What is a perceptual set?
Perceptual set is a tendency to perceive or notice some aspects of the available sensory data and ignore others.
Our bodies are magnificent machines. One of the ways they demonstrate this is by taking repetitive motions and actions and reducing the resources needed to perform them. For instance, when a baby is learning to walk, each step is planned and performed. But after a relatively short period of time, they are running without giving it a thought - they just run (and run and run and run...)
Our brains do the same thing. The world is full of information that continually enters our senses. In order to speed up processing time and reduce the energy needed to perform those functions, it operates largely on what is expected and not necessarily on what is actually there.
And that is what Perception Set Theory gets into - how the brain "perceives" - or as the below link describes it - "Perceptual set theory stresses the idea of perception as an active process involving selection, inference and interpretation."
Perceptual set is a tendency to perceive or notice some aspects of the available sensory data and ignore others. For instance, have you ever seen this:
Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.
The brain doesn't read every word but instead selects out important bits and teases out the rest based on expectation and inference.
Another kind of perceptual set is when we have a fear of snakes, to automatically assume that every suspicious looking thing in the grass is a snake - even though most times we're looking at a garden hose.
There are a number of ways perception sets can change. If we're hungry, the perception set will tend to look for food over other things.
The link has a great article about perception sets.