• Voluntary stimulation of one sensory or
cognitive pathway leads to involuntary
stimulation of another.
• People with synesthesia are called
• Topic of intense research in early 19th – 20th
• Synesthesia aids creative processes
• Diagnosis pattern suggested by Richard Cytowic
- Durable and generic
• Synesthetes tend to be in general women,
Neurologically normal people, left handed people
and can also be a hereditary phenomenon.
the sound to colour synesthesia, which is a type
of synesthesia in which heard sounds
automatically and involuntarily evoke an
experience of colour.
• Grapheme-Color Synesthesia
• This is one of the most common types of
• A person who experiences this may
associate/see individual letters or numbers
with a specific color. Usually, two people won’t
report the same color for letters and numbers.
• Hearing- touch Synesthesia
It is a very rare condition in which an individual
develops tactile feelings or senses upon
hearing some sounds.
For instance, people have claimed that they are
feeling some physical discomfort especially
with the background noise of the plane.
• Lexical-gustatory synesthesia
one of the more rare synesthesia types.
Synesthetes who experience this kind of synesthesia
evoke different kinds of tastes when they hear certain
words or phonemes.
According to research, associations between the words
and what a synesthete is able taste are constrained by
tastes he or she has experienced early in life. So, if an
individual hasn’t had mashed potatoes or bacon, they
won’t be tasting those flavors as a result of this
variation. What a shame!
• Mirror-touch synesthesia
a condition which causes individuals to
experience the same sensation (such as touch)
that another person feels.
Example: if someone with this condition were to
observe someone touching their cheek, they
would feel the same sensation on their own
A number form is essentially a mental map that consists of
numbers. When a person with number-form synesthesia
thinks about numbers, a number map is involuntarily
It is sometimes suggested that the number forms are a
product of “cross-activation” between regions in the
parietal lobe – a part of the brain that is involved in
numerical and spatial cognition.
An individual who experiences this will
associate ordered sequences with various
personalities. Ordered sequences may include
numbers, letters, months and so on.
For example, a person with OLP may look at the
letter ‘A’ and think in his mind that ‘A’ is a rude
In addition to thinking that certain ordinal
sequences have a personality, a synesthete
may also imbue a personality within an object.
People with time-space synesthesia literally
experience a time-space connection. They
feel like the phenomenon of time must have a
To them, time is like the applications and icons
in an iPad screen laid out for them. They can
physically point at specific dates in space like
you could flip or touch-select an icon in a
touchpad. They see time in definitive sizes,
dimensions, locations and even color
Touch-emotion synesthesia has been
documented by two researchers David Brang
and Vilayanur Ramachandran.
Condition in which individuals develop some
emotions when they touch particular surfaces
with some texture
Studies suggests that touch-emotional
synesthesia is caused by the cross activation of
the samatosensory cortex and the insula. The
samatosensory cortex is responsible for
processing the body's sensory information while
insula which is located in the temporal lobe is
responsible of the emotions
Why is 7 red?
Why do you hear the colours?
Why is the rainbow warm?
Grace Maria Jochan 1537326
Learned Association Theory (Estranged Theory)
• Mary Calkins
• Learned association between stimuli causes multiple
ie; distinct memories of sensory and auditory
• Does not explain the hereditary nature of synesthesia
• Focus on natural selection of traits essential for survival
• Synesthesia may be was once essential and may have been
present in a larger population
• Synesthesia not required now, therefore only among few
• Does not give explanation for what use it served in human
past except for art
• Synesthesia- recently discovered, so can’t compare with
• Synesthetic interactions may be common but only a
few are conscious or aware of it
• Cytowic (1993)- Theory of cortical suppression
synesthesia occurs in the subcortical regions of
limbic system and only come to conscious when
cortical areas are suppressed
Neural connectivity Theories
• Maurer (1997) – Neonatal synesthesia theory
Neural connections between visual and auditory
areas are found in infants. Later these connections are
• Ramachandran (2001) – Cross –wiring Theory
Synesthesia occurs due to functional connections
between specific senses either through excessive
proliferation or defective pruning of connections
A Single Case fMRI Study of Visually
Induced Olfactory Perception. (Chan, 2014)
In this study we describe a single individual (LJ) who experiences a
concurrent olfactory stimulus when presented with congruent visual
images. For some visual stimuli, he perceives a strong and automatic
olfactory percept, which has existed throughout his life. In this study,
we explore whether his experiences are a new form of synesthesia or
simply vivid imagery. Unlike other forms of synesthesia, the concurrent
odour is congruent to the visual inducer. For example, a photograph of
dress shoes will elicit the smell of leather.
LJ and several control participants were introduced with 75 images of
everyday objects. Their task was to indicate the strength of any perceived
odours induced by the visual images. LJ rated several of the images as
inducing a concurrent odour, while controls did not have any such
percept. Images that LJ reported as inducing the strongest odours
were used, along with colour-matched control images, in the context
of an fMRI experiment.
There was an increased BOLD response in the piriform
cortex (primary olfactory cortex) for the odour-inducing
images compared to the control images in LJ. There was
no difference in BOLD response between these two stimulus
types in the control participants.
A subsequent olfactory imagery task did not elicit
enhanced activity in the piriform cortex in LJ, suggesting
his perceptual experiences may not be based on olfactory
Colored-Speech Synesthesia Is Triggered by
Multisensory, Not Unisensory, Perception.
(Bargary, GaryBarnett, Kylie J.Mitchell, Kevin J.Newell, Fiona N. 2009)
Researcher tested 9 linguistic-color synesthetic and found
that the colors induced by spoken words are related to
what is perceived (i.e., the illusory combination of audio
and visual inputs) and not to the auditory component alone.
Research findings indicate that color-speech synesthesia
is triggered only when a significant amount of
information processing has occurred and that early sensory
activation is not directly linked to the synesthetic experience.
Chan, J. J. (2014). Synaesthesia or Vivid Imagery? A Single
Case fMRI Study of Visually Induced Olfactory Perception.
Multisensory Research, 27(3/4), 225-246.
Bargary, GaryBarnett, Kylie J.Mitchell, Kevin J.Newell,
Fiona N. 2009. "Colored-Speech Synaesthesia Is Triggered
by Multisensory, Not Unisensory, Perception." Psychological
Science (Wiley-Blackwell) 20, no. 5: 529-533. Psychology
and Behavioral Sciences Collection, EBSCOhost (accessed
September 6, 2015).