Attention, the presolution period, and choice accuracy in pigeons

Six pigeons were trained first on a color then on a form discrimination; four other pigeons were trained first on form and then on color. One of two colors or one of two forms (sample stimuli) appeared in the center of a touch sensitive monitor for 5 pigeons and in the center and in 16 other locations for 5 other pigeons. A peck anywhere within the region in which the sample stimuli appeared produced two white disks (comparison stimuli), one on the left and one on the lower right corners of the screen. Correct left-right choices provided food. Although of no consequence, the location of pecks in presence of the sample was predictive of the pigeon's subsequent choice. Accuracy, choice of the correct comparison stimulus, was greater when the sample stimuli appeared in the center as well as 16 other locations than when it appeared only in the center. The presolution period, the period of chance accuracy prior to evidence of discrimination learning, was decreased on each task following training on the other task. This evidence of facilitation following an extra-dimensional shift was attributed to continued relevance of the conditions under which the first task was learned. The duration of the presolution period was inversely related to asymptotic accuracy-data accounted for by Heinemann's (1983) theory of information processing during the presolution period.     

Matching-to-sample by pigeons: the dissociation of comparison choice frequency from the probability of reinforcement

It has been proposed that comparison choice in matching-to-sample should depend on two factors, the relative probability of reinforcement associated with each of the comparison stimuli and the conditional probability of each comparison stimulus being correct given presentation of one of the samples. DiGian and Zentall [DiGian, K.A., Zentall, T.R., 2007. Matching-to-sample in pigeons: in the absence of sample memory, sample frequency is a better predictor of comparison choice than the probability of reinforcement for comparison choice. Learn Behav. 35, 242-261] have shown that sample frequency together with the probability of choosing each of the comparison stimuli in training can influence comparison choice when delays are introduced, when the number of reinforcements associated with each of the comparison stimuli is equated. Furthermore, Zentall and Clement [Zentall, T.R., Clement, T.S., 2002. Memory mechanisms in pigeons: Evidence of base-rate neglect. J. Exp. Psych.: Anim. Behav. Proc. 28, 111-115] have found that sample frequency can affect comparison choice when delays are introduced independently of the number of choices of each of the comparison stimuli in training and the number of reinforcements associated with each of the comparison stimuli is equated. In the present experiment we found that the probability of choosing each of the comparison stimuli in training can affect comparison choice when delays are introduced, independently of sample frequency and when the number of reinforcements associated with each of the comparison stimuli is equated. Together, these experiments suggest that when the sample is not available, there is a partial dissociation between comparison choice and the probability of reinforcement associated with each of the comparison stimuli.     

Effects of training history on resurgence in humans

This experiment assessed the effects of training history on resurgence in three college students. Four-choice arbitrary-matching-to-sample trials occurred in two components of a multiple schedule. An A1 or A2 sample stimulus and four (B) comparison stimuli occurred on AB trials, and a C1 or C2 sample stimulus and four (D) comparison stimuli occurred on CD trials. By the end of training, accuracy and latency measures were comparable across separate discriminations, selecting B2 in the presence of A2 and selecting D2 in the presence of C2, despite a lengthier training correlated with the former discrimination. Next, in the presence of A2 and C2, respectively, responses to B2 and D2 were extinguished and responses to B3 and D3 were reinforced. These responses to B3 and D3 then were extinguished in a final condition. In this final condition, resurgence to B2 occurred for each participant, whereas resurgence to D2 occurred for only one participant. Thus, there was greater resurgence of the discrimination with the lengthier training history, despite the discriminations being similar in terms of accuracy and latency before extinction. This result, therefore, can be classified as a latent, or remote, behavioral history effect.     

Rats more readily acquire a time-of-day go no-go discrimination than a time-of-day choice discrimination

Male Sprague-Dawley rats were used to compare six time-place training procedures that differed with respect to housing or training conditions. All procedures involved training food-deprived rats to enter one choice arm of a T-maze during a morning test session and to enter the other choice arm during an afternoon session to obtain Cocoa Puffs(R). The task proved to be difficult. Only 39 of 49 rats attained a criterion of nine correct choices on ten consecutive trials within a total of 120 trials. Making one choice arm distinct, limiting consecutive same correct choices to two, giving one session during the light and one during the dark portion of the light cycle, extinguishing perseveration of the same choice responses, and housing the rats with a natural light cycle all failed to significantly decrease the errors or trials to a 90% correct choice criterion. In contrast, all responding rats (n=7) showed significantly better than chance performance within 48 trials when the task was a go no-go discrimination based on time of day. Learning to make a response during a session when a choice to either choice arm is reinforced and to withhold responding during a session when a choice to neither choice arm is reinforced was relatively easy for the rats to acquire. Continued high level performance after the light cycle was eliminated, a random feeding schedule was initiated, and other time-related cues were masked suggests that the rats used internal cues or an internal clock to make the correct go or no-go response. It was concluded that rats are prepared to use time of day as an occasion-setting stimulus, but have difficulty using time of day as a signal for a specific response.     

