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suspended leg, which varies in amount with the state of the animal and the strength of the stimulus. A sound, on the contrary, never causes the slightest movement, and that no matter how loud or high it be. This makes it possible to study the influence of sounds on tactual reactions, under different temporal relations of the stimuli, for even when the sound precedes the touch there is no reaction until after tactual stimulation.

The results now to be presented were given by the green frog, but test experiments indicate that both the leopard and the bull frog are influenced in similar manner by sounds.

After an ani

The experimental procedure was as follows. mal had been placed in the proper position and had ceased to struggle to escape, reactions to stimuli were taken in pairs regularly at half minute intervals, first a reaction to the tactual stimulus alone, then a reaction to the same intensity of touch when accompanied or preceded by an auditory stimulus.

The series consisted of 50 pairs of reactions taken without pause. So far as the frog is concerned there seems to be nothing undesirable in long series, for there is no indication of fatigue, and so long as the animal is kept moist and in a comfortable position it does not often struggle to escape. The advantage, for the purposes of this investigation, of taking the reactions in pairs is obvious. It permits us to compare directly the reactions of each pair, and to note at once whether the auditory stimulus has reinforced or inhibited the tactual reaction.

During a series the intensity of the tactual stimulus was changed as conditions demanded, but for any one pair of reactions it was always the same. It not unfrequently happened that an intensity which at first caused only slight movement of the leg, later in the series uniformly brought about a maximum contraction, or the reverse might be true, and since the maxi

Fig. 4. Auditory-tactual apparatus. (Drawn by Dr. Wм. E. HOCKING.) P, pendulum; p, contact point of P; b, attachment for electro-magnet, a; m, key for electric bell circuit; B, electric bell; n, key for magnet circuit of touch apparatus; K, hand-key for release of pendulum and temporary closing of electric bell circuit; k1, k3, 1⁄23, keys in circuits; e, f, g, magnetic release for touch apparatus; /, pivoted lever bearing rubber cone, T, and weights, w.

mum amount of movement left no opportunity for judging of the influence of the auditory stimulus it was always necessary in such cases so to alter the intensity of the tactual stimulus that a medium reaction would result.

The animals seldom struggled during experiments, but if too firmly bound they became irresponsive to the stimuli.1 It was therefore necessary to place them carefully in position, and then, after they had ceased to struggle, to draw the linen bands over them just tightly enough to prevent change in position. For the purpose of excluding the influence of visual stimuli a wire screen cap covered with black cloth was put over the head. This served to help keep the frog in the proper position as well as to exclude visual stimulation.

TABLE I.

THE INFLUENce of Sound ON THE TACTUAL REACTIONS OF THE GREEN Frog. Auditory and Tactual Stimuli

Green frog A. Tactual Stimulus Alone

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The two series of reactions of Table I, chosen at random from several hundred, will serve to indicate serve to indicate the method of recording the results as well as the nature of the results themselves. The first ten pairs of reactions fairly represent the variableness of the reactions; the second show still more clearly the influence of the auditory stimulus.

For each of the

The results obtained with four frogs, two males (Nos. I and 3) and two females (Nos. 2 and 4) will suffice to indicate the influence of sounds on tactual reactions. four frogs fifty pairs of reactions were taken in series, and that for each of seven different temporal relations of the two stimuli. The individual averages therefore are based upon fifty reactions, and the total number of reactions for each individual is seven hundred. As is clear from column one of Table II, the temporal relations of the stimuli ranged from simultaneity to .9" (i. e., the auditory preceded the tactual by .9").

The influence of the sound, which for these experiments was a sudden hammer blow, is discovered by direct comparison of the tactual reaction of each pair with its corresponding auditory-tactual reaction. When the tactual reaction is the greater, we infer that the sound has partially inhibited reaction ; when it is the smaller, that it has reinforced reaction; when the two are equal, that it has been without influence. The influence of sound may be expressed either in terms of the number of reactions reinforced, inhibited and equal, or in terms of the amount of reinforcement or inhibition. Both methods have been employed. Table II presents the percentage value of the auditory-tactual reactions in comparison with the tactual, and also the number of reactions over half which were reinforced or inhibited, while Figures 5 and 6 graphically represent the amount of influence in terms of the tactual reaction. The auditory-tactual reaction is always expressed as so many per cent greater (+ i. e., reinforcement) or less (-i. e., inhibition) than the tactual. In the table + always indicates reinforcement,-inhibition, and in the curves the portions above the zero line indicate reinforcement, those below it inhibition. The number of reactions over half, that is over twenty five, since there were

fifty pairs of reaction for each interval and each animal, which were reinforced or inhibited furnishes an excellent quantity for comparison with the averages. As such comparison reveals close agreement between amount of influence of the auditory stimulus and the number of reactions either reinforced or inhibited it is clear that the averages are trustworthy, even though the variability of the reactions is enormous.

TABLE II.

INFLUENCE OF SOUND ON THE TACTUAL REACTIONS OF THE GREEN FROG FOR DIFFERENT TEMPORAL RELATIONS OF THE STIMULI.

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The results tabulated in Table II show that the sound when occurring simultaneously with the tactual stimulus greatly increases the amount of the reflex, while on the contrary it decreases the amount of reaction if it precedes the tactual stimulus by .5 to 1.0". Number 1, for example, exhibited reinforcement equal to 62 % of the amount of the tactual reaction when the stimuli were given simultaneously, but when the sound occurred .65" before the touch the resulting reaction was 10 % less than the tactual.

In Figures 5 and 6 are curves, representing the amount of reinforcement and inhibition for the four frogs, constructed

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