Week 10 reading- Neurophenomenology of induced and natural synaesthesia Flashcards
Explain this term as it relates to natural synaesthesia: Inducer
-Synaesthesia is defined by the presence of additional perceptual experiences, which are automatically and consistently triggered by specific inducing stimuli.
-The inducer is the stimuli that elicits experience
e.g. In grapheme-colour synaesthesia, the letter ‘A’ printed in black (inducer) may elicit a red colour experience (concurrent)
Explain this term as it relates to natural synaesthesia: concurrent
-Synaesthesia is defined by the presence of additional perceptual experiences, which are automatically and consistently triggered by specific inducing stimuli.
-The concurrent is the experience which is triggered by a specific inducer
e.g. in grapheme-colour synaesthesia, the letter ‘A’ printed in black (inducer) may elicit a red colour experience (concurrent).
Explain this term as it relates to natural synaesthesia: automaticity
-The experiences of those with natural synaesthesia when they encounter a specific inducer are not under voluntary control (i.e. they happen automatically).
Explain this term as it relates to natural synaesthesia: specificity
-The defining hallmarks of genuine, natural, synaesthesia and the methods that should be used to verify their presence remain the subject of debate.
-However, there is broad consensus that synaesthesia consists of highly specific experiences that are consistent within individuals (i.e. repeated presentations of an inducer will reliably elicit the same or a very similar concurrent experience, even over long intervals of time)
-Usually the inducer-concurrent relationship is also specific it’s direction (i.e. unidirectional) although this is not always the case as sometimes there can be bidirectionality (i.e. a specific inducer will elicit a specific concurrent, but that concurrent will also elicit the experience of the inducer).
-Specificity and consistency heavily interlinked
Explain this term as it relates to natural synaesthesia: consistency
-The defining hallmarks of genuine, natural, synaesthesia and the methods that should be used to verify their presence remain the subject of debate.
-However, there is broad consensus that synaesthesia consists of highly specific experiences that are consistent within individuals (i.e. repeated presentations of an inducer will reliably elicit the same or a very similar concurrent experience, even over long intervals of time)
-Specificity and consistency heavily interlinked
Explain this term as it relates to natural synaesthesia: perceptual presence
-A less frequently noted subjective characteristic of synaesthesia is that concurrent experiences usually lack what can be called perceptual presence
-This means that concurrent experiences are not usually confused with, or perceived as, properties of the world.
-E.g. in graheme-colour synaesthesia the concurrent colour experience is typically not confused with the actual colour of the inducer. In other words, will still see the letter as it’s actual colour (back) the additionally perceptual experience (red) will be laid over top: think back to the lecture slides.
Explain this term as it relates to natural synaesthesia: colour consistency test
-Colour-consistency test is used for the behavioural diagnosis of synaesthesia
-Participants have to repeatedly chose the most appropriate colour associated with each grapheme
-A lower score reflected increased colour consistency.
-High consistency for natural synaesthetes
Explain this term as it relates to natural synaesthesia: veridical
Veridical= part-of the world percept. Actual perceptual qualities of the stimulus itself.
-Concurrent experiences are not confused with veridical percepts.
e.g. the black letter (veridical percept) is not confused with the red letter (concurrent)
Lack of perceptual presence of concurrent experiences allows this.
Explain this term as it relates to natural synaesthesia: cross-activation model
-Rapid changes in perceptual phenomology seen in artificially induced synaesthesia are hard to accommodate within this model
-The cross-activation model proposes that synaesthesia arises over months or years through a greater-than-normal structural connectivity between cortical representations of inducers and concurrents.
Explain this term as it relates to natural synaesthesia: disinhibited feedback model
-Rapid changes in perceptual phenomology seen in artificially induced synaesthesia are more consistent with this model than the cross-activation model
-Disinhibited feedback model posits that that synaesthesia occurs through the same neural connections as in a ‘non-synaesthetic’ brain, but it is the alterations in functionally driven disinhibited feedback between or within brain areas that generate concurrent experiences.
-Chat gtp: “the normal inhibitory processes that regulate neural activity and prevent cross-activation of sensory areas are disrupted or weakened. This disinhibition allows for enhanced communication or feedback loops between different brain regions, leading to the simultaneous activation of multiple sensory areas during perception.”
Concisely describe the four (five?) types of artificially induced synaesthesia covered in the article.
In your descriptions, be sure to include brief methodology and similarities/differences as compared to the natural synaesthetic experience.
-1: Trained synaesthesia
For example: Trying to get non-synaesthetes to acquire grapheme-colour synaesthesia via extensive associative training i.e. pairing the inducer and concurrent stimuli together repeatedly and then asking whether the presentation of the inducer alone produces the concurrent experience. This study failed to train synaesthesia-like experiences/ phenomenology (potential reason for failure: lack of training throughout development).
