Steve Reilly

Hippocampal lesions and associative learning in the pigeon.

The performance of pigeons with hippocampal lesions was compared with that of unoperated and neostriatal-lesioned control Ss in 3 experiments. In Experiment 1, hippocampal-lesioned birds were retarded in the acquisition and the maintenance levels of autoshaped responding. However, the deficit was attenuated following the addition of a response contingency to the autoshaping schedule. In Experiment 2, the hippocampal-lesioned birds showed impaired performance on a differential reinforcement of low rates of responding schedule. From the high levels of responding in Experiment 2, underresponding was observed in hippocampal-lesioned birds relative to control Ss on return to the autoshaping schedule in Experiment 3. Results are interpreted in terms of impaired classical conditioning in hippocampal-lesioned birds.

Enhanced DRL and impaired forced-choice alternation performance following hippocampal lesions in the pigeon.

In four experiments, pigeons with bilateral lesions of the hippocampus were compared to unoperated control birds and operated control subjects that received bilateral lesions of the neostriatum on tasks sensitive to hippocampal damage in mammals. Consistent with the mammalian literature, hippocampal birds were impaired on forced-choice alternation in the T-maze, although they were unimpaired on spatial alternation and reversal learning in an operant chamber. Furthermore, in contrast to hippocampal mammals, hippocampal pigeons showed enhanced performance on a differential reinforcement of low-rates of responding schedule of reinforcement. The results are discussed with respect to a behavioural homology between the avian and mammalian hippocampal formations.

Long-term memory of pigeons for stimulus-outcome associations involving multiple stimuli, each seen in a single brief trial

Experiment 1 explored performance of pigeons in two versions of a shortterm recognition memory procedure. In one version responding to entirely novel slides was rewarded, and responding to familiar slides (slides seen once, for 10 sec) was not rewarded; in the other version, responding to familiar slides was rewarded. Performance was initially below chance in both versions of the procedure. This result indicated that in this procedure associations were formed between the slides and the outcome (reward or non-reward) that followed their presentation. The result also suggested that the true capacity of pigeon recognition memory cannot be assessed using these procedures, as performance is inevitably disrupted by the birds associative memory. The tendency of pigeons to form one-trial associations was exploited in Experiment 2. Phase 1 consisted of 16 two-session cycles: in Session 1 of each cycle, birds were shown 20 novel slides and were rewarded for responding to 10 of those slides; in Session 2, the same slides were shown again, with the same reinforcement contingencies. The birds showed significant overnight retention of the one-trial associations formed in Session 1 of each cycle. Phase 2 showed significant retention over periods of more than 20 days of associations involving 320 slides seen twice only. Phase 3 re-exposed for nine daily sessions one of the sets of 20 slides used in Phases 1 and 2; a high level of discrimination emerged rapidly and 4 (of 8) birds showed, by the end of training, no overlap in response rates to positive and negative slides. Comparative implications of the results are discussed.

The role of local context in autoshaping

Abstract Three experiments used an autoshaping procedure with pigeons to examine the effects of nonreinforced, nontarget stimuli (ITI-fillers) during the intertrial interval on responding to a reinforced target CS. Experiment 1 replicated a previous demonstration that an ITI-filler that occupied a substantial portion of the ITI attenuated responding to the target CS relative to a group trained with a similar ITI but lacking the ITI-filler. Experiment 2 found that the superiority of responding typically found with a long ITI relative to a short ITI, that is, the trial-spacing effect, can be reversed by imposing a filler stimulus during the ITI in the former condition. Experiment 3, using a within-subject design, found that when one background stimulus condition occupied a majority of the interreinforcement interval, pairings of one target CS with reinforcement that were embedded within this background condition, that is, a long duration local context occurred for this CS, yielded better performance that a second, reinforced, target CS paired with reinforcement in the shorter duration background condition. These results confirmed predictions derived from a local context view of cycle time. Comparator theories of classical conditioning require incorporation of this notion into their conceptualization of effective cycle time in order to explain the present findings.

The effects of ITI fillers in autoshaping

Abstract The present experiments used pigeons in an autoshaping procedure to examine the effects of a nonreinforced, nontarget stimulus presented during the intertrial interval on responding to a target CS. Experiments 1 and 2 found that a filler stimulus presented during a substantial portion of the ITI retarded responding to the target CS relative to a group not exposed to the filler. This group difference in performance was subsequently abolished by continued training and omitting the filler in the former group (Experiment 1) or adding a filler for the latter group (Experiment 2). Experiment 3 found that when the “filler” occupied most of the interreinforcement interval, CS-US pairings embedded within the “filler” stimulus yielded superior autoshaping relative to a group that received CS-US pairings embedded in static apparatus cues in the absence of the filler. The results are discussed with reference to the ways that a nontarget stimulus during the ITI can influence contextual modulation of responding to a discrete CS and the necessity for comparator theories to incorporate a “local context” view of cycle time to explain the present findings.

