ArticlePDF AvailableLiterature Review

Abstract and Figures

Synesthesia is an extraordinary perceptual phenomenon, in which individuals experience unusual percepts elicited by the activation of an unrelated sensory modality or by a cognitive process. Emotional reactions are commonly associated. The condition prompted philosophical debates on the nature of perception and impacted the course of art history. It recently generated a considerable interest among neuroscientists, but its clinical significance apparently remains underevaluated. This review focuses on the recent studies regarding variants of color synesthesia, the commonest form of the condition. Synesthesia is commonly classified as developmental and acquired. Developmental forms predispose to changes in primary sensory processing and cognitive functions, usually with better performances in certain aspects and worse in others, and to heightened creativity. Acquired forms of synesthesia commonly arise from drug ingestion or neurological disorders, including thalamic lesions and sensory deprivation (e.g., blindness). Cerebral exploration using structural and functional imaging has demonstrated distinct patterns in cortical activation and brain connectivity for controls and synesthetes. Artworks of affected painters are most illustrative of the nature of synesthetic experiences. Results of the recent investigations on synesthesia offered a remarkable insight into the mechanisms of perception, emotion and consciousness, and deserve attention both from neuroscientists and from clinicians.
Content may be subject to copyright.
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
C
URRENT
O
PINION
Color synesthesia. Insight into perception, emotion,
and consciousness
Avinoam B. Safran
a,b
and Nicolae Sanda
a,c
Purpose of review
Synesthesia is an extraordinary perceptual phenomenon, in which individuals experience unusual percepts
elicited by the activation of an unrelated sensory modality or by a cognitive process. Emotional reactions
are commonly associated. The condition prompted philosophical debates on the nature of perception and
impacted the course of art history. It recently generated a considerable interest among neuroscientists, but
its clinical significance apparently remains underevaluated. This review focuses on the recent studies
regarding variants of color synesthesia, the commonest form of the condition.
Recent findings
Synesthesia is commonly classified as developmental and acquired. Developmental forms predispose to
changes in primary sensory processing and cognitive functions, usually with better performances in certain
aspects and worse in others, and to heightened creativity. Acquired forms of synesthesia commonly arise
from drug ingestion or neurological disorders, including thalamic lesions and sensory deprivation (e.g.,
blindness). Cerebral exploration using structural and functional imaging has demonstrated distinct patterns
in cortical activation and brain connectivity for controls and synesthetes. Artworks of affected painters are
most illustrative of the nature of synesthetic experiences.
Summary
Results of the recent investigations on synesthesia offered a remarkable insight into the mechanisms of
perception, emotion and consciousness, and deserve attention both from neuroscientists and from clinicians.
Keywords
cerebral disorders, color, consciousness, emotion, perception, synesthesia, vision
INTRODUCTION
Synesthesia is an extraordinary perceptual phenom-
enon, in which the world is experienced in unusual
ways. In this condition, a particular stimulation in a
given sensory modality (e.g., touch) or cognitive proc-
ess (e.g., computing) automatically triggers additional
experiences in one or several other unstimulated
domains (e.g., vision, emotion) [1]. An illustrative
presentation of the condition would be that of a given
person in whom hearing the sound of a trumpet
consistently elicits the vision of brightly colored
triangles dancing in front of his eyes, in association
with a sensation of pressure on his arms, letting him
feel uncomfortable to sit still. Stimuli generating
additional unusual experiences are termed ‘inducers’,
whereas internally produced synesthetic percepts are
termed ‘concurrents’ [2].
Synesthetic experiences have had over the cen-
turies far-reaching sociocultural implications. They
prompted philosophical debates on the nature of
perception, consciousness and even talent and
creativity, and significantly impacted the course
of art history, notably at the turn of the 20th Cen-
tury [36]. Moreover, favored by the emergence of
sophisticated tools for functional brain exploration,
they have generated a considerable interest among
neuroscientists [6,7]. Clinical significance of synes-
thesia, however, is still largely underevaluated.
Although some synesthetic phenomena express
the presence of a disease, developmental synesthesia
as a rule is considered an individual cognitive
a
Sorbonne Universite
´s, UPMC Univ Paris 06, UMR_S 968, Institut de la
Vision, INSERM, U968, CN RS, UMR_7210, Paris, France,
b
Department
of Clinical Neurosciences, Geneva University School of Medicine, Gen-
eva, Switzerland and
c
Neurology Department, Ho
ˆpital Foch, Suresnes,
Paris, France
Correspondence to Avinoam B. Safran, MD, 17 rue Moreau, Paris,
F-75012, France. E-mail: avinoam.safran@unige.ch
Curr Opin Neurol 2015, 28:36–44
DOI:10.1097/WCO.0000000000000169
This is an open-access article distributed under the terms of the Creative
Commons Attribution-NonCommercial-NoDerivatives 4.0 License, where
it is permissible to download and share the work provided it is properly
cited. The work cannot be changed in any way or used commercially.
www.co-neurology.com Volume 28 !Number 1 !February 2015
REVIEW
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
variant in the normal population [8]. Unfortu-
nately, the astonishing features of these percepts
have too often led the entourage of affected per-
sons, including physicians, to wrongfully consider
them as confabulators, drug users, or schizo-
phrenics [7]. In this regard, the following history
reported by Vincent Van Gogh is representative.
While in 1885 the painter was taking piano lessons,
his teacher noticed that he was continually relating
the sounds of the piano keys with specific colors;
considering then that his pupil was insane, the
teacher sent him away [9]. It is therefore under-
standable that synesthetes (i.e., persons affected
by synesthesia) commonly avoid mentioning their
percepts and even tend to close on themselves in
psychological distress [10–12]. For that very reason,
scientific studies probably underestimate synesthe-
sia prevalence in the general population.
SYNESTHESIA VARIANTS
Synesthesia is commonly classified as developmen-
tal and acquired. Developmental synesthesia
appears to be the most frequent type of this con-
dition, with a 4.4% estimated prevalence rate [13]. It
can run in families and demonstrate Mendelian
transmission [14]. Different forms of synesthesia
can be observed in the same person or in the same
family [15]. The condition is occasionally associ-
ated with autism spectrum disorders, like Asperger
syndrome [16].
The following criteria have been proposed to
help establishing a diagnosis of developmental syn-
esthesia: induced percepts should be elicited by a
specific stimulus, they should be automatically
generated, and typically have percept-like qualities
[8,17,18]. Usually, pairings of inducers and concur-
rents are specific (i.e., a particular stimulus consist-
ently triggers the same synesthetic percept). They
tend to be stable over time in a given individual,
although this has recently been challenged by the
finding that synesthetic ability can disappear over
time [19
&
].
Acquired forms of synesthesia have also been
reported, essentially associated with neurologic dis-
orders or following psychotropic drug ingestion
[2023]. In contrast to its developmental counter-
part, acquired synesthesia does not demonstrate
either idiosyncrasy or automaticity or stability
[3,24
&
].
So far, over 60 types of synesthetic phenomena
have been described. The apparently most common
form (with a 64.4% prevalence among synesthetes) is
grapheme– color synesthesia, in which achromatic
letters or digits automatically trigger an idiosyncratic
color perceptual experience (e.g., the letter ‘m’ indu-
ces blue color percepts) [25,26] (Fig. 1 [27]). The
second most prevalent form is time unit (e.g., Mon-
day, January)– color synesthesia (22.4%), followed by
musical sound– color synesthesia (18.50%) [26,28]
(Figs 2 and 3 [29,30]). Inducers and concurrents also
include smells, tastes, temperatures, personalities
and emotions [26], and can be multiple during a
single synesthetic experience. Thus, percepts
induced by grapheme–color synesthesia are
occasionally accompanied by shape, texture, move-
ment features, and even nonvisual percepts such as
smells and tastes, particularly emotions [31,32]. Syn-
esthetic colors generated in grapheme–color synes-
thesia are determined by systematic rules rather than
randomly occurring, and basedon the psycholinguis-
tic mechanisms of language processing. The same
occurs with both Latin characters and Chinese ideo-
grams [33,34
&
].
