Impact of stimulus format and reward value on quantity discrimination in capuchin and squirrel monkeys

Quantity discrimination abilities are seen in a diverse range of species with similarities in performance patterns, suggesting common underlying cognitive mechanisms. However, methodological factors that impact performance make it difficult to draw broad phylogenetic comparisons of numerical cognition across studies. For example, some Old World monkeys selected a higher quantity stimulus more frequently when choosing between inedible (pebbles) than edible (food) stimuli. In Experiment 1 we presented brown capuchin (Cebus [Sapajus] paella) and squirrel monkeys (Saimiri sciureus) with the same two-choice quantity discrimination task in three different stimulus conditions: edible, inedible, and edible replaced (in which choice stimuli were food items that stood in for the same quantity of food items that were given as a reward). Unlike Old World monkeys, capuchins selected the higher quantity stimulus more in the edible condition and squirrel monkeys showed generally poor performance across all stimulus types. Performance patterns suggested that differences in subjective reward value might motivate differences in choice behavior between and within species. In Experiment 2 we manipulated the subjective reinforcement value of the reward by varying reward type and delay to reinforcement and found that delay to reinforcement had no impact on choice behavior, while increasing the value of the reward significantly improved performance by both species. The results of this study indicate that species presented with identical tasks may respond differently to methodological factors such as stimulus and reward types, resulting in significant differences in choice behavior that may lead to spurious suggestions of species differences in cognitive abilities.     

Directed forgetting in pigeons

Pigeons performed a version of delayed matching-to-sample in which different postsample cues signaled different trial outcomes. Cues to remember (R cues) signaled the usual comparison stimuli. Cues to forget (F cues) signaled either cancellation of comparison stimuli (comparison-omission) or presentation of a sample-independent discrimination (comparison-substitution). As assessed by occasional probe trials, F cues decreased matching accuracy during comparison-omission more than during comparison-substitution. The loss in accuracy of matching in F-cue probes was directly related to length of delays during comparison-omission but not during comparison-substitution. Because trials generally terminated in reward during comparison-substitution but not during comparison-omission, these findings were interpreted as suggesting the importance of end-of-trial reinforcement for the maintenance of short-term memory.     

Memories of reward events and expectancies of reward events may work in tandem

A common assumption is that expectancies of reward events in instrumental tasks are established on the basis of Pavlovian conditioning. According to the tandem hypothesis, tested in the four runway investigations reported here employing rats, memories of reward events may serve as the conditioned stimuli eliciting expectancies. In Experiments 1–3, rats were trained under a schedule of partial reward (P), which did not produce increased resistance to extinction, and subsequently shifted to consistent reward (C). According to the tandem hypothesis, the shift to the C schedule should result in increased resistance to extinction if, as hypothesized, under the P schedule the memory of reward, S^R, came to elicit the expectancy of nonreward,_EN. This hypothesis was confirmed under a variety of conditions. It was shown that increased resistance to extinction could not be attributed to the P schedule alone, to the rats receiving two schedules, P and C, to stimuli other than S^R eliciting E_N, or to the rats forgetting reward-produced memories when expecting nonreward (Experiment 4). It was shown that the tandem hypothesis could explain the divergent findings obtained in prior studies employing a shift from P to C as well as in the present study.     

Stimulus duration and conditioned reinforcing value measured by a learning-tests procedure

The relationship between the duration of stimuli and their conditioned reinforcing effect was investigated using a learning-tests procedure. In Experiment 1, stimuli were the same duration on training (stimulus → reward) and test (choice response → stimulus). Ten- and 30-sec stimuli provided effective differential conditioned reinforcement but 3-sec stimuli did not. In Experiment 2, different pigeons had each combination of the 3- and 30-sec stimuli on training and test trials. Evidence of conditioned reinforcement was obtained only for the birds with 30-sec stimuli on both training and test. The results were interpreted as indicating that stimuli become effective conditioned reinforcers on test trials only when their duration exceeds the duration of differential short-term memory cues resulting from a difference in the events that precede them on training and test trials.     

An investigation of sex differences on incidental memory for verbal and pictorial material

Previous research has sometimes claimed a female advantage on tasks of incidental memory. However, it is uncertain whether the sex difference was due to the incidental, or to the heavily verbal, nature of the tasks used, since women are known to have better verbal memory than men. The current study asked whether a female superiority would be found under less verbally-loaded conditions. No sex difference was found on two different pictorial tasks, both of which measured incidental memory for the content of complex scenes. In contrast, a female advantage was observed across both incidental and intentional conditions when easily labeled stimuli were used. This advantage was eliminated on the incidental condition when the effects of intentional verbal memory were controlled for. These findings strongly suggest that previous reports of a female advantage on incidental memory may have been due to the choice of verbalizable stimuli.     

