In recent years, this field of inquiry has flourished into an active area of research that has accumulated of a large body of evidence on the neuro-cognitive mechanism of synesthesia.

This unusual condition has captured the imagination of philosophers, neuroscientists and psychologist alike, and been a curiosity for at least two centuries. These people are called grapheme-color synesthetes, and the experience of synesthesia is described as concurrent (the subjective colors) to inducing stimuli (the graphemes). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Д¬ompeting interests: The authors have declared that no competing interests exist.ДЄ small minority of people report a consistent and automatic experience of non-physical color when presented with a grapheme. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedДata Availability: All relevant data are available in the manuscript and its Supporting Information files.ДЇunding: The operating costs of this research were covered by a grant from the Kristian Holt-Hansen foundation. Received: NovemAccepted: JPublished: August 7, 2015Д¬opyright: В© 2015 ГЃsgeirsson et al. We also propose that enhanced visual short-term memory capacity for congruently colored graphemes can be explained by the synesthetesвЂ™ expertise regarding their specific grapheme-color associations.Д¬itation: ГЃsgeirsson ГЃG, Nordfang M, SГёrensen TA (2015) Components of Attention in Grapheme-Color Synesthesia: A Modeling Approach. To account for the benefit in processing speed, we propose that synesthetic associations become integrated into the categories of graphemes, and that letter colors are considered as evidence for making certain perceptual categorizations in the visual system.

The increase in processing speed, when synesthetes process congruent letters, suggests that synesthesia affects the processing of letters at a perceptual level. The models suggested that the synesthetes processed congruent letters faster than incongruent ones, and that they were able to retain more congruent letters in visual short-term memory, while the control groupвЂ™s model parameters were not significantly affected by congruence. A mathematical model, based on BundesenвЂ™s (1990) Theory of Visual Attention (TVA), was fitted to each observerвЂ™s data, allowing us to estimate discrete components of visual attention. Graphemes were either congruently or incongruently colored with the synesthetesвЂ™ reported grapheme-color association.

Their task was to report as many letters (targets) as possible, while ignoring digit (distractors). We briefly presented graphemes (10вЂ“150 ms) to 9 grapheme-color synesthetes and to 9 control observers. Here, we investigated how the visual processing of colored letters is affected by the congruence or incongruence of synesthetic grapheme-color associations. Many have studied how synesthesia affects the processing of achromatic graphemes, but less is known about the synesthetic processing of physically colored graphemes. Grapheme-color synesthesia is a condition where the perception of graphemes consistently and automatically evokes an experience of non-physical color.

Synthesia test