THE ACQUISITION OF SKILL IN ARCHERY. 125 



period, and the two-hour group shows no improvement after the first hour. A third minoi 

 factor was that those working for a short period at a time were more apt to work with 

 maximum concentration than those working for longer periods. 



The majority of investigators have been content to ascribe the results 

 obtained to "fatigue" or "interest," without attempting further analysis. 

 In planning further experimental work the writer has found the following 

 classified list of possible explanations helpful. It probabty is not exhaustive, 

 but may help to define the problem more accurately. 



TRIAL AND ERROR. 

 A. VARIETY OF PROPRIOCEPTIVE STIMULI. 



When an organism is confronted with a new set of conditions its reaction is 

 the summation effect of the elements of the external stimuli and the momen- 

 tary proprioceptive stimuli. The latter may remain fairly constant during a 

 single practice period, resulting in a rather stereotyped reaction. During the 

 relatively long interval between practice periods the proprioceptive "set" may 

 change and thus practice distributed over several days may offer the possibility 

 of a greater variety of activities (some of which may lead to improvement) than 

 the same practice confined to a period during which the same "set" persists. 



B. Loss OF CONFLICTING HABITS. 



W. F. Book has suggested that improvement during intervals without practice 

 is due to the dropping out of habits which make for low efficiency and which 

 have not had time to become well established, while the principal successful 

 actions, more firmly established by longer practice, persist. Such evanescent 

 habits, by restricting the variety of activities, may delay progress considerably 

 and give a decided advantage to the interrupted practice.* 



C. CHANGE IN THE PRIMARY STIMULUS. 



For successful learning by trial and error it is necessary that the organism 

 perform diverse activities in response to a given set of stimuli. In experi- 

 ments with animals such as those of Ulrich, the primary stimulus to this 

 activity is furnished by hunger, pain stimuli, unfamiliar surroundings, etc.; 

 in man by the many sublimations of instinctive reactions which constitute 

 " interest," "fear of ridicule," " rivalry," etc. The number and variety of trial 

 movements may depend upon the force of the primary stimulus, either as a 

 result of the amount of diverse activity produced or of the concentration of 

 the activity in responses to a limited number of stimuli, as when the hungry 

 rat spends its time before the door of the problem box and is not distracted 

 by the movements of other rats; or when the human subject keeps his atten- 

 tion strictly on the problem in hand. "Loss of interest through fatigue" 

 probably represents a change in the intensity of the primary stimulus to 

 activity. 



*The appearance and disappearance of habits of this type have been noted frequently during 

 the experiment. For example, a subject assumes an incorrect aiming position in order to avoid 

 catching the bowstring on his sleeve. This position persists for some time after the sleeve is 

 rolled back out of the way, and may even become firmly fixed. 