An additional type of colored synesthetic experi-
ence was recently described and termed ‘swimming-
style color synesthesia’. It is characterized by the
generation of specific colored percepts upon con-
ceptual representation of swimming in a particular
style (i.e., breast, backstroke, crawl, and butterfly)
[35,36]. This phenomenon could be triggered by
either presenting a picture of a swimming individual
or asking the tested individual to think about a
given swimming style. It was speculated that this
synesthetic type was caused by overactivity in the
mirror neuron system responding to the specific
representation [37].
Synesthetic experiences are labeled ‘lower’ when
triggered by elementary perceptual processes (e.g.,
texture) or ‘higher’ when involving a higher cogni-
tive process (e.g., semantic, computing) [7,38,39].
Synesthetes who experience the atypical percepts in
an internal space (‘in the mind’s eye’, as they some-
times describe it) have been categorized into ‘asso-
ciators’, whereas those for whom the additional,
KEY POINTS
!Persons presenting with synesthesia commonly avoid
mentioning their unusual percepts and even tend to
close on themselves in psychological distress.
!Developmental synesthesia predisposes to changes in
primary sensory processing and cognitive functions,
and heightened creativity.
!Affected individuals demonstrate distinct patterns in
cerebral activation and connectivity, compared
with nonsynesthetes.
!Acquired forms of synesthesia are commonly related to
drug ingestion or neurological conditions.
Color synesthesia Safran and Sanda
1350-7540 Copyright !2015 Wolters Kluwer Health, Inc. All rights reserved. www.co-neurology.com 37
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
atypical percept appears to be ‘out there’, overlaying
the actual, external surrounding, are designated as
‘projectors’ [40,41].
PAINTERS’ COMPREHENSION OF
SYNESTHESIA
Painters commonly demonstrate unique skills in
the observation of visual phenomena, in which
depiction offers an invaluable source of information
for neuroscientists investigating visual function in
health and disease [4246]. Regarding our under-
standing of synesthesia, painters’ contribution is
particularly precious. Among this population, the
prevalence of synesthesia was found higher than in
general population; in addition, their percepts are
frequently represented in their artworks [47].
Indeed, synesthete prevalence among fine art stu-
dents was estimated to be 23% [48]. Among art
students, prevalence of graphemecolor synesthesia
alone was reported to be 7%, compared to 2% in
controls [49].
Interestingly, synesthetes’ personality profile
favors their involvement in creative, artistic activi-
ties [50]. Recently evaluated by a structured measure
of personality (the ‘Big Five Inventory’) and by
(a) (b)
FIGURE 1. Visual segregation test demonstrating improved digit identification performances by grapheme–color synesthetes.
(a) Pattern presented to the tested individuals and (b) same pattern as perceived by a graphemecolor synesthete. To identify
digits ‘2’, a person with regular visual perception must perfom a systematic search; in contrast, for a grapheme color
synesthete, who links a specific color with a given number, digits ‘2’ instantly pop-out. Adapted with permission [27].
FIGURE 2. ‘Vision’ 1996, by Carol Steen, private
collection, represents a synesthetic visual experience elicited
in this synesthetic painter by a needle puncture during an
acupuncture session [29]. Reproduced with permission.
FIGURE 3. ‘Kondo’s Trumpet’ 2010, by Carol Steen, private
collection, depicts the synesthetic visual experience elicited by
the timbre of that trumpet [30]. Reproduced with permission.
Neuro-ophthalmology and neuro-otology
38 www.co-neurology.com Volume 28 !Number 1 !February 2015
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
questionnaires assessing empathy, synesthetes
exhibited higher levels of ‘Openness to Experience’,
considered to be related to imagination and artistic
tendencies, and higher levels of ‘Fantasizing’, con-
ceptually related to ‘Openness’ [51
&
]. Moreover, gra-
phemecolor synesthetes show a distinct cognitive
style, with a preference for processing information
in both verbal and vivid imagery styles [52
&
].
The peculiar world perception decisively
impacted the artistic work of numerous ‘synesthetic’
artists. Thus, Kandinsky’s nonfigurative paintings and
theory of synesthesia [53], prompted by his experi-
ence of extraordinary visions of lines and colors eli-
cited by the sound of musical instruments, paved the
way to abstract art and thus marked a turning point
in history of art [47]. A recent analysis of Kandin-
sky’s works using the Implicit Association Test
found no implicit association between the original
color–form combinations, and authors concluded
that these are probably not a universal property of
the visual system [44].
Most informative indications on the character
of percepts commonly observed by synesthetic
painters, as well as on the compulsive manner they
depict their visions, were provided by Carol Steen, a
remarkable synesthetic painter [54]. She emphasized
that synesthetes’ internal world differs tremendously
from what is commonly perceived by others. For
instance, colors can be perceived intensely bright,
‘similar to sunlight streaming through a stained glass
window’. Noteworthy, she felt that the ‘overwhelm-
ing beauty of what she has seen’ powerfully com-
pelled her to capture and reproduce her visions, and
that ‘urgency to paint needed to be expressed’. To
depict the brightness of colors perceived, synesthetic
painters reportedly often apply with speed, pure,
unmixed oil paint, or watercolor straight from the
tube. Faithfully representing their perceptions may
require breaking some long-standing rules, a feature
that – as underlined by Carol Steen – characterizes
modern art. The artist also specified that her visions
were never representational nor figurative. This is
apparently typical of many synesthetes’ experiences,
and probably explains why synesthetic artwork com-
monly looks abstract, even though it is a ‘ realistic’
depiction of the artist’s perceptions [54].
EMOTIONAL DIMENSION OF
SYNESTHESIA
Emotional reactions play a prominent role in synes-
thetic processes. They are commonly experienced in
such conditions [32,55], acting as either inducer,
concurrent, or modulator [32,56]. A conflict between
the actual color of a stimulus and synesthetically
induced percepts can generate discomfort, whereas
‘pleasantness’ is experienced when synesthetic and
actual stimulus features match. Some synesthetes
indicate that all disagreeable events generate same
color, specific for the given individual. Saturation of
evoked colors is susceptible to be altered by mood
[32]. In some personality–color type of synesthesia,
viewing known faces elicits emotionally mediated
color percepts, presenting either as colored faces or
colored auras around heads [1,32,57] (Figs 4 and 5
[58]), conceivably as a result of cross-activation
between right, face recognition area and neighboring
V4 color cortex [7,59]. In this regard, the following
delightful dedication by Julia Simner, a prominent
expert in synesthesia, is illustrative: ‘For my two
children: the blue one (Indigo) and the brown one
(Tommy Bruno)’ [60]. In the so-called ‘ordinal lin-
guistic personification’ synesthesia, letters have
emotional valences, as well as a sex and personality
[61,62]. Sexual arousalalso triggers synesthetic experi-
ences in some 2% of individuals [26]. These perceptual
phenomena mainly consist of colored shapes, less
commonly of flavors, smells, sounds,or temperatures,
and are associated with a higher degree of trance and
loss of environmental boundaries [63].
FIGURE 4. ‘I and the Village’ 1911, by Marc Chagall.
Museum of Modern Art, New York, USA. Reproduced with
permission, !Adagp, Paris 2014. Over decades, Chagall
repeatedly depicted using intense green or blue colors, the
faces of central characters in his paintings [58]. This most
probably reflected a variant of personality–color synesthesia.
Color synesthesia Safran and Sanda
1350-7540 Copyright !2015 Wolters Kluwer Health, Inc. All rights reserved. www.co-neurology.com 39
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
Cerebral structures processing emotion are
altered in developmental synesthestes. MRI explora-
tion of associator grapheme–color synesthetes
recently brought further evidence of structural
changes in emotional areas both at cortical and at
subcortical levels [64
&&
]. Acquired cerebral disorders
are also susceptible to cause emotional synesthetic
percepts. Thus, a patient who had sustained a post-
erolateral thalamus hemorrhage [24
&
] experienced
blue photisms, intense extracorporeal sensation,
and ‘orgasmic’ ecstasy when hearing brass instru-
ments, or severe disgust sensations when reading
words printed in blue characters. Occurrence, expres-
sion, and the underlying mechanisms of affect-
related forms of synesthesia have recently been
reconsidered [56].
