Synesthesia Terms

Question 1

Synesthesia

Answer 1

a stimulus in one sensory modality evokes an additional experience in an unrelated sensory modality (intermodal synesthesia) or a different aspect of the same modality (intramodel synesthesia), links two normally independent qualia. Stimulus that triggers synesthesia is the inducer and the modality in which the resulting synesthesia is experienced is the concurrent, Various types identified using inducer -> concurrent

Eg. grapheme -> colour synesthesia
Eg. hearing a word spoken causes a particular flavour sensation
Eg. seing an achromatic letter or number produces a colour experience

Question 2

Qualia

Answer 2

subjective qualities of conscious experience

Eg. synesthesia has been called qualia becoming deranged

Question 3

Automatic / Involuntary

Answer 3

Cytowic diagnostic criteria, occurs without any conscious effort

Question 4

Spatially Extended

Answer 4

Cytowic diagnostic criteria,

some synesthetes experience the concurrent in the same physical location as the inducer, for others it floats around them in space

Question 5

Consistent

Answer 5

Cytowic diagnostic criteria, consistent over time

Question 6

Elementary

Answer 6

Cytowic diagnostic criteria, not pictorial but generic in quality

Eg. not an entire visual scene but just a colour or a shape

Question 7

Specific

Answer 7

Cytowic diagnostic criteria, specific

Eg. not ‘green’ but ‘spring leaf green’ or ‘lime pale green’

Question 8

Highly Memorable

Answer 8

aids in remembering stimuli, synesthetes are more likely to have eidetic memory

Eg. grapheme -> colour synesthesia helps spelling

Question 9

Loaded with Affect

Answer 9

associations can be intensely aesthetically pleasing or displeasing

Eg. “Derek” tastes of earwax

Question 10

Congenital Synesthesia

Answer 10

present from birth, heritable up to 40% of a synesthetes first and second degree relatives also have it, can skip generations, family members with it do not necessarily have same kind of synesthesia, if family members do have same kind they do not necessarily have the same associations

Question 11

Adventitious Synesthesia

Answer 11

acquired after birth, may result from stroke or closed head trauma, temporal lobe epileptic seizures or blindness and can become permanent, may be temporary (due to hallucinogenic drugs, meditation or sensory deprivation)

Question 12

Idiosyncratic Synesthesia

Answer 12

if two synesthetes both have grapheme -> colour synesthesia they are not likely to have the same response

Eg. one synesthete may see the letter X as white and another may experience it as red

Question 13

Lower Synesthetes

Answer 13

processing is primarily bottom up, colours are elicited by the actual visual appearance of a grapheme

Eg. 7 -> yellow

Question 14

Higher Synesthetes

Answer 14

experience is affected by top-down processing, thus colours are elicited by the concepts conveyed by the stimuli

Eg. Arabic numerals, roman numerals and days of the week which all represent ordinality

Question 15

Projectors

Answer 15

strongly experience colours as overlays projected and bound to a grapheme in the outside world, proposed that projectors = lower synesthetes

Question 16

Associators

Answer 16

experience weaker synesthetic colours “in the mind’s eye” only, proposed that associators = higher synesthetes

Question 17

Cross-activation / Insufficient pruning

Answer 17

more connections’, neural model of synesthesia, gene in synesthesia fails to prune the excess synapses that are present in all infants, result is cross-activation from a certain stimulus due to direct cross-wiring between different brain areas,

Visual word form area (VFWA) in fusiform gyrus responds to visual letters, words and numbers

Areas around angular gyrus (specifically TPO junction), implicated in representing more abstract numerical ideas - concepts like ordinality

Anterior inferior temporal (AIT) cortex also found to encode conceptual representations of words, letters and numbers

In lower synesthetes there is cross activation between VWFA and V4 (explain grapheme -> colour synesthesia, in higher synesthetes there is cross activation between areas around the angular gyrus and V4 or another higher colour processing area in the superior temporal gyrus (explain month -> colour synesthesia) - difference between lower and higher results from where the genes for synesthesia are expressed

Eg. visual presentation of graphemes affects lower not higher synesthtes, accounts for fact that upper/lowercase make no difference because neither VWFA nor AIT respond differently to capitalization

Hubbard et al. visually identifiable graphemes presented at lower contrast failed to produce synesthetic colours, VWFA less activated by low-contrast letters, more by high conrtast

Problems: what about adventitious synesthesia, why is synesthesia not apparent until mid-childhood

Question 18

Long-Range Disinhibited Feedback

Answer 18

neural model of synesthesia, degree of neural connectivity is identical in synesthetes and non synesthetes, however activity is normally balanced by equal excitation and inhibition, synesthesia is due to (genetically determined) reduced inhibition i normally existing feedback pathways, feedback may come from a multisensory nexus (like the TPO junction)

Eg. accounts for top-down effects because feedback comes from multisensory areas, acquired synesthesia may be due to brain damage, meditation, hallucinogenic drug use cannot result in more connections

PROBLEMS: adventitious synesthesia and LSD-induced hallucinations are often complex, including visualizations of animals and complex scenes in contrast to the generic experiences of congenital synesthesia which generally are simply of colour, does not account for synesthesia emerging in mid-childhood

Question 19

Reduced Plasticity

Answer 19

neural model of synesthesia, if a certain letter is seen in a certain colour this will strengthen the connection between them, because we see letters in various colours this tends to average out, but if plasticity is reduced an initial letter colour pairing may not change, accounts for emergence of synesthesia in mid-childhood,

Eg. Ward and Simner: JIW’s spoken word -> taste synesthesia is likely to have originated during vocabulary acquisition, phonemes that trigger a certain taste also tend to appear in the name of the corresponding food stuff (eg. college -> sausage, Sydney -> kidney), often semantic association between triggering word and taste (eg. blue -> inky, bar -> milk chocolate), synesthetic tastes are generally childhood foods rather than foods first eaten in adulthood, implies synesthsia is not due to innate connections but can be influenced by conceptual knowledge

Problems: unclear how this theory accounts for other forms of synesthsia, does not account for adventitious synesthesia

Question 20

Hyper-Binding

Answer 20

model suggests that synesthesia arises through an overactivation of parietal binding mechanism, binding of qualia may be accomplished by coordinating subsystems using feedback connections which requires interconnections between differently specialized areas, resulting in a holistic percept

Eg. applying TMS to parietal binding regions disrupts synesthesia
May use cross-activation or disinhibited feedback to create simultaneously active areas which are anomalously bound together