VISUAL PERCEPTION OF THE CHICK 71 



A double switch was inserted in the connections so that the 

 relative locations of the slow and rapid flashes could be reversed. 

 The disc was driven by an "A.C." motor having a commercial 

 rating of one-eighth horse power and twelve hundred revolutions 

 per minute. The excessive speed was cut down by means of a 

 worm gear reducer so that the rotation rate of the disc in most 

 of the training tests was approximately once per second. The 

 lamp interrupted by a single insulation, therefore, flashed on and 

 off once every second. The rate was noted by recording with a 

 stop watch the time elapsing during 50 flashes. Practically no 

 variations were observable during the experiment. 



Three driving pulleys of different sizes on the motor and three 

 on the reducer made possible nine different speeds ranging between 

 50 revolutions of the disc in 162 seconds and 50 revolutions in 

 39 seconds. The rate of flashing, how^ever, was increased two or 

 more times depending upon the number of breaks on the circum- 

 ference of the disc. 



There is a definite objection to this method of measuring the 

 interruptions, but for the present purpose, rough tests indicate 

 that it may be ignored. Since each on interval heats the filament 

 of the illuminating lamp, there is a tendency for the illuminated in- 

 terval to last longer than the dark interval, and as the alternating 

 intervals become shorter there would be a tendency for the total 

 time of illumination to become greater than the total time of 

 darkness. Yet it seems justifiable to ignore this possibility since 

 the number of alternations is unchanged. Moreover, the glow 

 of a filament after the "flash-off" seemed to be completely swal- 

 lowed up by the opal flashed glass which served as a diffusing sur- 

 face. It was also found that the tungsten lamps responded 

 quite promptly to the off and on contacts and more promptly than 

 the carbon lamps. 



The training was begun with a one-three discrimination differ- 

 ence. The chick was trained to choose the slower rate. As in 

 the spatial tests, a visual complex consisting of greater brightness 

 added to the slower stimulus was presented at first and gradually 

 changed to the single detail of flicker. Control of the luminous 

 flux was gradually introduced by means of the upper illumination, 

 and, in a few tests, by an additional 2 c.p. lamp located at the 

 middle of the rear of the experiment box. Further controls were 

 made after the habit became established, by irregularly varying 



