[Comparative physiology of short-interval conditioned reflexes to time in different species of animals]

Conditioned reflexes (CR) to short time intervals (from 0.25 to 20 min) were studied in rabbits, white rats and pigeons by motor food-procuring method. Some significant distinctions between species were revealed. The mean duration of formation of CR to time in rabbits amounted to 74 pairings, in rats--to 121, in pigeons--to 217. The optimal time interval varied in rabbits from 2 to 10 min, in rats from 1 to 4 min and in pigeons in was from 1 to 1,5 min. The longest interval which allowed to form the trace CR to time was not in excess of 22 min in rabbits, 10 min in rats and 4-5 min in pigeons. The shortest interval was within 15-45 s. Unstable and incorrect CR to time was formed when the intervals were shorter or longer than the optimal one. The accuracy of CR to time was: in rabbits approximately equal to 0.93-0.95 in rats approximately equal to 0.85-0.94, in pigeons approximately equal to 0.78-0.85. The data obtained have satisfactory explanation in the light of I. P. Pavlov's hypothesis on physiological mechanism of CR to time.