perceptual pursuit of a moving object, the relationship between consciousness
and attention gets rapidly more complex.
And, of course, moving the eyes is not the whole story: the head and body move
as well, so there must be mechanisms for coordinating all these movements.
For example, information from the motor output for body and eye movements
can be used to maintain a stable relationship to the world, even while the body,
head, and eyes are all moving. Some control systems appear to be based on ret-
inocentric coordinates – keeping objects stable on the retina – while others use
craniocentric coordinates: keeping the world stable with respect to the head.
Although we can voluntarily control body and head movements, and some kinds
of eye movements, most of the time these complex control systems operate very
fast and unconsciously. These are just some of the mechanisms that would be
involved when you turned round to see who was coming in through the door.
Another form of involuntary visual attention occurs in perceptual ‘pop-out’. Imag-
ine you are asked to search for a particular stimulus which is displayed amongst a
lot of slightly different stimuli, say an upside-down L amongst a lot of upright Ls.
For many such displays, there is no alternative but a serial search, looking at each
item in turn to identify it. In other cases, the difference is so obvious to the visual
system that the target just pops out, for example when the target L is horizontal
or is a different colour. In these cases the search seems to be parallel and does
not take longer if the total number of items increases. An obvious item like this
can also act as a distractor, slowing down the search for other items – another
example of how attention can be grabbed involuntarily.
Directing the eyes towards a particular object is not, however, equivalent to
paying attention to it. This is true for several reasons. First of all, it is perfectly
possible to be blind to something we are looking right at, just because we are
not attending to it. In Chapter 3 we learned about the discovery of inattentional
blindness, beginning with Arien Mack and Irvin Rock’s work in the late 1990s, and
expanding to investigate the role of characteristics like familiarity, expectation,
and different kinds of salience in determining whether or not inattentional blind-
ness is experienced.
Other kinds of blindness are an integral part of paying attention. Attention always
has costs as well as benefits. Not only does directing attention to one thing mean
you have to neglect another, but there may be a short ‘attentional blink’ after-
wards. This has been shown in experiments where, for example, a series of letters
are rapidly flashed and participants asked to look for a given target letter. If they
successfully detect one, then they are less likely to detect another shown within
200–500 msec after the first, as though their capacity to attend ‘blinked’ for a
moment, even though they were looking right at the relevant stimulus.
It is also possible to attend visually to two different locations at once. In one fMRI
study, participants were asked to fixate a central point while selectively attending
to two different targets on either side; they were presented with a task-irrelevant
sequence of digits at the central fixation point, and had to identify matching dig-
its from rapid sequences of letters and digits in the left and right locations. Acti-
vation in the retinotopic maps in primary visual cortex was found corresponding
to both spots but not to the central stimulus in between, suggesting not just one
spotlight of attention but ‘multiple spotlights of attentional selection’ (McMains
DID I DIRECT MY
ATTENTION OR WAS IT
GRABBED?‘There is no conscious
perception without
attention’(Mack and Rock, 1998, p. 14)FIGURE 7.2 • Search for the two odd ones out
in each picture. In the top one
you will probably have to do a
serial search, looking at each L
in turn. In the bottom picture the
horizontal Ls just pop out.