Visual cortex activity predicts subjective experience after reading books with colored letters

Abstract

One of the most astonishing properties of synesthesia is that the evoked concurrent experiences are perceptual. Is it possible to acquire similar effects after learning cross-modal associations that resemble synesthetic mappings? In this study, we examine whether brain activation in early visual areas can be directly related to letter-color associations acquired by training. Non-synesthetes read specially prepared books with colored letters for several weeks and were scanned using functional magnetic resonance imaging. If the acquired letter-color associations were visual in nature, then brain activation in visual cortex while viewing the trained black letters (compared to untrained black letters) should predict the strength of the associations, the quality of the color experience, or the vividness of visual mental imagery. Results showed that training-related activation of area V4 was correlated with differences in reported subjective color experience. Trainees who were classified as having stronger 'associator' types of color experiences also had more negative activation for trained compared to untrained achromatic letters in area V4. In contrast, the strength of the acquired associations (measured as the Stroop effect) was not reliably reflected in visual cortex activity. The reported vividness of visual mental imagery was related to veridical color activation in early visual cortex, but not to the acquired color associations. We show for the first time that subjective experience related to a synesthesia-training paradigm was reflected in visual brain activation.

Creating Colored Letters: Familial Markers of Grapheme–Color Synesthesia in Parietal Lobe Activation and Structure

“…Some of the methods have been published (Colizoli et al, 2016), as the same sample of participants is used in the current study. We report here all methods and materials directly related to the current study.…”

“…The role of parietal cortex in synesthesia is generally proposed to be the "hyperbinding" of form to color in synesthesia (Weiss & Fink, 2009;Hubbard, 2007;Esterman et al, 2006;Robertson, 2003). We hypothesized that potential effects of additional color acquired by training would be evident in occipitotemporal (see Colizoli et al, 2016) and parietal brain regions, as it is for developmental synesthesia.…”

“…We used a reading-in-color paradigm ( Figure 1) to train letter-color associations (Colizoli, Murre, & Rouw, 2012). We have previously shown that behavioral congruency effects can be acquired by reading books with consistently colored letters (Colizoli et al, 2012(Colizoli et al, , 2016. We also examined visual cortex activation related to acquired letter-color associations (Colizoli et al, 2016).…”

“…We have previously shown that behavioral congruency effects can be acquired by reading books with consistently colored letters (Colizoli et al, 2012(Colizoli et al, , 2016. We also examined visual cortex activation related to acquired letter-color associations (Colizoli et al, 2016). The current study uses the same subject sample but, in contrast with the previous study, examines which regions are related to learning synesthesia in whole-brain analyses (rather than within visual cortex) and looks at structural as well as functional brain measurements.…”

Bridging the gap: Synaesthesia and multisensory processes

“…Gould van Praag et al (2016) show that synaesthetic phenomenology, namely the phenomenological localisation and automaticity of synaesthetic concurrents, is related to activity in colour areas in the brain. The paper is complemented by the contribution from Colizoli et al (2016) in which non-synaesthetes were trained to associate letters with colours by reading books with coloured letters. Colizoli et al show that activity within area V4 after training correlates with the subjective appearance of the trained colour associations.…”