延时折扣范式下大学生课堂媒体多任务现象的行为经济分析

为探讨中国大学生课堂媒体多任务行为背后的冲动性机制,采用由经典延时折扣范式改编的课堂假想情景实验考察了101名大学生的课堂发消息行为。拟合分析结果表明大学生课堂发消息行为本质上是一种在即时少量报酬和延迟丰厚报酬间权衡时做出的冲动性的选择。进一步采用曲线下面积辅助分析发现女生比男生更少进行课堂发消息行为,而且女生在有趣课堂中比在枯燥课堂中更少进行课堂发消息行为。文章提供了对于中国大学生课堂媒体多任务行为的行为经济学分析思路。     

Further studies of pigeons’ spatial working memory in the open-field task

In Experiments 1 and 2, pigeons’ spatial working memory in an open-field setting was examined under conditions that differed in terms of working-memory load (number of sites visited prior to a retention test) at various delays between initial choices and the retention test. In Experiment 1, pigeons were tested under two conditions of memory load (three or five sites visited prior to the delay) and two delay intervals (15 and 60 min). Accuracy declined as a function of delay but was not affected significantly by memory load. In Experiment 2A, pigeons were tested under three conditions of memory load (two, four, or six sites visited prior to the delay). In separate phases, the delay was 2, 15, and 60 min. Accuracy was not affected by memory load in any of these phases. In Experiment 2B, three conditions of memory load (two, four, or six sites visited prior to the delay) were tested at two delays (2 and 60 min) within a test phase. Accuracy declined with increasing delay, but memory load again had no significant effects. These results are inconsistent with previous suggestions that pigeons’ retention of spatial information may decline as working-memory load is increased. In Experiment 3, cue-manipulation tests confirmed that pigeons’ choice behavior in the open-field task is controlled by memory for previously visitad room locations.     

Phonological coding and children’s spelling

The goal of this study was to predict children’s spelling from their performance on pseudohomophone choice and rhyme matching tasks. A total of 222 nine- to twelve-year-old children in grades 4, 5, and 6 participated. The children were given, individually, a computerized pseudohomophone choice task with 30 item pairs in two conditions, and a computerized rhyme matching task with 68 word pairs in four conditions. Accuracy and speed of processing were assessed. Three memory tasks, a Spoonerism task, a general ability test, and a written spelling test were also administered. Analyses of variance and multiple regression analyses showed that both accurate and rapid choice of pseudohomophones sounding like real words and rhyme matching contributed substantially to variations in spelling. Orthographic knowledge played a role in spelling as shown by the contribution of word pairs that rhymed but were orthographically dissimilar. Phonological coding as tested by pseudohomophone choice was also important.     

The rat’s long-term preference for complexity in its environment

Locomotor, resting, and feeding responses to four levels of environmental complexity were measured in a two-phase study. In a long-term free-choice testing situation (ad-lib phase), subjects (N = 20) demonstrated a marked preference for high complexity during “day” conditions. This preference, present in the patterns of resting and locomotor behavior, was partially preserved under “night” conditions. The patterns of feeding behavior were essentially independent of complexity preference. The same subjects in the discrete trial phase of the study chose high complexity most often in a four-choice testing situation. The apparent preference for high environmental complexity was interpreted as a shelter/relaxation seeking response elicited by the number or complexity of elements in the complexity area. Complexity seemed to reduce the arousal level of the subject, arguing against current arousal hypotheses which suggest that complex stimuli are attractive because of their arousal-inducing qualities.     

Time and response matching with topographically different responses

Four pigeons were exposed to several nonindependent concurrent variable-interval schedules of reinforcement. One schedule component required a keypecking response; the other component required a treadlepressing response. The birds matched the ratio of their behavior (as measured by responses and time) between the two topographically different responses to the ratio of reinforcement in those two components. When additional foods not contingent on a keypeck or treadle-press were then added, the birds matched time spent in the components to total rates of food delivered in those components; response matching was somewhat disrupted. The matching law, developed under concurrent variable-interval schedules requiring similar responses, can thus account for choice behavior involving topographically different responses.     

