Associative memory advantage in grapheme-color synesthetes compared to older, but not young adults.

Gaby Pfeifer,Natasha Sigala,Jamie Ward,Dennis Chan,Nicolas Rothen

doi:10.3389/fpsyg.2014.00696

Abstract

People with grapheme-color synesthesia perceive enriched experiences of colors in response to graphemes (letters, digits). In this study, we examined whether these synesthetes show a generic associative memory advantage for stimuli that do not elicit a synesthetic color. We used a novel between group design (14 young synesthetes, 14 young, and 14 older adults) with a self-paced visual associative learning paradigm and subsequent retrieval (immediate and delayed). Non-synesthesia inducing, achromatic fractal pair-associates were manipulated in visual similarity (high and low) and corresponded to high and low memory load conditions. The main finding was a learning and retrieval advantage of synesthetes relative to older, but not to younger, adults. Furthermore, the significance testing was supported with effect size measures and power calculations. Differences between synesthetes and older adults were found during dissimilar pair (high memory load) learning and retrieval at immediate and delayed stages. Moreover, we found a medium size difference between synesthetes and young adults for similar pair (low memory load) learning. Differences between young and older adults were also observed during associative learning and retrieval, but were of medium effect size coupled with low power. The results show a subtle associative memory advantage in synesthetes for non-synesthesia inducing stimuli, which can be detected against older adults. They also indicate that perceptual mechanisms (enhanced in synesthesia, declining as part of the aging process) can translate into a generic associative memory advantage, and may contribute to associative deficits accompanying healthy aging.

Highlights

Synesthesia is a stable perceptual phenomenon whereby one sensory stimulus leads to a secondary experience such as colors, tastes, smells, etc
We hypothesized that if a retrieval advantage existed in synesthetes, a significant effect would emerge in the dissimilar condition that had the highest demands on discriminability
In line with our first hypothesis, the retrieval results of the 3 × 2 × 2 analyses of variance (ANOVA) demonstrated that the stimulus similarity manipulation was effective at influencing associative retrieval, as shown by significantly higher d prime scores during retrieval of similar compared to dissimilar pair-associates

Summary

Introduction

Synesthesia is a stable perceptual phenomenon whereby one sensory stimulus (e.g., a visual word or auditory tone) leads to a secondary experience such as colors, tastes, smells, etc. Grapheme-color synesthesia in particular refers to the experience of seeing specific colors in response to particular letters, words, or digits (graphemes), e.g., “five is blue.”. The most prevalent and generic cognitive model to explain the synesthetes’ verbal memory advantage (see Rothen et al, 2012 for a review) is the dual-coding theory (Paivio, 1991). According to this theory, more efficient and durable memory traces are obtained when words are associated with visual images. Dualcoding effects can be observed in the normal population when using memory strategies such as associating words with locations in space [Method of Loci (Verhaeghen and Marcoen, 1996)] or using visual imagery, e.g., forming a mental picture of the words’

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Conclusion