Donald A. Riley

Flexible Memory Processing by Rats: Use of Prospective and Retrospective Information in the Radial Maze

Four experiments investigated the content of the memory used by rats in mediating retention intervals interpolated during performance in a 12-arm radial maze. The delay occurred following either the 2nd, 4th, 6th, 8th, or 10th choice. A 15-min delay had the greatest disruptive effect when interpolated in the middle of the choice sequence and less of an effect when it occurred either earlier or later. This pattern of results was obtained when either a free- or forced-choice procedure was used prior to the delay and regardless of whether postdelay testing consisted of completion of the maze or two-alternative forced-choice tests. Assuming that the disruptive effect of a delay is a function of memory load, this implies that the rats used information about previously visited arms (retrospective memory) following an earlier interpolated delay but information about anticipated choices (prospective memory) following a delay interpolated late in the choice sequence. There appeared to be a recency effect only in the early and middle delay conditions. This provides converging evidence for the dual-code hypothesis. No evidence for prospective memory was obtained following a 60-min delay.

The role of test stimuli in matching to compound samples by pigeons

Two pigeons matched to sample in a three-key operant conditioning chamber. In Experiment I, two different kinds of samples were presented on the center key.Element samples were members of one of two sample sets — colors (a red or blue disk) or lines (a vertical or horizontal orientation of a set of white lines). These samples were followed by their respective sample sets on the side keys as comparison stimuli.Compound samples consisted of a set of lines superimposed on a colored disk. Following these samples, either sample set could appear as comparison stimuli. Matching to compound samples was less accurate than matching to element samples. One interpretation is that sharing of attention among elements of a compound sample weakened stimulus control by each element. A different interpretation is that an element sample controlled matching better because it was physically identical to a comparison stimulus whereas a compound sample was not. Experiments II–IV evaluated this “generalization decrement” alternative by testing element- vs. compound sample control with both element and compound comparison stimuli. Irrelevant elements were added to form compound comparison stimuli, some of which were physically identical to a preceding compound sample, but never identical to an element sample. In all experiments, the addition of irrelevant elements of comparison stimuli reduced sample control. However, the generalization decrement hypothesis failed to predict how differences in performance maintained by element and compound samples were affected by different tests of sample control. Matching accuracy appeared to be independently determined by the number of elements in a sample and whether irrelevant elements were present during tests of sample control.

Spatial and configural factors in compound stimulus processing by pigeons

Three matching-to-sample experiments examined whether spatial or configural factors determined how the element arrangement of compound sample stimuli influenced matching accuracy in pigeons. Seven types of compound stimuli were tested. The arrangement of color and line-orientation elements in these compounds varied in terms of the spatial separation between the elements, the degree of consistency in element spatial location, and the number of bounded areas containing the elements. Matching accuracy was examined upon initial exposure to the compounds, during asymptotic conditions of shared attention, and with variation of sample durations ranging from .04 to 5.935 sec. In all three experiments, when spatial proximity, locational certainty, and the number of lines were precisely controlled or equated, no evidence for the proposed configural processing of “unified” compounds was found (Lamb & Riley, 1981). Element spatial separation, and to a lesser degree perceptual limitations, determined compound performance. These results question our lab’s previous evidence for configural compound processing by pigeons (Lamb, 1988; Lamb & Riley, 1981). They suggest instead that pigeons independently and separately process the individual elements of color/line-orientation compounds, with element separation determining the distribution of processing between the elements.

Colour changes of Octopus rubescens during attacks on unconditioned and conditioned stimuli

Abstract Octopus rubescens exhibits a sequence of skin colour changes when it attacks and captures prey. These displays were observed during attacks on (1) free-swimming crabs, (2) crabs of different sizes impaled on thin rods, and (3) positive and negative discriminative stimuli. Animals were housed separately in light-blue aquaria which also served as experimental apparatuses. Animals in each condition showed the same typical sequence of colour displays. This sequence is (1) before detection of crab: various colours, (2) on detection and during a free-swimming attack: colours ranging from light orange to grey, (3) on landing: colourless and nearly transparent, (4) on seizing the crab: spotted or mottled, and (5) afterward: various colours. The colour changes may be tied to locomotor acts and postural adjustments.

