vi PREFACE 



express sincere appreciation. My only contribution to the 

 apparatus Is the simple mechanism described In Chapter VII, 

 yet in the development of this device his helpful suggestions 

 always were at my command. Likewise, my only contribution 

 to the main problem of visual perception In the chick is that 

 represented by the preliminary data on the reactions to flicker 

 stimuli. Gladly I acknowledge my Indebtedness to Professor 

 Yerkes for his patience in starting me on this experimental task 

 and for his kindly Interest throughout the study. 

 ' This opportunity is also taken to express my obligations to 

 Miss Doris M. Wood, who generously read the entire manu- 

 script, and to my wife, who assisted in various ways with the 

 preparation of the manuscript. 



Harold C. Bingham. 

 Washington, D. C, January 25, 1922. 



