- seCtIon tHRee: BoDY AnD WoRLD
UNCONSCIOUS PERCEPTION
Suppose you are sitting at dinner, chatting with your friends, oblivious to the hum
of the microwave in the corner – until it stops. Suddenly you realise that it was
humming along all the time. Only in its silence are you conscious of the noise.This simple, everyday phenomenon seems odd because – like the more extreme
cases of agnosia and blindsight we will consider later in the chapter – it suggests
perception without consciousness. It suggests that all along, in some unconscious
way, you must have been hearing the noise. It challenges the simplistic notion
that perception implies or requires consciousness, and that ‘I’ must know what my
own brain is perceiving (Merikle, Smilek, and Eastwood, 2001).
The phenomena of unconscious (or implicit, or subliminal) perception have been
known about since the very early days of psychology. For example, in the 1880s,
Charles Peirce and Joseph Jastrow (1885) studied how well they could discrimi-
nate different weights by judging the amount of pressure made on the forefinger
or middle finger by the end of the beam of a weighing scale. When two were so
closely matched that they had no confidence they could tell them apart, they
made themselves guess, and to their surprise did better than chance. This was
one of the earliest demonstrations of perception without consciousness. At about
the same time, Boris Sidis (1898), another American psychologist and friend of
William James, showed volunteers letters or digits on cards so far away they could
barely see them, let alone identify them. Yet when he asked them to guess, they
also did better than chance. In both cases, people deny consciously detecting
something while their behaviour shows that they have detected it.
Sidis concluded that his results showed ‘the presence within us of a secondary
subwaking self that perceives things which the primary waking self is unable to
get at’ (1898, p. 171). As Dan Wegner (2005) points out, the idea of this ‘subliminal
self ’ implies the existence of its alter ego: a real or conscious self which is capa-
ble of fine thoughts and freely willed actions. This is a trap that psychology still
falls into, he argues. Whenever there is talk of automatic behaviour, unconscious
processes, or subliminal effects, there is an implicit comparison with conscious
processes, yet those remain entirely unexplained. He even suggests that ‘psy-
chology’s continued dependence on some version of a conscious self makes it
suspect as a science’ (Wegner, 2005, p. 22).Even if we reject Sidis’s notion of the two selves, his results clearly seemed to
demonstrate unconscious perception. However, resistance to this possibility was
extraordinarily strong right from the start and continued that way for most of a
century (Dixon, 1971; Dijksterhuis, Aarts, and Smith, 2005).In the early experiments, conscious perception was defined in terms of what peo-
ple said. This fits with the common intuition that each of us is the final arbiter
of what is in our own consciousness: if we say we are conscious or unconscious
of something, then (unless we are deliberately lying) we are. Yet this intuition is
problematic for several reasons.
One problem is that whether people say they have consciously seen (or heard
or felt) something depends on how cautious they are being. This became clearer
in the mid-twentieth century with the development of signal detection theory.‘Even today, when the
reality of unconscious
perception has been
confirmed beyond
reasonable doubt [. . .]
there remains almost
unshakeable resistance’
(Dixon, 1971, p. 181)