| |
Abstract:
In the early stages of visual processing, objects and scenes
are represented by neurons with small visual receptive fields. Each
neuron provides information about local features of a scene, but to
describe a scene in terms of objects requires that these features
be combined. Objects can cover wide areas of visual space and be
partially occluded by other objects, so the problem of binding the
separate representations of parts into coherent wholes is not a
simple one. Some theorists have advanced the view that binding is a
special problem and requires a special solution because it is
necessary to "tag" each visual neuron to signify the object to
which its activity relates. Each neuron therefore has to carry two
distinct signals, one that indicates how effective a stimulus is
falling on its receptive field, and a second that tags it as a
member of a particular cell assembly. To make these signals
distinct, von der Malsburg proposed that the "effectivenes" signal
would be carried by a conventional rate code, while the "tag"
signal would be created by synchronizing the spike activity of the
neuron with spikes from other neurons in the same assembly. First,
I will consider whether the theory is an a priori reasonable
approach to solving the binding problem, and conclude that it is at
best incomplete. Next, I will ask whether spike synchrony can
plausibly be used as an informational code, and conclude that there
are significant practical and theoretical obstacles both to
encoding and to decoding information in this way. I will examine
the experimental evidence usually adduced to support the synchrony
hypothesis, and conclude that the evidence is largely indirect and
has no proven relevance to the issue of binding per se. I will
finish by asking whether the binding problem is truly of unique
difficulty and requires a unique solution, and by considering some
strategies for solving the binding problem that do not require the
creation of a special neural code.
|