Hyperstriatal lesions and attention in the pigeon.

In two experiments, pigeons with bilateral lesions of the hyperstriatum were compared with unoperated control birds on tasks designed to test an attentional account of hyperstriatal function. In both experiments, hyperstriatal lesions disrupted reversal learning but did not influence the retardation of learning associated with either nonreinforced preexposure to the to-be-conditioned stimulus (Experiment 1) or prior nondifferential reinforcement to the to-be-discriminated stimuli (Experiment 2). There was, however, evidence of an impairment in both the acquisition and maintenance of autoshaped responding in lesioned birds, an impairment which may reflect a disruption of classical associations in hyperstriatal pigeons.

Lateral hyperstriatal lesions disrupt simultaneous but not successive conditional discrimination learning of pigeons (Columba livia).

In 2 experiments we explored the effects of lateral versus medial laminar lesions of the hyperstriatum in pigeons (Columba livia); medical lesions were largely confined to the hyperstriatum accessorium, and lateral lesions to the hyperstriatum dorsale and hyperstriatum ventrale. In Experiment 1, lateral, but not medial, lesions disrupted acquisition of a simultaneous conditional discrimination; both medial and lateral lesions disrupted reversal of the discrimination. The reversal deficits of the medial and lateral groups were quantitatively similar, and both groups showed exaggerated positional responding. In Experiment 2, neither medial nor lateral lesions disrupted acquisition of a successive conditional discrimination. We conclude that lateral hyperstriatal damage does not obtain a general disruption of conditional learning; we speculate that the lateral hyperstriatum may play a critical role in configural learning.

Hyperstriatal lesions and short-term retention of non-visual information in pigeons

Short-term retention of non-visual information was investigated using three series of hyperstriatal-lesioned and unoperated control pigeons. Neither retention (Experiment 1) nor acquisition (Experiment 3) of go/no-go alternation was disrupted by the lesions. Similarly, Experiments 2 and 5 failed to detect significant disruption of either retention or acquisition of spatial alternation. Increases in the retention intervals used in these tasks reduced accuracy in both groups but did not differently affect hyperstriatal as opposed to control performance. A lasting deficit was, however, obtained in a delayed-response task (Experiment 4), but this deficit, which was independent of retention interval, appeared to be the result, not of a disruption of memory, but of an exaggerated perseverative tendency. Experiment 6 confirmed that all three series of hyperstriatal birds showed disruption of reversals of a spatial discrimination. It is concluded that hyperstriatal lesions do not disrupt memory processes, and the hypothesis that hyperstriatal damage induces perseveration of central sets is discussed.

Probability learning in pigeons (Columba livia) is not impaired by hyperstriatal lesions

Three experiments investigated the effects of hyperstriatal lesions on spatial and visual probability learning in pigeons. The lesions did not affect choice accuracy although they did reduce positional responding on error trials in the visual task. The results gave support to a perseverative, as opposed to an attentional, interpretation of the lesion effects. Increasing intertrial interval in the visual task resulted in decreased accuracy in both lesion and control groups, and the absence of a differential effect on the lesioned birds ran counter to an earlier suggestion that increased perseveration might be due to increased frustration. A fourth experiment confirmed that the lesions disrupted both acquisition and reversal of a conventional orientation discrimination; the deficits again appeared to be due to increased perseveration rather than to shifts in attention.

Medial versus lateral hyperstriatal lesions in pigeons: effects on autoshaping, non-matching-to-sample and spatial discrimination learning at short and long intertrial intervals

Three experiments contrasted the effects of medial and lateral hyperstriatal lesions in pigeons. Expt. 1 found that both types of lesion obtained slower acquisition of autoshaping, compared to unoperated controls. No group differences in maintained rate of autoshaped responding were found. Expt. 2 found that lateral but not medial lesions disrupted choice performance in a non-matching-to-sample (NMTS) task, in which initial preference was for the correct stimulus; birds with lateral lesions responded more slowly to the sample stimulus than did birds with medial lesions. Expt. 3 found that medial but not lateral lesions disrupted both acquisition and reversal of a spatial discrimination at a long, but not at a short intertrial interval (ITI). Medial lesions damage primarily the hyperstriatum accessorium and lateral lesions, the hyperstriatum ventrale; but no significant correlations between the extent of damage to either of these structures and severity of behavioural disruption were obtained. Implications of these findings for theoretical accounts of hyperstriatal involvement in learning processes are discussed.