L17: Synaesthesia

Synaesthesia

Someone who experiences the blending of the senses

What two things is synaethesia an interaction between

• Inducer (mainly linguistic), what prompts synthetic experience (numbers, words, letters, etc.)

• Concurrent (mainly visual), the synthetic experience (usually visual)

What did behavioursim think synaesthesia was

A learned association

How does test/re-test reliability suggest synaestheia is a perceptual experience not a learned experience: Baron-Cohen et al. (1993)

• Words read out to P’s who were asked for an associated colour after each word

• Controls tested 1 week later and told they could use any mnemonic technique

• Synaesthetes tested 1 year later, not warned they would be retested

• Results

  • Synaethetes 92.3%

What is used as a screening tool for synaesthesia

Test-retest paradigm

Is grouping more of a perceptual or cognitive process

Perceptual (Ramachandran & Hubbard, 2001)

Synaesthesia Stroop Task

• Instead of words, have numbers either in associated colour (congruent) OR in another colour (incongruent)

• Results

  • RT greatly increased in incongruent condition for syneasthetic individual

    • No difference for controls

• HOWEVER, could still maybe be a learned association (unlikely but technically could)

Mirror-touch synaethetes

If see someone being poked, a mirror-touch synaethetes feels the sensation of being poked

Apparent motion (Kim et al., 2006)

• If dots of all the same colour move around in a circle, ambiguous if they moves left or right

• White letters moving in a circle appears ambiguous to neurotypical BUT unambiguous to a ‘letter-colour’ synaesthete

What part of the visual cortex is most concerned with colour in terms of synaesthesia

V4

What happens in the V4 if control participants learn the colour word association?

No light up of the V4 (colour) area

Cause of synaesthesia

Inappropriate activation/connectivity between perceptual areas

Incomplete pruning? (Ward 2013)

• Born ‘synaesthetic’

  • Massive interconnectivity in neonatal brain

  • Major task of brain during development is functional differentiation between areas, synesthetes may not complete this successfully 

• We are born synaesthetic, for some reason individuals with synesthesia don’t learn to separate (prune) the sensory modalities

Incomplete pruning (difficult to test)