„ Data from 260 grapheme-color synesthetes (courtesy Sean Day) collected from personal correspondence and historical sources were analyzed. „ Of those, 97 had complete data sets, which were then analyzed. „ A sound confusion matrix was used to select two sets of five letters that were highly confusable within each group, and easily distinguished across groups. „ Based on a letter confusion matrix, two sets of five letters were chosen that had similar visual features within each group, and differing visual features across groups 6 . „ Visual features: K V W X Y and C U D O Q. „ Letter names: B P C T V and M N S X F. „ To assess distance between letters in color space, a normalized Euclidian distance was calculated: Introduction References 1. Ramachandran, V.S. & Hubbard, E.M. (2001). Synesthesia: A window into perception, thought and language. Journal of Consciousness Studies. 8(12): 3-34. 2. Rich, A. & Mattingley, J. (2002). Anomalous perception in synaesthesia: A cognitive neuroscience perspective. Nature Reviews Neuroscience. 3(1):43-52. 3. Hubbard, E.M., Arman, A.C., Ramachandran, V.S. & Boynton, G.M. (2005). Individual differences among grapheme-color synesthetes: Brain-behavior correlations. Neuron. 45(6):975-85. 4. Dixon M.J., Smilek, D. & Merikle, P.M. (2004). Not all synaesthetes are created equal: Projector versus associator synaesthetes. Cognitive, Affective and Behavioral Neuroscience. 4(3):335-343. 5. Day, S.A. (2005). Some demographic and socio-cultural aspects of synesthesia. In L. Robertson and N. Sagiv (Eds.) Synesthesia: Perspectives from Cognitive Neuroscience. (p. 11-33). 6. Gibson, E.J., Osser, H., Schiff, W., & Smith, J. (1963). An analyses of critical features of letters, tested by a confusion matrix. In A Basic Research Program on Reading. (Cooperative Research Project No. 639). Washington, DC: U.S. Office of Education. Grapheme and Letter Name Based Patterns in Synesthetic Colors Edward Hubbard, Pearl Ambrosio, Shai Azoulai, & V.S. Ramachandran Center for Brain and Cognition, UC San Diego Synesthesia is the experience of perceptual sensations in one domain eliciting perceptual sensations in another domain. Various subtypes of synesthesia that have been reported include taste-shape synesthesia, tone- color synesthesia, and grapheme-color synesthesia 1,2 . Recent evidence has suggested that synesthetic experiences may arise at distinct stages of neural processing 3,4 . Additionally, anecdotal evidence from synesthetes suggest that their colors are non-random. If so, then the patterns of synesthetic color experience may be useful in determining the representational stage at which colors are elicited for individual synesthetes. To further investigate the possibility that distinct representations underlie synesthesia in different subjects, we measured correlations among synesthetic experiences of grapheme-color synesthetes. Anecdotal evidence has suggested that some synesthetes have a feature dimension along which their colors are arranged. For example, some synesthetes have reported similar colors for letters that look alike, while others have reported similar colors for letters that sound similar 5 . We performed a correlational analysis to test this