Synesthesia Terms Flashcards
Synesthesia
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
Qualia
subjective qualities of conscious experience
Eg. synesthesia has been called qualia becoming deranged
Automatic / Involuntary
Cytowic diagnostic criteria, occurs without any conscious effort
Spatially Extended
Cytowic diagnostic criteria,
some synesthetes experience the concurrent in the same physical location as the inducer, for others it floats around them in space
Consistent
Cytowic diagnostic criteria, consistent over time
Elementary
Cytowic diagnostic criteria, not pictorial but generic in quality
Eg. not an entire visual scene but just a colour or a shape
Specific
Cytowic diagnostic criteria, specific
Eg. not ‘green’ but ‘spring leaf green’ or ‘lime pale green’
Highly Memorable
aids in remembering stimuli, synesthetes are more likely to have eidetic memory
Eg. grapheme -> colour synesthesia helps spelling
Loaded with Affect
associations can be intensely aesthetically pleasing or displeasing
Eg. “Derek” tastes of earwax
Congenital Synesthesia
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
Adventitious Synesthesia
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)
Idiosyncratic Synesthesia
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
Lower Synesthetes
processing is primarily bottom up, colours are elicited by the actual visual appearance of a grapheme
Eg. 7 -> yellow
Higher Synesthetes
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
Projectors
strongly experience colours as overlays projected and bound to a grapheme in the outside world, proposed that projectors = lower synesthetes
Associators
experience weaker synesthetic colours “in the mind’s eye” only, proposed that associators = higher synesthetes
Cross-activation / Insufficient pruning
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
Long-Range Disinhibited Feedback
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
Reduced Plasticity
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
Hyper-Binding
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
