synaesthesia - university of california, san diegodeepeco.ucsd.edu/~hye/files/synaesthesia.pdf ·...

SynaesthesiaHao Ye

synaesthesia (synesthesia):“a neurological condition in which two or more bodily

sense are coupled”*

* wikipedia

Specification

• inducer - stimulus that triggers synaesthesia

• concurrent - synaesthetic experience itself

• inducer → concurrent

• e.g. grapheme → color (most common)

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)

Heritability

• high prevalence among relatives

• 6-7 : 1 ratio of females : males

• x-linked autosomal dominance?

• theoretical ratio is 2 : 1

• reporting bias?

Genetics

• discordant female monozygotic twins

• Smilek et. al., 2002

• x - inactivation?

• discordant male monozygotic twins

• Smilek et. al., 2005

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

Drugs

• MDMA (ecstasy)

• LSD

• sex differences

• females report larger perceptual effects of MDMA (weight-adjusted dosages)

Is it real?

• two hypotheses

• memory association

• actual percept

• testable

• pop-out test

• Stroop task

Pop-out Test (normal)

tivation within the fusiform gyrus itself in num-ber-color synesthesia, because that structure is mainly involved in analyzing the visual shape, not the high-level meaning, of the number. One intriguing twist: Imagine an image with a large 5 made up of little 3’s; you can see either the “for-est” (the 5) or focus minutely on the “trees” (the 3’s). Two synesthete subjects reported that they saw the color switch, depending on their focus. This test implies that even though synesthesia can arise as a result of the visual appearance alone—not the high-level concept—the manner in which the visual input is categorized, based on attention, is also critical.

But as we began to recruit other volunteers, it soon became obvious that not all synesthetes who colorize their world are alike. In some, even days of the week or months of the year elicit colors.

The only thing that days of the week, months and numbers have in common is the concept of numerical sequence, or ordinality. For certain synesthetes, perhaps it is the abstract concept of numerical sequence that drives the color, rather than the visual appearance of the number. Could it be that in these individuals, the cross wiring occurs between the angular gyrus and the higher color area near the TPO instead of between areas in the fusiform? If so, that interaction would ex-plain why even abstract number representations, or the idea of the numbers elicited by days of the

week or months, will strongly evoke specifi c col-ors. In other words, depending on where in the brain the synesthesia gene is expressed, it can result in different types of the condition—“high-er” synesthesia, driven by numerical concept, or “lower” synesthesia, produced by visual appear-ance alone. Similarly, in some lower forms, the visual appearance of a letter might generate col-or, whereas in higher forms it is the sound, or phoneme, summoned by that letter; pho nemes are represented near the TPO.

We also observed one case in which we be-lieve cross activation enables a color blind synes-thete to see numbers tinged with hues he other-wise cannot perceive; charmingly, he refers to these as “Mar tian colors.” Although his retinal color receptors cannot process certain wave-

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In a test of visual-segregation capabilities, synes-thetes who link a specifi c hue with a given number can instantly see an embedded pattern in an im-age with black numbers scattered on a white page. Whereas a person with normal perception must undertake a digit-by-digit search to pick out, in this example, 2’s amid 5’s (left), the triangle-shaped group of 2’s pops out for an individual with synesthesia (right).

“Invisible” numbers show up for synesthetes in a perceptual test. When a person stares at a cen-tral object, here a plus sign, a single digit off to one side is easy to see with peripheral vision (left). But if the number is surrounded by others (right), it appears blurry— invisible—to the aver-age person. In contrast, a synesthete could de-duce the central number by the color it evokes.

Color-Coded World

(The Authors)

VILAYANUR S. RAMACHANDRAN and EDWARD M. HUBBARD collaborate on studies of synesthesia. Ramachandran directs the Center for Brain and Cognition at the University of California at San Diego and is adjunct pro-fessor at the Salk Institute for Biological Studies. He trained as a physi-cian and later obtained a Ph.D. from Trinity College, University of Cam-bridge. Hubbard recently received his Ph.D. from the departments of psychology and cognitive science at U.C.S.D. and is now a postdoctoral fellow at INSERM in Orsay, France. A founding member of the American Synesthesia Association, he helped to organize its second annual meeting at U.C.S.D. in 2001.

