. Design for a brain. Brain -- Physiology; Central nervous system -- Mathematical models; Neurophysiology. 15/3 DESIGN FOR A BRAIN It will be seen, therefore, that in a complex system, every group of stimuli will have a holistic quality, in that the response to the whole group will not be predictable from the responses to the separate stimuli, or even to sub-groups. The dog that. salivated to each of two stimuli but not to the two together is therefore behaving in no way surprisingly, and such behaviour is no evidence of any ' supra-mechanistic ' power. In complex systems such non-additive com
. Design for a brain. Brain -- Physiology; Central nervous system -- Mathematical models; Neurophysiology. 15/3 DESIGN FOR A BRAIN It will be seen, therefore, that in a complex system, every group of stimuli will have a holistic quality, in that the response to the whole group will not be predictable from the responses to the separate stimuli, or even to sub-groups. The dog that. salivated to each of two stimuli but not to the two together is therefore behaving in no way surprisingly, and such behaviour is no evidence of any ' supra-mechanistic ' power. In complex systems such non-additive compoundings are to be expected. 15/4. Another variation in stimulus-giving occurs when a pattern is varied in some mode of presentation without the pattern itself being changed, as when an equilateral triangle is shown both erect and inverted. The same argument as before prevents us from expecting any necessary relation between the two evoked responses. In some cases the two evoked responses are found to be the same, and to be characteristic of the particular pattern even though its presentation may have been much changed : an object may be recognised though its image falls on a part of the retina never before stimulated by it. This power of Gestalt- recognition was also sometimes thought to demand ' supra- mechanistic ' powers. But in 1947 Pitts and McCulloch showed that any mechanism can show such recognition provided it can form an invariant over the group of equivalent patterns. As the formation of such invariants demands nothing that cannot be supplied by ordinary mechanism, the subject need not be discussed further here. To sum up, these examples have shown that no matter how small the difference between stimuli, or initial states, we can, in general, if the system is complex, put no limits to the differ- ence that may occur between the subsequent lines of behaviour. From this we may deduce that if the system is one with many 168. Please note that these images are extracted
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