IMPACT OF SYNESTHESIA ON COGNITIVE
FUNCTIONS
Synesthetic experiences impact the cognitive func-
tions to a larger extent than believed in the
past [65,66
&&
,67,68]. Constitutional synesthesia
predisposes to better performances in certain aspects
and worse in others. Although having better color
perception compared with nonsynesthetes [69,70],
synesthetes present impaired motion [66
&&
,67] and
speech perception [71]. Speech perception deficit
could be a consequence of the impaired motion
perception, namely the biological movement of lips
or of a much wider deficit in multisensory integration
[71]. In grapheme– color and tone–color synesthetes,
increased gray matter volume in the left posterior
fusiform gyrus and decreased gray matter volume
of the anterior part of the same gyrus and in the left
MT/V5 support these hypotheses [72]. Improved
perception can occur within both inducing stimulus
and concurrent domains [68]. Memory was also
found enhanced when using synesthetic percepts
[25,73].
Improved performances depend partly on
preconscious mechanisms, operating early in sen-
sory processing [74]. Thus, a recent investigation
using pictures containing hidden letters found
that graphemecolor projectors recognized the
letters faster than nonsynesthetes; interestingly,
tested individuals noted that concurrent colors
were generated before conscious letter recognition
[75
&
]. Grapheme– color synesthesia even allows com-
puting via synesthetically perceived colors [68] and as
expected, emotional experience modulates synes-
thetes’ performances [55].
CEREBRAL DISORDERS CAUSING
SYNESTHESIA
Acquired forms of synesthesia have been related to
a variety of neurological conditions, including
migraine [76,77], multiple sclerosis radiologically
isolated syndrome [34
&
], posthypnotic suggestion
[78], and drug ingestion [20,79]. In recent years,
secondary synesthesia has been reported following
thalamic stroke [24
&
,8083]: two of these affected
individuals experienced colored synesthetic per-
cepts [24
&
,83]. Thalamic insult may induce large-
scale reorganization of the brain, modify the bal-
ance between excitatory and inhibitory connections
in high-order visual areas, and favor the develop-
ment of synesthesia [80].
Sensory deprivation favors the occurrence of
synesthetic phenomena. With blind people, non-
visual stimuli tend to elicit various percepts in the
suppressed sensory modality, including colored
photisms [84,85] presumably by cross-modal acti-
vation of the deafferented cortex [86]. Sound-
induced photisms in visually affected people are a
well recognized phenomenon [87]. Six late-blind
individuals were recently reported experiencing
colored phenomena when hearing or thinking
FIGURE 5. ‘Half-Past Three’ (‘The Poet’) 1911, by Marc
Chagall. Philadelphia Museum of Art, The Louise and Walter
Arensberg Collection, Philadelphia, PA, USA. Reproduced
with permission, !Adagp, Paris 2014. For comments, see
the legend of Fig. 4.
Neuro-ophthalmology and neuro-otology
40 www.co-neurology.com Volume 28 !Number 1 !February 2015
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
about letters, numbers, and time-related terms
[88,89]. In one of these individuals, touching Braille
characters induced colored photisms. A patient of
ours, blinded by bilateral arteritic anterior ischemic
optic neuropathy, reported perceiving colored
photisms when brushing his teeth or hearing a hand
clap (personal observation). We also recently
observed an unusual case of a late-blind individual
suffering from retinitis pigmentosa who volun-
teered consistently ‘seeing’ his limbs when moving
them, a phenomenon presumably related to cross-
modal activation of his visual cortex by propriocep-
tive inputs [90
&
].
Brain lesions disrupting canonical networks
and sensory input to associative areas are also
susceptible to induce synesthetic-like hallucina-
tory syndromes. A right monophtalm patient
with right parosmia reported intricate visual and
olfactory hallucinations following a right occipi-
totemporal stroke [91]. The patient described
seeing people with strong odors. The presumed
mechanism of these hallucinations was the desin-
hibition of the connections from the visual associ-
ation areas to perirhinal and parahippocampal gyri
[92].
ARTIFICIALLY ELICITED SYNESTHESIA
Sensory substitution devices (SSDs) have been devel-
oped to provide blind individuals with information
on their visual surrounding. They convey visual
information through another sensory modality, like
audition [93]. Visual-to-auditory SSDs proceed by
online translation of camera-captured views into
sounds, which represent the visual features of the
scene [93,94]. Users of such devices commonly claim
to ‘see’ the objects figured by sounds, and therefore
sensory substitution has been considered a kind of
synthetic synesthesia [93]. Interestingly, functional
magnetic resonance imaging (fMRI) investigations
using a visual-to-auditory SSD, both in blindfolded
healthy individuals [95] and in congenitally blind
individuals [96
&
], showed activation of visual areas.
Whether – and to what extent – SSD users also
perceive the auditory stimulus as a sound is debated
[97,98].
Sensory substitution, however, differs in some
respect from the naturally occurring synesthesia.
Indeed, intended to reliably figure the visual sur-
rounding, percepts elicited by SSDs are elaborated,
whereas regular synesthetic phenomena exhibit
essentially idiosyncratic features [8]. Further, in
contrast to SSD-provoked synesthetic experiences,
in developmental synesthesia, inducers do not
conform to sensorimotor contingencies of the con-
current modality [98].
NEURAL FOUNDATIONS OF SYNESTHESIA
Assumptions have been made on the mechanisms
underlying synesthesia, including hyperconnectiv-
ity between cortical areas [99], reduced level of feed-
back from inhibitory cerebral structures [2], learned
association in early life [100], and a normal percep-
tual mechanism incompletely suppressed in synes-
thetes [17]. Neurocognitive models have been
elaborated [101105].
In recent years, brain-imaging studies brought
further evidence that synesthetes connect more
inside and between sensory regions and less with
remote areas, especially the frontal cortex. Indeed,
these individuals exhibit increased intranetwork
connectivity in medial visual, auditory and intra-
parietal networks, and internetworks connectivity
between the medial and lateral visual networks,
the right frontoparietal network and between the
lateral visual and auditory networks. In contrast,
nonsynesthetes have more intranetwork connec-
tions within frontoparietal network [106]. When
presented with inducers, synesthetes exhibit a
clustering pattern of activated brain areas uniting
more visual regions, whereas nonsynesthetes acti-
vate particularly frontal and parietal regions [107
&&
]
(Fig. 6).
Involvement of the bottom-up and top-down
mechanisms has further been considered [105,108
111]. The bottom-up model stipulates that the con-
current representation is prompted by the inducer
representation via over represented and overactive
horizontal connections, whereas the top-down
model proposes that the inducer stimulates the
concurrent percept via an input from a convergent,
higher order integrator [2].
Using dynamic causal modeling, Van Leeuwen
et al. [106] have shown that projectors exhibited
effective connectivity patterns involving a bottom-
up mechanism, whereas associators used a top-down
mechanism. However, a recent electroencephalo-
graphic (EEG) study found evidence favoring the
top-down disinhibited feedback model as the
core of the synesthetic phenomenon [112
&&
].
Reduction of long-range couplings in the theta
frequency band could facilitate the top-down feed-
back. An fMRI study demonstrated that, in contrast
with projectors, associators’ synesthetic experience
was related to areas linked to memory processes,
including hippocampus and parahippocampal gyrus
[113,114].
THALAMUS AND DEVELOPMENTAL
SYNESTHESIA
It was suggested that congenital alterations
in thalamic circuitry might be responsible for
Color synesthesia Safran and Sanda
1350-7540 Copyright !2015 Wolters Kluwer Health, Inc. All rights reserved. www.co-neurology.com 41
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
atypical cortical morphology and connections,
found with different synesthetic phenotypes
[64
&&
,115]. Cytoarchitectonic maturation of the
primary sensory areas and the development of
their specific connections are highly dependent
on the thalamic input [116]. Enucleation in pre-
natal macaque drastically alters the equivalents of
V1 and V2 visual cortices, and induces rich non-
canonical connections with somatosensory, audi-
tory, and frontal areas [117], resembling transient
fetal connections [118]. Thus, the visual cortex
ends up treating other types of information. Like-
wise, congenitally blind humans exhibit occipital
cortex activation following auditory or somatosen-
sory stimulation [96
&
]. It is therefore conceivable that
in developmental synesthesia, congenitally anoma-
lous sensory input leads to abnormal synaptic
pruning and differences in brain connectivity. In
grapheme– color synesthetes, low white matter
densities in pulvinar, medial and lateral ventral
posterior nuclei, and low fractional anisotropy in
medial dorsal and ventral anterior nuclei suggest a
constitutional disconnection and hypoconnection
between thalamus and cerebral cortex [64
&&
]. The
concerned white matter tracts project to the left
prefrontal cortex and bilateral temporal and posterior
parietal cortex, regions that in synesthetes are dis-
tinct both in structure and function. Secondary syn-
esthesia after thalamic stroke also support the
involvement of thalamic output in synesthetic
phenomena [24
&
,80– 83].
