- seCtIon tWo: tHe BRAIn
chapter. On this view, as long as you pay attention to the flipping coin or the
image of the door, their various attributes are bound together. When you think
about something else, the diverse attributes fall apart, and the coin or door is no
longer experienced as a unified whole.
There is evidence that attention is required for binding. For example, when
people’s attention is overloaded or diverted, the wrong features can be bound
together to produce illusory conjunctions, such as when you are rushing along
the street and see a black dog, only to realise that it was in fact a golden Labrador
passing a black rubbish bag.
Bilateral damage to parietal cortex, which affects attention, can cause binding
deficits, and in visual search tasks focused attention is necessary for finding
unknown conjunctions. Anne Treisman, a British psychologist based at Princeton,
interprets the relationship in terms of ‘feature integration theory’ (Treisman and
Gelade, 1980). When we attend to objects, computationally understood ‘tem-
porary object files’ bind groups of features together on the basis of their spatial
locations. For Treisman (2003), binding is central to conscious experience, and
conscious access in perception is always to bound objects and events, not to
free-floating features of those objects or events (see also Merker, 2013).
Other factors suggest that, closely related as they are, binding and attention can-
not be the same thing. Think of how you caught the coin. The fast visuomotor
control system in the dorsal stream has a complex computational task to carry
out in real time. It must track the current speed and trajectory of the coin and
direct your hand, with the right fingers in position, to catch the coin as it drops.
For this task, the form and movement of the coin must be bound together with
each other and not with the movement of some other object in the vicinity. If you
swat away a fly, return a fast serve, or avoid a puddle as you run down the street,
the features of these objects must be well enough bound together to be treated
as wholes. Yet, as we will explore further in the next two chapters, you do all these
things very fast and often without paying attention. There are obviously close
relationships between attention, consciousness, and binding, but just what sort
of relationships is not yet clear.BINDING BY SYNCHRONY
The best-known theory relating binding and consciousness is that proposed by
Francis Crick and Christof Koch (1990). In the 1980s, studies of the cat’s visual cortex
had revealed oscillations in the range of 35 to 75 hertz (i.e. 35–75 cycles per second),
in which large numbers of neurons all fired in synchrony. These are often referred to
as ‘gamma oscillations’ or (rather inaccurately) as 40-hertz oscillations, and the idea
was that all the neurons dealing with attributes of a single object would bind these
attributes together by firing in synchrony. According to Crick and Koch, ‘this syn-
chronized firing on, or near, the beat of a gamma oscillation (in the 35- to 75-hertz
range) might be the neural correlate of visual awareness’ (Crick, 1994, p. 245).They argued that the thalamus controls attention by selecting the features to be
bound together by synchronisation of firing. The Columbian physiologist Rodolfo
Llinás used a similar idea to account for temporal binding and ultimately the unity of
self, arguing that ‘consciousness is a product of thalamocortical activity’ (2002, p. 131).