An example of a distinctly agreeable sensation of tickling is, curiously enough, supplied by another hairless surface, closely analogous to the sole, namely the palm. A lady, who is an excellent observer of children and endowed with an exceptional memory of her early experiences, tells me that when a child she loved to have her hands tickled. Her feeling was a kind of “awful joy,” the awfulness coming {56} from a vague suspicion that the pastime was not quite proper. Other preponderantly agreeable varieties appear to be the sensations produced by the lighter stimulation of those parts which seem in a special way to be laughter-provoking areas, e.g., the armpits and ribs. This is, at least, suggested by the fact that younger children love to be tickled in these parts in moderation, and will ask to have the pastime renewed.
An important characteristic of these feeling-tones is their unsteadiness or changefulness. Although at a particular moment we may be able to detect clearly a slight preponderance of the agreeable or of the disagreeable aspect, it is only for a moment. An increase in the degree of pressure, a further prolongation of the stimulation, or even a slight variation in the mode of contact, may suffice to bring up and render prominent the opposed feeling-phase.
We may now pass to the motor reactions, which are of more especial interest in the present connection. Overlooking the less conspicuous elements, such as the contraction of the muscles of the hairs, we find that there are two easily distinguishable groups of movements: (a) a number of protective or defensive reactions which are adapted to warding off or escaping from the attack of the tickling stimulus; (b) movements expressive of pleasure and rollicking enjoyment, from the smile up to uproarious and prolonged laughter.
The defensive movements are such as the following:—retraction of the foot and leg when the sole is tickled; the bending of the head to the shoulder when the neck is tickled; the rendering of the body concave on the side which is attacked; the thrusting away of the hand of the tickler; wriggling and fencing with the arms when a child is tickled lying on his back. These movements appear to {57} introduce important modifications into the sensations excited by tickling. Dr. Louis Robinson tells us that the flexing of the foot when tickled transforms an unpleasant sensation into a rather pleasant one.
We may now pass to the point of chief importance for our present study, the conditions of the laughter-reaction during a process of tickling. This reaction is clearly the typical form of childish risibility.
It has been already more or less clearly implied, that we cannot mark off the laughter in this case as an effect determined by any assignable differences in the characteristics of the sensations involved. Dr. Louis Robinson thinks that the tickling which provokes laughter is a special variety involving the stimulation of the deeper-lying nerves. Dr. Leonard Hill, who has specially tested this point for me, writes, “There is no difference in response to deep and superficial tickling”; and again, “I am sure that the most delicate superficial stimulation can provoke laughter”. This certainly seems to agree with ordinary observation. One of the most laughter-provoking forms of tickling consists of a series of pianissimo touches.
Again, in speaking of ticklish areas of the skin, we must be careful not to restrict the titillation which calls forth laughter to any assignable region. It is undeniable that there are areas which more readily respond, in the case of children generally, to the tickling provocation. The armpits perhaps will occur to most readers; and it is noticeable that Darwin speaks of the anthropoid apes giving out “a reiterated sound, corresponding with our laughter, when they are tickled, especially under the armpits”.[38] This {58} fact, however, does not imply that the area of sensibility is circumscribed. Dr. Leonard Hill assures me, as a result of his investigations, that laughter under favourable conditions may be excited by tickling any part of the body. Dr. L. Robinson in a letter explains to me that he agrees with Dr. L. Hill here. He finds that if a child is in a ticklish mood, the tickling of any part or even the threat of doing so will suffice to provoke laughter. On the other hand, we cannot speak of any part of the surface as one, the tickling of which will uniformly call forth laughter. Here again, as we shall see, the influence of mental agencies modifies the result.
Now these facts suggest that even those varieties of tickling which produce a sensation having a well-marked disagreeable tone may excite the response of laughter. The tickling of the sole of the foot not only provokes laughter in an infant; it tends to do so, I believe, in an adult, who may at the same time express his dislike of the sensation by a grimace.
It seems impossible then to conclude that the laughter which arises from tickling is a mere expression of the pleasure-tone of a sensational process. Even if we supposed that in all cases the sensations were preponderantly agreeable, it would still be impossible to account for the energy of the reaction by the intensity of the sensuous enjoyment experienced.
That we have not to do here merely with the effect of agreeable stimulation is shown by the fact that when a child laughs under, and is said to enjoy, a process of titillation, the laughter is accompanied by defensive movements. When, for example, a child is tickled on its back, it will, says Dr. Robinson, “wriggle about, fencing with its arms and dodging the attacks of its playmate . . . laughing all the time {59} with open mouth and teeth fully displayed”. This surely suggests that the laughter is not merely the result of an agreeable sensation, but rather of a complex mental state, in which the agreeable and disagreeable elements of sensation appear to play only a secondary rôle.