Reaction times identify a Pavlovian component in a two-choice discrimination

Six pigeons discriminated on discrete trials between two colors. In Experiment 1, two luminous spots were both either blue or green and the reinforced responses were “peck left” for blue and “peck right” for green. In Experiment 2, the hue of a center spot controlled subsequent choice pecks to left or right. In both experiments response bias was manipulated in two ways. During stimulus frequency (“SF”) sessions correct responses brought food on 40% of trials; in “imbalanced” blocks of sessions one hue appeared on 80% of trials and the other on 20%. During reinforcement probability (“RNF”) sessions the hues appeared equally often, but in imbalanced blocks the hues signaled different reinforcement probabilities, either 64% or 16%. In “balanced” control blocks the hues appeared equally often and were both reinforced at 40%. The experiments gave similar results. When bias was computed from choice percentages the imbalanced conditions yielded substantial response bias, and the amount of bias was about the same under RNF and SF treatments. However, reaction times (RTs) gave a different outcome. RNF imbalance slowed responses directed at the less reinforced stimulus, but SF imbalance had little RT effect (Experiment 1) or no effect (Experiment 2). These results suggest that choice was controlled by an instrumental stimulus-response-reinforcement association, whereas RTs were controlled by a Pavlovian stimulus-reinforcement association.     

Delayed matching-to-position performance in C57BL/6N mice

Delayed matching-to-sample is one of the most frequently employed behavioral tasks for assessing spatial working memory in animals. Although the advantages of the task have been widely acknowledged and it is used in the study of a variety of species, its application to mice has been rare. In the present study, we reported the efficacy of a delayed matching-to-position task in C57BL mice lever-pressing in an operant-conditioning chamber. Each trial started with the press of a back lever, followed by the presentation of either a left or right front lever. When the ratio requirement for presses to the front lever (sample) was met, a delay interval started. Delay interval continued until the mice made the first response after the elapse of the programmed delay interval. This was followed by the presentation of a choice of left or right front levers. The choice of the same front lever as the sample was reinforced, whereas the other was not. The proportion of correct choices showed a delay-dependent decrement. A higher ratio of response requirement to the sample resulted in increased accuracy, but the duration of the intertrial interval had no effect. Preceding trials also influenced response accuracy, indicating proactive interference. Overall, the results replicated the effects of parametric manipulations reported in other species, and thus, our findings validate the efficacy of the task for assessing spatial working memory in laboratory mice.     

Context effect in a temporal bisection task with the choice keys available during the sample

In a symbolic matching to sample task, six pigeons learned to associate different sample durations with different comparison stimuli. On “Short” trials, choice of Red and Green keylight comparisons were reinforced following 3-s and 9-s samples, respectively; on “Long” trials, Blue and Yellow keylight comparisons were reinforced following 9-s and 27-s samples, respectively. In contrast with previous studies, the comparison keys were available during the samples. After the temporal discriminations were learned, new pairs of comparison keys were presented and the preference for each was assessed during 27-s samples. One pair in particular, Green and Blue, was critical because it tested the predictions of two timing models, Scalar Expectancy Theory (SET) and the Learning-to-Time (LeT) model. The results showed that preference for Green increased during the sample, a result consistent with LeT but not with SET. Other test results, however, were predicted by neither model.     

Instrumental responding remains under the control of the consequent outcome after extended training