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Pop-out Test (synaesthete)

tivation within the fusiform gyrus itself in num-ber-color synesthesia, because that structure is mainly involved in analyzing the visual shape, not the high-level meaning, of the number. One intriguing twist: Imagine an image with a large 5 made up of little 3’s; you can see either the “for-est” (the 5) or focus minutely on the “trees” (the 3’s). Two synesthete subjects reported that they saw the color switch, depending on their focus. This test implies that even though synesthesia can arise as a result of the visual appearance alone—not the high-level concept—the manner in which the visual input is categorized, based on attention, is also critical.

But as we began to recruit other volunteers, it soon became obvious that not all synesthetes who colorize their world are alike. In some, even days of the week or months of the year elicit colors.

The only thing that days of the week, months and numbers have in common is the concept of numerical sequence, or ordinality. For certain synesthetes, perhaps it is the abstract concept of numerical sequence that drives the color, rather than the visual appearance of the number. Could it be that in these individuals, the cross wiring occurs between the angular gyrus and the higher color area near the TPO instead of between areas in the fusiform? If so, that interaction would ex-plain why even abstract number representations, or the idea of the numbers elicited by days of the

week or months, will strongly evoke specifi c col-ors. In other words, depending on where in the brain the synesthesia gene is expressed, it can result in different types of the condition—“high-er” synesthesia, driven by numerical concept, or “lower” synesthesia, produced by visual appear-ance alone. Similarly, in some lower forms, the visual appearance of a letter might generate col-or, whereas in higher forms it is the sound, or phoneme, summoned by that letter; pho nemes are represented near the TPO.

We also observed one case in which we be-lieve cross activation enables a color blind synes-thete to see numbers tinged with hues he other-wise cannot perceive; charmingly, he refers to these as “Mar tian colors.” Although his retinal color receptors cannot process certain wave-

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www.sc iammind.com 21

In a test of visual-segregation capabilities, synes-thetes who link a specifi c hue with a given number can instantly see an embedded pattern in an im-age with black numbers scattered on a white page. Whereas a person with normal perception must undertake a digit-by-digit search to pick out, in this example, 2’s amid 5’s (left), the triangle-shaped group of 2’s pops out for an individual with synesthesia (right).

“Invisible” numbers show up for synesthetes in a perceptual test. When a person stares at a cen-tral object, here a plus sign, a single digit off to one side is easy to see with peripheral vision (left). But if the number is surrounded by others (right), it appears blurry— invisible—to the aver-age person. In contrast, a synesthete could de-duce the central number by the color it evokes.

Color-Coded World

(The Authors)

VILAYANUR S. RAMACHANDRAN and EDWARD M. HUBBARD collaborate on studies of synesthesia. Ramachandran directs the Center for Brain and Cognition at the University of California at San Diego and is adjunct pro-fessor at the Salk Institute for Biological Studies. He trained as a physi-cian and later obtained a Ph.D. from Trinity College, University of Cam-bridge. Hubbard recently received his Ph.D. from the departments of psychology and cognitive science at U.C.S.D. and is now a postdoctoral fellow at INSERM in Orsay, France. A founding member of the American Synesthesia Association, he helped to organize its second annual meeting at U.C.S.D. in 2001.

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COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC.

Theories

• cross-wiring

• defective synaptic pruning

• excessive synaptic connections

• cross-activation

• epileptic patients

Inducer

• conscious processing

• unconscious processing

• concept-driven

• solution to arithmetic problem interfered with color patch naming

Crowding

Periphery

Neural Location?

• varies by subject

• “lower” synaesthesia

• “higher” synaesthesia

• concurrent is usually not complex

• inducer can be highly complex

Unconscious priming eliminated automatic binding of colour and

alphanumeric form in synaesthesiaMattingley et. al.