Attempts to demonstrate magnetic discrimination by homing pigeons in flight

Eight homing pigeons, trained to fly between two elevated feeders within a flight tunnel, were tested for their ability to discriminate between two magnetic field stimuli and two acoustic stimuli, using a unitary discrete-trials procedure with successive presentation of stimuli. Magnetic stimuli consisted of the ambient magnetic field and a reduced magnetic field in which the vertical component of the field was reduced to 50% of its ambient value. Acoustic stimuli consisted of an ambient white noise and the white noise plus a tone. Stimuli were paired with food reward and either a time penalty (Experiment 1) or electric shock (Experiment 2). Although subjects could discriminate sounds with our procedures, none of the subjects demonstrated discrimination of magnetic fields. The failure of pigeons to discriminate magnetic stimuli is discussed as a consequence of either the failure to provide conditions sufficient for such discrimination or the absence of a magnetic sense in these animals.     

Visual environment and delay affect cache retrieval accuracy in a food-storing rodent

Many scatter-hoarding species use spatial memory to relocate their food caches. Two factors can affect spatial memory: the availability of landmarks in the environment, and the latency between learning and recall. Using a 2 × 2 factorial design, we determined the effect of these factors on cache retrieval accuracy in Merriam’s kangaroo rats (Dipodomys merriami). Kangaroo rats cached seeds in an arena under conditions that varied by retrieval interval (1 or 10 days) and by number of landmarks (0 or 16 landmarks). After 1 day, they recovered equal proportions of caches in both landmark conditions. After 10 days, they recovered more caches in the 16-landmark condition than in the bare condition. This is the first study to show that landmarks are necessary for accurate cache recovery after long delays. This result is consistent with maze studies that have shown that landmarks reduce proactive interference and that delay increases proactive interference.     

Interstimulus interval and viewing time effects in monkey list memory

Two rhesus monkeys were tested in 6- and 10-item list memory tasks for performance changes as a function of the exposure duration of the list stimuli and the interstimulus interval (ISI) between successive list stimuli. Accuracy increased with longer item exposure duration and tended to decrease with longer ISI duration. Humans, by contrast, typically show increases in accuracy with ISI, a result taken as evidence of rehearsal. The decrease in accuracy for monkeys suggests that they were not using rehearsal processes in these list memory experiments. Further tests in which choice accuracy with predictable ISIs was compared with choice accuracy with unpredictable ISIs also yielded no evidence of rehearsal by the monkeys. This apparent absence of rehearsal mechanisms in monkeys, in situations also shown to support human rehearsal, is discussed as a potential difference in the visual working memory processes of the two species.     

The adjustment of goldfish to reduction in magnitude of reward in massed trials

For a group of goldfish trained in a runway under conditions of highly massed practice, reduction in magnitude of reward produced a gradual decline in performance to the level of a small-reward control group but no suggestion of negative successive contrast. These results are consistent with the suggestion that reward plays a somewhat different role in the learning of fish and rats. They also serve to extend the range of conditions under which the stimulus aftereffects of reward come to control the instrumental behavior of fish.     

Spatial localization of a goal: Beacon homing and landmark piloting by rats on a radial maze

We performed six experiments in order to examine the ability of rats to use moving beacons and landmarks as cues to the location of reward on an eight-arm radial maze. In Experiments 1–4, the cues and goals were moved before each trial, and groups in which a single beacon was placed on the rewarded arm, a single landmark indicated that reward was on the arm immediately to the left of a landmark, or two landmarks were placed on each side of the reward arm were compared. The rats rapidly learned to track the reward in the beacon condition, failed to find the reward sooner than chance expectation with a single landmark, and did only slightly better than chance with two landmarks. In Experiments 5 and 6, the rats were trained in five trials per day, with the landmark and goal locations constant over daily rewarded trials, and in two extinction trials that were inserted among the rewarded trials. The rats found the goal arm at substantially better than chance expectancy with both one and two landmarks. Our results, in agreement with data from recent swimming pool experiments (A. D. L. Roberts & Pearce, 1998), show that rats will use the relationship between moving landmarks and a goal in order to find reward.     

Control of pigeons’ keypecking topography by a schedule of alternating food and water reward

Food- and water-deprived pigeons keypecked for food or water reinforcement on alternate trials. Under one condition, explicit stimuli on the key provided information about the trial outcome; under another condition, only the alternation schedule provided this information. Latency and/or response rate differences between food- and water-rewarded trials emerged during both conditions. Response topography also differed on food- and water-rewarded trials. These differences, as revealed by duration and force measurements of the keypeck and by human ratings of the pecking responses as being water- or food-related, were anticipatory in nature. These results not only extend previous work on reward alternation and reward-specific response topographies, but also have implications for theories of animal memory. In particular, these results are amenable to memory models that assume that an animal “codes” information that later must be recalled.     

