Pigeons were given repeated two-day conditionings alternating with eight-day extinctions using a trial procedure. One group had different key colors during each of the first five conditioning-extinction pairs; another group had the same key color throughout. Total extinction responses of both groups were quite constant over successive extinctions. This finding differs from the rapid declines found in most previous studies with bar-press and key-peck responses. The difference probably was due to our longer extinctions, because responses early in each extinction did decrease. However, that decrease was neutralized by increases in responses late in each extinction. The two opposite changes indicate the influence of two different factors during repeated extinctions, with neither factor having much stimulus specificity. The reduction of early responses may result from feeding changes confounded with extinction. The increase in later extinction responses may result from a decrease in the effect of unreinforced responses after their repeated occurrence. Comparisons among the above studies indicate that the following influences on repeated extinctions are likely, though in view of extensive confouinding of variables these conclusions are tentative until carefully controlled comparisons are made. A decrease in successive extinctions seems to be favored by (1) use of bar-press or key-peck responses rather than alleys or jumping stands, (2) measurement of number of responses in extinction rather than latencies or running times, (3) massing of extinction responses by free-operant techniques or short ITIs as compared with several minute or 24-hr ITIs, (4) increase in extinction trials per extinction, (5) not giving reinforcements following the extinction and within the same daily session, (6) increasing the difference between the ITI during extinction and the ITI between the last unreinforced trial and the first reinforced trial, and (7) continuous rather than intermittent reinforcement.Most of the above studies involved rather brief extinction periods, often only part of a session, and few data are available concerning repetition of long extinction periods. Jenkins (1961) gave pigeons two 10-day extinctions and found the usual decline, but the duration of his second conditioning was less than one 181 1976, 26,[181][182][183][184][185][186][187][188][189][190] NUMBER 2 (SEPTEMBER)

Most previous research on the effect of the duration of preceding discrimination training on responding to a new stimulus has measured the responding during extinction. To reduce effects originating in the extinction procedure itself, the present study assessed the effect of discrimination training on responses to a new negative stimulus added during continued discrimination training. Pigeons were given a new negative stimulus (blue key) after 0, 1, 3, or 9 days of discrimination training with a yellow key as the positive stimulus, and both a green key and a red key as negative. Fewer responses were made to the blue key when it was introduced after nine days of discrimination training than after less discrimination training. That effect of long discrimination training agrees with reported results from extinction tests. However, the effect of briefer discrimination training in the present study differed from reported results with extinction testing. It appears that testing during continued discrimination training eliminates a distortion present in extinction tests of the effect of discrimination training on responding to a new stimulus. Extinction of all responses need not be used during generalization tests.