The effect of extensive training on the contribution of response--outcome learning to instrumental performance in rats was re-examined in two experiments using a transfer test. In each experiment, two discriminative stimuli were established as signals for different response--outcome combinations (e.g. light: nose poke-pellets and noise: handle pull-sucrose). Then, two different responses (lever press and chain pull) were concurrently trained with those outcomes. In Experiment 1, these responses underwent extensive training, each with a different outcome (e.g. lever press-pellets and chain pull-sucrose). In Experiment 2, these responses were trained moderately with one outcome (e.g. lever press-pellets and chain pull-sucrose) and extensively with a different outcome (e.g. lever press-sucrose and chain pull-pellets). Finally, transfer tests were conducted in which the discriminative stimuli, noise and light, were tested periodically with the lever and chain. In Experiment 1, the stimuli consistently and preferentially elevated performance of the response trained with the same outcome relative to that trained with a different outcome. In Experiment 2, the stimuli elevated both responses nondifferentially. However, a drive manipulation (thirst) designed to increase the value of sucrose relative to pellets revealed a significant preference for the response that had been extensively trained with sucrose. Overall, the results of these experiments confirm previous findings that instrumental behaviors do not become increasingly independent of their consequent outcomes with extended training. However, the transfer results of Experiment 2 highlight a potential limitation of the transfer test for assessing variations in the strength of R--O associations.     

Generalization gradients and representation modes after absolute and relative discrimination learning in young chickens

Perceptual relativity has become a central issue in animal psychophysics. In order to assess how the interplay of training experience and stimulus dimension might affect perceptual relativity, we investigated the role of 'absolute' and 'relative' training on the learning and representation of stimuli from two dimensions that might favor absolute or relative encoding to a different degree. Young chicks learned to discriminate 3D-objects by either color or size. During 'absolute' training always the choice of the same stimulus of a simultaneously presented pair was reinforced, while choice of the larger (smaller) or greener (bluer) stimulus was reinforced during 'relative' training. Overall, discrimination learning was faster with relative training, but size learning profited more from 'relative' training than color learning. Post-training generalization tests revealed a combined effect of training experience and stimulus dimension: a higher amount of absolute encoding occurred with absolute training and color learning, while relative choices prevailed with relative training and size learning.     

Hormones that increase maternal responsiveness affect accumbal dopaminergic responses to pup- and food-stimuli in the female rat

The present study investigated hormonal mediation of maternal behavior and accumbal dopamine (DA) responses to pup-stimuli, as measured in microdialysis samples collected from the nucleus accumbens shell of female rats in non-homecage environment. In Experiment 1, samples were collected before and after continuous homecage pup experience from either intact postpartum or cycling females. In Experiment 2, samples were collected before and after responding maternally in homecage from ovariectomized females given either parturient-like hormone or sham treatments. After baseline sample collection in the dialysis chamber, pup and food stimuli were individually presented to females. Upon sampling completion, all animals were placed back into their homecage with donor pups for several days, and then the sample collection procedure was repeated. Prior to stimulus presentation, postpartum and hormone-treated females had decreased basal DA release compared to their controls. In response to pup stimuli, only postpartum and hormone-treated females had increased DA release compared to basal release (both sampling days). In response to food stimuli, all females had increased DA responses from basal; although there were group differences on the initial day of sampling. Findings suggest that hormones associated with inducing maternal behavior in the postpartum rat play a significant role in modifying accumbal dopaminergic responses on first exposure to pup stimuli in the rat. However, the postpartum experience provides further modifications to this brain region to promote DA responses to pup stimuli.     

Discriminative proprieties of Vary and Repeat contingencies

Pigeons were trained on an arbitrary matching-to-sample task in which Vary and Repeat contingencies served as sample stimuli. During the sample component, two keys were lit red and a four-peck sequence was reinforced if its frequency was less than a certain threshold (Vary sample) or if it comprised one of two target sequences (Repeat sample). During the comparison component, two keys were lit white and green, and correct choices depended on the previous sample contingency. Pigeons learned to emit high and low variability levels during the sample, and correct matching choices were obtained. In two discrimination testing phases, the requirement of variation (Vary sample) or of repetition (Repeat sample) was parametrically manipulated such that behavioral variability became undifferentiated between samples (low sample disparity) and then differentiated (high sample disparity) again. Accurate choices fell to chance under low sample disparity conditions, but improved under high disparity conditions. The results provide evidence that high and low variability levels can be produced in the absence of antecedent cues and that pigeons can accurately report whether they had experienced a Vary or a Repeat contingency, thus indicating that those contingencies may serve discriminative functions.     

Optimal risky choice in humans: effects of amount of variability

The present study investigated whether the predictions of an optimal risk-sensitive foraging model (the energy-budget rule) would extend to humans’ choices between high- and low-variance monetary response options. In Experiment 1, participants were presented with repeated choices between two options that had the same mean values but different variances across positive- and negative-budget conditions. In Experiment 2, a within-subject comparison was conducted to investigate choice under positive- and negative-budget conditions when the options were either (a) a fixed option and a high-variance option, or (b) a low-variance option and a high-variance option. Session-wide choices were analyzed in relation to the predictions of the energy-budget rule and sequential choices were analyzed with dynamic optimization modeling. When both options were variable choice was generally consistent with predictions of the energy-budget rule and was more risk prone under negative-budget than positive-budget conditions. Sequential choices were sensitive to local budget conditions, but choices were less consistent with optimality when both options were variable, possibly because of the greater similarity in expected earnings for optimal and nonoptimal choices in these conditions. Overall, the results provide further evidence that the energy-budget rule may have broad applicability and that it can extend to human risky choice between multiple variable response options.     