The acquisition of trace supraordinate stimulus control in pigeons

Match-to-sample and oddity-from-sample problems with four colors were acquired by two pigeons under the supraordinate control of a line tilt superimposed on samples, Since the supraordinate stimulus terminated before the comparison stimuli were presented, accurate matching and oddity performance indicated trace stimulus control as well, The temporal extent of trace control was assessed in one subject by presenting probes—trials without a line tilt on the sample—in which the basis of correct responding was the supraordinate stimulus presented on the previous trial, Trace supraordinate control did not extend between trials, Subsequently, the delay between the termination of the supraordinate stimulus and the presentation of the comparison stimuli was gradually increased within a trial, Both subjects were able to perform matching and oddity over longer delays, and eventually on probe trials, although accuracy decreased, Results were discussed in terms of instructional stimulus control and memory.     

Pigeons’ spatial memory: V. Proactive interference in the delayed matching of key location paradigm occurs only under restricted conditions

In the delayed matching of key location procedure, pigeons must remember the location of the sample key in order to choose correctly between two comparison keys. The deleterious effect of short intertrial intervals on key location matching found in previous studies suggested that pigeons’ short-term spatial memory is affected by proactive interference. However, because a reward expectancy mechanism may account for the intertriai interval effect, additional research aimed at demonstrating proactive interference was warranted. In Experiment 1, matching accuracy did not decline from early to late trials within a session, a finding inconsistent with a proactive interference effect. In Experiment 2, evidence suggestive of proactive interference was found: Matching was more accurate when the locations that served as distractors and as samples were chosen from different sets. However, this effect could have been due to differences in task difficulty, and the results of the two subsequent experiments provided no evidence of proactive interference. In Experiment 3, the distractor on Trialn was either the location that had served as the sample on Trialn ? 1 or one that had been a sample on earlier trials. Matching accuracy was not inferior on the former type of trial. In Experiment 4, the stimuli that served as samples and distractors were taken from sets containing 2, 3, 5, or 9 locations. Matching accuracy was no worse, actually slightly better, with smaller memory set sizes. Overall, these findings suggested that pigeons’ memory for spatial location may be immune to proactive interference. However, when, in Experiment 5, an intratrial manipulation was used, clear evidence of proactive interference was found: Matching accuracy was considerably lower when the sample was preceded by the distractor for that trial than when it was preceded by the sample or by nothing. Possible reasons why interference was produced by intratrial but not intertrial manipulations are discussed, as are implications of these data for models of pigeons’ short-term spatial memory.     

Overcoming response bias using symbolic representations of number by chimpanzees (Pan troglodytes)

We previously reported that chimpanzees were unable to optimally select the smaller of two candy arrays in order to receive a larger reward. When Arabic numerals were substituted for the candy arrays, animals who had had prior training with numerical symbols showed an immediate and significant improvement in performance and were able to select reliably the smaller numeric representation in order to obtain a larger reward. Poor performance with candy arrays was interpreted as reflecting a response bias toward the intrinsic incentive and/or perceptual features of the larger array. In contrast, the Arabic numerals represent numerosity symbolically and appear to promote response choice on the basis of abstract processing of numerosity, with minimal interference from the inherent properties of the choice stimuli. The present study tested the hypothesis that, for mixed symbol-candy choice pairs, the requisite processing of the abstract numeral may foster a mode of numerical judgment that diminishes the interfering incentive/perceptual effects of the candy stimuli. The results were consistent with this hypothesis. Whereas performance on candy-candy arrays was significantly below chance levels, performance on numeral-candy choice pairs was significantly above chance and comparable with performance on numeral-numeral pairs.     

Effects of signaled retention intervals on pigeon short-term memory

In three delayed matching-to-sample experiments, pigeons were given distinctive stimuli that were either correlated or uncorrelated with the scheduled retention intervals. Experiment 1 employed a single-key, go/no-go matching procedure with colors as the sample and test stimuli; lines of differing orientations signaled short or long delays for one group, whereas the lines and the delays were uncorrelated for the other group. The function relating discriminative test performance to delay length was steeper in the correlated group than in the uncorrelated group. In addition, the line orientation stimuli controlled differential rates of sample responding in the correlated group, but not in the uncorrelated group. In Experiment 2, subjects extensively trained with correlated line orientations were exposed to reversed cues on probe trials. Miscuing decreased discriminative test responding at the short delay, but enhanced it at the long delay. As in the correlated group of the first experiment, rates of sample keypecking were higher in the presence of the “short” time tag than in the presence of the ”long” time tag. Experiment 3 used a three-key choice-matching procedure and a within-subjects design, and equated reinforcement rate at the short and long delays. When auditory stimuli were correlated with delay length, the function relating choice accuracy to delay was steeper than when the stimuli and the delays were uncorrelated. The consistent effects of signaled retention intervals on memory performance may be understood in terms of differential attention to the sample stimuli.