Rather than concentrating exclusively on consequences in early vocal instruction, the manipulation of antecedent conditions has been recommended. Few empirical data have been collected on the effect of different antecedent events. Therefore, a series of three experiments was conducted with three severely retarded children to investigate the vocalization-producing potential of two antecedent conditions: adult talk, a commonly cited antecedent, and adult silence. The conditions were evaluated using a modified alternating treatments design. In Experiment 1, 5 min of continuous adult talk was alternated with 5 min of adult silence: the results indicated that adult silence occasioned more vocalizations than did adult talk. In Experiment 2, a mixed (alternating 30-s periods of silence and talk) condition was compared to a silence condition; again the results indicated a higher frequency of vocalization during the silence condition. In Experiment 3, a modified talk (a question or comment presented every 10 s) condition was compared to a silence condition; the results indicated that the two conditions occasioned similar vocalization frequencies for two children, and the questions/comments condition occasioned more vocalizations for one child. In addition to studying optimal conditions for adult talk, the present investigation provides a methodology for deriving empirical data on the effects of differing antecedent conditions on vocalization frequencies.
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