Color perception in synaesthesia: an fMRI-study

NemoImage

11, Number

5, 2000,

Part 2 of 2 Parts 1 DE

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PERCEPTION

Color perception in synaesthesia: an fMRI-study. Peter H. Weiss*, Ivan Toni*, Nadim J. Shah*, Gereon R. Fink*?, Karl Zilles*t *Institute TDepartment

of Medicine,

Forschungszentrum

of Neurology,

SC. & 0. Vogt Hirnforschungsinstitut,

Jiilich,

52425 Jiilich,

Heinrich-Heine-University, Heinrich-Heine-University,

Diisseldorj

Germany Germany

Diisseldoti

Germany

Introduction Synaesthesia is a condition in which a sensory experience normally associated with one modality occurs when another modality is stimulated (I). The most common form of synaesthesia is the experience of colours when hearing or reading words. Information about the neural basis of synaesthesia is scarce (2). Using tMRI we here examined the neural mechanisms of colour perception in a group of synaesthetes, who experience colour, when reading specific letters. Methods 3 women and 2 men with synaesthesia (3) underwent standard neuro-psychological testing to exclude dysfunction of the visual system. Based on extensive testing for each subject, an individual set of stimulus letters, which induced the experience of synaesthetic colour (Syn +), and an individual set of stimulus letters, which did not induce a synaesthetic colour experience (Syn-). was created. These stimuli were then presented visually to the subjects in either a randomly assigned colour (Co1 +) or in grey (Co1 -). During scanning, blocks of 12 letters were used (ISI 2s, SOT 500 ms). Each block was alternated with a rest period of the same length. Subjects indicated by button presses whether or not they experienced synaesthetic colour. This constitutes a 2x2 factorial design (Synaesthesia +I-, Colour +/-), which allowed us to explore the difference between internal synaesthetic colour experience and the perception of externally presented colour. Functional MR images were acquired on a Siemens Vision 1.5T whole-body scanner using standard EPI imaging procedures and statistical analysis (SPM 97) was performed as described elsewhere (4).

The main effect of Colour revealed activation of extrastriate cortex bilaterally (+30/-52/-l& 2=5.47, -341.54/-22, Z=5.16; p
S. Baron-Cohen, J. Harrison, Synaesthesia ( Blackwell, Oxford, 1997). E. Paulesu, et al, Brain 118, 661 (1995). S. Baron-Cohen, M.A. Wyke, C. Binnie, Perception 16, 761 (1987). G.R. Fink, Neurology (2000). MI. Sereno, et al, Science 268, 889 (1995). G.R. Fink, et al, Brain 122, 497 (1999).

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emphasised that the conflict between the sensory experience area in monitoring