CONCLUSION
Over the last few years, substantial advances have
been made in the understanding of synesthesia,
and hence more globally in the comprehension of
perception and consciousness. Fortunately, aware-
ness of this condition in the societal environment
also significantly improved, finally allowing syn-
esthetes to feel relieved by the so badly needed
recognition of their particular situation. In a near
future, in addition to the expected deepening of
the explorations undertaken, elaborating a more
comprehensive definition of synesthesia would be
welcomed. Currently used criteria are rather
restrictive for a condition that is quite polymor-
phic in nature. This process, however, is customary
in the history of medicine, which consists of
initially establishing a restricted definition to
encapsulate the core of the condition and then
broadening it, taking into account the numerous
subtle presentations encountered.
Acknowledgements
The authors thank Katia Marazova, MD, PhD, for
editorial assistance.
Financial support and sponsorship
Funding: This study was supported in part by grants from
LABEX and Humanis.
Conflicts of interest
There are no conflicts of interest.
Graphemes
All
Pseudographemes
3
D
S
Synesthetes
Control
FIGURE 6. Cerebral activation revealing distinct activity patterns for controls and synesthetes during grapheme and pseudo-
grapheme presentation. Synesthetes demonstrate the most significant activity in the bilateral posterior inferior temporal gyri.
Reproduced with permission [107
&&
].
Neuro-ophthalmology and neuro-otology
42 www.co-neurology.com Volume 28 !Number 1 !February 2015
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
REFERENCES AND RECOMMENDED
READING
Papers of particular interest, published within the annual period of review, have
been highlighted as:
&of special interest
&& of outstanding interest
1. Hochel M, Mila
´n EG, Martı
´n JLM, et al. Congruence or coherence? Emotional
and physiological responses to colours in synaesthesia. Eur J Cogn Psychol
2009; 21:703– 723.
2. Grossenbacher PG, Lovelace CT. Mechanisms of synesthesia: cognitive and
physiological constraints. Trends Cogn Sci 2001; 5:36 –41.
3. Sinke C, Neufeld J. Synaesthesia: a conceptualization (‘synthesis’-)
phenomenon. Philosophical and neurobiological aspects. Theor Hist
Sci 2013; 10:37– 54.
4. Auvray M, Deroy O. How do synesthetes experience the world? In: Matthen
M, editor. Oxford handbook of the philosophy of perception. New York:
Oxford University Press, Inc; in press.
5. Sagiv N, Frith C. Synesthesia and consciousness. In: Simner J, Hubbard EM,
editors. Oxford handbook of synesthesia. Oxford: Oxford University Press;
2013. pp. 924– 940.
6. Hubbard EM. Synesthesia and functional imaging. In: Simner J, Hubbard E,
editors. Oxford handbook of synesthesia. Oxford: Oxford University Press;
2013. pp. 475– 499.
7. Ramachandran VS, Hubbard EM. Synaesthesia a window into perception,
thought and language. J Conscious Stud 2001; 8:3 –34.
8. Ward J. Synesthesia. Annu Rev Psychol 2013; 64:49 –75.
9. Voskuil PHA. Van Gogh’s disease in the light of his correspondence. In:
Bogousslavsky J, Dieguez S, editors. Frontiers of neurology and neuro-
science. Basel: Karger AG; 2013. pp. 116 –125.
10. Zedler M, Rehme M. Synesthesia: a psychosocial approach. In: Simner J,
Hubbard E, editors. Oxford handbook of synesthesia. Oxford: Oxford Uni-
versity Press; 2013. pp. 459– 472.
11. Van Campen C. The discovery of synesthesia in childhood. Theor Hist Sci
2013; 10:195– 206.
12. Day S. Synesthesia: a first-person perspective. In: Simner J, Hubbard EM,
editors. Oxford handbook of synesthesia. Oxford: Oxford University Press;
2013. pp. 903– 923.
13. Simner J, Mulvenna C, Sagiv N, et al. Synaesthesia: the prevalence of atypical
cross-modal experiences. Perception 2006; 35:1024 –1033.
14. Brang D, Ramachandran VS. Survival of the synesthesia gene: why do
people hear colors and taste words? PLoS Biol 2011; 9:e1001205.
15. Jackson TE, Sandramouli S. Auditory –olfactory synesthesia coexisting with
auditory– visual synesthesia. J Neuroophthalmol 2012; 32:221 –223.
16. Neufeld J, Roy M, Zapf A, et al. Is synesthesia more common in patients with
Asperger syndrome? Front Hum Neurosci 2013; 7:847.
17. Cytowic RE. Synesthesia: a union of the senses – second edition. Cam-
bridge, MA: A Bradford Book; 2002.
18. Mattingley JB. Attention, automaticity, and awareness in synesthesia. Ann N
Y Acad Sci 2009; 1156:141– 167.
19.
&
Simner J, Bain AE. A longitudinal study of grapheme color synesthesia in
childhood: 6/7 years to 10/11 years. Front Hum Neurosci 2013; 7:603.
The authors observed the development of child synesthetes over 4 years and found
that in some individuals, synesthesia apparently died out over time or developed
more slowly in some individuals over others. This demonstrated that synesthetic
phenomena are not as consistent over time as previously thought.
20. Brogaard B. Serotonergic hyperactivity as a potential factor in develop-
mental, acquired and drug-induced synesthesia. Front Hum Neurosci
2013; 7:657.
21. Luke DP, Terhune DB. The induction of synaesthesia with chemical agents: a
systematic review. Front Psychol 2013; 4:753.
22. Terhune DB, Song SM, Duta MD, Cohen Kadosh R. Probing the neuro-
chemical basis of synaesthesia using psychophysics. Front Hum Neurosci
2014; 8:89.
23. Van Hout MC. Nod and wave: an Internet study of the codeine intoxication
phenomenon. Int J Drug Policy 2014. [Epub ahead of print]
24.
&
Schweizer TA, Li Z, Fischer CE, et al. From the thalamus with love: a rare
window into the locus of emotionalsynesthesia.Neurology2013;
81:509– 510.
The authors for the first time report a case of acquired emotional synesthesia after
focal thalamic lesion.
25. Brang D, Rouw R, Ramachandran VS, Coulson S. Similarly shaped letters
evoke similar colors in grapheme –color synesthesia. Neuropsychologia
2011; 49:1355– 1358.
26. Day S. Types of synesthesia. Synesthesia 2014. Available at http://www.day-
syn.com. [Accessed October 2014].
27. Ramachandran VS, Hubbard EM. Hearing colors, tasting shapes. Sci Am
2003; 288:52– 59.
28. Day S. Some demographic and socio-cultural aspects of synesthesia. In:
Robertson LC, Sagiv N, editors. Synesthesia: perspectives from cognitive
neuroscience. New York: Oxford University Press, Inc; 2005. pp. 11– 33.
29. Steen C. Visions shared. A firsthand look into synesthesia and art. Leonardo
2001; 34:203– 208.
30. McDonald F. Synesthesia: bringing out the contours. Aust Art Rev 2006.
Available at http://www.synesthesia.info/Steen-Australian_Art_Review.pdf.
[Accessed 12 October 2014]
31. Tyler C. Varieties of synesthetic experience. In: Robertson LC, Sagiv N,
editors. Synesthesia: perspectives from cognitive neuroscience. New York:
Oxford University Press, Inc; 2005. pp. 34– 44.
32. Ward J. Emotionally mediated synaesthesia. Cogn Neuropsychol 2004;
21:761– 772.
33. Hung W-Y, Simner J, Shillcock R, Eagleman DM. Synaesthesia in Chinese
characters: the role of radical function, position. Conscious Cogn 2014;
24:38– 48.
34.
