Chapter
Six
The unity
SUPERUNITY AND DISUNITY
In the penultimate section of this chapter, we will ask
what can be learned about unity by studying cases
where consciousness seems more or less unified
than usual.
SYNAESTHESIA
In synaesthesia, people hear sounds in colour, see
shapes in tastes, listen to touches on their skin,
or feel tactile sensations on their own skin when
seeing someone else being touched. Grapheme–
colour synaesthesia is the most common form, and
brain imaging has shown that the associative areas
at the boundary between the language and visual
systems play a key role. In particular, occipital cor-
tex, which is active when we read real words but
not non-word strings of letters, offers a possible
neural basis for how linguistic stimuli are system-
atically linked with sensory visual attributes like
colour.
Sometimes described as ‘a special case of inte-
grated cross-modal perception’ (Frith and Paulesu,
1997, p. 124), synaesthesia is arguably only a
heightened version of what our minds do all the
time: combine visual, kinaesthetic, and vestibular
signals to track our own bodies in space; attribute
olfactory inputs to taste; make consistent multi-
sensory associations between high-pitch tones
and brighter/lighter colours, or between warmth
and affection or light and truth. Maybe the divi-
sions between sensory modalities are not as neat
as we tend to assume, implying that we may be
wrong to make a mystery out of conscious unity
by assuming that that everything is separate to
begin with and somehow needs unifying. ‘[T]he
existence of synesthesia invites psychologists to
reconsider their notions of what “normal” is’ (Ward,
2013, p. 51).
By contrast, there are situations in which the unity
of consciousness is lost, whether briefly or lastingly.
Some of the most dramatic instances are those of
multiple personality and the effects of splitting the
brain by cutting the corpus callosum. We will con-
sider multiple personality in Section Six, in connec-
tion to concepts of self, and will here focus on the
more directly brain-related phenomena of disunity:
split brains, amnesia, and neglect.
‘The long “a” of the
English alphabet has for
me the tint of weathered
wood, but a French “a”
evokes polished ebony’(Vladimir Nabokov, BBC inter-
view, 1962)sYnAestHesIA
‘What a crumbly, yellow voice’, said s. ‘I
can’t escape from seeing colors when I hear
sounds. What first strikes me is the color of
someone’s voice’. s was the famous ‘mne-
monist’, or memory man, studied by the
great Russian psychologist Aleksandr Luria. s
could remember vast tables of numbers and
learn poems in languages he did not under-
stand, yet he found communication difficult,
and could not hold down a job or forget the
pains of his childhood; ‘for s. there was no
distinct line, as there is for others of us,
separating vision from hearing, or hearing
from a sense of touch or taste’ (Luria, 1968,
pp. 24–25, 27).
In synaesthesia, events in one sensory modal-
ity induce vivid experiences in another. In the
most common form, grapheme–colour syn-
aesthesia, written letters or numbers are seen as coloured,
but people can hear shapes, see touches, or even have
coloured orgasms (Cytowic, 1993). the experiences are
vivid and precise and cannot be consciously suppressed,
and when tested after many years, most synaesthetes
report exactly the same forms or colours induced by the
same stimuli (Cytowic and eagleman, 2009).
many synaesthetes hide their special abilities, so it is dif-
ficult to know how common synaesthesia is. In the 1880s
Galton estimated it at 1 in 20, whereas other estimates
range from 1 in 200 to 1 in 100,000 (Baron-Cohen and
Harrison, 1997). many people experience days, months,
numbers, and the alphabet in a spatial form such as spi-
rals or circles, and this is arguably a weak form of syn-
aesthesia. synaesthesia runs in families, is more common
in left-handers, and is six times more common in women
than men. It is associated with artistic ability and good
memory but poorer maths and spatial ability.
synaesthesia has often been dismissed as fantasy, overly
concrete use of metaphor, or exaggerated childhood
memory, but none of these ideas can explain the phe-
nomena. the induced colours produce cross-modal stroop
interference (Ward, Huckstep, and tsakanikos, 2006)C
on
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6.1