Synaesthesia. Hao Ye

Transcription

1 Synaesthesia Hao Ye

2 synaesthesia (synesthesia): a neurological condition in which two or more bodily sense are coupled * * wikipedia

3 Specification inducer - stimulus that triggers synaesthesia concurrent - synaesthetic experience itself inducer concurrent e.g. grapheme color (most common)

4 Prevalence 1 in 20 (Galton, 1883) 1 in 200 (Ramachandran & Hubbard, 2001b) 1 in 2000 (Baron-Cohen et. al. 1996) 1 in 25,000 (Cytowic, 1989)

5 Heritability high prevalence among relatives 6-7 : 1 ratio of females : males x-linked autosomal dominance? theoretical ratio is 2 : 1 reporting bias?

6 Genetics discordant female monozygotic twins Smilek et. al., 2002 x - inactivation? discordant male monozygotic twins Smilek et. al., 2005

7 Sex Differences recent studies suggest 1:1 ratio Stephen, 2004 Simner et. al., 2005 age of subjects? neural pruning hypothesis complex genetic and environmental interactions

8 Drugs MDMA (ecstasy) LSD sex differences females report larger perceptual effects of MDMA (weight-adjusted dosages)

9 Is it real? two hypotheses memory association actual percept testable pop-out test Stroop task

10 Pop-out Test (normal)

11 Pop-out Test (synaesthete)

12 Theories cross-wiring defective synaptic pruning excessive synaptic connections cross-activation epileptic patients

13 Inducer conscious processing unconscious processing concept-driven solution to arithmetic problem interfered with color patch naming

14 Crowding

15 Periphery

16 Neural Location? varies by subject lower synaesthesia higher synaesthesia concurrent is usually not complex inducer can be highly complex

17 Unconscious priming eliminated automatic binding of colour and alphanumeric form in synaesthesia Mattingley et. al.

18 Summary 15 subjects experiments color association consistency standard Stroop task (color-naming of color words) Stroop task (color-naming of letters) Stroop task (color-naming of primed targets)

19 Color Association 150-item list (letters, numbers, words) subjects describe synaesthetic color (or arbitrary color) synaesthetes tested 3 months later controls tested 1 month later

20 Results Consistency (%) Letters Arabic numerals Number words Weekdays Months First names Place names Occupations Animals Other nouns Abstract words

21 Standard Stroop Task results as expected all subjects slower on incongruent items no difference between synaesthetes and controls

22 Synaesthetic Stroop Task I subjects name color of stimuli for synaesthetes: congruent w/ synaesthetic color incongruent w/ synaesthetic color neutral (non-alphanumeric) blocked or randomized

23 Results Voice onset time (ms) a b c 0 Congruent Incongruent Congruent Incongruent Congruent Incongruent Neutral Synaesthetic condition

24 Synaesthetic Stroop Task II masked achromatic prime three durations (28 ms, 56 ms, 500 ms) subjects name color of target patch for synaesthetes: congruent w/ synaesthetic color incongruent w/ synaesthetic color neutral (non-alphanumeric)

25 Prime Identification 100 Prime identification (% correct) Synaesthetes Group Controls

26 Target Patch Identification a 650 c Voice onset time (ms) Congruent Incongruent Neutral Congruent Incongruent b 650 d Voice onset time (ms) Congruent Incongruent Neutral Congruent Incongruent Synaesthetic condition

27 Prime Processing letters instead of colored target patch congruent (a A) incongruent (b A) unconscious priming prime durations of 28 ms and 56 ms slower at incongruent condition

28 Conclusions Task I (name color of letter) blocking benefitted synaesthetes in congruent condition Task II (name color of patch) weak color percept for neutral stimuli results in incongruency unconscious processing results in no effect of congruency

29 Synaesthetic photisms influence visual perception Smilek et. al.

30 Summary C, digit color synaesthete experiments masked digit identification visual search

31 Masked Digit Identification fixation cross (800 ms) randomly chosen digit (32 ms) congruent background incongruent background mask (% or $)

32 Task Congruent Incongruent $% $% Figure 1. Examples of the stimulus displays used in the identification task.

33 Results p <.005 all p s >.250 Congruent Incongruent p >.254 Proportion Correct C Non-synaesthetes (n = 7) Matched Nonsynaesthete Participants

34 Visual Search target (2 or 4) distractor digits (8) 6, 12, or 18 distractors congruent background incongruent background

35 Task Congruent Incongruent

36 Results Reaction Time (msec) (3.3%) (5.2%) (1.0%) (1.0%) (5.2%) (5.2%) Congruent Incongruent (4.3%) (4.9%) (2.1%) (2.1%) (9.4%) (9.4%) Set Size (7.4%) (7.6%) (3.1%) (2.1%) (15.6%) (11.5%) Non-synaesthetes (n = 7) C Matched Non-synaesthete

37 Contradictions? Variability among synaesthetes type of synaesthesia level of processing at which synaesthesia occurs

38 Questions

39 Stuart Anstis: Ramachandran made a stylized 2 from five segments, and mirror-reversed it to make a 5. In a visual search task, a 2 hidden among 5 s is very hard to find. However, he finds that for a synaesthete who sees 2 s as pink and 5 s as green, the hidden digit pops out pre-attentively. It s hard to see what neural pathways could accomplish this. Is it inconsistent with Mattingley s findings that masked digits are ineffective, and that digits must be fully processed before color is attached?

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41 Gedanken experiment to identify the neural site of syn-colors. It s known that one can generate colored aftereffects contingent on direction of motion. Now, make motion-defined digits: a 5 shaped window filled with random dots drifting upwards, and a 2- shaped window with random dots drifting downwards, against twinkling random backgrounds. Adapt to these. Now show a synaesthete square windows filled with upward or downward drifting dots. Will they see McCollough-style subjective colors? (Control observers won t).

42 McCollough Effect

43 Adaptation

44 Adaptation II

45 Test Stimulus

46 Synaesthetic Inducer

47 Test Stimulus

48

49 Alan Robinson: When you show these subjects a colored letter, does the real color mix with the illusionary color? Or is it more of a bistable percept?

50 Synaesthetes differ on where the concurrent appears: color fills the letter color floats on top of the letter color appears in the mind s eye

51 The stroop effect goes away if it is tested in a paradigm where the subject has to click on one of 4 colored rectangles which matches the color that the text was shown in, suggesting that stroop interferences occurs at response selection, and not at a perceptual level. Would we predict that the same manipulation would eliminate the synaesthesia stroop effect?