perception 17 - synaesthesia

synaesthetes experience

Experience blending of the senses

-when stimulate one sense see response of multiple areas in brain

-one sensory input yields secondary sensory response

-still rounded in reality its an overlay

synaesthesia prevalance

1000 who have sound and colour

500 sound and taste

1 sound, colour and taste - person in vid

Synaesthesia is

-Within or Across modalities (eg grapheme trigger colour is within vision)

-Experience is real not hallucination (is it perceptual or cognitive linkages)

-Automatic (can't stop it)

-Can feel 'normal' to the synaesthete

interactio in synaesthesia

Interaction between 2 things inducer (mainly linguistic) concurrent (mainly visual)

One direction e.g. letter -> colour not colour -> letter

Within head- visual image- ('associator') or out there ('projector')

-grapheme colour is majority of cases but are some more "bizarre" ones realise words taste

history

(very brief) History

Early/mid 1800s

-tended to be colour ones

-Hyperchromaticity (additional new types of cones!) - that was there proposed explanaiton

Late 1800s

-more and more types discovered

-Explosion of types, inc. cross-modal

1900s

-Interest declined - rise of behaviourism = learnt association

-therfore less interested in perception

dd percept vs cog

-study used as a measure of whether people have it

Test / Re-test reliability - Baron-Cohen et al (1993)

117 word list read to participants: (animals, places, objects, occupations, days-of-week, first names, alphabet letters, abstract terms, pronouns/prepositions, nonsense)

Asked for an associated colour after each word

- Controls tested 1 week later (told they could use any mnemonic technique, knew a memory experiment)

age- , IQ- memory- matched controls

- Synaesthetes tested 1 year later ! (not warned) 

Baron-Cohen et al (1993) - results

Consistency of colour-word associations

Control - 37.6%

spoken word - colour synaesthetes - 92.3%

(maybe some people werent synesthaates, maybe mood affects who knows)

evidence of atypical perceptual experience or just super-memory?

-if have this automatic trigger don't need amazing memory

People with synesthesia generally have consistent pairings

(consider association question?)

Stroop study

Stroop' - Dixon et al (2000)

"C" - a digit-colour synaesthete vs control

(photism just means perceptual experience)

Baseline - name colours

Congruent colour naming - real colour of numbers is the same as C's photism

Incongruent colour naming - real colour of numbers is different from C'ss photism

-C's choice RT is slowed in incongruent condition

-for non-syensthate doesn't really make a difference

-this feels more of a perceptual thing but could be cognitive too

Stroop mirror

Banissy & Ward (2007)

mirror-touch synaesthetes

-if look at someone being touched feel that touch in that part of their body

Look at a video of someone being touched on face and are also touched on the face by the research

Congruent and incongruent trials (touch by reacher on same or different side as video)

need to say if they felt two or left, right or none

Banissy & Ward (2007) results

Mirror touch error rate much higher in the incongruent condition

-control and congruent have w error rates

RT also increases

Some evidence of perpcpetual but is it? What level is stroop affect at - dont understand

More than learnt association

Grouping - Ramachandran & Hubbard (2001)

Apparent motion - Kim, Blake & Palmeri (2006)

Brain scan -Nunn et al (2002)

Grouping

Ramachandran & Hubbard (2001)

-using Gestalt principles

Rows of 3 +8 and 7 +0

-non-syneasthates group horizontally

...but to synaesthete ER the numerals trigger colours (= 'photisms') that allign in colums so she groups vertically (3,7 +8,0)

Black Fs,Ps, Hs - there is a triangle of H's

--non-synaesthetes take time to find the triangle of Hs

...but to JC photisms make grid appear...so the triangle pops out

Much more perceptual!

Apparent motion

Kim, Blake & Palmeri (2006)

-the direction of apparent motion in a circle can be ambigous, but if the circles are different colours becomes unambiguous as you can track the movement of spec coloured circles

Therefore circles of letters doing apparent motion can be ambiguous to nt but unambgous to a "lettercolour syneasthet"

50/50 versus ceertainty

Synaesthesia cause

nappropriate activation/connectivity between perceptual areas

-stimulus causes activity in correct/nrmal area but also another one

brain scanning

Nunn et al (2002)

-synaesthete with word/colour association

Overlap shows that when you activate word specific area also elicits activity in colour

ADD

Expt 3: no activity in V4 when non- synaesthetes trained on synaethetes' word-colour associations found in Expt 1

Train controls till reasonably high association but colour still doesn't light up, only syneasthesia

-shows not assoiciation is perceptual

why this extra activation?

Incomplete pruning? (see Ward 2013)

- everyone born 'synaesthetic' - massive interconnectivity in neonatal brain

-throgh early experience learn what goes together and what doesn't

- major task of brain during development is functional differentiation between areas ... synaesthetes may not complete this successfully

-functional differetiantion allows different areas to do different things