hypothesis. The two dimensions analyzed were visual features of each letter and the sound of the letter names. √ (Red Gun 1 - Red Gun 2 ) 2 + (Blue Gun 1 - Blue Gun 2 ) 2 + (Green Gun 1 - Green Gun 2 ) 2 √(255) 2 + (255) 2 + (255) 2 ____________________________________________________________________ ___________________________________________________________________ 1- 2* ___________________ Methods 0 0 0 Black Z 178 178 178 Grey Y 178 178 178 Grey X 178 178 178 Grey W 178 178 178 Grey V 0 51 153 Brown U 0 128 0 Green T 255 0 0 Blue S 0 0 255 Red R 0 153 204 Yellow / Brown Q 0 51 255 Red / Orange P 0 255 255 Yellow O 127 127 255 Red / Yellow N 0 128 0 Green M 127 64 0 Green / Blue L 166 76 191 Pink / Purple K 0 153 204 Yellow / Brown J 127 255 255 White / Yellow I 204 153 255 Pink H 0 89 76 Green / Brown G 0 128 0 Green F 229 204 255 White / Pink E 0 76 204 Brown / Orange D 0 255 255 Yellow C 178 178 178 Grey B 255 0 0 Blue A B G R Color Letter Correlation Methods 0.19 0.69 Within Visual Features Type of Synesthete 0.35 Overall Difference 0.13 0.58 Difference 0.06 0.07 Between Letter Names Visual Features -0.09 -0.09 Between 0.43 0.19 Within Letter Name Type of Synesthete -0.24 Overall Difference 0.52 0.28 Difference Letter Names Visual Features Raw Data (WA) Correlation Matrices Visual Features Letter Names Raw Data (PF) Correlation Matrices Visual Features Letter Names _______________________ _________________ ________________________ 1- 2 * √ (R 1 -R 2 ) 2 + (B 1 -B 2 ) 2 + (G 1 -G 2 ) 2 √(255) 2 + (255) 2 + (255) 2 1.00 -0.16 -0.29 -0.29 1.00 -0.16 1.00 -0.29 -0.21 -0.16 F -0.16 1.00 -0.19 0.52 -0.16 1.00 -0.16 0.06 -0.05 1.00 X -0.29 -0.19 1.00 -0.41 -0.29 -0.19 -0.29 -1.00 -0.65 -0.19 S -0.29 0.52 -0.41 1.00 -0.29 0.52 -0.29 0.18 0.33 0.52 N 1.00 -0.16 -0.29 -0.29 1.00 -0.16 1.00 -0.29 -0.21 -0.16 M -0.16 1.00 -0.19 0.52 -0.16 1.00 -0.16 0.06 -0.05 1.00 V 1.00 -0.16 -0.29 -0.29 1.00 -0.16 1.00 -0.29 -0.21 -0.16 T -0.29 0.06 -1.00 0.18 -0.29 0.06 -0.29 1.00 0.08 0.06 C -0.21 -0.05 -0.65 0.33 -0.21 -0.05 -0.21 0.08 1.00 -0.05 P -0.16 1.00 -0.19 0.52 -0.16 1.00 -0.16 0.06 -0.05 1.00 B F X S N M V T C P B ‘WA’ has been classified as a visual features synesthete because not only does she have high correlations for the ‘within’ groups of visual features and low correlations for the ‘between’ groups, but she also has a weak correlation for letter names. ‘PF’ has been classified as a letter name synesthete because not only does she have high correlations for the ‘within’ groups of letter names and a slightly negative correlation for the ‘between’ groups, but she also has weak correlations for visual features. Future Directions „ We were able to classify some of the synesthetes along two different dimensions. „ Many other dimensions may exist along which synesthetes could classify their letters, e.g. the motor commands which define the way letters are written or the way the letter sounds are articulated. „ These results help us to gain insight into how synesthetic colors may be acquired and reinforced. „ These results suggest that, for some synesthetes, colors are elicited based on letter form, and for some based on letter names. „ These results are consistent with other recent work