Associative symmetry and stimulus-class formation by pigeons: The role of non-reinforced baseline relations

Two experiments tested the assumption of Urcuioli's (2008) theory of pigeons’ equivalence-class formation that consistent non-reinforcement of certain stimulus combinations in successive matching juxtaposed with consistent reinforcement of other combinations generates stimulus classes containing the elements of the reinforced combinations. In Experiment 1, pigeons were concurrently trained on symbolic (AB) and two identity (AA and BB) successive tasks in which half of all identity trials ended in non-reinforcement but all AB trials were reinforced, contingent upon either responding or not responding to the comparisons. Subsequent symmetry (BA) probe trials showed evidence of symmetry in one of four pigeons. In Experiment 2, pigeons learned three pair-comparison tasks in which left versus right spatial choices were reinforced after the various sample-comparison combinations comprising AB, AA, and BB conditional discriminations. Non-differentially reinforced BA probe trials following acquisition showed some indication of symmetrical choice responding. The overall results contradict the theoretical predictions derived from Urcuioli (2008) and those from Experiment 2 challenge other stimulus-class analyses as well.     

Behavioral research in pigeons with ARENA: An Automated Remote Environmental Navigation Apparatus

Three experiments established the effectiveness of an Automated Remote Environmental Navigation Apparatus (ARENA) developed in our lab to study behavioral processes in pigeons. The technology utilizes one or more wireless modules, each capable of presenting colored lights as visual stimuli to signal reward and of detecting subject peck responses. In Experiment 1, subjects were instrumentally shaped to peck at a single ARENA module following an unsuccessful autoshaping procedure. In Experiment 2, pigeons were trained with a simultaneous discrimination procedure during which two modules were illuminated different colors; pecks to one color (S+) were reinforced while pecks to the other color (S−) were not. Pigeons learned to preferentially peck the module displaying the S+. In Experiment 3, two modules were lit the same color concurrently from a set of six colors in a conditional discrimination task. For three of the colors pecks to the module in one location (e.g., upper quadrant) were reinforced while for the remaining colors pecks at the other module (e.g., lower quadrant) were reinforced. After learning this discrimination, the color-reinforced location assignments were reversed. Pigeons successfully acquired the reversal. ARENA is an automated system for open-field studies and a more ecologically valid alternative to the touchscreen.     

Features of differential inhibition in choice between alimentary and defensive response

Instrumental defensive (avoidance/escape) and alimentary responses (reinforced with palatable food) in dogs were conditioned by the same stimulus (6-Hz light flashes). Differential inhibition for these responses (0.6-Hz flashes) was formed in unalterable series. Later on, alternative experiments with choice between reinforcements were carried out. In both of experimental series, the degree of alimentary excitability (hunger, satiation) was changed. Numbers of responses to differential and positive conditioned stimuli and their latencies were calculated. Under condition of choice (electrodes on a leg and a pedal in front of a dog) the response depended on a dominant motivation. The dogs differed in the degree of motivation dominance. Differential inhibition was less perfect in unalterable experimental series with dominant motivation. Under conditions of choice between alimentary and defensive reinforcements, the response to the differential stimuli depended on the balance between these motivations: two days of hunger increased the number of alimentary responses, defensive responses prevailed after satiation.     

Role of stimulus-stimulus pairing in matching-to-sample procedure: cross-species comparison of humans and pigeons

The present experiment examined whether, in a matching-to-sample (MTS) procedure, a relation between two stimuli, a sample and a comparison, could be established as a result of just stimulus–stimulus pairing, even if back up reinforcers were never provided for the conditional relation between the sample and comparison stimuli, but rather only for the comparison stimulus. A procedure called “pseudo matching-to-sample” was used in which, when S1 was presented as a sample stimulus, two comparison stimuli (C1 and C2) were presented, and only responses to C1 were reinforced. Conversely, when S2 was presented, only responses to C3 (and not C4) were reinforced. In other words, organisms experiencing this procedure could discriminate C1 from C2, and C3 from C4, by simple discrimination without regard to the conditional sample stimuli. In order to examine cross-species differences, responding by humans in this procedure was compared to that by pigeons. Although the humans developed a discriminative function for the sample stimuli, that is, the humans’ responding was affected by both the sample stimuli and the reinforcers, responding by the pigeons was affected solely by the reinforcers. These data suggest that, in this procedure, humans (but not pigeons) are able to learn relations among stimuli simply as a result of stimulus–stimulus pairing.     

