The present series of experiments examined pigeons' spatial working memory using two variants of the delayed matching of key location paradigm (Wilkie & Summer, 1982). Exposure to the sample location was extended to 15 min and pecks to this stimulus (S+) produced grain on a variable interval 30-s schedule (the 1 Cue group). For some subjects (the 2 Cues group) both the positive and negative (S-) stimuli were presented during the sample period. In a subsequent test phase subjects were exposed to both the S+ and S- for 1 min. If the subject made more responses to the S+ an additional 15 min of access to the S+ occurred, with grain available on the previous schedule. If more responses were made to the S- the trial terminated and the subject was immediately removed from the apparatus. In the first experiment all subjects performed well with retention intervals of up to 30 s, a level of performance better than previously demonstrated in the delayed matching of key location (Wilkie & Summers, 1982). However, subjects' performance was disrupted when they were removed from the apparatus during the retention interval. Subjects in the 1 Cue group were more severely disrupted than the subjects in the 2 Cues group. Performance improved dramatically when these subjects were subsequently trained and tested on the 2 cues condition. Experiment 2 examined the differences between the 1 cue and 2 cues tasks further. All subjects were run for 30 trials on each task and removed from the apparatus during the retention interval. Performance on the 2 cues task was significantly higher for all subjects. When subjects were switched to the 1 cue task, performance immediately dropped and remained at a low level for all blocks tested. The observed differences probably reflect the operation of transfer appropriate processing (cf. Morris, Bransford, & Franks, 1977), given the similarity between training and testing on the 2 cues task. Experiment 3 used the 2 cues task to examine the performance of pigeons when retention intervals longer than 30 s were imposed between training and testing. The retention interval was incremented in the following stages: 5 min, 15 min, 30 min, 1 hr, 2 hr, 4 hr, 8 hr, 12 hr and 24 hr. Subjects were run until their performance fell below a criterion (70% accuracy or better for a block of 10 trials). When a subject failed to attain criterion within 3 blocks, no further data were collected from that subject. Subjects' upper retention limit varied somewhat, ranging from a minimum of 30 min to a maximum of 24 hr, but the performance of most subjects began to deteriorate at about 4 hr, a level considerably above the upper limit previously demonstrated in other paradigms (30 min-Spetch & Honig, 1988). Experiment 4 was a systematic replication of Experiment 3, using a mixed, rather than an incremental, schedule of retention intervals. Performance was not quite as good. For most subjects performance began to deteriorate at about 2 hr, somewhat sooner than in Experiment 3, but nevertheless higher than the level of performance seen in other paradigms. The results of the present experiments are interpreted in terms of the ecological validity of the procedures employed. The implications of the present studies for the study of "adaptive specializations in cognition" (Sherry, 1984; Sherry & Schacter, 1987), are also discussed, as are the implications for the distinction between reference and working memory. / Arts, Faculty of / Psychology, Department of / Graduate

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This thesis examines whether juvenile feral pigeons, Columba livia, form sibling alliances when competing for access to a defensible food source. When tested as a flock at a non-depletable column feeder, with room for either one or two birds to feed, siblings associated with each other more often than expected by chance. Frequency of aggression between siblings at these feeders tended to be lower than expected on the basis of their association. Removal experiments showed that sibling presence had a positive effect on relative feeding success at the single column feeder: a juvenile who lost to another juvenile on a one-to-one basis tended, in the presence of its sibling, to lose less badly to, or even beat, that same juvenile. In contrast, presence of the winner's sibling tended not to affect the relative feeding success of competitors. These results support the hypothesis that pigeon siblings form aggressive alliances when competing for food that is defensible.

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Photocopy of typescript. / Bibliography: leaves 58-62. / Microfiche. / vii, 62 leaves ill. 29 cm