Temporal patterns of key pecking by pigeons were shaped by a schedule in which the delivery of food was contingent upon a measure of the overall extent to which the temporal pattern of behavior within a 5-sec trial conformed to a required pattern. This pattern approximated a constant rate of change in the rate of key pecking throughout the 5-sec trial. In comparison with behavior maintained by a classical fixed-interval 5-sec schedule, the new schedule controlled a better approximation to a "scallop" within individual trials and greatly reduced intersubject variability. These results are consistent with the view that the delivery of a reinforcer after a behavioral pattern a few seconds in duration may strengthen the entire pattern as a unit, or operant. The response topography contiguous with reinforcement may be a negligible fraction of the strengthened operant. One implication of this view is that mean response rate for such brief responses as key pecks and lever presses is a byproduct of whatever patterns are strengthened, and generally will not reveal fundamental controlling relationships, whenever a reinforcer is not contiguous with all the behavior on which it is contingent.

Three pigeons were required to peck a single key at a higher and a lower rate, corresponding to two classes of shorter and longer concurrently reinforced interresponse times. Food reinforcers arranged by a single variable-interval schedule were randomly allocated to the two reinforced interresponse times. The absolute durations of reinforced interresponse times were varied while the total reinforcements per hour was held constant and the relative duration, i.e., the relative reciprocal, of the shorter reinforcer class was held constant at 0.70. forcement density is sufficiently high, a subject spends virtually all of the time responding at the two reinforced rates; part of the time at the lower rate and the rest of the time at the higher rate (Shimp, 1968;Staddon, 1968). The total behavioral output is a mixture of these two reinforced response rates. It is possible to measure a subject's preference for a particular one of two such rates by computing the relative frequency of all responses that terminate IRTs conforming to that rate, i.e., belonging to the corresponding class of reinforced IRTs. This preference measure is formally analogous to preference measures in multi-operanda experiments. But the analogy is more than a formal one: the preference functions obtained in compound paced VI schedules appear to be independent of the number of operanda. Whether the subject is required to respond at different rates on the same operanda, or is required to respond at different rates on different operanda, the resulting preference functions are the same (Moffitt and Shimp, 1971

Four experiments established complex choice responses a few seconds in duration. A response was reinforced if it sufficiently approximated a `target' response. The two target responses in each experiment were linear in the sense that they involved either constant rates, or constant rates of change, in component key pecking by pigeons. For example, in Experiment 4, one target response consisted of the linearly increasing pattern of 0, 1, 2, and 3 pecks per s in four successive seconds, and the other response consisted of 3, 2, 1, and 0 pecks per s. Contingencies were `tolerant' in the sense that they permitted variability across different reinforced exemplars of a response. Responses approximated target responses, at least crudely in terms of overall cumulative records, and sometimes even quantitatively in terms of within-trial, local sequential organization. In this sense, the `contents' of at least some choice responses, like their `envelopes', can be shaped. That is, patterning within their boundaries, in addition to their relative and absolute durations, can be shaped. Some responses may have emerged from variability inherent in component pecking occurring at a constant probability, thereby demonstrating a few cases where the relation between molecular and molar analyses fully legitimizes a molar analysis.

A variable-interval schedule arranged food reinforcement for key pecking by pigeons on a single operandum at two rates, corresponding to two classes of reinforced interresponse times ranging from 1.5 to 2.5 sec and from 3.5 to 4.5 sec. The scheduled reinforcemiient rate for the higher component response, rate was constant and equivalent to that of a variableinterval 4-min schedule. The scheduled reinforcement rate for the lower comnponent response rate varied from zero to over 100 per hour. The number of occurrences of the constant component response rate varied inversely with the reinforcement rate for the variable component. This result, by definition a concurrent reinforcement interaction, or contrast, was the combined effect of two time-allocation functions, which together determine mean response rate: the time allocated to both component rates as a function of the total reinforcement rate, and the time allocated to a particular component rate as a function of the percentage of reinforcenments for that component. The present experiment reveals a further parallel between the controlling relations for free responding on a single operandum and those for choice between two operanda; in each case, a concurrent reinforcement interaction can be found that corresponds to matching.In a concurrent variable-interval variableinterval (conc VI VI) schedule, response rate in one component witlh a constant reinforcement rate varies inversely with the reinforcement rate for the other component (Catania, 1963;Rachlin and Baum, 1969, 1972 (Shimp, 1968). Behavior in this context may be partitioned into three classes: responding at either of the two reinforced component response rates, and responding at non-reinforced response rates.

Backward masking functions were obtained for a single-letter (SL) visual display, and for 12-letter (12-L) circular displays presented with either a simultaneous or 150-msec. leading indicator. The 5s were required to report both the indicated letter (first position) and the letter directly opposite (second position) in the 12-L conditions. The first-position forward indicator function asymptoted to its No-Mask Control approximately 100 msec, faster than the first-position simultaneous indicator functions, and at about the same mask delay as the SL function. The pattern of results suggest that differences in masking ranges between single-and multiple-element displays are a function of encoding strategy rather than a difference in icon formation time.