&
Simner J, Carmichael DA, Hubbard EM, et al. Rates of white matter hyper-
intensities compatible with the radiological profile of multiple sclerosis within
self-referred synesthete populations. Neurocase (in press).
The study reported an apparent statistical link between synesthesia and multiple
sclerosis – radiologically isolated syndrome.
35. Nikolic
´D, Ju
¨rgens UM, Rothen N, et al. Swimming-style synesthesia. Cortex
2011; 47:874– 879.
36. Rothen N, Nikolic
´D, Ju
¨rgens UM, et al. Psychophysiological evidence for the
genuineness of swimming-style colour synaesthesia. Conscious Cogn 2013;
22:35– 46.
37. Mroczko-Wasowicz A, Werning M. Synesthesia, sensory –motor contin-
gency, and semantic emulation: how swimming style –color synesthesia
challenges the traditional view of synesthesia. Front Psychol 2012; 3:
279.
38. Meier B. Semantic representation of synaesthesia. Theor Hist Sci 2013;
10:125– 134.
39. Mroczko-Wasowicz A, Nikolic D. Semantic mechanisms may be responsible
for developing synesthesia. Front Hum Neurosci 2014; 8:509.
40. Dixon MJ, Smilek D, Merikle PM. Not all synaesthetes are created equal:
projector versus associator synaesthetes. Cogn Affect Behav Neurosci
2004; 4:335– 343.
41. Mohr C. Synesthesia in space versus in the ‘mind’s eye’: how to ask the right
questions. In: Simner J, Hubbard E, editors. Oxford handbook of synesthesia.
Oxford: Oxford University Press; 2013. pp. 440 –458.
42. Cavanagh P. The artist as neuroscientist. Nature 2005; 434:301 307.
43. Blanke O, Forcucci L, Dieguez S. Don’t forget the artists when studying
perception of art. Nature 2009; 462:984.
44. Makin ADJ, Wuerger SM. The IAT shows no evidence for Kandinsky’s color –
shape associations. Front Psychol 2013; 4:616.
45. Zeki S. Neurobiology and the humanities. Neuron 2014; 84:12 –14.
46. Safran AB, Sanda N, Sahel J-A. A neurological disorder presumably underlies
painter Francis Bacon distorted world depiction. Front Hum Neurosci 2014; 8:581.
47. Van Campen C. Synesthesia in the visual arts. In: Simner J, Hubbard E,
editors. Oxford handbook of synesthesia. Oxford: Oxford University Press;
2013. pp. 631– 646.
48. Domino G. Synesthesia and creativity in fine arts students: an empirical look.
Creat Res J 1989; 2:17–29.
49. Rothen N, Meier B. Higher prevalence of synaesthesia in art students.
Perception 2010; 39:718–720.
50. Ward J, Thompson-Lake D, Ely R, Kaminski F. Synaesthesia, creativity and
art: what is the link? Br J Psychol 2008; 1953:2008; 99:127 –141.
51.
&
Banissy MJ, Holle H, Cassell J, et al. Personality traits in people with
synaesthesia: do synaesthetes have an atypical personality profile? Personal
Individ Differ 2013; 54:828– 831.
The authors found that, relative to matched controls, synaesthetes reported higher
levels of imagination, artistic tendencies, and ‘fantasizing’.
52.
&
Meier B, Rothen N. Grapheme –color synaesthesia is associated with a
distinct cognitive style. Front Psychol 2013; 4:632.
The authors reported that grapheme–color synesthetes showed higher ratings on
verbal and vivid imagery style dimensions.
53. Kandinsky W. Concerning the spiritual in art. London: Constable and Co Ltd;
1914.
54. Steen C, Berman G. Synesthesia and the artistic process. In: Simner J,
Hubbard E, editors. Oxford handbook of synesthesia. Oxford: Oxford Uni-
versity Press; 2013. pp. 671– 691.
55. Perry A, Henik A. The emotional valence of a conflict: implications from
synesthesia. Front Psychol 2013; 4:978.
56. Dael N, Sierro G, Mohr C. Affect-related synesthesias: a prospective view on
their existence, expression and underlying mechanisms. Front Psychol 2013;
4:754.
57. Cytowic RE, Eagleman D. Wednesday is indigo blue: discovering the brain of
synesthesia. Cambridge, MA: MIT Press; 2009.
58. Salcman M. The fiance
´e with a blue face by Marc Chagall (1887– 1985).
Neurosurgery 2007; 61:1322–1324.
59. Hubbard EM, Brang D, Ramachandran VS. The cross-activation theory at 10.
J Neuropsychol 2011; 5:152–177.
60. Simner J, Hubbard E. Oxford handbook of synesthesia. Oxford: Oxford
University Press; 2013.
61. Simner J, Holenstein E. Ordinal linguistic personification as a variant of
synesthesia. J Cogn Neurosci 2007; 19:694 –703.
Color synesthesia Safran and Sanda
1350-7540 Copyright !2015 Wolters Kluwer Health, Inc. All rights reserved. www.co-neurology.com 43
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
62. Smilek D, Malcolmson KA, Carriere JSA, et al. When ‘3’ is a jerk, ‘E’ is a king:
personifying inanimate objects in synesthesia. J Cogn Neurosci 2007;
19:981– 992.
63. Nielsen J, Kruger THC, Hartmann U, et al. Synaesthesia and sexuality: the
influence of synaesthetic perceptions on sexual experience. Front Psychol
2013; 4:751.
64.
&&
Melero H, Pen
˜a-Melia
´nA
´, Rı
´os-Lago M, et al. Grapheme– color synesthetes
show peculiarities in their emotional brain: cortical and subcortical evidence
from VBM analysis of 3D-T1 DTI data. Exp Brain Res 2013; 227:343–
353.
This study demonstrates morphological differences in thalamocortical connections
in synesthetes as well as increased gray matter volume in brain regions involved in
emotional processing. It provides morphological evidence about the importance of
emotion in synesthetic phenomena.
65. Mottron L, Bouvet L, Bonnel A, et al. Veridical mapping in the development
of exceptional autistic abilities. Neurosci Biobehav Rev 2013; 37:209
228.
66.
&&
Banissy MJ, Tester V, Muggleton NG, et al. Synesthesia for color is linked to
improved color perception but reduced motion perception. Psychol Sci
2013; 24:2390– 2397.
This study showed that synesthesia for color is linked to facilitated color sensitivity,
but decreased motion sensitivity.
67. McCarthy JD, Caplovitz GP. Color synesthesia improves color but impairs
motion perception. Trends Cogn Sci 2014; 18:224 –226.
68. McCarthy JD, Barnes LN, Alvarez BD, Caplovitz GP. Two plus blue equals
green: grapheme– color synesthesia allows cognitive access to numerical
information via color. Conscious Cogn 2013; 22:1384 –1392.
69. Cohen Kadosh R, Gertner L, Terhune DB. Exceptional abilities in the spatial
representation of numbers and time: insights from synesthesia. Neuroscien-
tist 2012; 18:208– 215.
70. Brang D, Miller LE, McQuire M, et al. Enhanced mental rotation ability in time-
space synesthesia. Cogn Process 2013; 14:429 –434.
71. Sinke C, Neufeld J, Zedler M, et al. Reduced audiovisual integration in
synesthesia – evidence from bimodal speech perception. J Neuropsychol
2014; 8:94– 106.
72. Banissy MJ, Stewart L, Muggleton NG, et al. Grapheme– color and tone–
color synesthesia is associated with structural brain changes in visual
regions implicated in color, form, and motion. Cogn Neurosci 2012;
3:29– 35.
73. Witthoft N, Winawer J. Learning, memory, and synesthesia. Psychol Sci
2013; 24:258– 265.
74. Rothen N, Scott RB, Mealor AD, et al. Synesthetic experiences enhance
unconscious learning. Cogn Neurosci 2013; 4:231 –238.
75.
&
Ramachandran VS, Seckel E. Synesthetic colors induced by graphemes that
have not been consciously perceived. Neurocase (in press).
In pictures that contained hidden letters, grapheme–color projector synesthetes
recognized the letters faster and reported that the colors were evoked before
conscious letter recognition, suggesting that in some synesthetes colors are
evoked preconsciously early in sensory processing.