suggesting that synesthesia may be elicited at multiple stages of representation. „ Compare synesthetes’ introspective reports with our results to determine if they are consistent with their experiences. „ Further develop the correlation method by expanding our analysis to all 26 letters e.g., MDS. „ Investigate other possible dimensions along which synesthetic experiences can be organized. „ Implement a bootstrapping technique in order to provide more reliable results than a correlational analysis. Conclusions Data Summary 60 17 20 Number 60% Unclassifiable 18% Letter Names 22% Visual Features Percentage Classification E298 0 0 0 Black Z 0 255 255 Yellow Y 0 0 0 Black X 0 0 0 Black W 128 0 128 Purple V 0 51 153 Brown U 0 51 153 Brown T 0 0 255 Red S 102 76 255 Red R 0 255 255 Yellow Q 204 153 255 Pink P 255 255 255 White O 0 128 0 Green N 0 128 0 Green M 178 178 178 Light Gray L 178 178 178 Light Gray K 255 0 0 Blue J 178 178 178 Light Gray I 128 0 128 Purple H 0 153 204 Yellow / Brown G 0 128 0 Light Green F 0 128 0 Light Green E 0 255 255 Yellow D 178 178 178 Light Grey C 102 127 255 Orange/Pink B 0 102 255 Orange A B G R Color Letter 1.00 0.48 0.65 0.48 0.48 0.18 0.18 0.18 0.18 0.17 Q 0.48 1.00 0.16 -0.04 1.00 0.06 0.06 0.06 0.06 -0.14 O 0.65 0.16 1.00 0.74 0.16 0.06 0.06 0.06 0.06 0.25 D 0.48 -0.04 0.74 1.00 -0.04 0.00 0.00 0.00 0.00 0.22 U 0.48 1.00 0.16 -0.04 1.00 0.06 0.06 0.06 0.06 -0.14 C 0.18 0.06 0.06 0.00 0.06 1.00 1.00 1.00 1.00 0.53 Y 0.18 0.06 0.06 0.00 0.06 1.00 1.00 1.00 1.00 0.53 X 0.18 0.06 0.06 0.00 0.06 1.00 1.00 1.00 1.00 0.53 W 0.18 0.06 0.06 0.00 0.06 1.00 1.00 1.00 1.00 0.53 V 0.17 -0.14 0.25 0.22 -0.14 0.53 0.53 0.53 0.53 1.00 K Q O D U C Y X W V K 1.00 0.42 -0.29 1.00 1.00 0.00 0.22 -0.16 -0.48 -0.24 F 0.42 1.00 -0.15 0.42 0.42 0.18 0.27 -0.39 -0.63 -0.37 X -0.29 -0.15 1.00 -0.29 -0.29 0.18 0.48 -0.19 -0.15 0.26 S 1.00 0.42 -0.29 1.00 1.00 0.00 0.22 -0.16 -0.48 -0.24 N 1.00 0.42 -0.29 1.00 1.00 0.00 0.22 -0.16 -0.48 -0.24 M 0.00 0.18 0.18 0.00 0.00 1.00 0.37 0.13 0.04 0.18 V 0.22 0.27 0.48 0.22 0.22 0.37 1.00 0.00 -0.13 0.26 T -0.16 -0.39 -0.19 -0.16 -0.16 0.13 0.00 1.00 0.62 0.45 C -0.48 -0.63 -0.15 -0.48 -0.48 0.04 -0.13 0.62 1.00 0.52 P -0.24 -0.37 0.26 -0.24 -0.24 0.18 0.26 0.45 0.52 1.00 B F X S N M V T C P B 1.00 -0.15 1.00 -0.03 0.06 1.00 -0.63 -0.63 -0.41 0.06 Q -0.15 1.00 -0.15 -0.54 0.39 -0.15 -1.00 -1.00 -0.41 0.39 O 1.00 -0.15 1.00 -0.03 0.06 1.00 -0.63 -0.63 -0.41 0.06 D -0.03 -0.54 -0.03 1.00 0.00 -0.03 0.27 0.27 0.37 0.00 U 0.06 0.39 0.06 0.00 1.00 0.06 -0.40 -0.40 0.13 1.00 C 1.00 -0.15 1.00 -0.03 0.06 1.00 -0.63 -0.63 -0.41 0.05 Y -0.63 -1.00 -0.63 0.27 -0.40 -0.63 1.00 1.00 0.18 -0.40 X -0.63 -1.00 -0.63 0.27 -0.40 -0.63 1.00 1.00 0.18 -0.40 W -0.41 -0.41 -0.41 0.37 0.13 -0.41 0.18 0.18 1.00 0.13 V 0.06 0.39 0.06 0.00 1.00 0.05 -0.40 -0.40 0.13 1.00 K Q O D U C Y X W V K „ Normalized distance ranges from -1 to 1 (analogous to a correlation coefficient). „ We then computed distance for groups of letters defined by similar visual features or letter names. „ Predict high within group similarity, but low between group similarity. „ To determine which group a synesthete belonged to we compared correlations for visual features and letter names.