Week 10- Synaesthesia & Idiosyncratic perception Flashcards
First documented case of synaesthesia
-Georg Tobias Ludwig Sachs
-Born in modern day Austria (1786)
-Was an albino who was writing a doctorate about his experiences
-In one chapter he goes off topic and starts talking about synaesthesia specifically that ideas appear in colours to him and that things like numbers, colours, days of the week appear in colours.
Early definitions of synaesthesia
-Term was coined by French neurophysiologist Vulpian in 1866 who referred to it as the melding of the senses
-Galton (1881) called it “visions of sane persons.”
What else other than labelling synaesthesia as “visions of sane persons” did Galton contribute?
-Noted it was seen in “ a certain portion of the population”
-Noted in ran in families
Described three types for synaesthesia:
-sound-colour associations
-number/letter- colour associations
-Number forms
What are number forms
-An automatic, involuntary arrangement of numbers into spatial dimensions
-Galton called them “visualized numerals” i.e. people experience numbers not just in sequences but each actually occupying space in an arrangement (think back to the slide diagram)
Controversary with synaesthesia in the early days
-Often met with skepticism
-Being thought it was another kind of hallucination, an overactive imagination or potentially that individuals were just making up their experiences
-Wasn’t a subject of serious scientific study for most of the 20th century
Explosion of interest of synaesthesia research
-Midway through the 20th century there was a huge rise in public awareness for synaesthesia as people began to share their experiences through books
-The first tests of phenomenology of synaesthesia (e.g. content, specificity and constancy of synaesthetic experiences) then occurred in the later part of the 20th century
-These occurred as people became interested in the link between creativity and cognitive ability and the advent of brain imaging technology (e.g. fMRI) allowed for such research.
Phenomenology
Study of consciousness or human experience
What is synaesthesia?
-A “joining of the senses”
-When one sensory stimulus evokes two or more specific, consistent, involuntary, concurrent perceptual experiences
In synaesthesia what are the words used to describe the trigger stimulus and the response stimulus?
-Trigger stimulus: inducer
-Response stimulus: concurrent
So an inducer will trigger the concurrent
e.g. if shapes elicit tastes for you then shapes are the inducer in this case and taste the concurrent
What portion of the population have synaesthesia?
0.1-4% of the population (would put more faith in the higher end of that scale)
Which gender experiences more synaesthesia?
Women > men [but range 1:1 to 6:1]
Why is there so much variability in population estimates of synaesthesia and across genders?
-Traditionally has been a lot of stigma with synaesthesia so people not wanting to come forward and accept the ‘label’
- Response bias has reduced as stigma has decreased.
-Difficulties in defining synaesthesia makes drawing the line of what counts as synaesthesia hard
Is synaesthesia purely congentially?
-Synaesthesia often runs and families and seems to be congenital but not always….
- ‘adventitious synaesthesia’ e.g. mediation, sensory deprivation, drugs
-‘induced synaesthesia’
Common types of synaesthesia
Grapheme to colour
tone to colour (chromesthesia)
taste to touch
visual motion to sound
Note: always written in the format inducer to concurrent
What is a grapheme?
-A number or letter
Grapheme to colour is the most common type of synaesthesia by far!
Bidirectional synaesthesia? Example?
-Usually the relationship between the inducer and concurrent is unidirectional i.e. the inducer elicits the concurrent
-However, there are cases where the relationship between the inducer and concurrent can go both ways in the same individual (indicated by a double headed arrow)
-Example:
lexical <~> gustatory
Kandinsky
-Russian artist whose paintings were knowing as being an ‘orchestra of colour’
-Gave vivid accounts of his synaesthesia in letters
-Had chromesthesia (i.e. tone to colour synaesthesia) that appeared to be bidirectional
-An AI has been made to mimick the experience of a Kandinsky painting as described by him (writings, colour theories etc.). Although giving the subjectivity of qualia this will never be entirely accurate.
Synaesthesia pairings
-Pairings can be highly individualized (specific) & consistent throughout life
-May be:
1) completely arbitrary e.g. 7= light blue with a nice, calm personality
2) semantically influenced e.g. Barbara elicits rhubarb
3) heightened levels of common cross-modal associations e.g. low-pitch sounds elicit darker colours
-Pairings are concurrent e.g. if a shape triggers a sound, both are experienced. Because of this depending on the paring experiences can overlay: for example, if the number 7 induces blue, but I write it in grey with pencil then an individual would see both the grey 7 and the blue 7 ‘overtop’.
Development of Synaesthesia? Is it something you are born with or acquire?
-Could be learned by early childhood experience
An example of this is the fridge magnets (Withhold & Winawer, 2006, 2013):
-There was a popular fridge magnet set that had every 6 letters with a particular pattern of colours and then this repeated again and again for the whole alphabet.
-The idea is that people who learnt to read with this set may have deep ingrained associations between certain colours and certain letters.
-These individuals may have gone on to develop grapheme- colour synaesthesia
-Interestingly studies have found that there is a high portion of grapheme-colour synaesthetes that report learning to read with this fridge magnet set and can even present it as evidence!
