Читать книгу The Form Within - Karl H Pribram - Страница 46

Finally, Hubel’s faith in “grandmother cells” was well placed. As we proceed from the primary sensory receiving cortex to the temporal lobe of the brain, we find receptive fields that are “tuned” to an ever “higher order,” that is, to ever more complex stimuli. The receptive fields of these “grandmother cells” are nodes in an assembly that is capable of representing features as higher-order properties abstracted from lower-order properties. Thus, we can come to understand how a property like “blue jeans” in the metaphor I’ve used can become abstracted from the population of persons who wear them. Sales counters at retail stores handle blue jeans; cells in the brain’s temporal lobe respond to pictures of grandmother faces and other sensory images such as flowers and hands.

Cells responding primarily to pictures of hands were the first “grandmother cells” to be discovered. Charles Gross at Princeton University was the first to record them. I asked Gross, who had attended a course I was teaching at Harvard and as a consequence became a student of Larry Weiskrantz at Cambridge and Oxford, whether the face cells responded to stimuli other than faces. They did, but not as vigorously (as noted by Hubel in our symposium). However, in my laboratory, we unexpectedly found, in one monkey who’d had considerable experience choosing a green rather than a red set of stripes, that his cell’s activity went wild when he was shown the combination as a green hand!

As had also been found by Gross, in experiments in my laboratory, we found that the amount of activity elicited from these “hand cells” was almost as great when we visually presented broad stripes to the monkey. We presented stripes because they could provide the basis for a frequency interpretation of how the cells might process a hand.

We can derive two important conclusions from the results of these experiments:

1 Higher-order processing locations in the brain enable us to make distinctions among complex stimuli.

2 Our ability to make such distinctions can be learned.