Unit 5C - Synesthesia

Cross-modal perception

occurs where perception involves interactions between two or more different sensory modalities.

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).

Key aspects: consistency, automaticity, multi-sense (multi-synthetic)

Graphemecolor

[written letters/numbers evoke colors]

Soundcolor

[sounds evoke colors; also called chromesthesia]

Lexicalgustatory

[spoken or written words evoke tastes (and often also temperature, textures of food)]

Number-form & spatial-sequence

[numbers and sequences evoke shapes and forms]; these types may overlap significantly

Ordinal-linguistic personification

[ordered sequences like numbers and letters are associated with personalities and/or genders]

Misophonia

[possible synesthesia vs. neurological disorder; sounds evoke strong negative emotions; also associated with anxiety, obsessive compulsive disorder, Tourrette’s syndrome, and maybe autism

Developmental

from differences in white matter connections, such as a decrease in synaptic pruning

Acquired

from sensory, drugs, or trauma

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.

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.

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.