76. Podoll K, Robinson D. Auditory –visual synaesthesia in a patient with basilar
migraine. J Neurol 2002; 249:476– 477.
77. Alstadhaug KB, Benjaminsen E. Synesthesia and migraine: case report.
BMC Neurol 2010; 10:121.
78. Terhune DB, Carden
˜aE,LindgrenM.Disruptionofsynaesthesiaby
posthypnotic suggestion: an ERP study. Neuropsychologia 2010;
48:3360– 3364.
79. Sinke C, Halpern JH, Zedler M, et al. Genuine and drug-induced synesthesia:
a comparison. Conscious Cogn 2012; 21:1419 –1434.
80. Ro T, Farne
`A, Johnson RM, et al. Feeling sounds after a thalamic lesion. Ann
Neurol 2007; 62:433– 441.
81. Beauchamp MS, Ro T. Neural substrates of sound –touch synesthesia after a
thalamic lesion. J Neurosci 2008; 28:13696 –13702.
82. Naumer MJ, van den Bosch JJF. Touching sounds: thalamocortical plasticity
and the neural basis of multisensory integration. J Neurophysiol 2009;
102:7– 8.
83. Fornazzari L, Fischer CE, Ringer L, Schweizer TA. ‘Blue is music to my ears’:
multimodal synesthesias after a thalamic stroke. Neurocase 2012;
18:318– 322.
84. Niccolai V, van Leeuwen TM, Blakemore C, Stoerig P. Synaesthetic percep-
tion of colour and visual space in a blind subject: an fMRI case study.
Conscious Cogn 2012; 21:889–899.
85. Armel K, Ramachandran VS. Acquired synesthesia in retinitis pigmentosa.
Neurocase 1999; 5:293–296.
86. Merabet LB, Pascual-Leone A. Neural reorganization following sensory loss:
the opportunity of change. Nat Rev Neurosci 2010; 11:44– 52.
87. Jacobs L, Karpik A, Bozian D, Gøthgen S. Auditory visual synesthesia:
sound-induced photisms. Arch Neurol 1981; 38:211 –216.
88. Steven MS, Hansen PC, Blakemore C. Activation of color-selective areas of
the visual cortex in a blind synesthete. Cortex 2006; 42:304 308.
89. Steven MS, Blakemore C. Visual synaesthesia in the blind. Perception 2004;
33:855– 868.
90.
&
Safran AB, Sabbah N, Sanda N, Sahel JA. The blind man who saw his hands.
Cross-modal plasticity revisited. In: The Association for the Research in
Vision and Ophthalmology (ARVO); 2014 Annual Meeting; Poster no: 4147.
A patient blinded as a result of retinitis pigmentosa volunteered that he visually
perceived the shape of his hands when waving them; the visual synesthetic
percept was presumably elicited by proprioceptive inputs.
91. Gubernick D, Ameli P, Teng Q, et al. Visual –olfactory hallucinatory synesthe-
sia: the Charles Bonnet Syndrome with olfactory hallucinations. Cortex
2014; 50:204– 207.
92. Ninomiya T, Sawamura H, Inoue K-I, Takada M. Multisynaptic inputs from the
medial temporal lobe to V4 in macaques. PLoS One 2012; 7:e52115.
93. Suslick KS. Synesthesia in science and technology: more than making the
unseen visible. Curr Opin Chem Biol 2012; 16:557 563.
94. Proulx MJ. Synthetic synaesthesia and sensory substitution. Conscious Cogn
2010; 19:501– 503.
95. Striem-Amit E, Cohen L, Dehaene S, Amedi A. Reading with sounds: sensory
substitution selectively activates the visual word form area in the blind.
Neuron 2012; 76:640– 652.
96.
&
Striem-Amit E, Amedi A. Visual cortex extrastriate body-selective area activa-
tion in congenitally blind people ‘seeing’ by using sounds. Curr Biol 2014;
24:687– 692.
This study demonstrates the presence of selective activation of extrastriate body
area in congenitally blind while detecting body shapes with a sensory substitution
device, supporting the view that brain has a sensory independent, task-selective
organization.
97. Ortiz T, Poch J, Santos JM, et al. Recruitment of occipital cortex during
sensory substitution training linked to subjective experience of seeing in
people with blindness. PLoS One 2011; 6:e23264.
98. Ward J, Wright T. Sensory substitution as an artificially acquired synaesthe-
sia. Neurosci Biobehav Rev 2014; 41:26 35.
99. Ramachandran VS, Hubbard EM. Psychophysical investigations into the
neural basis of synaesthesia. Proc Biol Sci 2001; 268:979–983.
100. Calkins M. Synesthesia. J Psychol 1895; 7:90 107.
101. Harvey JP. Sensory perception: lessons from synesthesia: using synesthesia
to inform the understanding of sensory perception. Yale J Biol Med 2013;
86:203– 216.
102. Froese T. Steps toward an inactive account of synesthesia. Cogn Neurosci
2014; 5:126– 127.
103. O’Regan JK, Degenaar J. Predictive processing, perceptual presence, sen-
sorimotor theory. Cogn Neurosci 2014; 5:130 –131.
104. Rouw R, Ridderinkhof KR. The most intriguing question in synesthesia
research. Cogn Neurosci 2014; 5:128 –130.
105. Van Leeuwen TM. Constructing priors in synesthesia. Cogn Neurosci 2014;
5:124– 126.
106. Van Leeuwen TM, den Ouden HEM, Hagoort P. Effective connectivity
determines the nature of subjective experience in grapheme –color synesthe-
sia. J Neurosci 2011; 31:9879–9884.
107.
&&
Tomson SN, Narayan M, Allen GI, Eagleman DM. Neural networks of colored
sequence synesthesia. J Neurosci 2013; 33:14098 –14106.
This study demonstrates hodological differences between synesthetes and non-
synesthetes. Synesthetes cluster more in visual areas and nonsynesthetes in
frontal and parietal areas. These clustering patters may provide an explanation for
the different cognitive performances associated with synesthetic phenotype.
108. Hubbard EM. Neurophysiology of synesthesia. Curr Psychiatry Rep 2007;
9:193– 199.
109. Hubbard EM. A real red-letter day. Nat Neurosci 2007; 10:671 672.
110. Brogaard B, Vanni S, Silvanto J. Seeing mathematics: percept ual experience
and brain activity in acquired synesthesia. Neurocase 2013; 19:566 575.
111. Brogaard B, Marlow K, Rice K. The long-term potentiation model for gra-
pheme– color binding in synesthesia. In: Bennett D, Hill C, editors. Sensory
integration and the unity of consciousness. Cambridge, MA: MIT Press; in
press.
112.
&&
Volberg G, Karmann A, Birkner S, Greenlee MW. Short- and long-range
neural synchrony in grapheme–color synesthesia. J Cogn Neurosci 2013;
25:1148– 1162.
This study provides electrophysiological arguments that favor the top-down
disinhibited model as the core of synesthetic phenomena.
113. Rouw R, Scholte HS. Neural basis of individual differences in synesthetic
experiences. J Neurosci 2010; 30:6205 –6213.
114. Rouw R, Scholte HS. Increased structural connectivity in grapheme color
synesthesia. Nat Neurosci 2007; 10:792–797.
115. Mitchell KJ. Synesthesia and cortical connectivity a neurodevelopmental
perspective. In: Simner J, Hubbard EM, editors. Oxford handbook of
synesthesia. Oxford: Oxford University Press; 2013. pp. 530 –550.
116. Dehay C, Kennedy H. Cell-cycle control and cortical development. Nat Rev
Neurosci 2007; 8:438– 450.
117. Rakic P, Sun
˜er I, Williams RW. A novel cytoarchitectonic area induced
experimentally within the primate visual cortex. Proc Natl Acad Sci USA
1991; 88:2083– 2087.
118. Price DJ, Kennedy H, Dehay C, et al. The development of cortical connec-
tions. Eur J Neurosci 2006; 23:910 –920.
Neuro-ophthalmology and neuro-otology
44 www.co-neurology.com Volume 28 !Number 1 !February 2015
... Emotional reactions play a part in the synesthetic process. Additionally, cerebral structure processing emotions are differents in developmental synesthesia and in the acquired form [11,12]. Given this and the research that demonstrates that all three types of synesthesia link to music perception [13], we hypothesize that forms of synesthesia that include music potentially have an in uence on well-being. ...