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)

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

Results

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Standard Stroop Task

• results as expected

• all subjects slower on incongruent items

• no difference between synaesthetes and controls

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

Results

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?7A=8BA F9:?:57:@ A5@AMA@86BBK <5 6 ;<=F87:9 @A?FB6K4 N5 <5::OF:9A=:57G ?K56:?7D:7A;6BBK ;<5E98:57 65@ A5;<5E98:57 ?7A=8BA3:9: F9:?:57:@ A5 ?:F6967: >B<;P? <L 79A6B?4 QK56:?7D:7:? 7<<P?AE5AR;657BK B<5E:9 7< 56=: @A?FB6K ;<B<89? 3D:5 7D:?: 3:9:A5;<5E98:57 3A7D 7D:A9 A5@8;:@ ?K56:?7D:7A; ;<B<89?G 6? ;<=F69:@3A7D 7D: ;<5E98:57 ;<5@A7A<5 A53DA;D 7D: FDK?A;6B 65@ ?K56:?7D:7A;;<B<89? 3:9: =67;D:@ H!,G.S T ,.4--G "! -4-,U VAE4 .>I4 !<76>BKG7D:9: 36? 5< @ALL:9:5;: >:73::5 ;<5E98:57 65@ A5;<5E98:57 ;<5C@A7A<5? L<9 7D: 5<5C?K56:?7D:7A; ;<579<B? H!,G.S T -4W,G "" -4,-UVAE4 .>I4N5 6 ?:;<5@ :OF:9A=:57G ;<5E98:57 65@ A5;<5E98:57 79A6B? 3:9:

965@<=BK A57:9=A5EB:@4 "@@A7A<56B X5:8796BY ?7A=8BAG ;<=F9A?A5E5<5C6BFD658=:9A; 7KF<E96FDA;6B ?K=><B?G 3:9: 6B?< A5;B8@:@ H?::0:7D<@?I4 QK56:?7D:7:? 6E6A5 ?D<3:@ 6 ?AE5AR;657 :LL:;7 <L ;<5CE98:5;K H!.G.S T Z4+WG "! -4-,U VAE4 .;IG 3D:9:6? 7D: ;<579<B? @A@ 5<7H!.G.S T ,4,ZG "" -4,-I4 #D:?: 9:?8B7? ?D<3 7D67 ;<B<89CE96FD:=A;?K56:?7D:7:? ;655<7 ;<5?;A<8?BK ?8FF9:?? 7D:A9 858?86B ;<B<89?:5?67A<5?4 #DA? A? ;<5?A?7:57 3A7D A5@AMA@86B ;6?: 9:F<97? <L

?K56:?7D:7A; A57:9L:9:5;:Z[/G,,G 6? 3:BB 6? <89 ?K56:?7D:7:?Y ?8>\:;7AM::OF:9A:5;:? <L <M:93D:B=A5E =:576B :LL<97 A5 7D: ?K56:?7D:7A;6BBKA5;<5E98:57 79A6B?4]: 5:O7 @:7:9=A5:@ 3D:7D:9 7D: A5M<B85769K >A5@A5E <L ;<B<89

65@ L<9= <;;89? 3D:5 7D: 79AEE:9A5E ?7A=8BA 69: 5<7 6M6AB6>B: L<9;<5?;A<8? 9:F<974 (A?86B ?7A=8BA 7D67 69: @A?FB6K:@ >9A:^K 65@=6?P:@ =6K 9:;:AM: ;<5?A@:96>B: 85;<5?;A<8? F9<;:??A5E,_[,S4 ]:=<@AR:@ <89 ?K56:?7D:7A; Q79<<F 76?P ?< 7D67 65 6;D9<=67A;6BFD658=:9A; ;D696;7:9 36? F9:?:57:@ >9A:^K 65@ =6?P:@4 J697A;ACF657? 56=:@ 7D: ;<B<89 <L 6 769E:7 F67;D F9:?:57:@ A==:@A67:BK6L7:9 7D: =6?P:@ F9A=:4 #D: ;<B<89 <L 7D: 769E:7 F67;D 36?;<5E98:57G A5;<5E98:57 <9 5:8796B 3A7D 9:?F:;7 7< 7D: ?K56:?7D:7A;;<B<89 A5@8;:@ >K 7D: 6BFD658=:9A; F9A=:4 N5 65 A5A7A6B :OF:9AC=:57G 7D: F9A=: 36? F9:?:57:@ L<9 `--=? ?< 7D67 A7 36? ;B:69BKMA?A>B:4 ]: 7:?7:@ F9A=: A@:57AR;67A<5 A5 6 ?:F6967: 76?P A5 3DA;DF697A;AF657? D6@ 7< 56=: 7D: 6BFD658=:9A; F9A=:G A5?7:6@ <L56=A5E 7D: ;<B<89 <L 7D: 769E:7 F67;D H?:: VAE4 WI4N5 7D: ;<B<89C56=A5E 76?PG ?K56:?7D:7:? 3:9: ?AE5AR;657BK 6LL:;7:@

