neurophysiology: an integration 



1939 



sion of particular individual instances (232). 

 Reverberation is also probably related to the storing of 

 particular experiences, and perhaps to perception, to 

 anxiety and to consciousness itself, as will appear 

 later. 



sheets and masses. It will be convenient to defer full 

 consideration of sheets and masses of neurons, espe- 

 cially since a specific model has been worked out in 

 this case (24). Several contributors to the Handbook 

 have touched on this topic (Pribram; see also 71); 

 others have reviewed segments of neurophysiological 

 knowledge which fit admirably into such a formal 

 model. 



When large numbers of elements arc involved, 

 provided they enter into activity as individuals rather 

 than in predetermined large groups, then small 

 discontinuities become smoothed into large conti- 

 nuities. Whether neurons are subjected to a 

 continuously increasing concentration of intercellular 

 potassium or to an increasingly heavy barrage of 

 nerve impulses, they can alike show a graded change 

 in state. Actually, the potassium concentration also 

 changes discontinuously, at least by one ion, but the 

 large numbers swamp out such small quanta. Under 

 both field and net conditions, then, (he statistical 

 distributions of neuron properties become of prime 

 importance. It will obviously be of help both in 

 understanding and in characterizing the actions of 

 varied neuron populations, to know the distribution of 

 thresholds of the units in a large population, whether 

 they follow a Gaussian curve [which explains the 

 stimulus-response magnitudes in a spinal reflex, in 

 the view of Rosenbluelh el i'l. (253)], or whether a 

 Poisson distribution is involved (as in the excitation 

 of photoreceptors by quanta, as shown hv Ilartline), 

 or whether still other distribution curves obtain [the 

 assumption of an exponential distribution of synaptic 

 delays in series parallel chains accounts lor the ob- 

 served complex reaction times in many situations, 

 according to Christie & Luce (43) and Rapoport 

 (•241)]. 



coding. From the rain of stimuli carrying messages to 

 receptors, external and internal, certain items arc 

 transduced into nerve impulses. At successive junc- 

 tional regions throughout the nervous system, 

 incoming and outgoing signals are discontinuous but 

 related, and an over-all convergence and loss of 

 information occur. The vast and redundant detail of 

 raw experience is filtered, grouped, generalized, inter- 

 preted and used; percepts, concepts, plans and actions 



arise, and are shuffled into and out of attention and 

 execution. The flow of information is highly structured 

 and depends on the transform functions at junctions 

 and on the interconnection patterns. These constitute 

 the coding used by the nervous system, and the study 

 of this is becoming intense and productive. [See also 

 Hick (137), MacMillan (120), Luce (189) and 

 Quastler (235).] 



The possible inflow of information is in the millions 

 of bits per second, but the amount that can be handled 

 is only in the tens [e.g. Barlow ( 15)]. Problems of input 

 overload are met everywhere and several devices are 

 used in 'defense' — as queuins;, grouping and omission 

 (211). Rats learn a simple discrimination in 10 to 20 

 trials, while monkeys, with richer awareness, may 

 require 20-fold more (135). Men, similarly, having 

 had their attention drawn to minute variations in the 

 coloring of marbles, may fail 10 sort on the basis of 

 major color differences (19). Repeatedly, students 

 have outperformed experi social psychologists in 

 judging group discussions, as secretaries have sur- 

 passed psychiatrists in rating reviews, when usin',; 

 given rules lor selecting particular information from 

 the total offered. Sophisticated problem-solvers often 

 become entrapped in an hypothesis more inextricably 

 than do naive ones; die trees may blot out the woods 

 for anyone. The real skill of the talented thinker is in 

 discarding all irrelevancies, in 'going lor the jugular of 

 the problem." What is omitted in perception, memory 

 and reason is of the highest moment. 



An important way of eliminating details is by 

 grouping messages and by neglecting uniformities. 

 Nerve impulses are rare, or absent, from most photo- 

 receptors except with discontinuities in space or time, 

 so much st) that visual patterns disappear when 

 retinal movements are prevented. Marked changes in 

 frequency of discharge of ganglion cells accompany 

 small transitions in intensity of receptor stimulation 

 (Bartley). Edges in a visual pattern are emphasized 

 by the reciprocal inhibition of Limulus ganglion cells 

 which automatically strengthen the bright and 

 weaken the pale areas (242). Comparable integrating 

 effects have been studied in the frog eye (170) and 

 are operative in other receptor organs, as ear and 

 skin (285). Further interaction occurs throughout the 

 nervous system. Neff has discussed the general coding 

 of perceived attributes — intensity, pattern, quality, 

 etc. Information is certainly carried in the spatial 

 arrangements of active elements and in the fre- 

 quencies of impulses in them; but in all probability 

 the coding is far more subtle, and depends on intricate 

 on-and-off activity patterns, with changes of frequency 



