Role of differential sample responding in the differential outcomes effect involving delayed matching by pigeons.

The role of differential sample responding in the differential outcomes effect was examined. In Exp 1, pigeons were trained on a one-to-many matching task with differential sample responding required. Differential outcomes were associated with samples and comparisons, with comparisons only, or with neither samples nor comparisons. Slopes of delay functions for trials with pecked versus nonpecked samples suggested use of a single-code-default strategy in the nondifferential-outcomes group but not in the differential-outcomes groups. In Exp 2, differential sample responding and differential outcomes were manipulated independently. Again, there were significant differences in the relative slopes of the delay functions. Results suggest that differential outcomes exert their effect independently of differential sample responding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrospective coding in pigeons' delayed matching-to-sample.

In Exp I, 2 groups of 6 White Carneaux pigeons initially learned 0-delay matching-to-sample with identical comparison stimuli (vertical and horizontal lines) but with different sample stimuli (red and green hues or vertical and horizontal lines). Longer delays were then introduced between sample offset and comparison onset to assess whether Ss were prospectively coding the same events (the correct line comparisons) or retrospectively coding different events (their respective sample stimuli). The hue-sample group matched more accurately and showed a slower rate of forgetting than the line-sample group. In Exp II, 20 mixed-breed pigeons were trained (1) with either hues or lines as both sample and comparison stimuli or (2) with hue samples and line comparisons or vice versa. Subsequent delay tests revealed that the hue-sample groups remembered more accurately and generally showed slower rates of forgetting than the line-sample groups. Comparison dimension had little or no effect on performance. Data suggest that pigeons retrospectively code the samples in delayed matching-to-sample. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhancement of matching acquisition by differential comparison-outcome associations.

Two experiments investigated whether differential outcomes in matching-to-sample (MTS) would enhance acquisition even in cases in which the outcomes could not be anticipated at the beginning of a trial. In Exp 1, food and no-food outcomes were differential with respect to both hue and line comparisons in one-to-many MTS but were nondifferential with respect to samples. Overall acquisition and acquisition with each comparison set were faster in relation to controls that received each outcome equally often on all trials. In Exp 2, hue and line comparisons were associated with either different probabilities of food (p?=?1.0 vs 0.2) or with the same probability (p?=?.6). Again, matching acquisition was more rapid in the differential group. These data demonstrate that differential comparison-outcome associations are sufficient to enhance conditional discrimination learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control of Matching by Differential Outcome Expectancies in the Absence of Differential Sample-Outcome Associations: A serial compound view.

In this study, pigeons learned 2 separate one-to-many conditional discriminations in which they matched form samples to line and hue comparisons. Correct choices within each comparison dimension yielded differential (food vs. no-food) outcomes that were not predictable from the samples alone. At asymptote, latency to make a correct choice was shorter when food was the contingent outcome than when no food was the outcome. More important, when the samples from each task were subsequently exchanged, comparison choice varied systematically as a function of the sample and the set of new comparison alternatives that followed them. Together, these results indicate that choices were cued by differential outcome expectancies arising from serial compounds consisting of each sample and the dimensional characteristics of the comparisons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquired equivalence and distinctiveness in matching to sample by pigeons: Mediation by reinforcer-specific expectancies.

Assessed the ability of a reinforcer to mediate an association between 2 stimuli that independently predict the occurrence of that reinforcer (acquired equivalence of cues). In Exp I, 12 male White Carneaux pigeons were trained on shape (plus and circle) and color (red and green) matching-to-sample tasks. Correct responses were systematically reinforced with corn on some trials and wheat on others to establish associations between 1 stimulus from each task and a "common" outcome. Following training, Ss were transferred to a symbolic matching-to-sample task wherein a stimulus from one training task was presented as the sample, and the stimuli from the other training task were presented as comparisons. In the 1st session, experimental Ss made significantly more correct responses than controls (i.e., Ss "matched" stimuli previously associated with a common outcome). Exp II with 18 Ss replicated this acquired equivalence effect and controlled for food preference. Delayed matching-to-sample training demonstrated enhanced memory performance for Ss exposed to different reinforcement contingencies, but this effect was confined to the shape task. Results indicate that a reinforcer can serve as the basis for organizing otherwise unpaired predictive cues in memory and that animals will selectively use differential expectancies as cues for solving complex discrimination tasks, depending on the difficulty of the discrimination. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the role of differential sample behaviors in matching-to-sample.

