Two pigeons were trained to peck a key under several multiple variable-interval variableinterval schedules of reinforcement; different numbers of reinforcements were scheduled in two components of equal duration which were correlated with red and green illumination of the response key respectively. The results showed: (1) that the total number of responses in a scssion was proportional to the one-sixth power of the total number of reinforcements delivered in that session; and (2) that the ratio of responses between the two components was equal to the one-third power of the ratio of reinforcements between them. This latter exponent may be regarded as reflecting the sensitivity of the distribution of responses between the components to the distribution of reinforcements. It was suggested that the effects of a number of complex schedules of reinforcement could be summarized by different values of this exponent.When two variable-interval (VI) schedules of reinforcement are combined, responding maintained by each is partly determined by reinforcements delivered under the other schedule. This interaction occurs both under concurrent schedules, in which two or more schedules operate simultaneously for responses on dlifferent keys, and under multiple schedules, in which two or more schedules operate successively for responses on a single key. This similarity between concurrent and multiple schedules, however, does not extend to the way in which responses are distributed between each of the component schedules which constitute the total schedule. Under concurrent VI VI schedules, pigeons match the distribution of responses between keys to the distribution of reinforcements between keys (Herrnstein, Catania, 1963). Under multiple VI VI schedules these distributions are not matched (Reynolds, 1963).Catania (1963) has written a series of equations which gives a precise quantitative de-'The data presented are from Exp.

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Pigeons were trained to discriminate between the presence and absence oe a pigeon in photographie displays projected on a response key. Irrelevant cues were reduced as much as possible, while the differences between the objects were of sufficient variety and complexity to ensure that mastery of the discrimination would require the use of a concept. The Ss learned this discrimination very rapidly. On a test given following training, the Ss showed almost complete transfer to new displays containing fancy breeds of pigeons and showed significantly less transfer to new displays containing other species of birds. These results indicate that discrimination was based on a concept of "pigeon. "

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Pigeons sometimes peck a key at different rates in the presence of different stimuli, even when the same schedule of reinforcement is correlated with each of these stimuli. The possibility that the occurrence of such stimulus bias is dependent on adventitious effects of food reinforcement in the presence of the stimuli was evaluated by correlating extinction with two stimuli. Both pigeons showed stimulus bias, indicating that the occurrence of this phenomenon is not critically dependent upon any effects of scheduled food reinforcements.

Despite the use of preventive devices, film-loop programs sometimes attain an embarrassing length. A simple strategy halves the length of a loop without altering the program in any way. This consists of constructing the loop in the form of a Mobius ring by twisting one end through 1800 before splicing the two ends together. The program can then be punched in two halves on opposite sides of the center line of the film. Since a Mobius ring has only one continuous side, the complete program can be presented by circulating the loop through the programmer twice. Since in effect this strategy involves adding a second channel to a film loop of half the length, it is necessary to alter the programmer so that it will be operated by punched holes at the side, rather than at the center of the film. This requires that the film sprocket on the programmer be offset by the same amount the punched holes are offset from the center line. In the case of 16-mm film, offsetting these by 2 mm is sufficient. This strategy can be adapted to film programs involving more than one channel by offsetting the channels an appropriate amount. This technique in no way interferes with either the life or serviceability of film-loop programs. A. M. LYSONS

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