The effects on behavioral variability of differential reinforcement of response sequences that differed from preceding response sequences were investigated in college students. Two-response sequences were used as response units in Experiment 1 and three-response sequences were used in Experiment 2. Development of variability was compared across the following two settings : (a) systematic changes in the number of preceding responses used as the reference for differential reinforcement, and (b) two kinds of yoked conditions, within -subject yoking and between-subject yoking, in which response sequences were not differentially reinforced but distribution and frequency of reinforcement were equal to the differential reinforcement condition. Both experiments showed high behavioral variability and more frequent responses that differed from preceding responses under the differential reinforcement condition, but less variability and less frequent responses under the yoked condition. The effect was smaller when the number of preceding responses used as a reference for differential reinforcement was one than when greater than one. These results suggest that the increase in behavioral variability was produced by the differential reinforcement of responses that differed from preceding responses.

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Four students with developmental disabilities were trained to establish sentences with giving and receiving verbs and particles (ga, ni) through a higher-ordered conditional discrimination procedure. Students were required to select verbs, persons'names or particles and construct the sentence, when presented with motion picture or real movement of themselves. In Experiment 1, a motion picture in which Teacher A gave an object to Teacher B or vice versa was presented by computer display, and the students were required to select words and construct a sentence. All of the students could not make an appropriate sentence. In Experiment 2 and 3, students were required to walk to a teacher giving or receiving the object and walk back to the listener, then to construct the sentence using appropriate verbs and particles. Baseline, training and test trials were conducted. "Watashi-mashita" (giving) and "morai-mashita" (receiving) were used in Experiment 2, and "age-mashita" (giving) and "kure-mashita" (receiving) were used in Experiment 3. The results showed that appropriate sentence construction by selecting particles and person's names both for trained and untrained sentences was aquired by all of the students. These results were discussed in terms of the applicability of a conditional and higher-ordered conditional discrimination paradigm to the analysis of sentences with syntactical structure and to the development of a remedial program for acquisition of grammar in students with developmental disabilities.

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