Responding by pigeons on one key of a two-key chamber alternated the color of the second key, on which responding produced food according to a variable-interval schedule of reinforcement. From time to time, reinforcement would be available for a response, but in the presence of a particular stimulus, either red or green light on the key. Red or green was chosen irregularly from reinforcement to reinforcement, so that a proportion of the total number of reinforcements could be specified for each color. Experimental manipulations involved variations of (1) the proportions for each color, (2) changeover delay, or, alternatively, (3) a fixed-ratio changeover requirement. The main findings were: (1) relative overall rates of responding and relative times in the presence of a key color approximated the proportions of reinforcements obtained in the presence of that color, while relative local rates of responding changed little; (2) changeover rate decreased as the proportions diverged from 0.50; (3) relative overall rate of responding and relative time remained constant as the changeover delay was increased from 2 to 32 sec, with reinforcement proportions for red and green of 0.75 and 0.25, but they increased above 0.90 when a fixed-ratio changeover of 20 responses replaced the changeover delay; (4) changeover rate decreased as the delay or fixed-ratio was increased.Concurrent schedules specify that two (or more) reinforcement schedules function simultaneously. There are two (or more) operants, and reinforcement for each is scheduled independently. By one method, each operant and its schedule are assigned to an individual response key. By a second, all of the schedules are assigned to the same key (main key) and different exteroceptive stimuli are associated with each operant-schedule pair. Responses on a second key (changeover key) alternate the exteroceptive stimulus and the schedule in effect on the main key. Each schedule functions continuously, whether or not it is assigned to the main key at a given moment. The two procedures appear to be equivalent (Catania, 1966) Pliskoff, 1968;Catania, 1963Catania, , 1966Herrnstein, 1961

Thirteen pigeons were exposed to a variety of second-order schedules in which responding under a component schedule was reinforced according to a schedule of reinforcement. Under different conditions, completion of each component resulted in either (1) the brief presentation of a stimulus also present during reinforcement (pairing operation), (2) the brief presentation of a stimulus not present during reinforcement (nonpairing operation), or (3) no brief stimulus presentation (tandem). Brief-stimulus presentations engendered a pattern of responding within components similar to that engendered by food. Patterning was observed when fixed-interval and fixed-ratio components were maintained under fixed-and variable-ratio and fixed-and variable-interval schedules. There were no apparent differences in performance under pairing and nonpairing conditions in any study. The properties of the stimuli presented in brief-stimulus operations produced different effects on response patterning. In one study, similar effects on performance were found whether brief-stimulus presentations were response-produced or delivered independently of responding. Response patterning did not occur when the component schedule under which a nonpaired stimulus was produced occurred independently of the food schedule. The results suggest a reevaluation of the role of conditioned reinforcement in second-order schedule performance. The similarity of behavior under pairing and nonpairing operations is consistent with two hypotheses: (1) the major effect is due to the discriminative properties of the brief stimulus; (2) the scheduling operation under which the paired or nonpaired stimulus is presented can establish it as a reinforcer.

Because graphs provide a compact, rhetorically powerful way of representing research findings, recent theories of science have postulated their use as a distinguishing feature of science. Studies have shown that the use of graphs in journal articles correlates highly with the hardness of scientific fields, both across disciplines and across sub-fields of psychology. In contrast, the use of tables and inferential statistics in psychology is inversely related to subfield hardness, suggesting that the relationship between hardness and graph use is not attributable to differences in the use of quantitative data in subfields or their commitment to empiricism. Enhanced "graphicacy" among psychologists could contribute to the progress of psychological science by providing alternatives to significance testing and by facilitating communication across subfields.

Studies comparing the cognitive status of the sciences have long sought to identify the distinguishing features of `hard' and `soft' science. Attempts by philosophers of science to ground such distinctions in abstract principles and by sociologists of science to detect relevant differences (for example, in consensus levels) have met with limited success. However, recent investigations of scientists' concrete practices of data representation provide new leads on this problem. In particular, Bruno Latour has argued that graphs are essential to science due to their ability to render phenomena into compact, transportable and persuasive form. Applying Latour's notion of `graphism' to the hierarchy of sciences, we found that the use of graphs across seven scientific disciplines correlated almost perfectly with their hardness, and that the same pattern held up across ten specialty fields in psychology.

Pigeons were presented with a series of key-illumination time periods. During these periods two response keys were lit, one by white light and the other by red or green. White-key responses changed the color on the other key and green-and red-key responses intermittently produced food. Choice responses were reinforced at either of two intervals timed from the onset of the stimulus period. Food was scheduled for green responses during the shorter interval in some stimulus periods and food was scheduled for red-key responses at the longer interval during alternate stimulus periods. The temporal location of food in the stimulus periods was varied across conditions. Across conditions, the pigeons responded on the green key until the time at which green-key responses might be reinforced had passed; then, the probability of red-key responses increased as the time approached at which red-key responses might be reinforced. In all conditions, the pigeons, changed from green-key to red-key responses at the time that was an equal relative temporal distance from the two intervals where these responses were reinforced.