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Cross-modal perception
occurs where perception involves interactions between two or more different sensory modalities
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Synesthesia
- A phenomenon where stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway
- a type of cross-modal perception.
- May be associated with improved memory and faster reaction times on certain tasks (e.g., visual search task).
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Key Aspects of Synesthesia
consistency, automaticity, multi-sense (multi-synthetic)
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Grapheme --> color
written letters/numbers evoke colors
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Sound --> color
sounds evoke colors; also called chromesthesia
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Lexical --> gustatory
spoken or written words evoke tastes (and often also temperature, textures of food)
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Number-form & spatial-sequence
- numbers and sequences evoke shapes and forms
- these types may overlap significantly
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Ordinal-linguistic personification
ordered sequences like numbers and letters are associated with personalities and/or genders
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Misophonia
- possible synesthesia vs. neurological disorder
- sounds evoke strong negative emotions
- also associated with anxiety, obsessive-compulsive disorder, Tourrette’s syndrome, and maybe autism
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Synesthesia Causes
- Developmental: from differences in white matter connections, such as a decrease in synaptic pruning
- Acquired: from sensory, drugs, or trauma
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Projector synesthetes
- these people experience their synesthetic percepts as similar in quality to real-world perceptions.
- For example, synesthetic colors might appear as projected onto external objects and be difficult to dissociate from real-world colors.
- These synesthetes might not be able to tell whether letter are in black/white or color.
- This type likely arises from changes earlier in the sensory processing pathways (like apperceptive agnosia) and is rarer.
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Associator synesthetes
- these people experience their synesthetic sensations within their internal mental space.
- For example, they would see letters as appearing black/white, but would automatically associate the letters with colors in their mind/memory.
- This type is more common, and may arise from higher-order sensory regions (like associative agnosia), linking basic sensory perception with an associated memory, emotion, or sensory mental imagery.
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Visual search task
- In the visual search task, it takes longer to find the number 2 hidden among 5’s when they are all the same color.
- Reaction time is much faster when there is a color difference.
- Grapheme-color synesthetes have a reaction time like there is a clear color difference when the numbers used match their synesthetic perceptions, even when the written text is all in black.
- This speeded-up response is driven by the pop-out effect of the colored number.
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