Prototype symbolization in hooded crows

The ability in prototype symbolization was studied in four crows trained in matching concept. The experimental approach was characterized by the absence of direct training providing an association between the pictured arrays and Arabic numerals. Experimental sessions were divided into demonstrative and test phases. In the demonstrative phases, the sample and the reinforced stimulus belonged to the same category: if the sample was a pictured array, the reinforced stimulus was also the pictured array, if the sample was a numeral, the reinforced stimulus was likewise a numeral. Matching-to-sample competence was sufficient to perform this task successfully. In case of a correct choice a crow received some mealworms, their number was equal to the number of items in the pictured array or the Arabic numeral. In the test phases, the sample and the comparison stimuli were of different categories. If the sample was a pictured array, the comparison stimuli were numerals; if the sample was a numeral, the comparisons were the pictured arrays. Such tests required the birds to choose a numeric symbol corresponding to the pictured array or to choose the array of pictured items numerically equal to the Arabic symbol. All four crows performed this task successfully. Birds were able to set up a correspondence between the Arabic numeral from 1 to 4 and the number of elements in pictured arrays by way of mental juxtaposition of the earlier received information. Similar experiments showed that crows are likely to be able to perform mental operations with numerals analogous to simple arithmetic addition.     

Temporal generalization and diffusion in forgetting

Two processes may contribute to the decrement in discriminability with increasing temporal distance between the occasioning event and later choice. One is the length of the interval and the other is generalization decrement. In the model described by White and Wixted [J. Exp. Anal. Behav. 71 (1999) 91-113], choice was predicted by the relative payoff for correct delayed matching responses, conditional on the current value of the stimulus sampled from Thurstone-like probability distributions of the effect of the sample stimuli. In the model, discriminability decreased with increasing temporal distance because the variance of the distributions increased with time. However, White and Wixted did not specify the function relating variance to temporal distance. If a diffusion process is assumed, and if diffusion increases exponentially with time, the resulting forgetting function is a negative exponential. An additional process involves exponential generalization of remembering from one time to other times. Alternative diffusion functions result in hyperbolic or power forgetting functions. The combination of two exponential processes yields forgetting functions that are double exponential in form and which appear consistent with a wide range of data.     

Visual discrimination learning in zebrafish (Danio rerio)

Three experiments demonstrated visual discrimination learning in zebrafish (Danio rerio). In each experiment, zebrafish were given a choice between two visually distinct arms of a T-maze. Choice of one stimulus was always followed by a food reward, but choice of the other stimulus was not rewarded. Different colored sleeves fitted around the arms of the T-maze were used in Experiments 1 (green and purple) and 2 (red and blue). The stimuli used in Experiment 3 were white sleeves lined with horizontal or vertical black stripes. In all three experiments, zebrafish acquired a significant preference for the stimulus that led to a food reward. Experiments 1 and 2 also showed that zebrafish could learn a reversal of the discrimination. Finally, the effect of discontinuing food rewards was examined after reversal training in Experiment 2 and after initial discrimination training in Experiments 1 and 3. Non-reinforcement led to a decrease in correct responding in Experiments 2 and 3 independent of stimulus identity, but to an asymmetrical pattern of responding in Experiment 1. The median latency to make a choice response decreased over the course of acquisition in all three experiments; during extinction, median response times did not change at all in Experiment 1 and increased only very slightly in Experiment 2, but showed a substantial increase in Experiment 3. The implications of these results for the zebrafish as a model system for genetic studies of learning and memory are discussed.     

Attention to uninformative features expressed by pigeons in a duration matching-to-sample task

Pigeons were trained on a matching-to-sample task in which they had to respond to a different choice stimulus following the same durations (2 or 10 s) of two different signals. The duration signals consisted of a white light presented from the ceiling and a red light presented from the front wall. Subsequent test performance indicated that matching accuracy declined (1) when the set of choice stimuli following a duration signal differed from the set presented during training, and (2) when the color or location of the duration signal was changed from values used during training. These results are discussed in terms of attention to uninformative features of a visual stimulus.