%) and within (31-54%) pain levels. Our results show that adult vocalisers can volitionally simulate and modulate pain vocalisations to influence listeners’ perceptions of pain in a manner consistent with authentic human infant and nonhuman mammal pain vocalisations, and highlight potential for the development of a practical quantitative tool to improve pain assessment in populations unable to self-report their subjective pain experience