Individual differences among grapheme-color synesthetes: brain-behavior correlations.
Grapheme-color synesthetes experience specific colors associated with specific number or letter characters. To determine the neural locus of this condition, we compared behavioral and fMRI responses in six grapheme-color synesthetes to control subjects. In our behavioral experiments, we found that a subject's synesthetic experience can aid in texture segregation (experiment 1) and reduce the effects of crowding (experiment 2). For synesthetes, graphemes produced larger fMRI responses in color-selective area human V4 than for control subjects (experiment 3). Importantly, we found a correlation within subjects between the behavioral and fMRI results; subjects with better performance on the behavioral experiments showed larger fMRI responses in early retinotopic visual areas (V1, V2, V3, and hV4). These results suggest that grapheme-color synesthesia is the result of cross-activation between grapheme-selective and color-selective brain areas. The correlation between the behavioral and fMRI results suggests that grapheme-color synesthetes may constitute a heterogeneous group.
Hubbard
Edward M
EM
Salk Institute for Biological Studies, Systems Neurobiology Laboratory - B, 10010 North Torrey Pines Road, La Jolla, California 92037, USA. edhubbard@gmail.com
Arman
A Cyrus
AC
Ramachandran
Vilayanur S
VS
Boynton
Geoffrey M
GM
D001931:Brain Mapping; D002560:Cerebrovascular Circulation / Q000502:physiology; D003118:Color Perception / Q000502:physiology*; D003117:Color Vision Defects / Q000503:physiopathology*; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D009483:Neuropsychological Tests; D015588:Observer Variation; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology*; D014795:Visual Pathways / Q000033:anatomy & histology / Q000502:physiology*