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`_ <9

.S=?G A5 ?:F6967: >B<;P? <L 79A6B?4 "7 7D:?: @8967A<5?G ;<5?;A<8?A@:57AR;67A<5 <L 7D: 6BFD658=:9A; F9A=:? 36? ?:M:9:BK ;8976AB:@HVAE4 WIU A5@::@G F697A;AF657? 3:9: 5<7 6369: <L 7D:A9 F9:?:5;:4 "??D<35 A5 VAE4 +6G 7D: :LL:;7 <L ;<5E98:5;K <5 ;<B<89C56=A5E 7A=:?67 7D:?: ?D<97:9 F9A=: @8967A<5? 36? ;<=FB:7:BK 6>?:57 A5 7D:

a

Congruent Incongruent

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Congruent Incongruent Neutral

!"#$%& ' !"#$ %&'(")&$*"+ +',"* -#. */"/0 1&2 (&3&42 $#,'$5 '$ +6" *+#$7#27 #$7

*8$#"*+6"+'( 9+2&&: +#*;*< :3&++"7 #* # 14$(+'&$ &1 (&$524"$(8 (&$7'+'&$/ =#+# #2" *6&>$

#* *":#2#+" 3'$"* 1&2 *8$#"*+6"+"* -*&3'7 *8,?&3*0 #$7 $&$)*8$#"*+6"+'( (&$+2&3* -&:"$

*8,?&3*0/ (< @#$7&,'A"7 :2"*"$+#+'&$ &1 (&$524"$+ #$7 '$(&$524"$+ (&3&42 >&27* '$ +6"

*+#$7#27 9+2&&: +#*;/ !"#$* 1&2 ?#*"3'$" (&$7'+'&$ #2" 2":&2+"7 '$ +6" +"B+/ )< C3&(;"7:2"*"$+#+'&$ &1 *8$#"*+6"+'(#338 (&$524"$+ #$7 '$(&$524"$+ #3:6#$4,"2'( (6#2#(+"2*/

*< @#$7&,'A"7 :2"*"$+#+'&$ &1 *8$#"*+6"+'(#338 (&$524"$+< '$(&$524"$+ #$7 $"4+2#3

#3:6#$4,"2'( (6#2#(+"2*/ D6" 1#*+"2 2"*:&$*"* &1 *8$#"*+6"+"* 2"3#+'%" +& (&$+2&3* '$ +6"

(&$524"$+ (&$7'+'&$ &1 ) -?4+ $&+ *0 ',:3'"* # *+2#+"5'( ?"$"E+ 12&, ?3&(;"7 :2"*"$+#+'&$/

Group

Synaesthetes Controls

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!"#$%& + !"#$ :"2("$+#5" (&22"(+ :2'," '7"$+'E(#+'&$ -F. */"/0 1&2 +6" :2','$5

"B:"2',"$+*/ =#+# #2" :3&++"7 *":#2#+"38 1&2 *8$#"*+6"+"* #$7 $&$)*8$#"*+6"+'( (&$+2&3*/

G2'," 742#+'&$* >"2" HI,* -&:"$ ?#2*0< JK,* -6#+(6"7 ?#2*0 #$7 JLL,* -E33"7 ?#2*0M

'7"$+'E(#+'&$ *(&2"* >"2" $&+ 7'11"2"$+ 1&2 +6" +>& 52&4:* #+ #$8 &1 +6" 742#+'&$*

-!" L/.L 1&2 #33 (&,:#2'*&$*0/


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!"#$%& , !"#$ %&'(")&$*"+ +',"* -#. */"/0 1&2 (&3&42 $#,'$5 '$ +6" %'*'?3" :2','$5