-There is also lots of overlap between the colours they see for certain letters and the actual fridge magnet colours. In 2015, a study of graheme-colour synaesthetes found that 15% have experiences that highly align with the magnet set.
GUY LOVES THIS STORY IT’S “HIS FAVOURITE STORY IN SCIENCE” SO EXPECT TO BE ASKED ABOUT IT
Association learning in synaesthesia
-Remember semantically influence synaesthesia
e.g. Barbara elicts rhubarb
-Pairings are very seldom random. For instance, high-frequency graphemes pair with high-frequency colours (A> red). And tone-colour pairings frequently associate based on scales (e.g. low-pitch =dark colour, high-pitch= light colour)
-Semantic associations must be learnt and other non-random parings are likely shaped by experience. These examples therefore, provide further evidence (aside from the fridge magnets) that synaesthesia may not be purely congenital/ genetic in nature.
Is Synaesthesia just association learning?
-Stories like the fridge magnets have lead to people questioning the legitimacy of the synaesthetic experience i.e. Is not just learned associations?
Couldn’t we all do that?
-If this is true then why do people report vivid qualia? They report a sensory component (seeing/ hearing/ tasting) the concurrent beyond just simply picturing or thinking it.
Important distinction: associative and projective synaesthesia
-Some people with synaesthesia report seeing a concurrent colour as “floating in their mind’s eye” = associative synaesthesia
-Others report the concurrent as “projected onto the inducer” = projective synaesthesia
(for example, think about the number 7 drawn in grey with the blue overlaid like in the lecture slides)
Bouba- Kiki effect: hints that synaesthesia isn’t entirely learned
-Present shapes and ask which is “Bouba” and which is “Kiki”
-Over 95% will identify the curvy shape as “Bouba” and the point shape as “Kiki”.
-This effect starts in infancy and is seen across cultures. Indicating a predisposition to sound-shape correspondence
-This is not the same as synaesthesia of course but what it is demonstrating is that we might have a predisposition for making certain associations
Further evidence for a predisposition to certain associations
-Bouba-Kiki effect
-People with/ without grapheme-colour synaesthesia tend to be biased when making letter-colour associations e.g. a=red, b=blue, c= yellow
Colour blindness: evidence against experience driving synaesthesia
-Grapheme-colour blindness in a congenitally “colour-blind person”
-Music-colour synaesthesia in a congenitally “colour-blind person”
-No experience of colour!
Brain imagining and synaesthesia
-PET, fMRI
-Paulesu et al. (1995): blindfolded synaesthetic participants presented with spoken words… activation of speech areas AND visual cortex (Not seen in controls)
-Nunn et al. (2002): present grapheme, get activity in V4 and V8 (again, not in controls). Note V4= colour perception, V8= grapheme perception
-Both of these are evidence for a sensory basis of synaesthesia (i.e. additional wiring in the brain triggering concurrent sensory experience)
Brain electrophysiology and synaesthesia
-Beeli et al. (2008) looked at “event-related potentials” measurements of brain electrical responses to a stimulus
-ERP seen in V4 100-150ms after seeing a grapheme or hearing a sound- far too fast for language processing (> 300ms)
-Again consistent with a sensory basis to synaesthesia
Evidence of synaesthesia: psychophysics
-Several ways of looking at altered processing via reaction times
e.g. A synaesthetic Stroop test: get someone with grapheme-colour synaesthesia to say the ink colour of a number. They will be slower if this colour is incongruent with their concurrent perception as will see two colours (the concurrent on top of the original ink colour). Will be slower than control!
e.g. Perceptual grouping: What shape are the 2s arranged in? Grapheme-colour synesthete scan use the evoked colour differences to rapidly group and segregate the 2s from the 5s and distinguish the Gestalt triangle. Will be faster than control!
-Both of these are consistent with a sensory basis in synaesthesia
-NOTE: Only for projective not associative. There will be much less of an effect on response times for associative synaesthesia.
Why is the evidence for Synaesthesia controversial?
-Even with imaging, electrophysiology and psychophysics you are still matching activity/ performance with a subjective self- report measure
-Because of this can’t infer causality i.e. can’t know whether the performance being observed is linked to synaesthetic experience
-Additionally, still no evidence of perceiving versus use of imagery versus neither
-Role of attention? (e.g. colours only appear after attending to grapheme- psychophysics experiments reflect improved attention?)
-Role of motivation? (trying to prove that you have synaesthesia so maybe more motivated to do well in tasks like the perceptual grouping task and so increased performance is not related to synaesthetic experience)
Synaesthetic Stroop Test
get someone with grapheme-colour synaesthesia to say the ink colour of a number. They will be slower if this colour is incongruent with their concurrent perception as will see two colours (the concurrent on top of the original ink colour). Will be slower than control!
ONLY PROJECTIVE
Perceptual Grouping
What shape are the 2s arranged in? Grapheme-colour synesthete scan use the evoked colour differences to rapidly group and segregate the 2s from the 5s and distinguish the Gestalt triangle. Will be faster than control!
ONLY PROJECTIVE
