In zero-delay matching procedures the performance of three groups of pigeons was examined when exteroceptive stimuli, response-produced stimuli associated with the completion of either of two fixed ratios, or a compound of exteroceptive and response-produced stimuli were available as samples. Exteroceptive samples were found to control a higher level of matching accuracy than response-produced samples, while compound samples controlled a higher level of accuracy than did exteroceptive samples alone. When all subjects were placed on a transfer procedure, during which the previously used red and green samples were replaced by horizontal and vertical lines, the availability of sample-specific fixed-ratios facilitated acquisition of the task.

Three pigeons were trained on oddity matching in which either 1, 4, 8, 16, or 32 samplekey observing responses were required to turn off the sample stimuli and turn on the comparison stimuli. Oddity accuracy increased when the observing-response requirement was raised and decreased when the requirement was lowered. Next, while the observing requirement was maintained at one response, the number of responses required to the comparison stimuli was either 1, 4, 8, 16, or 32. Under these conditions, choice was defined as the comparison that first accumulated the required number of responses. In general, increasing the comparison-response requirement decreased accuracy and lowering the comparison requirement increased accuracy. The fixed-ratio observing requirements appeared to facilitate control by stimuli serving an instructional function.

Rats' lever pressing terminated visual or auditory stimuli associated with fixed-time or variable-time schedules of food delivery and produced a timeout period during which food delivery could not occur. Lever pressing during a timeout period reinstated the food-associated stimuli and again permitted food delivery according to the fixed-time or variable-time schedules. The mean interfood interval ranged from 1 minute to 16 minutes (variable-time schedules) or 32 minutes (fixed-time schedules); the timer controlling schedule intervals did not stop during timeout periods. The percentage of session time spent in timeout increased when the mean interfood intervals were lengthened and decreased when the mean interfood intervals were shortened. Timeouts were initiated most frequently about half way between successive food deliveries (fixed-time schedules) or after 15 seconds or more had lapsed since the last food delivery (variable-time schedules). Elimination of food delivery increased the percentage of session time spent in timeout, and elimination of the timeout contingency decreased lever press rates. When timeout was produced only when the lever was held in the depressed position, little time was spent in timeout. The main determinants of timeout initiation and termination appeared to be the rate of food delivery, freedom of movement during timeout, and the stimulus change associated with initiation and termination of timeout.

The acquisition of delayed matching to sample in two groups of pigeons was examined when three delay values (2, 4, and 6 sec.) were mixed across trials and when each of the three delay values was correlated with one of three standard stimuli (i.e., multiple delays). Extended training resulted in the acquisition of matching by all multiple-delay Ss, while only one of three mixed-delay Ss showed comparable performance. The one S which acquired matching under the mixed condition emitted standard, specific, delay behaviors. The results suggest that acquisition of delayed matching may be highly dependent upon the availability of some source of delay-stimuli that are consistently correlated with standard stimuli.