In 3 experiments, 8 White Carneaux pigeons were trained on matching-to-sample (MTS) with differential sample-response requirements (SRRs) that were identical with respect to 2 pairs of sample stimuli but either correlated or uncorrelated with correct choice. Ss in the uncorrelated condition were slower to reach criterion levels of accuracy than Ss in the correlated condition in spite of their equivalent sample discriminations. However, correlated Ss were more disrupted in their matching performances than the uncorrelated Ss when subsequently switched to nondifferential SRRs. Differential sample behaviors (DSBs) also generated higher levels of accuracy on delayed MTS when correlated with choice, and accuracy in this condition did not differ as a function of whether the samples were hues or lines. However, sample dimension did affect memory performance in the uncorrelated condition. Reversing differential SRRs for 1 pair of samples substantially reduced matching accuracy in the correlated group but had almost no effect in the uncorrelated group. Findings demonstrate that DSBs directly control pigeons' matching performances and also overshadow conditional stimulus control by the samples when these behaviors are predictive of correct choice. The facilitation in matching produced by DSBs apparently arises from the additional cue these behaviors provide. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Matching to element and compound samples in pigeons: The role of sample coding.

Pigeons initially trained to match using element samples and element comparisons demonstrate reduced matching accuracy on trials in which the sample is a compound stimulus. Two interpretations of this phenomenon, the shared attention account and the coding decrement account, were assessed in 3 experiments with 8 Silver King pigeons. Exp I obtained the typical outcome of reduced matching accuracy to compound samples following training to match to element samples. However, in a 2nd group trained initially to match to compound samples, Ss matched more accurately on compound sample trials than on element sample trials. Sample duration was manipulated in Exp II, and Ss were tested on simultaneous and 0-sec delayed matching trials in Exp III. Neither manipulation influenced the magnitude of the element–compound difference in either group. It is concluded that the coding decrement interpretation best accounts for these and other findings on matching to element and compound samples in pigeons. This account holds that (a) pigeons do not decompose compound samples; (b) presentation of a familiar sample activates a code; and (c) a novel sample that is sufficiently similar to a sample that activates a code will also tend to activate that code. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial memory in pigeons on the radial maze.

A series of 7 experiments with 10 pigeons showed, contrary to recent suggestions that pigeons show little or no spatial memory on the radial maze, highly accurate performance by Ss on an 8-arm radial maze. In Exp I, Ss were trained on successive phases that raised the number of alleys to be remembered from 1 to 4. In Exp II, Ss were allowed to search the maze for food with all 8 arms open. Measures of spatial memory showed that Ss performed at a level equivalent to that found with rats in previous research by A. B. Bond et al (see record 1982-25052-001). In Exp III, testing with massed trials revealed proactive interference. Ss were able to form reference memory for subsets of baited and unbaited alleys in Exp VI. In Exp VII, Ss learned about quantities of food associated with 4 different alleys and ordered their alley choices from the largest to the smallest reward. Contrary to the previous findings with rats, Ss in Exp IV showed forgetting over retention intervals of 0–360 sec between forced and free choices. It is concluded that spatial memory in pigeons generally shows the same properties as that in rats. (49 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Associative processes in differential outcome discriminations.

This study assessed the role of stimulus–outcome (S–O) and response–outcome (R–O) associations in differential outcome performances. In Experiment 1, pigeons learned one-to-many matching-to-sample with differential R–O associations but with either differential or nondifferential sample-outcome (S–O) associations. Later, both groups showed strong transfer of matching to novel samples that were differentially associated with the same outcomes used in training. Experiment 2 reversed the training conditions for each group. The switch from differential to nondifferential S–O associations produced a large drop in matching accuracy, whereas the opposite switch had only a small effect. Following recovery, both groups again showed positive transfer to novel samples, although transfer was stronger following differential S–O training. These data support a 2-process ("outcome expectancy") account of differential outcome performances but also indicate a contribution of bidirectional R–O associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Further tests of response–outcome associations in differential-outcome matching-to-sample.

Two transfer-of-control experiments assessed pigeons' sensitivity to response-outcome associations in differential-outcome discriminations. In Experiment 1, pigeons were trained on one-to-many matching-to-sample with food and no-food outcomes that were differential or nondifferential with respect to correct choice. The samples were then replaced by novel stimuli that had differential or nondifferential associations with those same outcomes. Transfer of matching occurred only when the novel samples and their respective choice responses had identical differential-outcome associations. Experiment 2 showed that the outcomes themselves were effective samples if the choices they cued yielded those outcomes in training. These data provide further evidence that the relations between comparison choice and consequent outcomes influences pigeons' matching performances. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential effects in pigeon delayed matching-to-sample performance.

