Animals are believed to focus their attention in two ways. The first, which is most common in lower animals, is the use of specialized sensing organs. Many of these animals have severely limited, but highly specialized vision which allow them to see just what they need to see in order to function successfully in their environments [Tansley1965]. For example, anteater's eyes are placed very low in their heads and they have only monocular vision but with extremely high acuity. Birds, on the other hand, have excellent binocular vision that is good for judging distances. The second way can be thought of as cognitive, where the animals only perceive what they attend to; i.e., they pay attention only to what is important in their particular situation at hand.
Under certain circumstances nesting herring-gulls behave as though their eggs were invisible to them. If, in the gull's absence, the eggs are removed and put just outside the nest the parent bird will retrieve them, but if the distance is made a little greater the bird will sit happily on the empty nest with the eggs in full sight. That the eggs can be seen perfectly well is indicated by removing them still further away, the gull will then eat them as it does its neighbour's eggs if it should find them unguarded. Herring-gull chicks show camouflage colouring very similar to that of the eggs but the parent bird never has any difficulty in seeing and recognizing its own chicks. There is nothing wrong with the herring-gull's eyes. The explanation of the different reactions to eggs and chicks appears to be that, under normal circumstances, the eggs do not leave the nest and it is, therefore, sufficient if the parent knows the position of the nest, while the active chicks often wander away and have to be got back [Tansley1965].
The best example of a natural attention mechanism that employs both mechanical and cognitive means may lie in the vision of humans and animals. The retinal image from an eye has in its center a high-acuity region known as the fovea, beyond which the image resolution drops in the visual periphery. Humans and animals, motivated by their behavioral needs, are able to focus their sight (by moving their eyes or turning their heads) onto the object of interest such that an accurate image of that object is obtained in their foveas while its immediate surroundings fall into the low-resolution peripheral region.
|Xiaoyuan Tu||January 1996|