In 1890 William James described a paradox in vision . He noted that if a branch of a tree cast a very faint shadow onto a path, the shadow may be so faint that we can’t see it. But that such a faint shadow may be immediately seen if the wind blows the branch and the shadow moved. How was it that we can’t see the shadow when it’s stationary, but once we see that it’s moved we see it?
The solution to this paradox came much later when we realised that we don’t simply have a single visual system, rather we have several visual systems (or streams) which operate in parallel, though integrated, way .
We have one system which is good at analysing the form of an object. It’s good at seeing fine detail of stationary objects (like when you take an eye test), but it's not so good at seeing differences in contrast.
We have another system which analyses the motion of an object. It’s blind to stationary objects, not particularly good at fine detail, but is very sensitive to slight contrast differences.
And so, the paradox was resolved. When the faint shadow of the branch was stationary, it was too faint (not enough contrast) to be seen by the form system. It was also stationary – and so not seen by the motion system. But when the shadow moved, it was immediately seen by the motion system. Paradox resolved.
A similar paradox was described by Cherry in 1953 . He noted that if you’re at a party and talking to someone, you won’t notice the individual voices of people in the background. But if one of those voices mentions your name – you are immediately aware of them and their conversation. How was it that we don’t hear their conversation, but once we hear our name we hear it?
Legion Theory conceptualises the cortical processes underlying the self in an analogous manner to modern models of cortical processes underlying vision. At the party, the self with executive control of the body is maintaining a conversation with one person. But other selves are not constrained to simply focus on that conversation. In parallel, another self may attend to other voices in the background. Once your voice is heard, the self attending to the background conversation immediately shares that experience with other selves of the corporate self.
- James, 1890
- Livingstone & Hubel, 1988
- Cherry, 1953
Cherry, E. C. (1953). Some experiments in the recognition of speech, with one and two ears. Journal of the Acoustical Society of America, 25, 975-979.
James, W. (1890). The Principles of Psychology. New York: Holt.
Livingstone, M. S., & Hubel, D. H. (1988). Segregation of form, color, movement and depth: Anatomy, physiology and perception. Science, 240, 740-749.