Five pigeons were tested in a 3-alternative delayed matching-to-sample task in which 2nd choices were permitted following 1st-choice errors. Sequences of responses both within and between trials were examined in 3 experiments. In Exp I, the sample information contained in 1st-choice errors was not sufficient to account for the observed pattern of 2nd choices. This implies that 2nd choices following 1st-choice errors are based on a 2nd examination of the contents of working memory. Proactive interference was found in Exp II in the form of a dependency, beyond that expected on the basis of trial-independent response bias, of 1st-choices from 1 trial on the 1st-choice emitted on the previous trial. Samples from the previous trial did not exert a significant influence on later trials. The magnitude of the intertrial association (Exp III) did not depend on the duration of the intertrial interval. In contrast, longer intertrial intervals and longer sample durations facilitated choice accuracy by strengthening the association between current samples and choices. Results are incompatible with a trace-decay and completion model; they suggest that multiple influences act simultaneously and independently to control delayed matching-to-sample responding. These influences include memory for the choice occurring on the previous trial, memory for the sample, and general effects of trial spacing. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of stimulus compounds by pigeons.

Used a matching-to-sample (MTS) procedure to investigate short-term memory for compound visual stimuli in 10 mixed-breed pigeons. In Exp I, a symbolic MTS procedure was used. Three Ss were trained to match element samples, and 3 were trained to match compound samples. Findings indicate that the compound-trained group did not learn to match the compound samples in terms of element matching rules but rather processed them as unitary events. In Exp II, Ss were trained to match either element or compound samples in a true MTS task. Both groups were able to match elements and compounds in the transfer test. Findings show that at least some compound stimuli were represented in a unitary, nonanalytic fashion until the S was exposed to the elements of the compound in isolation from the compound. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Food searching strategies of rats: Variables affecting the relative strength of stay and shift strategies.

Examined the extent to which the food searching strategies of rats are influenced by training, information about food in an initially visited site, and type of memory required for correct choices. Exp I used a discrete-trial, delayed conditional-discrimination procedure on a T-maze with 32 male Sprague-Dawley rats. Ss entered 1 arm of the maze and were given a choice between that arm (stay strategy) or the other arm (shift strategy). During the initial visit, S either consumed all the food (depletion condition) or only some of it (nondepletion condition). Ss given the shift-depletion task learned most rapidly; those given the stay-depletion task learned most slowly. Depletion increased the rate at which the shift discrimination was learned but decreased the rate at which the stay discrimination was learned. Exp II used a similar procedure with the Maier 3-table maze and 16 male albino rats; the same pattern of results was found. Exp III, conducted with 15 male Sprague-Dawley rats, required each S to learn both a win-stay and a lose-shift contingency and to use associative memory. Early in training, Ss used only a shift strategy but eventually learned the discrimination. Results indicate that the shift-stay balance is influenced by the rat's species-specific predisposition, reinforcement contingencies, amount of food in the initially visited place, and the extent to which recognition memory by itself is sufficient to solve the discrimination. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned helplessness and immunization: Sensitivity to response–reinforcer independence in immunized rats.

Exps I and II, with 62 male Holtzman rats, examined the learned helplessness and immunization effects using a test in which appetitive responding was extinguished by delivering noncontingent reinforcers. Contrary to learned helplessness theory, "immunized" Ss showed performance virtually identical to that of Ss exposed only to inescapable shock and different from that of nonshock controls. Exp II suggested that the helplessness effect and the lack of immunization were not due to direct response suppression resulting from shock. In Exp III, in which the immunization effect was assessed in 28 Ss by measuring the acquisition of a response to obtain food when there was a positive response–reinforcer contingency, immunization was observed. Results cannot be explained on the basis of proactive interference and instead suggest that Ss exposed to the immunization procedure acquired an expectancy of response–reinforcer independence during inescapable shock. Thus, immunization effects may reflect the differential expression of expectancies rather than their differential acquisition as learned helplessness theory postulates. (55 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

One-trial associative memory in black-capped chickadees.

Black-capped chickadees (Parus atricapillus), birds that store food, inspected feeders in an aviary (1 of which was baited) and returned after a 5-min retention interval to consume the then-hidden food. In Exp 1, Ss quickly learned this task but only if different feeders were used on each trial. In Exp 2, memory for the baited feeder decayed substantially after 24 hrs but not after 30 min. In Exps 3 and 4, there were 4 alternatives to the baited feeder. Ss performed better than chance from the beginning of these experiments. When Ss made errors on their 1st choice, Ss performed better than chance on their 2nd choice. Exp 4 tested the notion that increasing the cost of inspecting the feeders would reduce errors; however, this did not improve performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorical shape and color coding by pigeons.