... Synesthesia has only recently been seen as a pathological condition in neurodevelopmental disorders like Asperger's syndrome and Williams syndrome [78,79]. While we characterize pathological synesthesia, which is acquired or adulthood variety [12] as a separate type here, it is prudent to note that this is largely because recent research has re ned our understanding of the synesthete experience. With the range of current research in mind, it is also important to note that historical papers did identify pathologically acquired synesthesia in epilepsy, migraine, and in other neurological disorders, so there is a connection between recent work. ...
Chapter
Full-text available
Synesthesia gave rise to an important debate in nineteenth-century Europe that was influenced by the Symbolist movement and research into the physiology of perception. Yet, efforts to understand sensory modalities and to pictorially translate musical effects, or vice versa, are very ancient in origin. For example, the ability to coordinate colors and sounds was well known in the ancient cultures of India and China. Similarly, in sixth-century Greece, Pythagoras (570 BC–495 BC) assigned numbers as well as colors to musical notes. There was also interest in how the various sensory modalities were able to reveal the distinctive properties of an object and if these experiences could be translated or shared with others. This chapter examines the foundations of the nineteenth-century debate, the importance of the cultural aspect of synesthesia, and the subsequent search for a neurological explanation. As we show, the lively European debate included Italian, French, English, Swiss, and German scientists who were stimulated to study the relationship between color and sound, music and painting, and the creativity associated with synesthetes. Among the researchers discussed are Carlo Botta (1766–1837), Alfred Vulpian (1826–1887), Filippo Lussana (1820–1897), and Eugene Bleuler (1857–1939). The paper also looks at the three forms of synesthesia related to the debate (metaphoric, constitutional, and pathological) from both historical and contemporary perspectives. Finally, we examine the role of emotion in the various forms of musical synesthesia and possible neuronal well-being.KeywordsMusic synesthesiaEmotionBrainWell-being
... This hypothesis proposed a relationship between color perception and psychological as well as behavioral processes. Psychology also includes the concept of color association, defined as 'the perception of color generated from non-visual sensory organs' encompassing 'color of hearing, color of shape, color of gustation, color of smell and color of touch' (Safran and Sanda 2015). ...
Preprint
Full-text available
The pivotal role of color imagery analysis and activation has been insufficiently explored in the realm of historic heritage conservation. This study addresses this issue by introducing a comprehensive methodological framework that encompasses acquisition, analysis, activation, and application of color information based on the NCD color system, an innovative color semantic quantification theory. Utilizing the venerable Yuelu Academy (from A.D. 976) as a case study, color imagery analysis methods across diverse spatial scales have been summarised. Subsequently, these results are applied to activate the surrounding environment color, as well as its cultural souvenirs. The methodologies outlined herein hold profound significance in addressing challenges concerning visual color continuity in the preservation of historic architectural landscapes, offering innovative perspectives.
... Color is known as the soul of interior design, and it is the most sensitive visual feeling of people in the interior environment. With people's deepening knowledge of color and increasing understanding of color function, color plays an increasingly important role in home interior design [1][2][3]. Interior design is the design of the interior space of a building. Interior design can be broadly divided into residential interior design, collective public interior design, open public interior design, and specialized interior design [4][5][6]. ...
Article
Full-text available
In this paper, the HSV color space model is used to collect the color characteristics of modern interior design and classify them into three types: hue (H), saturation (S), and luminance (V). At the same time, it combines with the theory of color psychology to construct a PAD emotion model for interior design. Then, it selects experimental samples and data analysis tools to carry out an example analysis of interior design from the emotional perspective. The data show that the selection of people warm and bright color interior design in the interior design of the background color across the amplitude of the largest and more concentrated in the 47.5°, the main body color across the amplitude of the smallest and most stable, the accent color value of the whole relatively high, the highest 123.6°, the background color saturation is the highest of 34.6°, and the brightness of more than 63.9°, the overall presentation of the warmth of comfort indoor environment. Error-values were 0.004, 0.0698, and 0.038 in order, with the errors all below 10%. This study integrates psychology and color into interior emotional design to better create visually appropriate, comfortable, and culturally rich interior environments for people, and also to promote the development of the interior design field.
... The principles of rehabilitation treatment were: 1) anchoring to a positive emotion through the choice of a color; 2) "here and now": listen and perceive your "own" body in motion; 3) conscious breathing; 4) "close your eyes": improve interoceptive awareness during exercise; 5) relaxation: Breathe, moving slowly and without pain (Safran and Sanda, 2015;Kawai et al., 2020). ...
Article
Full-text available
Fibromyalgia (FM) syndrome is characterized by the close correlation of chronic widespread pain and other non-pain related symptoms. Aim of this study was to investigate whether telerehabilitation that provides physical and psychological support services of the mind-body techniques can affect the clinical profile and pain relief of FM patients. The study included twenty-eight female FM patients, mean aged 56.61 ± 8.56 years. All patients underwent a rehabilitation treatment (8 sessions, 1/week, 1 h/each) through Zoom platform, with the following principles of rehabilitation treatment: Anchoring to a positive emotion; listen and perceive your “own” body; conscious breathing; improve interoceptive awareness; relax. All patients then underwent clinical assessment of the physical distress and fear of movement for the Numeric Rating Scale (NRS); the Fatigue Assessment Scale (FAS); the Fear Avoidance Belief Questionnaire (FABQ); with measures of physical and mental disability for the Fibromyalgia Impact Questionnaire (FIQ); the 12-Items Short Form Survey; the Resilience Scale for Adults and the Coping Strategies Questionnaire-Revised. The evaluations were performed at T0 (baseline), T1 (after 8 weeks of treatment), and T2 (after 1 month of follow-up). The main finding was that telerehabilitation reduced physical and mental distress, fear, and disability (p < 0.001). Resilience and coping ability were less affected by the rehabilitative treatment. Our attempt of mind-body technique telerehabilitation has shown good results in the improvement of painful symptoms and quality of life for the FM patients but showed fewer positive impacts for the resilience and coping abilities aspects.
Article
Full-text available
The theme of embodied engagement with art is explored in relation to the work Return to Chaos, which was created by South African visual artist AntheA Delmotte in 2017. Following a brief introduction to the artist and her works, my own embodied, sensual encounters with Return to Chaos are investigated in order to establish the usefulness, or not, of this way of looking. Delmotte's oeuvre shows that she intertwines painting styles of carefully planned studio based realism with deep trance-state public performance paintings that usually result in relatively unplanned abstract artworks. The latter painting performances are often conducted to the accompaniment of live music. Sound, and the presence of co-performing musicians, play an important role for Delmotte while delving into her subconscious to find colour and imagery that best expresses her emotions at any particular moment while deep trance-state painting. This article goes on to explore the possibility that Delmotte's incremental creation of artworks such as Return to Chaos give insight into colour synaesthesia and cymatic effects in action, and that this artwork shows visible manifestation of deep trance-state feelings embodied by her in response to the music at that particular moment in time. Finally, it is suggested that enrichment offered by analysis of artworks arising from full bodied encounters be extended to include investigations into embodied acts performed by artists as they explore and express their ideas.
Book
Creative metaphor has been of central interest to the cognitive linguistic research community in recent years. However, little is known about what propels people to use metaphor in a creative way. In this Element, the authors identify and explore some of the clues that synaesthesia may provide to help us better understand the factors that drive creativity, with a particular focus on creative metaphor. They identify the factors that seem to trigger the production of creative metaphor in synaesthetes, and explore what this can tell us about creativity in the population more generally. Their findings provide insights into the nature of creativity as it relates to metaphor, emotion and embodied experience. They argue that the production of creative metaphor arises from strong affective reactions to sensory and emotional stimuli and that there is an embodied symbiotic relationship between sensory experiences, embodiment, emotion, hyperbole, empathy, metaphor and creativity.