-JLL,*0 #$7 ,#*;"7 :2','$5 -JK #$7 HI,*0 "B:"2',"$+*< :3&++"7 #* # 14$(+'&$ &1

*8$#"*+6"+'( (&$524"$(8 (&$7'+'&$/ (< 98$#"*+6"+"*N *+#$7#27 :2','$5/ )< O&$+2&3*N*+#$7#27 :2','$5/ *< 98$#"*+6"+"*N +",:&2#3)5#: :2','$5/ -< O&$+2&3*N +",:&2#3)5#:

:2','$5/ =#+# #2" *6&>$ #* *":#2#+" 3'$"* 1&2 "#(6 &1 +6" +62"" :2'," 742#+'&$* &1 JLL,*

-E33"7 +2'#$53"*0< JK,* -&:"$ ('2(3"*0 #$7 HI,* -&:"$ *P4#2"*0/


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)

Prime Identification

!"##"$% #& '(#)$"

!"#$%& ' ()* +,- ' ./ 0"%12 .--, ' 333456789:4;<= *+,








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!"#$%& ' !"#$ %&'(")&$*"+ +',"* -#. */"/0 1&2 (&3&42 $#,'$5 '$ +6" *+#$7#27 #$7

*8$#"*+6"+'( 9+2&&: +#*;*< :3&++"7 #* # 14$(+'&$ &1 (&$524"$(8 (&$7'+'&$/ =#+# #2" *6&>$

#* *":#2#+" 3'$"* 1&2 *8$#"*+6"+"* -*&3'7 *8,?&3*0 #$7 $&$)*8$#"*+6"+'( (&$+2&3* -&:"$

*8,?&3*0/ (< @#$7&,'A"7 :2"*"$+#+'&$ &1 (&$524"$+ #$7 '$(&$524"$+ (&3&42 >&27* '$ +6"

*+#$7#27 9+2&&: +#*;/ !"#$* 1&2 ?#*"3'$" (&$7'+'&$ #2" 2":&2+"7 '$ +6" +"B+/ )< C3&(;"7:2"*"$+#+'&$ &1 *8$#"*+6"+'(#338 (&$524"$+ #$7 '$(&$524"$+ #3:6#$4,"2'( (6#2#(+"2*/

*< @#$7&,'A"7 :2"*"$+#+'&$ &1 *8$#"*+6"+'(#338 (&$524"$+< '$(&$524"$+ #$7 $"4+2#3

#3:6#$4,"2'( (6#2#(+"2*/ D6" 1#*+"2 2"*:&$*"* &1 *8$#"*+6"+"* 2"3#+'%" +& (&$+2&3* '$ +6"

(&$524"$+ (&$7'+'&$ &1 ) -?4+ $&+ *0 ',:3'"* # *+2#+"5'( ?"$"E+ 12&, ?3&(;"7 :2"*"$+#+'&$/

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!"#$%& + !"#$ :"2("$+#5" (&22"(+ :2'," '7"$+'E(#+'&$ -F. */"/0 1&2 +6" :2','$5

"B:"2',"$+*/ =#+# #2" :3&++"7 *":#2#+"38 1&2 *8$#"*+6"+"* #$7 $&$)*8$#"*+6"+'( (&$+2&3*/

G2'," 742#+'&$* >"2" HI,* -&:"$ ?#2*0< JK,* -6#+(6"7 ?#2*0 #$7 JLL,* -E33"7 ?#2*0M

'7"$+'E(#+'&$ *(&2"* >"2" $&+ 7'11"2"$+ 1&2 +6" +>& 52&4:* #+ #$8 &1 +6" 742#+'&$*

-!" L/.L 1&2 #33 (&,:#2'*&$*0/


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!"#$%& , !"#$ %&'(")&$*"+ +',"* -#. */"/0 1&2 (&3&42 $#,'$5 '$ +6" %'*'?3" :2','$5

-JLL,*0 #$7 ,#*;"7 :2','$5 -JK #$7 HI,*0 "B:"2',"$+*< :3&++"7 #* # 14$(+'&$ &1

*8$#"*+6"+'( (&$524"$(8 (&$7'+'&$/ (< 98$#"*+6"+"*N *+#$7#27 :2','$5/ )< O&$+2&3*N*+#$7#27 :2','$5/ *< 98$#"*+6"+"*N +",:&2#3)5#: :2','$5/ -< O&$+2&3*N +",:&2#3)5#:

:2','$5/ =#+# #2" *6&>$ #* *":#2#+" 3'$"* 1&2 "#(6 &1 +6" +62"" :2'," 742#+'&$* &1 JLL,*

-E33"7 +2'#$53"*0< JK,* -&:"$ ('2(3"*0 #$7 HI,* -&:"$ *P4#2"*0/


Target Patch Identification

!"##"$% #& '(#)$"

!"#$%& ' ()* +,- ' ./ 0"%12 .--, ' 333456789:4;<= *+,








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!"#$%& ' !"#$ %&'(")&$*"+ +',"* -#. */"/0 1&2 (&3&42 $#,'$5 '$ +6" *+#$7#27 #$7

*8$#"*+6"+'( 9+2&&: +#*;*< :3&++"7 #* # 14$(+'&$ &1 (&$524"$(8 (&$7'+'&$/ =#+# #2" *6&>$

#* *":#2#+" 3'$"* 1&2 *8$#"*+6"+"* -*&3'7 *8,?&3*0 #$7 $&$)*8$#"*+6"+'( (&$+2&3* -&:"$

*8,?&3*0/ (< @#$7&,'A"7 :2"*"$+#+'&$ &1 (&$524"$+ #$7 '$(&$524"$+ (&3&42 >&27* '$ +6"

*+#$7#27 9+2&&: +#*;/ !"#$* 1&2 ?#*"3'$" (&$7'+'&$ #2" 2":&2+"7 '$ +6" +"B+/ )< C3&(;"7:2"*"$+#+'&$ &1 *8$#"*+6"+'(#338 (&$524"$+ #$7 '$(&$524"$+ #3:6#$4,"2'( (6#2#(+"2*/

*< @#$7&,'A"7 :2"*"$+#+'&$ &1 *8$#"*+6"+'(#338 (&$524"$+< '$(&$524"$+ #$7 $"4+2#3

#3:6#$4,"2'( (6#2#(+"2*/ D6" 1#*+"2 2"*:&$*"* &1 *8$#"*+6"+"* 2"3#+'%" +& (&$+2&3* '$ +6"

(&$524"$+ (&$7'+'&$ &1 ) -?4+ $&+ *0 ',:3'"* # *+2#+"5'( ?"$"E+ 12&, ?3&(;"7 :2"*"$+#+'&$/

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!"#$%& + !"#$ :"2("$+#5" (&22"(+ :2'," '7"$+'E(#+'&$ -F. */"/0 1&2 +6" :2','$5

"B:"2',"$+*/ =#+# #2" :3&++"7 *":#2#+"38 1&2 *8$#"*+6"+"* #$7 $&$)*8$#"*+6"+'( (&$+2&3*/

G2'," 742#+'&$* >"2" HI,* -&:"$ ?#2*0< JK,* -6#+(6"7 ?#2*0 #$7 JLL,* -E33"7 ?#2*0M

'7"$+'E(#+'&$ *(&2"* >"2" $&+ 7'11"2"$+ 1&2 +6" +>& 52&4:* #+ #$8 &1 +6" 742#+'&$*

-!" L/.L 1&2 #33 (&,:#2'*&$*0/


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!"#$%& , !"#$ %&'(")&$*"+ +',"* -#. */"/0 1&2 (&3&42 $#,'$5 '$ +6" %'*'?3" :2','$5

-JLL,*0 #$7 ,#*;"7 :2','$5 -JK #$7 HI,*0 "B:"2',"$+*< :3&++"7 #* # 14$(+'&$ &1

*8$#"*+6"+'( (&$524"$(8 (&$7'+'&$/ (< 98$#"*+6"+"*N *+#$7#27 :2','$5/ )< O&$+2&3*N*+#$7#27 :2','$5/ *< 98$#"*+6"+"*N +",:&2#3)5#: :2','$5/ -< O&$+2&3*N +",:&2#3)5#:

:2','$5/ =#+# #2" *6&>$ #* *":#2#+" 3'$"* 1&2 "#(6 &1 +6" +62"" :2'," 742#+'&$* &1 JLL,*

-E33"7 +2'#$53"*0< JK,* -&:"$ ('2(3"*0 #$7 HI,* -&:"$ *P4#2"*0/


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

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

Synaesthetic photisms influence visual perception

Smilek et. al.

