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EUPHA FOLEY TUGMAN 



half and the last half of the trials required to learn the prob- 

 lem. The figures also show a decided decrease in the percent- 

 ages of error as the birds gradually learn the problem. 



The curve (Fig. 2) is plotted from these results. The ordi- 

 nates indicate the percentage of error and the abscissa, the 

 number of the series — each series consisting of 15 consecutive 



trials. The solid line ( ) is the error curve for Female VI 



and the broken line ( ) for Male V, while learning to go 



to the darker side. The table and curve show that the sparrows 

 varied in their daily record as well as in the time required to 

 learn completely the problem. The table shows also that the 



Figure 2. Curves showing percentage of errors made by two birds, Male V ( ) 



and Female VI ( ) while learning to choose the darker of two illuminated 



areas. Despite occasional lapses the learning appears to be a gradual process. 



birds exhibited great instability even until the end of the experi- 

 ment. Male V made one wholly perfect series of 15 trials — the 

 ninth series. Female VI did not make a perfect daily record 

 until the 30 correct choices were made in succession. 



The progress of Male V toward the threshold was very slow. 

 The observer felt that the bird really could discriminate the 

 lights long before it gave perfect tests. But it was more hasty 

 in making a choice than Female VI, with less attention and 

 effort at discrimination. When Male V died he had been given 

 1515 tests and was working with the difference in intensities 

 at .03 c.p. When Female VI had been given 1515 tests she was 

 working with the lights at the discriminable difference .017 c.p. 



