Steven Pinker -- How the Mind Works - Hampshire High Italian ...

180 J HOW THE MIND WORKScommon view is that lower animals have a few fixed reflexes, and that inhigher ones the reflexes can be associated with new stimuli (as inPavlov's experiments) and the responses can be associated with rewards(as in Skinner's). On this view, the ability to associate gets bettei- in stillhigher organisms, and eventually it is freed from bodily drives and physicalstimuli and responses and can associate ideas directly to each other,reaching an apex in man. But the distribution of intelligence in real animalsis nothing like this.The Tunisian desert ant leaves its nest, travels some distance, andthen wanders over the burning sands looking for the carcass of an insectthat has keeled over from the heat. When it finds one, it bites off achunk, turns, and makes a beeline for the nest, a hole one millimeter indiameter as much as fifty meters away. How does it find its way back?The navigation depends on information gathered during the outwardjourney, not on sensing the nest like a beacon. If someone lifts the ant asit emerges from the nest and plunks it down some distance away, the antwanders in random circles. If someone moves the ant after it finds food,it runs in a line within a degree or two of the direction of its nest withrespect to the abduction site, slightly overshoots the point where thenest should be, does a quick U-turn, and searches for the nonexistentnest. This shows that the ant has somehow measured and stored thedirection and distance back to the nest, a form of navigation called pathintegration or dead reckoning.This example of information processing in animals, discovered by thebiologist Rudiger Wehner, is one of many that the psychologist RandyGallistel has used to try to get people to stop thinking about learning asthe formation of associations. He explains the principle:Path integration is the integration of the velocity vector with respect totime to obtain the position vector, or some discrete equivalent of thiscomputation. The discrete equivalent in traditional marine navigation isto record the direction and speed of travel (the velocity) at intervals, multiplyeach recorded velocity by the interval since the previous recordingto get interval-by-interval displacements (e.g., making 5 knots on a northeastcourse for half an hour puts the ship 2.5 nautical miles northeast ofwhere it was), and sum the successive displacements (changes in position)to get the net change in position. These running sums of the longitudinaland latitudinal displacements are the deduced reckoning of theship's position.