Synaesthesia is linked to more vivid and detailed content of autobiographical memories and less fading of childhood memories

Grapheme-Color Synesthesia and Its Connection to Memory

Synesthesia is the involuntary association of different senses, where individuals experience one sensory modality in response to the stimulation of another. For example, a synesthete may perceive colors when reading certain numbers or associate specific tastes with particular words. Synesthesia manifests differently for individuals grouping the condition in subcategories such as grapheme-color, sound-to-color, lexical-gustatory, mirror-touch, and much more. This review covers grapheme-color synesthesia, described as the involuntary perception of specific colors or color associations when seeing or thinking about certain letters, numbers, or symbols. This review explores the performance of declarative memory tasks in individuals with grapheme-color synesthesia. A comprehensive search of controlled trials published between 2014 to 2024 was conducted through PubMed and Google Scholar databases. In Google Scholar, the search terms grapheme-color synesthesia, grapheme-color synaesthesia, and memory were used. In PubMed, additional MeSH (Medical Subject Headings) terms were used which included grapheme-color synesthesia and memory. Studies that measured declarative memory and grapheme-color synesthesia were included yielding a total of seven controlled trials. Grapheme-color synesthetes demonstrated advanced performance in declarative memory tasks; however, this may not have any clinical significance. Grapheme-color synesthetes demonstrated a better performance in their ability to recall colors, but not as much recalling words. Synesthetes were shown to outperform non-synesthetes in visual memory tasks. Synesthetes showed better recall of paired patterns, shape-color associations, and visual grids compared to control groups, but the influence of synesthesia on word memory remains unclear. Future research should consider adding control for confounding factors, collaborating with other institutions, and increasing sample size.

Sharing the load: How a personally coloured calculator for grapheme-colour synaesthetes can reduce processing costs

Synaesthesia refers to a diverse group of perceptions. These unusual perceptions are defined by the experience of concurrents; these are conscious experiences that are catalysed by attention to some normally unrelated stimulus, the inducer. In grapheme-colour synaesthesia numbers, letters, and words can all cause colour concurrents, and these are independent of the actual colour with which the graphemes are displayed. For example, when seeing the numeral '3' a person with synaesthesia might experience green as the concurrent irrespective of whether the numeral is printed in blue, black, or red. As a trait, synaesthesia has the potential to cause both positive and negative effects. However, regardless of the end effect, synaesthesia incurs an initial cost when compared with its equivalent example from normal perception; this is the additional processing cost needed to generate the information on the concurrent. We contend that this cost can be reduced by mirroring the concurrent in the environment. We designed the Digital-Colour Calculator (DCC) app, allowing each user to personalise and select the colours with which it displays its digits; it is the first reported example of a device/approach that leverages the concurrent. In this article we report on the reactions to the DCC for a sample of fifty-three synaesthetes and thirty-five non-synaesthetes. The synaesthetes showed a strong preference for the DCC over its normal counterpart. The non-synaesthetes showed no obvious preference. When using the DCC a subsample of the synaesthete group showed consistent improvement in task speed (around 8%) whereas no synaesthete showed a decrement in their speed.

Synaesthesia as a model system for understanding variation in the human mind and brain

The aim of this article is to reposition synaesthesia as model system for understanding variation in the construction of the human mind and brain. People with synaesthesia inhabit a remarkable mental world in which numbers can be coloured, words can have tastes, and music is a visual spectacle. Key questions remain unanswered about why it exists, and how the study of synaesthesia might inform theories of the human mind. This article argues we need to rethink synaesthesia as not just representing exceptional experiences, but as a product of an unusual neurodevelopmental cascade from genes to brain to cognition of which synaesthesia is only one outcome. Specifically, differences in the brains of synaesthetes support a distinctive way of thinking (enhanced memory, imagery etc.) and may also predispose towards particular clinical vulnerabilities. In effect, synaesthesia can act as a paradigmatic example of a neuropsychological approach to individual differences.

