Have you ever noticed that you associate certain colours with specific days of the week? For example, Monday might feel “blue” while Thursday is “green.” This phenomenon is called colour-graphemic synesthesia – when an individual’s perception of graphemes, or written letters and numbers, is associated with specific colours.
Synesthesia is a fascinating neurological condition that causes the brain to blend normally separate sensory modalities. While synesthetes make up only a small percentage of the population, most people have experienced cross-sensory associations like colours with days or letters at some point. Let’s explore some leading theories on why we form these connections and how these associations develop.
Theories on Colour-Grapheme Synesthesia
There are a few key theories that aim to explain grapheme-colour synesthesia:
Cross-Wire Theory
The cross-wire theory suggests adjacent brain regions become accidentally “cross-wired” during development. In grapheme-colour synesthesia, regions involved in colour perception and grapheme processing are thought to be cross-wired, causing certain letters/numbers to trigger colour sensations. Evidence for this theory comes from the fact that grapheme area and colour area are anatomically adjacent in the brain.
Disinhibited Feedback Theory
This theory proposes feedback connections between brain areas do not properly regulate, causing leaking of sensory signals. For example, faulty inhibition may lead signals from grapheme regions to reach colour regions, associating the two. Support comes from the extensive connectivity between sensory brain regions.
Hyper-binding Theory
The hyper-binding theory suggests synesthesia arises from stronger than normal connections between sensory brain areas. An overly strong link between the grapheme and colour regions would lead to binding of the two senses. Evidence indicates synesthetes do show hyper-connectivity and enhanced structural brain connectivity.
When Do These Associations Develop?
Research indicates colour-grapheme associations develop during early childhood, between ages 5-7 years typically. Studies show grapheme-colour pairings remain consistent over time within an individual but associations vary across different synesthetes. The developing brain may be particularly prone to cross-wiring during this age range.
Common Patterns in Grapheme-Colour Mappings
While individual grapheme-colour mappings vary, some common patterns have emerged:
Early Letter/Number Primacy
Letters and numbers learned earlier in childhood tend to be mapped to more primary, salient colours like red and yellow. Later learned graphemes map to secondary colours like purple or brown. This likely reflects the sequence of grapheme learning.
First Letter Primacy
First letters of words, months, and days (e.g. M for Monday) tend to be linked to brighter colours than later letters. Again, learning sequence may strengthen these early grapheme mappings.
Cross-Linguistic Patterns
Some letters show similar colour mappings across different languages. For example, A is commonly red, B green, and O white. Shared anchoring points during grapheme learning may lead to cross-cultural consistencies.
Opponent Colour Pairings
Graphemes that commonly appear together become linked to opponent colours like red-green or blue-yellow. Contrast may help distinguish frequently co-occurring letters.
Factors That Influence Colour Mappings
What other factors may shape the specific colour associations we form with graphemes?
Cultural Influences
Culture and language likely play a key role. For example, English speakers associate A with red more often than non-English synesthetes. Exposure to coloured letters in childhood toys, books, and media affects mappings.
Individual Experiences
Personal experiences with coloured graphemes can reinforce particular letter-colour pairings. Encountering an orange “A” as a child may link the letter to that colour permanently.
Innate Colour Perception
Our innate colour perception mechanisms may predispose certain cross-sensory mappings. The colours yellow and blue have intrinsic ties to luminance that may make them prone to association with salient graphemes like “A” and “B”.
Personality
Personality traits like openness to experience correlate with more vivid, atypical grapheme-colour mappings. So your personality style may shape the subjective colours you link to letters and numbers.
Prevalence Across Genders
Research consistently shows grapheme-colour synesthesia is significantly more common in females compared to males, with some studies showing over 6X higher prevalence in women. The reason for this gender difference remains unclear but may be related to genetic differences or brain lateralization patterns between the sexes.
Is Synesthesia Genetic?
