Neuroscience 2003 Abstract
| Presentation Number: | 338.10 |
|---|---|
| Abstract Title: | Psychophysical and neuroimaging investigations of synesthetic colors. |
| Authors: |
Hubbard, E. M.*1,2
; Ramachandran, V. S.1
; Boynton, G. M.2
1Ctr. Brain Cogn, UCSD, La Jolla, CA 2CA, 9500 Gilman Dr, 92093-0109, |
| Primary Theme and Topics |
Sensory Systems - Multisensory |
| Secondary Theme and Topics | Sensory Systems<br />- Vision<br />-- Visual cortex: Attention and cognition |
| Session: |
338. Visual Cortex: Coding, Synchronization & Interareal Integration Slide |
| Presentation Time: | Monday, November 10, 2003 10:15 AM-10:15 AM |
| Location: | Morial Convention Center - Room 287 |
| Keywords: | psychophysics, fMRI |
Subjects with grapheme-color synesthesia report that a given number is always associated with a certain color (e.g., '5' may be green). We have shown that synesthetic colors can lead to segregation or pop-out (Ramachandran & Hubbard, 2001) and decreasing contrast reduces the vividness of the synesthetic colors monotonically. Below about 10% contrast the color disappeared, even though the letter was still visible (Hubbard & Ramachandran, SFN 2002). We now show that the synesthetic color induction depends on physical (retinal) rather than perceived contrast by using the Mach Card Illusion and cast shadows. We also find that synesthetic colors can lead to apparent motion. We alternated two frames: in frame 1 a cluster of 5s was embedded in a matrix of randomly placed 2s; in frame 2, the cluster of 5s was displaced by 4 degrees and the 2s randomly repositioned. Controls saw random incoherent motion; synesthetes saw apparent motion of the 5s based on the synesthetically induced colors. These results suggest that synesthesia is a sensory effect, perhaps due to cross-activation between color selective occipital brain areas (V4v/V8) and a nearby brain area responsive to graphemes. To test this, we have conducted fMRI experiments with four grapheme-color synesthetes and four non-synesthetic controls. Subjects performed an upright versus italic discrimination on letters or numbers alternating in a block-design with nonsense graphemes. Synesthetes showed significantly greater BOLD responses than control subjects to letters and numbers in color selective areas (V4v/V8), but not V1 or V2. Activity in retinotopically organized visual areas (V1, V2, V4v, V8), but not grapheme selective areas, was positively correlated with behavioral performance on our tasks. These results further support our hypothesis that synesthesia may arise from cross-activation of color selective areas by visually presented graphemes.
Supported by NIMH, Legler Benbough Foundation
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2003 Neuroscience Meeting Planner. New Orleans, LA: Society for Neuroscience, 2003. Online.
Copyright © 2003-2026 Society for Neuroscience; all rights reserved. Permission to republish any abstract or part of any abstract in any form must be obtained in writing by SfN office prior to publication.