Summary

• C, digit → color synaesthete

• experiments

• masked digit identification

• visual search

Masked Digit Identification

• fixation cross (800 ms)

• randomly chosen digit (32 ms)

• congruent background

• incongruent background

• mask (% or $)

Task

As can be seen from the figure, C was less accurate atidentifying a briefly presented digit when the color of

the background was congruent with her photism for thedigit (M = 0.88), than when the color of the backgroundwas incongruent with her photism for the digit (M =0.96), x2 (1) = 8.59, p < .005. This result stronglysuggests that C’s photisms influence her perception ofdigits.In contrast to C’s rather large mean difference (0.08)

between digit identification on congruent and incongru-ent trials, seven nonsynaesthetes showed only a smallmean difference in digit identification between congru-ent and incongruent trials (0.02). When the seven non-synaesthetes were considered individually, thedifferences in accuracy between congruent and incon-gruent trials ranged from !0.01 to 0.04. Importantly,none of these differences were statistically significant (allx2s < 1.20, ps > .250), including the nonsynaestheteswho were either similar to or better than C in overallaccuracy. The middle and the right side of Figure 3 showthe average results of seven nonsynaesthetes and theone nonsynasthete most similar to C in overall accuracy,respectively.

Localization of Digits

RT Data1

The mean RTs for C to localize target digits are shown inthe middle of Figure 4. The data were submitted to a 2(congruent vs. incongruent) " 3 (6, 12, 18 distractors)independent sample analyses of variance (ANOVA). Ascan be seen from Figure 4, C was slower at localizingtarget digit when her photism for a target digit wascongruent with the color of the background, than when

+

4

+

4


$% $%

Figure 1. Examples of the stimulus displays used in the identificationtask.

8

8

884

8

48

8

8

Congruent

Incongruent

8

8

8

8

Figure 2. Examples of the stimulus displays used in the localizationtask.

0.70

0.75

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0.95

1.00

C Non-synaesthetes(n = 7)

Matched Non-synaesthete

Participants

Pro

port

ion

Cor

rect

Congruent

Incongruentp < .005

all ps > .250

p > .254

Figure 3. Proportion correct identification of digits on congruent andincongruent trials for C, the group of seven nonsynaesthetes, and thenonsynaesthete most closely matched to C in overall accuracy.

Smilek et al. 931

Results





RT Data1


+

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$% $%


8

8

884

8

48

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8

Congruent

Incongruent

8

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Participants

Pro

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Incongruentp < .005

all ps > .250

p > .254


Smilek et al. 931

Visual Search

• target (2 or 4)

• distractor digits (8)

• 6, 12, or 18 distractors

• congruent background

• incongruent background

TaskAs can be seen from the figure, C was less accurate atidentifying a briefly presented digit when the color of




RT Data1


+

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$% $%


8

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884

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48

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Incongruent

8

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Participants

Pro

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Cor

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Incongruentp < .005

all ps > .250

p > .254


Smilek et al. 931





RT Data1


+

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+

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$% $%


8

8

884

8

48

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8

Congruent

Incongruent

8

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0.70

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1.00



Participants

Pro

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Cor

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Congruent

Incongruentp < .005

all ps > .250

p > .254


Smilek et al. 931

Results

her photism for a target digit was incongruent with thecolor of the background, F(1,550) = 5.214, MSE =17526.8, p < .025. These results suggest that the pho-tisms elicited by the target digits influenced C’s percep-tion of the digits. The analyses revealed that searchdifficulty was equivalent across set size, F(2,550) =2.281, MSE = 17526.8, p > .103, and that the smalldifference in slopes between congruent and incongruenttrials shown in Figure 4 was not statistically significant,F(2,550) = 0.701, MSE = 12287.5, p > .496.