Multiple studies indicate a strong genetic component to synesthesia. The condition tends to run in families and correlates between identical twins. Specific genes related to brain connectivity have been associated with higher synesthesia prevalence. So the tendency to form cross-sensory associations does appear highly heritable in origin.
How Is Synesthesia Measured and Verified?
To verify grapheme-colour synesthesia, researchers use the following tools:
Consistency Testing
Testing across time shows synesthetes maintain consistent mappings over months or years, while non-synesthetes do not.
Stroop Tasks
On colour naming tasks, synesthetes show Stroop effects if letter colours conflict with synesthetic colours.
EEG/fMRI
Brain imaging reveals synesthetes show early activation of colour regions when viewing black and white graphemes.
Threshold Testing
Synesthetes better detect grapheme shapes made up of similarly-coloured patterns linked to that grapheme.
| Day | Colour Association |
|---|---|
| Monday | Blue |
| Tuesday | Orange |
| Wednesday | Yellow |
| Thursday | Green |
| Friday | Red |
| Saturday | Purple |
| Sunday | Pink |
My Personal Grapheme-Colour Mappings
As an example, here are the colour associations I form with days of the week:
Potential Benefits of Synesthesia
While synesthesia has commonly been viewed as a cognitive peculiarity, research now suggests certain benefits may be associated with this trait:
Enhanced Memory
Synesthetes appear to have an advantage in recalling information like dates and phone numbers. The extra colour cues seem to strengthen memory encoding and retrieval.
Increased Creativity
Synesthetes are overrepresented in creative professions like artists, musicians, and writers. Seeing cross-sensory connections may aid their creativity.
Added Emotional Depth
Some synesthetes report their colourful perceptions make music, words, or time periods more emotionally evocative.
Improved Sensory Processing
Synesthesia has been linked to enhanced low-level perception and discrimination of sensory stimuli.
So in the right contexts, these cross-wired senses may provide cognitive benefits for some synesthetes.
Is Synesthesia Related to Other Conditions?
Research shows synesthesia seems to coincide at above chance levels with certain other neurological conditions:
Autism
Estimates indicate 5-10% of autistics may experience synesthesia, above the 4-6% in the general population. Shared neural differences may underlie both traits.
Savant Abilities
A portion of synesthetes appear to possess savant skills like mathematical, artistic, or memory abilities. Synesthesia may enable savant talent in some cases.
Phantom Touch
Seeing letters/numbers can trigger a tactile sensation in some synesthetes’ fingers, indicating neural cross-talk with somatosensory cortex.
Chromesthesia
A subset of synesthetes experience colours in response to sounds like music. This audio-visual form of synesthesia has parallels to grapheme mappings.
So synesthetic tendencies seem interconnected with other atypical neurological traits.
Can Adults Develop Synesthesia?
Most evidence indicates grapheme-colour synesthesia arises early in life and remains highly stable over time. However, some case studies suggest synesthetic abilities can rarely emerge in adult years, often after an unusual event like brain injury, stroke, drug use, or sensory deprivation. It appears the mature brain maintains some capacity for developing new sensory connections, given the right trigger.
Is Synesthesia a Disorder or Difference?
Synesthesia was long viewed as a neurological disorder or confusion of the senses. But modern research frames it as a benign trait associated with distinctive perceptual experiences rather than a pathological dysfunction. Many synesthetes do not view it as a condition that needs to be treated or cured. Instead, synesthesia can be appreciated as a unique way of perceiving the world.
Conclusions
In summary, grapheme-colour synesthesia provides an intriguing window into how the brain integrates information across different sensory modalities. Research remains ongoing into the developmental mechanisms that give rise to these involuntarily cross-wired senses. But progress has been made in understanding the genetic basis, neural origins, perceptual experiences, and cognitive impacts of synesthesia. While relatively rare, these blended perceptions illustrate the diverse ways our minds and nervous systems can be wired. Synesthesia serves as a reminder of the complexity of the human brain and the variety of possible conscious experiences.