Chapter
All over the world, parents sing to their babies to soothe them and help them fall asleep. Among adults, the use of music as a sleep aid is also common, and research suggests that music can be effective for improving sleep in various populations with sleep problems. A number of studies have evaluated the effect of music on sleep in elderly persons with sleep problems, insomnia related to mental disorders, and hospitalized patients. These studies suggest a potential for the use of music as an intervention to improve sleep, even though the effect on objective sleep measures remains unclear. Music may facilitate sleep through relaxation, distraction, and mood regulation, and the mechanisms can be considered from a neurological, physiological, and psychological level. To improve sleep, it has been suggested that sleep music should be slow and predictable, but studies on the music people use to sleep show a large variation in genres, artists, and music characteristics.
Chapter
Sensory information reaches the cerebral cortex via several parallel channels that involve different receptor subtypes, sensory pathways, and first-order thalamic relay nuclei, which then relay modality-specific inputs to the primary sensory cortex. From primary sensory areas, information is first processed by unimodal (modality-specific) sensory association areas organized into two parallel streams; a dorsal stream for processing of visuospatial information via the posterior parietal cortex to guide attention, motor behavior, and spatial navigation, and a ventral stream for processing of object feature information via temporal lobe for object recognition. Impairment of these pathways at subcortical level or primary sensory cortex produces modality-specific sensory loss, involvement of association areas manifest with visual spatial neglect, and several forms of agnosia.
Chapter
Full-text available
Article
Full-text available
We investigated grapheme--colour synaesthesia and found that: (1) The induced colours led to perceptual grouping and pop-out, (2) a grapheme rendered invisible through `crowding' or lateral masking induced synaesthetic colours --- a form of blindsight --- and (3) peripherally presented graphemes did not induce colours even when they were clearly visible. Taken collectively, these and other experiments prove conclusively that synaesthesia is a genuine perceptual phenomenon, not an effect based on memory associations from childhood or on vague metaphorical speech. We identify different subtypes of number--colour synaesthesia and propose that they are caused by hyperconnectivity between colour and number areas at different stages in processing; lower synaesthetes may have cross-wiring (or cross-activation) within the fusiform gyrus, whereas higher synaesthetes may have cross-activation in the angular gyrus. This hyperconnectivity might be caused by a genetic mutation that causes defective pruning of connections between brain maps. The mutation may further be expressed selectively (due to transcription factors) in the fusiform or angular gyri, and this may explain the existence of different forms of synaesthesia. If expressed very diffusely, there may be extensive cross-wiring between brain regions that represent abstract concepts, which would explain the link between creativity, metaphor and synaesthesia (and the higher incidence of synaesthesia among artists and poets). Also, hyperconnectivity between the sensory cortex and amygdala would explain the heightened aversion synaesthetes experience when seeing numbers printed in the `wrong' colour. Lastly, kindling (induced hyperconnectivity in the temporal lobes of temporal lobe epilepsy [TLE] patients) may explain the purp...
Article
Full-text available
Neurobiological aspects of synaesthesia are discussed from the perspective of the broader philosophical topic of “syn-aisthesis” and the basic fundamentals of a neuropsychological understanding of perceptual inter-modal integration. Herein, the predominance of conceptualization processes in regard to top-down functions of the brain appears as a prerequisite for perception. Functional Magnet Resonance Imaging (fMRI) data of synaesthetes compared to controls are discussed, providing evidence for the theory that prefrontal and parietal conceptualization processes by themselves exert transmodal functions and thus contain properties of “binding”. A partial hyperactivity of such processes in synaesthesia may thus be a causal factor of this condition.
Article
Full-text available
We studied two otherwise normal, synaesthetic subjects who 'saw' a specific colour every time they saw a specific number or letter. We conducted four experiments in order to show that this was a genuine perceptual experience rather than merely a memory association. (i) The synaesthetically induced colours could lead to perceptual grouping, even though the inducing numerals or letters did not. (ii) Synaesthetically induced colours were not experienced if the graphemes were presented peripherally. (iii) Roman numerals were ineffective: the actual number grapheme was required. (iv) If two graphemes were alternated the induced colours were also seen in alternation. However, colours were no longer experienced if the graphemes were alternated at more than 4 Hz. We propose that grapheme colour synaesthesia arises from 'cross-wiring' between the 'colour centre' (area V4 or V8) and the 'number area', both of which lie in the fusiform gyrus. We also suggest a similar explanation for the representation of metaphors in the brain: hence, the higher incidence of synaesthesia among artists and poets.
Chapter
Full-text available
Synaesthetes experience additional sensory features (concurrents) when presented with certain objects such as letters (inducers). Because synaesthetic experiences are involuntary, vivid, and systematic, scientists assimilate them with perceptual experiences—an assimilation which turns out to be difficult to reconcile with the dominant philosophical theories of perception. However, this chapter stresses that the philosophical difficulties dissolve once certain questionable assumptions are corrected. First, synaesthesia is a very varied condition, perhaps not even unified, and only rare cases might count as being similar enough to perceptual experiences. Second, synaesthetic experiences should not be analysed as a conjunction of two distinct phenomena: one for the inducer, enjoyed by synaesthetes and non-synaesthetes alike, and one for the concurrent, enjoyed only by synaesthetes. This chapter proposes an alternative account, whereby synaesthetic experiences are better captured as richer, unified experiences, where an additional sensory attribute gets hosted in the perceptual experience of the inducer. This novel account leads us to reconsider the philosophical challenges raised by synaesthesia.
Chapter
Full-text available
The phenomenon of synesthesia has undergone an invigorationof research interest and empirical progress over the past decade. Studies investigating the cognitive mechanisms underlying the condition have yielded insight into neural processes behind such cognitive operations as attention, memory, spatial phenomenologyand cross-modal processes. However, the structural and functional mechanisms underlying synesthesia still remain contentiousand hypothetical. In this chapter, BeritBrogaard, Kristian Marlow, and Kevin Rice critically review recent research on grapheme-color synesthesia, one of the most common forms of the condition, and address the ongoingdebate concerning the role of selective attention in eliciting synesthetic experience.
Chapter
Owing to its bizarre nature and its implications for understanding how brains work, synesthesia has recently received a lot of attention in the popular press and motivated a great deal of research and discussion among scientists. The questions generated by these two communities are intriguing: Does the synesthetic phenomenon require awareness and attention? How does a feature that is not present become bound to one that is? Does synesthesia develop or is it hard wired? Should it change our way of thinking about perceptual experience in general? What is its value in understanding perceptual systems as a whole? This volume brings together a distinguished group of investigators from diverse backgrounds--among them neuroscientists, novelists, and synesthetes themselves--who provide fascinating answers to these questions. Although each approaches synesthesia from a very different perspective, and each was curious about and investigated synesthesia for very different reasons, the similarities between their work cannot be ignored. The research presented in this volume demonstrates that it is no longer reasonable to ask whether or not synesthesia is real--we must now ask how we can account for it from cognitive, neurobiological, developmental, and evolutionary perspectives. This book will be important reading for any scientist interested in brain and mind, not to mention synesthetes themselves, and others who might be wondering what all the fuss is about.
Book
A biologically oriented introduction to synesthesia by the leading authority on the subject. For decades, scientists who heard about synesthesia hearing colors, tasting words, seeing colored pain just shrugged their shoulders or rolled their eyes. Now, as irrefutable evidence mounts that some healthy brains really do this, we are forced to ask how this squares with some cherished conceptions of neuroscience. These include binding, modularity, functionalism, blindsight, and consciousness. The good news is that when old theoretical structures fall, new light may flood in. Far from a mere curiosity, synesthesia illuminates a wide swath of mental life. In this classic text, Richard Cytowic quickly disposes of earlier criticisms that the phenomenon cannot be "real," demonstrating that it is indeed brain-based. Following a historical introduction, he lays out the phenomenology of synesthesia in detail and gives criteria for clinical diagnosis and an objective "test of genuineness." He reviews theories and experimental procedures to localize the plausible level of the neuraxis at which synesthesia operates. In a discussion of brain development and neural plasticity, he addresses the possible ubiquity of neonatal synesthesia, the construction of metaphor, and whether everyone is unconsciously synesthetic. In the closing chapters, Cytowic considers synesthetes' personalities, the apparent frequency of the trait among artists, and the subjective and illusory nature of what we take to be objective reality, particularly in the visual realm. The second edition has been extensively revised, reflecting the recent flood of interest in synesthesia and new knowledge of human brain function and development. More than two-thirds of the material is new. Bradford Books imprint