Selective Attention in Animal Discrimination Learning

Abstract The traditional approach to the study of selective attention in animal discrimination learning has been to ask if animals are capable of the central selective processing of stimuli, such that certain aspects of the discriminative stimuli are partially or wholly ignored while their relationships to each other, or other relevant stimuli, are processed. A notable characteristic of this research has been that procedures involve the acquisition of discriminations, and the issue of concern is whether learning is selectively determined by the stimulus dimension defined by the discriminative stimuli. Although there is support for this kind of selective attention, in many cases, simpler nonattentional accounts are sufficient to explain the results. An alternative approach involves procedures more similar to those used in human information-processing research. When selective attention is studied in humans, it generally involves the steady state performance of tasks for which there is limited time allowed for stimulus input and a relatively large amount of relevant information to be processed; thus, attention must be selective or divided. When this approach is applied to animals and alternative accounts have been ruled out, stronger evidence for selective or divided attention in animals has been found. Similar processes are thought to be involved when animals search more natural environments for targets. Finally, an attempt is made to distinguish these top-down attentional processes from more automatic preattentional processes that have been studied in humans and other animals.

A Classification and Analysis of Short-Term Retention Codes in Pigeons1

Publisher Summary This chapter examined three alternative hypotheses about the nature of the code that exists between a sample stimulus and a response in simple conditional discrimination experiments. Each of the three types of codes considered mediate between the sample and the response to test under some conditions. Observation of conditional discrimination performance is not sufficient to determine the type of code which is occurring. Evidence comes from experiments where (1) the situation is arranged so that the different possible types of codes refer to discriminably different properties such as when sample stimuli are colors and test stimuli are line orientations; and (2) the situation is arranged so that error patterns or other response measures that are sensitive to interference or facilitation can be used, and the effects of operations known to influence one code but not another can be analyzed. Sample code may be unified with more than one attribute represented in a single code, or multiple sample attributes may be coded separately. Codes may or may not include information concerning the appropriate response.

The Logic of Species Comparisons

The purpose of this symposium was to address how the field of comparative animal cognition might best advance (Hulse, this issue). The diversity and excellence of the symposium papers are testimony to the proposition that the field is a thriving enterprise. All the participants, including the authors of this symposium summary, agree that species comparisons are important to the study of cognitive psychology, but on issues related to the purposes of, and specific strategies for, making comparisons, there is disagreement. Table I gives a summary of each participants research, including species studied and critical issues raised. To sharpen thinking about issues facing the field, we have chosen to emphasize the differences between participants by dividing them into two groups in the table: the generalists and the ecologists.

Limited capacity information processing and pigeon matching-to-sample: Testing alternative hypotheses

The limited capacity hypothesis explains the element superiority effect observed in pigeons’ element-compound matching-to-sample performance as the result of a central information processing overload occurring at the time of sample exposure. Major alternative hypotheses offered in the literature to date argue that element superiority is due to a difference in element- and compound-sample memory codes or to a peripheral sensory limitation during sample exposure. These alternative factors weresimultaneously prevented from influencing matching performance in the present experiment, but the element superiority effect remained. A central information processing account of the element superiority effect is supported by the strong tests of alternative hypotheses provided herein. The discussion addresses remaining challenges to the hypothesis that information overload for compound samples occurs at the time of sample exposure.

Evidence for a shift in the choice criterion of rats in a 12-arm radial maze

Rats were trained in a standard 12-arm radial maze task. Following training, each trial consisted of a sequence of 2, 4, 6, 8, or 10 choices, followed by a 15-min delay, which then was followed by a choice between a single arm and a response manipulandum mounted in the center of the maze. An arm visit was reinforced if the arm had not been visited prior to the delay, whereas a manipulandum response was reinforced if the arm had been visited. It was found that rats are relatively more likely to reject arms by responding to the manipulandum following a delay occurring late in the choice sequence. This indicates that the choice criterion used by rats in the radial maze becomes more strict as the choice sequence progresses. Such a process provides an alternative explanation for some of the data recently reported by Cook, Brown, and Riley (1985).

The relation between response and attentional shifts in pigeon compound matching-to-sample performance

Pigeons’ pecks to the two elements of spatially separated compound samples were observed during matching-to-sample performance. An attentional biasing procedure was used in which the birds were tested on a subset of the information contained in the sample (either one of the two dimensions or one of the two sample key locations) for a large number of sessions. This procedure resulted in a greater proportion of sample pecks to the positively biased (tested during biasing) sample attribute. Increases in accuracy on the positively biased attribute as well as decreases in accuracy on the negatively biased (not tested during biasing) attribute were also found. However, not all of the shifts in matching accuracy could be explained by the shifts in pecking behavior.