Poster B8, Sunday, March 25, 8:00-10:00 am, Exhibit Hall C
Dissociations Between Explicit Number Forms and Implicit SNARC Effects in Number-Form Synesthetes
Elizabeth Y. Toomarian1, Radhika S. Gosavi1, Edward M. Hubbard1; 1University of Wisconsin-Madison
In number-form (NF) synesthesia, people report vivid, automatic spatial layouts for numerical sequences. While these forms are consistent within individuals over time, the shape and direction of these forms differ across NF synesthetes. This phenomenon is similar to the implicit association between numbers and space demonstrated by the Spatial-Numerical Association of Response Codes (SNARC) effect, in which Western participants associate small numbers with the left side of space and large numbers with the right. Some researchers have suggested that explicit NFs and the implicit SNARC rely on shared mechanisms of co-activation, specifically in regions of parietal cortex underlying spatial and ordinal/numerical processing (Hubbard et al., 2005, Tang et al., 2008). To test this, previous research has examined single cases where SNARC effects corroborate subjective reports of NFs that go in non-canonical directions (e.g., right-to-left or bottom-to-top). We tested four NF synesthetes and compared the direction of their NF with the direction of their SNARC effects, for whole numbers and fractions. Contrary to our hypotheses, only one NF synesthete demonstrated SNARC effects congruent with her reported forms (both in the canonical left-to-right direction). One synesthete exhibited a canonical SNARC effect for whole numbers and no SNARC for fractions despite reporting a non-canonical number form direction for both. Two others showed no evidence of a SNARC for either stimulus type. These results demonstrate important dissociations between implicit measures of number processing and explicit reports, and challenge the hypothesis that NF synesthesia and implicit measures of spatial-numerical associations share a common unitary mechanism.
Topic Area: ATTENTION: Spatial