Nor again does it seem as if the mere transition from an agreeable to a disagreeable sensation, or the reverse process, would account for the laughter of tickling. A person highly sensitive to the effect of tickling can imitate the process by movements of his own fingers, and produce quite similar sensations of varying feeling-tone without experiencing the faintest impulse to laugh. Again we know that other experiences, such as scratching a sore place when it is healing up, involve an alternation of moments of agreeable and disagreeable feeling-tone, and yet are not provocative of laughter.
These and other familiar facts point to the conclusion that the laughter excited by tickling is not a net effect of the sensory stimulation. It is no doubt broadly determined by the characteristics of the sensations. Intensely disagreeable ones would certainly not call forth the laughing response. But the determining conditions include, in addition to a sequence of sensations, a higher psychical factor, namely, an apperceptive process or assignment of meaning to the sensations. This conclusion is borne out by the fact that the laughter-reaction occurs first of all (to give the earliest date) in the second month—presumably in the second half of this month. The presence of such a psychical factor is more strongly supported by the fact, already referred to, that the reaction does not occur in the first three months save when mental agencies co-operate; and that throughout the ticklish period an exactly similar process of titillative stimulation applied to the same area of the {60} skin will now produce laughter, now fail to do so, according to the varying mood of the child.[39]
That the interpretation of the sensation is the decisive element in eliciting laughter may, I think, be seen by a simple experiment which any reader who is ticklish may carry out upon himself. The next time he happens to have a subjective, creepy skin sensation, he will find that he can bring on either laughter or a very different state of feeling by adopting one of two ways of mentally envisaging what is happening. The merest suggestion of an invading parasite suffices, I believe, to set up a mental state which completely inhibits the impulse to laugh.
We may now seek to assign with more precision the mental conditions which induce the mode of apperception favourable to laughter.
Beginning with the “objective” characteristics, those which reside in the tickling experience itself, we may observe how much apprehension of meaning has to do with the “funniness” of the experience. It is to be noticed at the outset that when we are tickled there is an element of the unknown in the process. This seems to have been recognised by Darwin when he laid emphasis on the fact that the more ticklish parts are those rarely touched, at least on small areas, and, one may add, lightly.[40] The familiar fact that one cannot tickle oneself points to the same conclusion. A person who tries to do this knows too much about what is going on. Dr. Ch. Richet observes, however, that one can tickle oneself by means of a feather; and he, as I think {61} rightly, explains this apparent exception by saying that in the attempt to tickle oneself with the finger, the double sensation, of the finger and the part tickled, seems to inhibit the effect, whereas, when the feather is interposed this obstacle is eliminated.[41]
Other facts, too, seem to point to the importance of an element of the unknown. The common way of tickling a child is by running the fingers with discontinuous contact over the skin. Dr. L. Hill describes his mode of tickling in one case as running the fingers up the child’s arm like a mouse. This evidently brings in an element of local uncertainty as well as of change. The effect is increased when, as frequently happens, there are pauses between the attacks of the fingers.
The invasion of the skin-territory, like that of larger territories, is, it would seem, likely to be more effective when it has an element of unpredictableness. The uncertainty is, I believe, sometimes increased by half-voluntary variations in the direction and in the velocity of the tickling movements. Whether the fact communicated by Dr. L. Robinson, that a child is more ticklish when dressed than when undressed, is explained by the increased obscurity of the process in the former case, I am not sure. It is worth noting, however, that some of the areas said to be most ticklish, e.g., the armpits and the neck, are inaccessible to sight. I believe, too, that when a child gives himself up to the full excitement of tickling he makes no attempt to see what is going on.
Now touches of unknown origin at places not closely observable have something of a disturbing character. A touch is always an attack, and has, so to speak, to be {62} condoned. This disturbing element I regard as an essential element in the experience: it goes along with the faintly disagreeable element of sensation, which, as we have assumed, is commonly, if not always, more or less clearly recognisable in the experience.[42] Yet it is certain that the disturbing effect (like the disagreeableness of the sensation) is limited. If the unknown bulks too largely and comes near the point of the alarming, the effect of laughter is wholly counteracted. This is a part of the explanation of the refusal of a child to be tickled by a stranger: for he knows here too little of what is going to happen, and consequently is disposed to fear. Again, Dr. L. Hill informs me that “tickling a child unexpectedly and from an unseen quarter will not provoke laughter”: the element of surprise would seem in this case to be too great. Possibly the comparative difficulty of making a child laugh when naked may be explained by the increased apprehensiveness which goes with the defenceless state of nudity. The familiar fact that the readiness to laugh increases with practice, points to the same need of a certain comfortable assurance lying safely below the slight superficial apprehensions which are excited by the stimuli.
All this suggests, that in order to call forth the glad response of laughter, we must secure a certain adjustment of stimulus to mental attitude. The tickling must fit in with a particular mood, the state of mind which makes enjoyment of fun not only possible but welcome.
Now it is clear that non-adjustment may arise, not only from the presence of unsuitable characteristics in the mode {63} of stimulation, but from some antagonistic force in the child’s previous state of mind. The acceptance of the attack in good part depends on the preceding attitude. The dreadfully serious, “on-the-alarm” attitude of the child when nursed by a stranger is an effectual bar to playful overtures. A child when cross will not, says Dr. L. Hill, give genial response, even if the attacker be his familiar tickler, father or nurse; and the same is true, he adds, of a child when suffering from vaccination, or when mentally preoccupied with some hurt for which he is seeking for sympathy, or with a story which he wants you to tell him. As Darwin puts it, the great subjective condition of the laughter of tickling is that the child’s mind be in “a pleasurable condition,” the state of mind which welcomes fun in all its forms. Possibly the position of lying on the back, which, according to Dr. L. Robinson, makes children more responsive to tickling, may, through a relaxation of the muscles, favour this compliant attitude of self-abandonment to the tickling fingers.