A persistent memory advantage is specific to grapheme-colour synaesthesia

For people with synaesthesia ordinary stimuli such as digits or letters induce concurrent experiences such as colours. Synaesthesia is associated with a memory advantage and the aim of this study was to investigate whether this advantage persists across time. We tested recognition memory of four different types of synaesthesia with different inducer-concurrent pairings across two sessions with a one-year retention interval. In the study phase, participants learned three kinds of stimuli (i.e., related to their inducer, related to their concurrent, or synaesthesia-unrelated): music, words and colours. Recognition memory was tested after one hour and after one year. After one hour, grapheme-colour and grapheme-colour-and-sound-colour synaesthetes showed synaesthesia-specific advantages. After one year, only grapheme-colour synaesthetes still showed an advantage. The results imply that a benefit through enhanced colour-processing is particularly strong and that synaesthesia can lead to a long-lasting memory benefit.

Synaesthesia: a distinct entity that is an emergent feature of adaptive neurocognitive differences

In this article, I argue that synaesthesia is not on a continuum with neurotypical cognition. Synaesthesia is special: its phenomenology is different; it has distinct causal mechanisms; and is likely to be associated with a distinct neurocognitive profile. However, not all synaesthetes are the same, and there are quantifiable differences between them. In particular, the number of types of synaesthesia that a person possesses is a hitherto underappreciated variable that predicts cognitive differences along a number of dimensions (mental imagery, sensory sensitivity, attention to detail). Together with enhanced memory, this may constitute a common core of abilities that may go some way to explaining why synaesthesia might have evolved. I argue that the direct benefits of synaesthesia are generally limited (i.e. the synaesthetic associations do not convey novel information about the world) but, nevertheless, synaesthesia may develop due to other adaptive functions (e.g. perceptual ability, memory) that necessitate changes to design features of the brain. The article concludes by suggesting that synaesthesia forces us to reconsider what we mean by a 'normal' mind/brain. There may be multiple 'normal' neurodevelopmental trajectories that can sculpt very different ways of experiencing the world, of which synaesthesia is but one. This article is part of a discussion meeting issue 'Bridging senses: novel insights from synaesthesia'.

A meta-analysis of memory ability in synaesthesia

People with synaesthesia (e.g., experiencing colours for letters and numbers) have been reported to possess enhanced memory relative to the general population. However, there are also inconsistencies in this literature and it is unclear whether this reflects sampling error (exacerbated by low Ns) or more meaningful differences that arise because synaesthesia relates to some aspects of memory more than others. To this end, a multi-level meta-analysis was conducted. Synaesthetes have enhanced long-term (episodic) memory with a medium population effect size ( dˆ  = 0.61), whereas the effects on working memory (short-term memory) were significantly smaller ( dˆ  = 0.36) but still exceeded that of controls. Moderation analyses suggested that, aside from the division between long-term vs. working memory, the effects of synaesthesia are pervasive, i.e., they extend to all kinds of stimuli, and extend to all kinds of test formats. This pattern is hard to reconcile with the view that synaesthetic experiences directly support memory ability: for instance, digit span (where synaesthesia could be helpful) showed a small effect whereas episodic memory for abstract images (where synaesthesia is irrelevant) yielded larger effects. Synaesthesia occupies a unique position of being the only known neurodevelopmental condition linked to a pervasive enhancement of long-term memory.

New insights into mechanisms of enhanced synaesthetic memory: Benefits are synaesthesia-type-specific

The goal of this study was to test the nature of the memory advantage in synaesthesia. We compared four different types of synaesthetes (27 grapheme-colour, 21 sound-colour-, 25 grapheme-colour-and-sound-colour- and 24 sequence-space synaesthetes) to their matched controls. Recognition memory for three types of stimuli (music, words, colour) was tested. We anticipated a general advantage in memory for synaesthetes and potentially additional synaesthesia-specific benefits. The results showed a general advantage for synaesthesia. Further, a benefit for colour stimuli resulted for grapheme-colour synaesthetes and a benefit for music stimuli resulted for grapheme-colour-and-sound-colour synaesthetes, indicating synaesthesia-type specific effects. These results suggest different mechanisms for the explanation of the memory benefit for different types of synaesthesia such as synaesthesia-related colour expertise for grapheme-colour synaesthesia and additional encoding opportunities for grapheme-colour-and-sound-colour synaesthesia.