Other studies using more extensive, adaptative and targeted cognitive training, however, have gone on to train synaesthetic phenomenology in participants although the nature of this varied (projective versus associator- type reports). Additionally, this type of training results in experiences that appear to lack perceptual presence (like natural synaesthesia) and can lead to neurophysiological changes, akin to natural synaesthesia.
-2: Pharmacologically induced synaesthesia
Drug (e.g. psychedelic) induced synaesthetic like experiences are hard to study because of methodological limitations. The experiences induced by them seem to lack consistency, do not occur automatically and are heavily influenced by the current state of the individual (unlike in natural synaesthesia).
One study tried to use LSD, however, it only found weak spontaneous synaesthesia like experiences which lacked inducer specificity. Also no difference in the consistency of concurrent experiences between LSD and placebo conditions.
Unlikely to be much perceptual presence with pharmacologically induced synaesthesia.
-3: Hypnotically induced synaesthesia
For example, Hypnosis to associate digits with specific colours. Following a digit detection task was done whereby participants are asked to detect the presence of absence of a digit presented on differing colour background. Align with the automaticity of natural synaesthesia in that when a black digit was presented on a congruent background participants made substantially more errors (I think this means that the number would blend in i.e. 1 elicits red put on a red background would be bad). Experiences reported after had a degree of consistency resembling grapheme-colour synaesthetes.
Overall post-hypnotic induction is able to rapidly induce additional perceptual experience that bear some similarities to natural synaesthesia (i.e. automaticity, consistency) but the area of perceptual presence is again a difference (has it when natural synthaesia does not).
-4: Synaesthesia as a result of sensory deprivation
Studies primarily focus on profound visual loss. Patients experienced photisms (simple flashes or kaleidoscopic patterns) in response to sound within as little as 1-3 days following visual loss. Little evidence for the consistency of the inducer (sound) and concurrent (photisms) coupling. Some studies have blindfolded sighted participants and used sound to get a similar effect (photisms) but again experience lacks the consistency of natural synaesthesia which the same tone either not eliciting a concurrent experience or eliciting a different visual experience at different times.
To sum only superficial similarities to natural synaesthesia. Additionally because of blindfolding/ lack of visual experience perceptual presence cannot be examined in these cases.
-5: Synaesthesia due to brain injury.
Result of functional and structural reorganisation (neuroplasticity) of the brain following injury.
For example, auditory stimuli now producing tactile percepts. Highly consistent but simple in nature (i.e. tingling/ pressure) compared to natural synaesthesia.
Most compelling of methods in mimicking natural synaesthesia is training, then post-hypnotic induction. The rest only share superficial similarities.
What are two neurophysiological differences that have been observed in some Grapheme-Colour synaesthetes’ brains? Would these differences mean that visual pathways are (more/less?) excitable? that cross-modal integration is (more/less?) likely?
-Greater cortical excitability (lower phosphene threshold) for projector synaesthetes than for associator synaesthetes with both exhibiting lower thresholds compared to controls.
-Differences related to enhanced enhanced visual perceptual processing found in grapheme-colour synaesthetes.
With lower thresholds compared to controls I think this means the visual pathways are more excitable
Cross-modal integration (the brain combines information from different sensory modalities to form a unified perception/ understanding of the world) would be more likely in synesthetes (connections between the visual cortex and other brain regions stronger/ more active).
Some of the techniques discussed in the reading produced rapid changes in perceptual experience. Why is this fast time-scale important to note (e.g., what does it suggest about the nervous system)?
-Rapid onset of perceptual changes
e.g. 24hr of training resulting in perceptual experiences for letter stimuli, or post-hypnotic suggestion and sensory deprivation which demonstrate synaesthesia like phenomology brought about in as little as 5 Mins
-Highlight the potential plasticity of perceptual phenomology even in adults i.e. cortical perceptual representations in adults are not fixed, but rather dynamic and continuously altered by experience.
What do the authors speculate is one common neurological mechanism that may drive certain forms of induced synaesthesia? Does this idea align with (or disagree with) instances of synaesthesia observed secondary to brain damage?
“We speculate that for some forms of induced synaesthesia, the common mechanism that underlies the alterations in perceptual experiences may be an increase in cortical excitability within perceptual brain regions.”
-The idea of increased cortical excitability aligns with instances of synaesthesia observed secondary to brain damage because… brain damage can disrupt the balance of neural activity and enhance the excitability of certain brain regions. This heightened excitability can lead to abnormal patterns of sensory activation, allowing for the co-activation or cross-activation of sensory modalities and giving rise to synesthetic experiences.
Projector versus associator type reports of synaesthetic phenomenology…
-Projector-type reports: concurrents are experienced as being outside of bodily space, ‘projected’ into the world
e.g. Seeing a sign in the real world in which the letters were coloured according to training associations
- Associator-type reports: concurrents are experienced within an internal mental space without any distinct spatiality.
e.g. “When I look a the letter ‘p’ I know the colour pink goes with it, it’s like inside my head is pink”