The top of Figure 4 shows the combined results forthe seven nonsynaesthetes. A 2 (congruent vs. incon-gruent) ! 3 (6, 12, 18 distractors) repeated measuresANOVA showed that the performance of the sevennonsynaesthetes as a group was considerably differentfrom C. In contrast to C’s results, the seven nonsynaes-thetes showed no difference between congruent andincongruent trials, F < 0.001, p > .995. The results alsoshowed that for the nonsynaesthetes search becamemore difficult as set size increased, F(2,12) = 10.118,MSE = 1870.70, p < .01, and the search slopes forlocalizing the target digits on congruent and incongru-ent trials were similar and did not statistically differ,F(2,12) = 1.258, MSE = 515.51, p > .30.

The RT data for each nonsynaesthete were also sub-mitted to a 2 (congruent vs. incongruent) ! 3 (6, 12, 18distractors) independent sample ANOVA. When consid-ered individually, five of the nonsynaesthetes showed no

difference between congruent and incongruent trials(Fs < 1.64, ps > .200), and two nonsynaesthetes wereslower at localizing the targets on incongruent trials thancongruent trials (Fs > 3.739, ps < .055)—a pattern ofresults opposite to the pattern shown by C. Importantly,none of the seven nonsynaesthetes, including the non-synaesthetes who were either similar to or faster than Cin overall RT, showed a pattern of results similar to C—apattern characterized by slower localization of the targetdigits on congruent than incongruent trials.

The individual results of the nonsynaesthetes alsoshowed that for five of the nonsynaesthetes searchbecame more difficult with increases in set size (Fs >4.350, ps < .02) and for two of the nonsynaesthetes thedifficulty of search was equivalent across all set sizes (Fs< 1.687, ps > .186). Analysis of the error data suggests,however, that the RT results of the latter two non-synaesthetes may have been due to speed–accuracytradeoffs. That is, for both of these nonsynaesthetes,errors increased as set size increased (Fs > 3.021, ps <.051). Finally, the search slopes for congruent andincongruent trials did not differ for any of the sevennonsynaesthetes (Fs < 1.200, ps > .144). The bottom ofFigure 4 shows the results for the nonsynasthete thatwas most similar in overall RT to C.

Error Data

The mean percentage errors are shown in parentheses inFigure 4. A 2 (congruent vs. incongruent) ! 3 (6, 12, 18distractors) independent sample ANOVA revealed thatC’s errors were comparable across conditions (Fs < 1, ps> .52). When the error data for the seven nonsynaes-thetes were submitted to a 2 (congruent vs. incongru-ent) ! 3 (6, 12, 18 distractors) repeated measuresANOVA, the analysis revealed that the nonsynaesthetesmade a comparable number of errors on congruent andincongruent trials, F(1,6) = 4.273, MSE = 0.000664,p> .084. The analysis also revealed that errors increasedas the number of distractors increased, F(2,12) = 5.529,MSE = 0.0008145, p < .021, and that there was nointeraction between set size and trial congruency (F < 1,p > .50). These findings indicate that interpretation ofthe RT data is not compromised by speed–accuracytrade-offs. The error data for each nonsynaesthete werealso submitted to a separate 2 (congruent vs. incon-gruent) ! 3 (6, 12, 18 distractors) independent sampleANOVA. The results showed that the only significantdifferences in errors were observed in the two non-synaesthetes who showed increased errors as set sizeincreased (Fs > 3.021, ps < .051). There appeared tobe no other speed–accuracy tradeoffs.

DISCUSSION

In two experiments, we evaluated whether the photismselicited by digits in a digit–color synaesthete influenced

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C

Figure 4. Mean reaction times and percentage errors (in parentheses)for localizing target digits on congruent and incongruent trials for C,the group of nonsynaesthetes, and the nonsynaesthete most closelymatched to C in overall RT. Error bars depict one standard error of themean.

932 Journal of Cognitive Neuroscience Volume 13, Number 7

Contradictions?

• Variability among synaesthetes

• type of synaesthesia

• level of processing at which synaesthesia occurs

Questions

• 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?

• 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).

McCollough Effect

Adaptation

Adaptation II

Test Stimulus

Synaesthetic Inducer

Test Stimulus

• 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?

• 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”

• 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?

synaesthesia - university of california, san diegodeepeco.ucsd.edu/~hye/files/synaesthesia.pdf ·...

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