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.If regarded here as a reflex process, it must be reflex there as well.The current inboth places runs out into the muscles only after it has first run in; but whilst the path by which itruns out is determined in the lower centres by reflections few and fixed amongst the cell-arrangements, in the hemispheres the reflections are many and instable.This, it will be seen, isonly a difference of degree and not of kind, and does not change the reflex type.The conceptionof all action as conforming to this type is the fundamental conception of modern nerve-physiology.So much for our general preliminary conception of the nerve-centres! Let us defineit more distinctly before we see how well physiological observation will bear it out in detail.[p.24]THE EDUCATION OF THE HEMISPHERESNerve-currents run in through sense-organs, and whilst provoking reflex acts in the lowercentres, they arouse ideas in the hemispheres, which either permit the reflexes in question, checkGet any book for free on: www.Abika.comTHE PRINCIPLES OF PSYCHOLOGY15them, or substitute others for them.All ideas being in the last resort reminiscences, the questionto answer is: How can processes become organized in the hemispheres which correspond toreminiscences in the mind ?[3]Nothing is easier than to conceive a possible way in which this might be done, provided fourassumptions be granted.These assumptions (which after all areinevitable in any event) are:1) The same cerebral process which, when aroused from without by asense-organ, gives the perception of an object, will give an idea of thesame object when aroused by other cerebral processes from within.2) If processes 1, 2, 3, 4 have once been aroused together or inimmediate succession, any subsequent arousal of any one of them(whether from without or within) will tend to arouse the others in theoriginal order.[This is the so-called law of association.]3) Every sensorial excitement propagated to a lower centre tends to spread upwards and arousean idea.4) Every idea tends ultimately either to produce a movement or to check one which otherwisewould be produced.Suppose now (these assumptions being granted) that we have a baby before us who sees acandle-flame for the first [p.25] time, and, by virtue of a reflex tendency common in babies of acertain age, extends his hand to grasp it, so that his fingers get burned.So far we have two reflexcurrents in play: first, from the eye to the extension movement, along the line 1-1-1-1 of Fig.3;and second, from the finger to the movement of drawing back the hand, along the line 2-2-2-2.If this were the baby's whole nervous system, and if the reflexes were once for all organic, weshould have no alteration in his behavior, no matter how often the experience recurred.Theretinal image of the flame would always make the arm shoot forward, the burning of the fingerwould always send it back.But we know that 'the burnt child dreads the fire,' and that oneexperience usually protects the fingers forever.The point is to see how the hemispheres maybring this result to pass.We must complicate our diagram (see Fig.4).Let the current 1-1, from the eye, dischargeupward as well as downward when it reaches the lower centre for vision, and arouse theperceptional process s1 in the hemispheres; let the feeling of the arm's extension also send up acurrent which leaves a trace of itself, m1; let the burnt finger leave an analogous trace, s2; and letthe movement of retraction leave m2.These four processes will now, by virtue of assumption 2),be associated together by the path s1-m1-s2-m2 running from the first to the last, so that ifanything touches off s1, ideas of the extension, of the burnt finger, and of the retraction will passin rapid succession [p.26] through the mind.The effect on the child's conduct when the candle-flame is next presented is easy to imagine.Of course the sight of it arouses the grasping reflex;but it arouses simultaneously the idea thereof, together with that of the consequent pain, and ofGet any book for free on: www.Abika.comTHE PRINCIPLES OF PSYCHOLOGY16the final retraction of the hand; and if these cerebral processes prevail in strength over theimmediate sensation in the centres below, the last idea will be the cue by which the final action isdischarged.The grasping will be arrested in mid-career, the hand drawn back, and the child'sfingers saved.In all this we assume that the hemispheres do not natively couple any particular sense-impressionwith any special motor discharge.They only register, and preserve traces of, such couplings asare already organized in the reflex centres below [ Pobierz całość w formacie PDF ]