Chapter
Six
The unity
Wilhelm Wundt did early experiments on time and sensory consciousness
towards the end of the nineteenth century. He asked people to judge the
relative timings of visual and auditory stimuli and found many examples of
what he called ‘subjective time displacement’, in which people made mistakes
about which event occurred first. In the 1920s, F. W. Fröhlich observed that if a
moving object suddenly appears, its perceived initial location is misplaced in
the direction of motion.
Modern illusions include the flash-drag, flash-jump, and flash-lag effects. In the
last of these, one object moves continuously and another is flashed just as it is
aligned with the moving one. The flash then appears to lag behind the moving
object. One proposed explanation is that the visual system predicts where the
moving stimulus is going so as to allow for processing delays. Another is that
processing is done ‘online’ but moving objects are processed more quickly
than static ones. Eagleman and Sejnowski (2000) argue that neither of these
explains the effect, and propose that visual awareness is not predictive but
postdictive, so that events which happen shortly after the flash (within about
80 milliseconds) affect what is perceived.
These and many other experiments make the point that we do not always
experience things, or report their occurrence, in the order in which they
actually happen in the world. From this we might be tempted to imagine
something like this: there are two worlds—a physical world in which events
really happen in one order, and an inner experienced world of consciousness
in which they happen in another order. This dualist view is tempting, but illu-
sions like this do not necessarily imply duality, and some further phenomena
will help to show just how problematic it is.
If two lights in different positions are flashed quickly one after the other,
there appears to be one light moving, rather than two separate lights flash-
ing. This is the well-known phi phenomenon. In ‘colour phi’, the lights are dif-
ferent colours, say red and green. In this case, something very odd happens.
Observers often report that the light not only moved but also changed from
red to green as it did so. How can this be? The light seems to start changing
colour before the second flash, but how could the person know that a green
light was coming?
A similar problem occurs with the ‘cutaneous rabbit’ (Geldard and Sherrick, 1972;
Dennett, 1991) (see Activity 6.3). If a person’s arm is tapped, say five times at the
wrist, twice near the elbow, and then three times on the upper arm, they report
not a series of separate taps coming in groups, but a continuous series moving
upwards – rather as though a little creature were running up their arm. Once
again, we might ask how taps two to four came to be experienced as moving
up the arm when the next tap in the series had not happened yet. How did the
person know where the next tap was going to be?
This certainly seems mysterious, so what is going on? We might, perhaps, think
that colour phi works like this: first the person consciously experienced a station-
ary red light, then when the green light flashed this experience was wiped out
and replaced with the new experience of the light changing to green. Alterna-
tively, we might suppose that the person never did consciously experience the