A Simon Effect in Pigeons.

Pigeons pecked left versus right keys contingent upon the color presented at 1 of those locations. Spatial-response latencies were shorter when the color appeared at the same location as the required response than at the opposite location. This Simon effect occurred when the stimulus on the alternative key was constant, varied from trial to trial, or changed when the color cue appeared and when the reinforcement probability for correct responses was the same on corresponding as on noncorresponding trials. Humans performing the same task by touching the keys also showed the Simon effect. These findings demonstrate that for pigeons, too, a relevant symbolic cue activates a spatial code that produces faster responses at the location corresponding with the activated code. (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)     

Transfer across delayed discriminations: Evidence regarding the nature of prospective working memory.

Pigeons were trained successively either on 2 delayed simple discriminations or on a delayed simple discrimination followed by delayed matching-to-sample. During subsequent transfer tests, the initial stimuli from the 1st task were substituted for those in the 2nd. Performances transferred immediately if both sets of initial stimuli had been associated with the presence vs absence of food on their respective retention tests, and the direction of transfer (positive or negative) depended on whether the substitution involved stimuli with identical or different outcome associates. No transfer was found, however, when the initial stimuli were associated with different patterns of responding but food occurred at the end of every trial. These results are consistent with outcome expectancy mediation but are incompatible with response intention and retrospective coding accounts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control by sample location in pigeons'' matching to sample

Ultrastructural characteristics of 15 strains and isolates of ehrlichiae belonging to three genogroups, or clades of genetically related organisms united in the genera Ehrlichia, Cowdria, Anaplasma, Neorickettsia and a strain of Wolbachia pipientis which represents a fourth genogroup in this cluster of species, were studied in continuous cell culture or in vivo: E. canis (Oklahoma strain and VHE isolate), E. muris (AS 145), E. chaffeensis (Arkansas, 91HE17 and Sapulpa), human granulocytic ehrlichiae (HGE)(BDS, 96HE27, 96HE37, #54, #55 and #72), E. equi (MRK), E. sennetsu (Miyayama), E. risticii (HRC-IL). Wolbachia pipientis was studied in the naturally infected Aedes albopictus mosquito cell line Aa23. All organisms were similar in the normal ultrastructure of individual cells and in the ability to form abnormal, pathological ehrlichial cells of the same type irrespective of the species. Normally all ehrlichiae studied in cell culture existed in two morphological forms - reticulate and dense-cored cells, both of which could divide by binary fission. Most alterations were related to their membranes, especially the cell wall. Differences in the structure of intravacuolar microcolonies (morulae) of ehrlichiae and their inter-relations with the host cells allowed differentiation of the genogroups: the E. canis-E. chaffeensis-E. muris genogroup formed large morulae, with many ehrlichiae, often suspended in a fibrillar matrix, and the host cell mitochondria and endoplasmic reticulum usually aggregated near the morulae and were in contact with the morula membrane; the E. phagocytophila-E. equi-HGE group morulae had no fibrillar matrix, no contacts with host cell mitochodria, and they did not aggregate around the morulae; E. sennetsu-E. risticii group usually developed in small individual vacuoles that did not fuse with each other and divided along with the ehrlichiae.     

On the relationship between differential outcomes and differential sample responding in matching-to-sample.

Four experiments involving 24 experimental pigeons and 24 experimentally naive pigeons examined control over choice by differential sample responding in matching-to-sample with differential outcomes. In Exp 1, Ss initially learned to match with food vs no-food outcomes. Their performances later transferred to other samples to which responding vs not responding had been explicitly reinforced with a single outcome (food). In Exp 2, Ss initially learned to produce the comparisons by pecking 1 sample but not the other. Transfer was then observed to new samples associated with food vs no food (and thus often vs seldomly pecked). Exps 3 and 4 showed that transfer of matching required differential behavior to each sample set and did not depend on explicit conditioning of that behavior prior to acquisition. Results show that differential sample behavior provides a redundant cue for choice in differential outcome matching-to-sample. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer across delayed discriminations: II. Differences in the substitutability of initial versus test stimuli.

In 2 experiments, pigeons were trained on, and then transferred to, delayed simple discriminations in which the initial stimuli signalled reinforcement versus extinction following a retention interval. Experiment 1 showed that discriminative responding on the retention test transferred to novel test stimuli that had appeared in another delayed simple discrimination but not to stimuli having the same reinforcement history off-baseline. By contrast, Experiment 2 showed that performances transferred to novel initial stimuli whether they had been trained on-baseline or off-baseline. These results suggest that the test stimuli in delayed simple discriminations acquire control over responding only in the memory task itself. On the other hand, control by the initial stimuli, if coded as outcome expectancies, does not require such task-specific training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Assessing the contributions of S–O and R–O associations to differential-outcome matching through outcome reversals.

Pigeons were trained on symbolic matching with 2 samples, 2 pairs of comparisons, and different outcomes for the correct responses within each comparison pair. For one group, the 2 samples were also associated with different outcomes, whereas for another group, they were not. When the response–outcome (R–O) relations for one pair were subsequently reversed, the group trained with differential sample–outcome (S–O) associations was significantly disrupted in its performance on both reversed- and nonreversed-outcome trials. By contrast, the group trained with just differential R–O associations was disrupted only on reversed-outcome trials. These results were replicated when the outcomes on the initially nonreversed trials were then reversed. The findings indicate that differential S–O associations, when present, have a stronger influence on matching performances than differential R–O associations. They are also consistent with hierarchical and configural models of discriminative control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

When discrimination fails (or at least falters).

Pigeons learned 2 concurrent simultaneous discriminations in which the pecking of left keys versus right keys was reinforced depending on a color that appeared on one of the keys. When the reinforced choice was to peck directly at the color, accuracy was very high initially, but dropped noticeably with continued training. Partial reinforcement of these choices exacerbated the dropoff, sometimes causing accuracies to fall close to zero. By contrast, when the reinforced choice was to peck the alternate-key stimulus, accuracy was very low, initially, but remained high and stable following acquisition. Lowering the reinforcement probability, even to zero, for the latter choices had little effect on their accuracy but yielded increased accuracy on color-choice trials. These results resemble the ambiguous-cue effect and suggest the process of value transfer. (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)     

Evidence for common coding in many-to-one matching: Retention, intertrial interference, and transfer.

Two experiments indicated that pigeons commonly code samples associated with same comparison in many-to-one matching. Experiment 1 showed that retention was similar for pigeons matching four sample stimuli (two hues and two lines) to a different pair of comparisons (hues or lines). Accuracy was slightly higher with hue than with line samples, but this did not interact with delay. Alternative samples from each dimension and associatively different samples from the different dimensions both produced intertrial interference. In Experiment 2, pigeons learned new comparison associations to two samples from a prior many-to-one task. Later, their ability to match the remaining samples to the new comparisons was tested. Positive transfer occurred when samples previously paired with the same comparison replaced one another. Negative transfer occurred when opposing samples were interchanged. Apparently, the associatively related samples in many-to-one matching evoke similar representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)