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Two experimental chambers were electrically connected so that the component selected by a pigeon confronting concurrent variable‐interval schedules in one chamber could be successively presented as a multiple schedule to a second pigeon in the other chamber. Component duration was regulated by the use of a changeover delay, the value of which was systematically varied between 0 and 30 sec. It was found that the relative local response rates on the preferred key (absolute response rate to that component divided by the sum of the absolute response rates during both components) tended to increase with increasing component durations for the birds in the concurrent chamber, but decreased for the birds in the multiple chamber. These data support the interpretation that there are fundamental differences in the mode of responding to multiple and concurrent schedules. Based on these findings, it was concluded that previous demonstrations of matching on multiple schedules do not establish that response allocation is controlled by a process equivalent to that found on choice paradigms. It now appears that matching on multiple (but not concurrent) schedules is a consequence of selecting short component durations. The implications of these data for Herrnstein's (1970) and Rachlin's (1973) formulations of the relationship between multiple and concurrent schedules are examined.

Two pigeons that attacked a taxidermically prepared target pigeon during a schedule of positive reinforcement for key pecking, and two that did not, were shocked through implanted electrodes in the presence of the target. Shock intensities of 2 and 4 mA, durations of 0.1 and 1.3 sec, and frequencies of 2, 6, 20, and 35 per minute were delivered across 16 sessions with 180 shocks per session. No pigeon attacked the target; one pecked the shockplug on its back. The two pigeons that had not attacked during the positive reinforcement schedules were conditioned to peck the target for food reinforcement before another 16 sessions of shock. No attack was observed in these shock sessions. During subsequent positive reinforcement of key pecking, the target was attacked by the two pigeons that had originally attacked and by one that had not. Absence of shock‐elicited attack in these pigeons may be related to the parameters of the experiment or may be yet another instance of the absence of shock‐elicited attack in the class Aves. At least under the present conditions, it was not possible to predict the level of attack during electric shock from the level of attack during schedules of positive reinforcement for key pecking.

Two severely retarded Down's‐syndrome boys learned a matching‐to‐sample performance through mediated transfer. The transfer paradigm involved three sets of stimuli, one auditory set (A) and two visual sets (B and C). The subjects were taught directly to do B‐A and C‐B matching, but experienced no direct association between C and A. They acquired the ability to do C‐A matching without having been taught that performance directly. They also learned indirectly to name some of the visual stimuli, but naming was apparently not the mediator in the emergent C‐A matching. The use of words and letters as stimuli highlighted the possible relevance of mediated associations in the indirect acquisition of elementary reading comprehension and oral reading. The acquisition of matching via mediated transfer also raised some new considerations concerning the role of coding responses in arbitrary matching to sample.

Rats responded in a two‐segment (variable‐interval variable‐interval) chain schedule. In one experiment, three subjects had either clicker, light, or clicker plus light as terminal‐segment stimuli. All three responded at the highest rate when clicker plus light were present, thus showing additive summation. For three other subjects, initial‐segment stimuli were either clicker, light, or clicker plus light. Two subjects responded at the lowest rate when clicker plus light were present, thus showing suppressive summation. In a second experiment, three subjects had either clicker, light, or neither clicker nor light as terminal‐segment stimuli. None of these subjects showed reliable additive summation. Three other subjects had clicker, light, or neither as the initial‐segment stimulus, and all three showed suppressive summation. Additive and suppressive summation both can be demonstrated with chain schedules, but stimulus parameters may be major variables in producing the effect.

Three pigeons learned to match three colors in a matching‐to‐sample procedure. The sample hue was presented on the center one of three keys, and the comparison hues were presented on the side keys. Forty responses on the center key produced the stimuli on the side keys and left the sample on the center key. A single response on the correct side key produced 3‐sec access to grain, which was followed by a 25‐sec intertrial interval. A correction procedure was employed when an error was committed. Before attaining asymptotic levels, there was no evidence of learning, responses were independent of the preceding response, and distributions of errors in four‐trial blocks were binomial. Distributions of error runs, runs of various lengths, autocorrelations of errors of several lags, alternations of correct responses and errors, etc., were shown to fit Bower's (1961) all‐or‐none model better than a gradual learning model of Bush and Sternberg (1959). A transfer test employing a novel color showed only transitory degradation of performance.

The rapid proliferation of courses based on Keller's Personalized System of Instruction (PSI) calls for a prompt evaluation of the relative costs involved in PSI and more traditional forms of college instruction. To determine the cost in student time required by a course taught with PSI relative to lecture, students did their studying in a special Study Center where course materials could be used but not removed. Students in the PSI section spent an average of about 50% more time in the Study Center (46 hr) than did students in the lecture section (30 hr), but that difference was made up by the lecture students spending an average of 20 hr attending lectures. Thus, total preparation time was about the same. PSI students scored slightly higher on common course exams, and while college entrance exam scores correlated highly with course exam scores, Study Center time was reliably related to course exam score only for PSI students. An analysis of the study records of individual students revealed that PSI produced fairly regular patterns of study by all students, while lecture students varied greatly in their patterns.

Children were asked to describe pictures in alternation with an adult model who used either descriptive adjectives in one condition or no adjectives in another condition. No reinforcement or instructions to imitate were given. The variables of age and family income were also studied in a 2 × 2 × 3 factorial design. The effect of modelling on the children's use of adjectives was significant, as were the main effects for family income and age. All two‐ and three‐way interactions were also significant. The significant interactions reflect the fact that the modelling effect was less strong for the preschool children, especially for those from low‐income families. Inspection of the individual data for these subjects suggests that the effect was weak and inconsistent across subjects. These results only partially confirm the stronger effects found by Lahey (Journal of Applied Behavior Analysis, 1971, 4, 19–22) using a similar population. Clear modelling effects on descriptive adjectives were found with second‐ and fourth‐grade children at both economic levels, however. In the second part of the experiment, the effect of modelling on prepositional constructions was studied using the same procedure and design. Although a statistical test of the modelling effect was significant, no clear evidence for the influence of modelling on prepositional constructions was found.