WEEK 6 - Synaesthesia PDF

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COGS101 LECTURE B WEEK 6 – SYNAESTHESIA WHAT IS SYNAESTHESIA?       

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Commonly described as a mixing of the senses – in a sense that’s actually a misnomer Ordinary stimulus such as a sound elicits an extraordinary experience Sound might be accompanied by a colour Extraordinary response to an ordinary stimulus E.g. Ordinary sound might have a colour attached or a taste or a smell It is not a disorder, so it does not interfere in any way Two camps - Had it all their lives, but reaction is different - Known since a young age by the way they talk Different parts of the brain process different attributes of that object - Occipital lobe receives your visual information Common – vivid consistent colours associated with letters of the alphabet, numbers and words Highly consistent It’s involuntary – measuring the effect of synaesthesia Perception of a specific stimulus induces a concurrent and distinct experience in a separate modality, or within the same modality Prevalence: 0.05-4% Gender bias? ~2-6 females to every 1 male Familiarity: high prevalence among biological relatives Not a disorder!

TYPES OF SYNAESTHESIA 

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In theory, every sense could be involved: - Sound  Vision  Touch  Smell  Proprioception - Vision  Sound  Touch  Smell  Proprioception …etc. Some types of synaesthesia are more common than others Less commonly: - Colours from pain, internal sensations (e.g., hunger), touch, smells, tastes - Non-colour experiences such as synesthetic smells, tastes, touch

COGS101 LECTURE GRAPHEME – COLOUR SYNAESTHETES   

As a child I can remember puzzling over why not everyone knew that 4 was red’ When I’m reading I can see that what I’m looking at is in black and white, but I also see the ‘correct’ colours for the letters and symbols’ Tuesday is yellow. I don’t ‘see’ it anywhere in particular; rather, I have a general awareness of yellowness in relation to the word’

AUDITORY-VISUAL, TOUCH-COLOUR, TIME-SPACE, MIRROR-TOUCH      

‘Every sound has a colour…people hitting golf balls at the driving range…each of their shots produces a slightly different shade of colour’ ‘I can’t stand loud music, there are too many colours’ ‘He had a yellow, crumbly kind of voice’ ‘Stroking is pink, scratching is ‘Time and dates are arranged in space around me. January is here, to the left, and then the months go around.’ ‘Whenever I see someone being touched, I feel that touch.’

OLFACTORY-VISUAL SYNAESTHETES  

“Garlic has a pale-yellow smell, rosemary a deep purple smell.” “Butter is brown. Most dog smells are yellow or black. Air conditioning is silver. The smell of smoke is red, but cigarettes are blue.”

WHAT CAUSES SYNTHAESTHESIA?     

Possible genetic predisposition - Runs in families Many synaesthetes without synaesthetic relatives Must depend on learning at some point May generalise from other stimuli (e.g., sounds) to learned items (e.g., letters) Hypotheses: - Extra connections between brain areas - Extra strength of connections between brain areas - Lack of normal inhibition of connections between brain areas

ARE SYNTHAESTHETS REALLY SO DIFFERENT?

COGS101 LECTURE

AUDITORY-VISUAL SYNAESTHETES’ RESPONSES TO TONES:

CONCLUSION PART A  

Synaesthesia is an unusual phenomenon (not a disorder!) in which an ordinary stimulus results in an extraordinary experience There are some similarities between synaesthetes and non-synaesthetes responses to stimuli that suggest synaesthesia builds on common mechanisms

COGS101 LECTURE HOW DO YOU MEASURE SYNAESTHESIA?     

Can use subjective measures – ask them about their experiences – rich and fascinating stories Does not tell us what’s going on in the brain or how the cognitive mechanisms that underpin synaesthesia Objective measures where you try and look for an objective way of measuring the effect of synaesthesia Inherently subjective Difficult to get at the exact nature of that perception

HOW CAN WE MEASURE SYNAESTHESIA? 

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Direct: Ask people about their experiences (Subjective report, consistency) - fascinating, rich, intriguing - difficult to describe - doesn’t tell us about how synaesthesia occurs Indirect: Look at the effect synaesthesia has on some other task - objective - might tell us more about the way it occurs - the ‘mechanisms’’

DIRECT - CONSISTENCY OVER TIME  

150 items from various categories Test - retest interval: - Synesthetes  3 months - Controls  1 month

COGS101 LECTURE CONSISTENCY ACROSS REPETITIONS

CONSISTENCY ACROSS SESSIONS

INDIRECT MEASURE 

Objective behavioural measures: - The “synaesthetic congruency” effect - Synaesthetic priming: exploring the role of awareness

OBJECT MEASURES OF OTHER FORMS? 

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Most research is on grapheme-colour synaesthesia - Most common - Amenable to objective measurement Work on multisensory synaesthesia (e.g., auditory-visual, mirror-touch) can also use can also use ‘Stroop-type’ tasks as an objective index Cross-modal forms might tell us more about multisensory integration generally

CONCLUSION PART B 

Direct and indirect measures tell us: - Synaesthetic colours are usually highly consistent - Synaesthesia is involuntary - Synaesthesia requires awareness of the inducing stimulus

COGS101 LECTURE THE NATURE OF SYNAESTHETIC COLOURS  

‘Real’ (wavelength-based) colours can guide or capture attention very effectively Widely reported claim that synaesthetic colours cause ‘pop-out’ in the same way as real colours (Ramachandran & Hubbard, 2001) => Do synaesthetic colours capture attention?

IS THIS EVIDENCE OF ATTENTIONAL CAPTURE?  

Advantage was not ‘pop-out’ like real colour Advantage only occurred when the distractors induced synaesthesia => Not ‘pop-out’ or preattentive synaesthesia - Different from ‘real’ colour => Perhaps synaesthesia provides “extra” information that aids the decision

CONCLUSION PART C  

Synaesthesia does not guide attention like ‘real’ colour There is an advantage for some synaesthetes in visual search/embedded figures tasks => may reflect a higher-level ‘decision’ or grouping benefit from synaesthetic colours

DOES SYNAESTHESIA REQUIRE ATTENTION?  

Normal ‘binding’ of object features requires attention Synaesthesia is an anomalous form of binding

COMBINING TASKS  

Measure of synaesthesia: Synaesthetic priming effect (Part B) Manipulation of attention: The attentional blink (Raymond, Shapiro, & Arnell, 1992)

CONCLUSION PART D  

Attention to the inducing stimulus (e.g., letter) is critical for synaesthesia to arise - Consistent with normal object feature binding Synaesthetic binding might tell us more about: - Normal feature binding - Links between objects & other attributes...