• Bottom-up processing
: The brain doesn’t recognise
objects directly. It looks for features, such as shape and
colour. The networks that look for features operate
independently of each other, and in parallel. ‘Bottom-
up’ processing occurs, appropriately, in the lower – and
more primitive – parts of the brain, including the brain
stem and the cerebellum. The neural networks in these
regions send information upwards, into the higher
regions of the brain: the neo-cortex.
• Top-down processing
: Meanwhile, the higher-level
centres of the brain – in the neo-cortex, sitting above
and around the lower parts of the brain – are doing
‘top-down’ processing: providing the mental networks
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8 Improve your Communication Skills
that organise information into patterns and give it
meaning. As you read, for example, bottom-up
processing recognises the shapes of letters; top-down
processing provides the networks to combine the
shapes into the patterns of recognisable words.
When the elements processed bottom-up have been matched
against the patterns supplied by top-down processing, the brain
has understood what’s out there.
Top-down and bottom-up processing engage in continuous,
mutual feedback. It’s a kind of internal conversation within
the brain. Bottom-up processing constantly sends new
information upwards so that the higher regions can update and
adjust their neural networks. Meanwhile, top-down processing
constantly organises incoming information into new or existing
patterns.
The brain often has to make a calculated guess about what it
has perceived. Incoming information is often garbled,
ambiguous or incomplete. How can my brain distinguish your
voice from all the other noise in a crowded room? Or a flower
from a picture of a flower? How does it recognise a tune from just
a few notes?
Top-down processing often completes incoming information
by using pre-existing patterns. The brain creates a
mental model:
a
representation of reality, created by matching incomplete
information to learned patterns in the brain.
Visual illusions demonstrate how the brain makes these
calculated guesses. In the image in Figure 1.2, for example, we
appear to see a white triangle, even though the image contains no
triangle. The brain’s top-down processing completes the
incoming information by imposing a ‘triangle’ pattern – its best
guess of what is there. (The triangle is named after Gaetano
Kanizsa, an Italian psychologist and artist, founder of the
Institute of Psychology of Trieste.)
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