6i6 



BRAIN MECHANISMS AND LEARNING 



signihcancc to the stimulus. If this darkness-flicker association was pro- 

 longed for a time without modifications, they once again lost interest in 

 the stimulus, their attention decreasing accordingly (rehabituation). 



I I I I I I I I I I I I I I I I i I i I I I 



i 5 5 7 9 11 {? 15 1? ^? 21 25 25 ?? ?9 ?1 



TRIALS (DfS) 



Fig. 7 

 Cliain;cs of the risiial evoked rdipome by effect of diicoiiliniioiis flicker st'uniiLitioii. 

 Ordinates, percentage of initial peak to peak amplitude of the evoked response. 

 Abscissas, trials carried out every 20 seconds with discontinuous flicker stimulation 

 (DFS) at 2/scc. for 20 seconds. Lead 02-right mastoid. Stroboscope at a distance 

 of 3 m. from the retina. Eyes open. Two experiments carried out in different 

 subjects who had had no previous knowledge of the conditions of the test, are 

 plotted. The temporal course of changes in experiment number 21 (white dots) 

 is faster than the one of experiment 26 (black dots). In experiment 21 the ampli- 

 tude increases quickly and reaches its highest value in the 5th trial. After the 

 1 3 th trial it begins to decrease regularly. In experiment 26, the amplitude increases 

 slowly and retains high values until the end of the test at the 31st trial. 



INTERACTION BETWEEN THE DISCONTINUOUS FLICKER STIMULATION 



AND A TONE 



The association ot a sound in the period ot darkness during the discon- 

 tinuous flicker also provoked modifications in the response. When after 

 the establishment of habituation to the discontinuous flicker an intense and 