Two studies with 32 pigeons assessed the categorical coding of shapes and the existence of a higher-order color category (all colors). Ss were trained on 2 independent tasks (matching-to-sample and oddity-from-sample). One task involved red and a plus sign, the other a circle and green. On test trials, 1 of the 2 comparison stimuli from one task was replaced by one of the stimuli from the other task. Differential performance based on which of the 2 stimuli from the other task was introduced suggested categorical coding rules. In Exp I, evidence for the categorical coding of sample shapes was found. Categorical color coding was also found; however, it was the comparison stimuli rather than the samples that were categorically coded. Exp II replicated the categorical shape sample effect and ruled out the possibility that the particular colors used were responsible for the categorical coding of comparison stimuli. Results support the view that pigeons can develop categorical rules involving shapes and colors and that the color categories can be hierarchical. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial delayed matching-to-sample performance by rats: Learning, memory, and proactive interference.

Nine Sprague-Dawley rats were trained in a 3-alternative delayed matching-to-sample task in which the samples were rewarded forced choices of 1 arm of a 3-arm starburst maze, and retention was indicated by returning to that arm following a delay or retention interval. If the S made an error on its 1st free choice of a trial, the chosen arm was blocked off, and the S was allowed a 2nd choice between the remaining 2 arms. Ss quickly acquired this task. Exp II showed that choice accuracy was lower with 1-min retention intervals than with immediate tests. In Exp III, there was evidence for 2 separable proactive interference effects. The degree to which prior events influenced responding decreased as the intertrial interval increased. Choice accuracy improved with increasing intertrial interval and declined with increasing retention interval durations. Additionally, choice accuracy was higher when the sample from the previous trial matched the sample from the current trial and lower when they did not match. These results suggest that encoding information about visited spatial locations is a gradual process rather than an all-or-none process in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeon visual memory capacity.

Four experiments examined visual memory capacity in 13 White Carneaux pigeons. In Exp I, Ss learned to discriminate between 80 pairs of random shapes. Memory for 40 of those pairs was only slightly poorer following 490 days without exposure. In Exp II, 80 pairs of photographic slides were learned; 629 days without exposure did not significantly disrupt memory. In Exp III, 160 pairs of slides were learned; 731 days without exposure did not significantly disrupt memory. In the final experiment, Ss learned to respond appropriately to 40 pairs of slides in the normal orientation and to respond in the opposite way when the slides were left–right reversed. After an interval of 751 days, there was a transient disruption in discrimination. These experiments demonstrate that pigeons have a heretofore unsuspected capacity with regard to both breadth and stability of memory for abstract stimuli and pictures. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Active avoidance behavior following archistriatal lesions in pigeons.

Exp I examined the performance of 10 pigeons, 5 with bilateral medial archistriatal lesions and 5 sham-operated controls, in the acquisition and maintenance of a discrete-trial treadle-press avoidance response. The archistriatal Ss had longer response latencies and never attained the level of performance achieved by the controls. In Exp II, 8 pigeons learned a treadle-press response to avoid or escape shock on a signaled free-operant schedule. After 17 daily sessions, 4 Ss received bilateral lesions in the medial archistiatum, and 4 received control lesions in the neostriatum. After recovery from surgery, all Ss were returned to the experimental procedure. Avoidance of those Ss with archistriatal lesions was impaired relative to the postoperative level while that of the control group was unchanged. Results are interpreted in the light of earlier experiments showing reduced escape and avoidance behavior both in other avian species and in mammals with lesions in the amygdala, to which the archistriatum is considered homologous. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distinction between places and paths in rats' spatial representations.

Rats were trained on a 3-dimensional, 4-arm radial maze. In Exp 1, Ss trained to climb to the single goal platform chose fewer novel routes to the goal than Ss trained to climb to the 4 spatially distinct platforms. In Exp 2, a reinforcement contingency was imposed, requiring a novel route choice on each trial to receive reinforcement. Learning to associate route choice with reinforcement outcome was much more difficult for Ss tested with the single goal than for Ss tested with the 4 distinct goals. In Exp 3, a partitioned central platform group learned the reinforcement contingency as quickly as the Ss given 4 spatially distinct platforms. In Exp 4, distinctive floor inserts did not affect performance relative to no inserts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)