This is the view that single neurons could represent complex entities such as a particular grandmother. What is the evidence for grandmother cells? A researcher may claim to have found a neuron responding more or less exclusively as a test subject sees different pictures of a known person, such as a famous actor. The suggestion is that somehow this neuron recognizes the person in the picture. But how are grandmother cells supposed to have knowledge? What we have in the demonstration where a neuron fires in response to a person is simply a correlation. If I get a stomachache whenever I see a local policeman (because of a history of speeding tickets), and a specific neuron in my stomach fires only when I see him, that would not mean it recognizes him.
Neuroscience views the brain as a parallel processing organ. A common way of thinking about parallel processing is as division. For example, the problem of visual perception is often analyzed into subproblems, such as recognizing an object and finding its location in space. These two tasks are thought to occur in parallel. In other cases, however, we may think in terms of competition. The way an ambiguous Necker cube is perceived at any given moment could be the result of a perceptual competition. Normally, the aspects are immediately clear. I see a dog and not a cat, a small table and not a chair, and so on. But in ambiguous pictures, aspectual competition occurs. The brain entertains parallel competing interpretations as the same stimulus is seen from different aspects.