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Three previous studies have failed to demonstrate conditioning in infants using a 3-s delay of reinforcement. The effects of a delayed reinforcement schedule on vocalization rates therefore were explored in a single-subject repeated-reversal experimental design for 3 4-to 6-month-old normally developing infants. Each infant received delayed social reinforcement from his or her parent for vocalizing. The comparison condition was a schedule of differential reinforcement of behavior other than vocalizations to control for elicitation by social stimulation. An operant level of infant vocalizations was the initial condition, after which the differential reinforcement schedule was implemented in an across-subjects multiple baseline design. Infants' vocalization rates increased above levels measured during differential reinforcement following onset of the delayed reinforcement condition. Also, vocalization rates decreased during differential reinforcement compared to operant levels. The successful use of delayed reinforcement schedules with infants in this study, as opposed to others, is discussed in terms of procedural differences among them.Key words: delayed reinforcement, vocalizations, differential reinforcement of other behavior, social reinforcement, methodology, infants Dating back to Plato and Aristotle, the notion of temporal contiguity has been invoked as a relevant feature in stimulus association (Leahey, 1980). When the temporal interval between a response and a consequence is lengthened, the subsequent association may be weaker than associations formed with more contiguous events. The association between delayed reinforcement and responding has been investigated in several species, including rats (Grice, 1948;Wolfe, 1934), pigeons (Dews, 1960;Ferster, 1953;Gleeson & Lattal, 1987;Sizemore & Lattal, 1977;Williams, 1976), and monkeys (Ferster & Hammer, 1965), in addition to human infants (Millar, 1972;Millar & Watson, 1979;Ramey & Ourth, 1971) and children (R. Baer, Williams, Osnes, & Stokes, 1984;Fowler & Baer, 1981

This study is an exploration of the parameters of delayed reinforcement with 6 infants (2 to 6 months old) in two experiments using single-subject repeated-reversal designs. In Experiment 1, unsignaled 3-s delayed reinforcement was used to increase infant vocalization rate when compared to a differential-reinforcement-of-other-than-vocalization condition and a yoked, no-contingency comparison condition. In Experiment 2, unsignaled 5-s delayed reinforcement was used to increase infant vocalization rate when compared to an alternating-treatments comparison condition. The alternating-treatments comparison consisted of 3-min components of differential reinforcement of other behavior and 3-min components of a nontreatment baseline. Successful conditioning was obtained in both experiments. These results contrast with those of previous infancy researchers who did not obtained conditioning with delays of 3 s and who attributed their findings to the limitations of the infant's memory capacity. We present an alternative conceptual framework and methodology for the analysis of delayed reinforcement in infants.

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