Changes in Human Performance with Age 155 



Older subjects are, however, sometimes unwilling to 

 sustain their initial effort. The first instance noted among the 

 experiments by the unit of which the writer was a member 

 was in an extremely irritating, noisy task which required the 

 subjects to make several long series of judgments with no 

 knowledge of whether they were doing so correctly or not. 

 It seems reasonable in this case to suppose that the older 

 subjects found the task disappointingly trivial and unreward- 

 ing. Subsequent instances, however, seemed to be due to a 

 different cause. They were all in very difficult experiments, 

 and what appeared to happen was that the older subjects 

 would try the task but then realize it was beyond them and 

 give up. A clear example of this behaviour is contained in a 

 series of experiments by Clay (1954, 1957) in which subjects 

 had to arrange numbered counters on chequer-boards to 

 add up simultaneously to marginal totals on the rows and 

 columns. She found that with a 3 X 3 board the task was 

 done willingly, and usually successfully, by all subjects from 

 the twenties to the seventies, although the older were a little, 

 but not significantly, slower. With a 5 X 5 board, however, 

 striking age changes appeared. Time taken rose from the 

 thirties through the forties and to the fifties but in the sixties 

 and seventies suddenly dropped. There was, however, at 

 these latter ages a substantial increase in the number of errors 

 made and some subjects failed to complete the task. Results 

 for a 6 X 6 board were similar but with the " break " appearing 

 between the forties and fifties. It seems as if the subjects up 

 to the age at which the "break" occurred could complete the 

 task by taking extra time and were willing to do so, but that 

 for the oldest subjects the task was virtually impossible. 

 They came to realize this fairly quickly and gave up after a 

 short time. They did, in fact, take the most sensible course 

 open to them in the circumstances, but it is clear that their 

 unwillingness to continue was essentially the result and not 

 the cause of their poorer performance. 



Between the two extremes of irritatingly trivial and im- 

 possibly difficult, older people seem to enjoy experiments 



