6. The reënforcement-inhibition curves for the frog are very similar to those for man.
7. In case of the several pairs of stimuli whose interference effects have been studied reënforcement-inhibition appears. The first stimulus reënforces reaction to the second so long as the interval between them is not more than about .4˝, while it inhibits the reaction when the interval is longer. Whether this reënforcement-inhibition curve as given in the experiments described may similarly be obtained for any and every pair of stimuli, no matter what their relation to reactions, remains to be determined.
8. In connection with the study of the mutual relations of stimuli of which this paper gives an account certain facts concerning the sense of hearing have been discovered. A summary statement of the results on hearing may be found on page 551.
THE TEMPORAL RELATIONS OF NEURAL PROCESSES
BY ROBERT M. YERKES
Muscle contraction-time, according to the determinations of several investigators, varies about .0035˝.[175] Sanderson states that the time for direct stimulation of the muscle is approximately .0035˝ and for indirect stimulation, by means of the nerve, .007˝. The rate of nerve-transmission in the frog ranges from 25 to 35 metres per second.
Reflex reaction-time, as might be expected, varies widely with the nature of the reaction elicited by a stimulus, the condition of the animal, and the quality and strength of the stimulus. For many of the simple motor reactions of the frog it ranges between 20 and 60σ.[176] Whether reflex reaction-time is to be sharply contrasted with instinctive and voluntary reaction-times, or whether they indistinguishably merge into one another is a question of considerable interest and importance for the student of the evolution of activity.
Voluntary reaction-time may be as short as 150σ or as long as life, in an animal capable of profiting by experience as does the frog. It is preëminently the delayed type of reaction-time.