title: Grapheme-color synesthesia subtypes: Stable individual differences reflected in posterior alpha-band oscillations.
abstract: Grapheme-color synesthesia is a condition in which seeing letters and numbers produces sensations of colors (e.g., the letter R may elicit a sky-blue percept). Recent evidence implicates posterior parietal areas, in addition to lower-level sensory processing regions, in the neurobiological mechanisms involved in synesthesia. Furthermore, these mechanisms seem to differ for "projectors" (synesthetes who report seeing the color "out there in the real world") versus "associators" (synesthetes who report the color to be only an internal experience). Relatively little is known about possible electrophysiological characteristics of grapheme-color synesthesia. Here we used EEG to investigate functional oscillatory differences among associators, projectors, and non-synesthetes. Projectors had stronger stimulus-related alpha-band (~10 Hz) power over posterior parietal electrodes, compared to both associators and non-synesthetes. Posterior alpha activity was not statistically significantly different between associators from non-synesthetes. We also performed a test-retest assessment of the projector-associator score and found strong retest reliability, as evidenced by a correlation coefficient of .85. These findings demonstrate that the projector-associator distinction is highly reliable over time and is related to neural oscillations in the alpha band.
authors.affiliation: a Department of Psychology , University of Amsterdam , Amsterdam , The Netherlands.
authors.forename: Michael X
authors.initials: MX
authors.lastname: Cohen
authors.forename: Kathrin
authors.initials: K
authors.lastname: Weidacker
authors.forename: Judith
authors.initials: J
authors.lastname: Tankink
authors.forename: H Steven
authors.initials: HS
authors.lastname: Scholte
authors.forename: Romke
authors.initials: R
authors.lastname: Rouw
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods; D003116:Color; D003118:Color Perception / Q000502:physiology*; D003463:Cues; D004569:Electroencephalography / Q000379:methods; D005260:Female; D006801:Humans; D008875:Middle Aged; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010468:Perceptual Disorders / Q000503:physiopathology*; D010775:Photic Stimulation / Q000379:methods; D015203:Reproducibility of Results; D000080311:Synesthesia; D055815:Young Adult
keywords: Alpha-band; Brain Networks; Grapheme-color; Individual differences; Synaesthesia