Showing papers in "Journal of Experimental Psychology: Animal Behavior Processes in 2013"

Mechanisms of renewal after the extinction of instrumental behavior.

Abstract: Four experiments with rats examined renewal of extinguished instrumental behavior when the reinforcement histories of the contexts were equated by giving complementary training and extinction of a different response (lever press and chain pull) in each context. In Experiments 1–3, renewal occurred when the response was tested in the acquisition context (ABA) or outside the extinction context (AAB and ABC). Further, in Experiments 1–3, when both responses were simultaneously available there was a clear preference for the response that was not in its extinction context. In Experiment 4, renewal was not reduced when testing occurred in a context that had been associated with extinction of the other instrumental response. The experimental designs rule out differential context-reinforcer associations being the only contributing mechanism of renewal, and also raise questions about configural and occasion-setting accounts. The results are consistent with the idea that during extinction an inhibitory association is formed between the context and the response.

Hierarchical and binary associations compete for behavioral control during instrumental biconditional discrimination.

Abstract: Experiments investigating instrumental conditioning typically train animals to perform an action to earn a specific outcome in the presence of particular stimuli. Both theory and evidence accumulating over many decades suggest that, as a consequence of this training, the animals encode various binary associations, whether between representations of the stimulus and response (S–R associations), the response and outcome (R–O associations), or the stimulus and outcome (S–O associations) (Bolles, 1972; Colwill & Rescorla, 1986; Dickinson, 1994). In addition to these binary associations, however, it has been suggested that instrumental training can also encourage the formation of hierarchical associations. For example, Colwill and Rescorla (1990) presented evidence that hierarchical associations between a discriminative stimulus and specific response-outcome associations are formed as a consequence of instrumental biconditional discrimination training. In Experiment 2 they used a design in which rats learned to perform two responses (R1 and R2) to earn two distinct outcomes (O1 and O2) during two discriminative stimuli (S1 and S2) such that, when S1 was presented, the rats earned O1 for performing R1 and O2 for performing R2 whereas, when S2 was presented these response-outcome contingencies were reversed (i.e. R1 earned O2 and R2 earned O1). Thus four hierarchical associations should have formed: S1-(R1-O1), S1-(R2-O2), S2-(R1-O2), and S2-(R2-O1). To establish evidence of hierarchical associations one of the two outcomes (O1) was subsequently devalued by pairing its consumption with lithium chloride after which the rats were allowed to choose between R1 and R2 in an extinction test in the presence of S1 and S2. If, as a consequence of training, the animals only encode the binary associations between the S's, R's and O's, then no difference in the performance of R1 and R2 should be predicted because both R1 and R2 were equally associated with both O1 and O2 and both S1 and S2. If, however, rats are able to encode hierarchical associations, such that the specific R-O associations are controlled by the discriminative stimuli, then differences in the performance of R1 and R2 should emerge with the direction of the difference depending on stimulus presentation. Colwill and Rescorla's results were consistent with this latter prediction; that is, when S1 was presented R1 was reduced relative to R2 (S1: R1 R2). Although simple binary associations cannot account for this result, there are possibilities other than the S-(R-O) hierarchical association favoured by Colwill & Rescorla that can. The simplest alternatives are perhaps other types of hierarchical association such as those illustrated in Figure 1. For example, an (S-O)-R structure, which provides that the performance of a response can be controlled by a specific S-O association, can explain biconditional discrimination performance if it is accepted that devaluing a specific O reduces this control. Likewise, an (S-R)-O structure can resolve the discrimination if the influence of a specific S-R association on performance is controlled by the value of the outcome with which it is associated. Another alternative is provided by Rescorla's (1991) suggestion that the rats in his experiments may have combined binary associations into ternary ones; i.e. having formed both an S-R and an R-O association from the S, R and O elements, the rats might then have formed a ternary S–R–O association (see Figure 1). This account can explain discrimination given that any one element can retrieve the other elements of the association and if performance is ultimately determined by the value of the outcome component. Figure 1 Alternative associative structures mediating biconditional discrimination. (a) The hierarchical structure favoured by Rescorla (1991) allowing S to control specific R-O associations. (b) The two-process alternative allowing the performance of R to be ... Of these various explanations, only the (S-O)-R alternative has received any experimental attention, perhaps as a consequence of expectancy-based two-process theory (Trapold, 1970) and its popularity as an explanation of the differential outcomes effect in discrimination learning (Trapold & Overmeir, 1972). Rescorla (1992 - Experiment 3) devised a means of testing predictions from the (S-O)-R and S-(R-O) accounts by constructing a discrimination situation in which two antecedent S-O associations, S1-O1 and S2-O2, controlled two responses, R1 and R2, each earning the outcome that was not signaled by the stimulus; i.e. R1→O2 and R2→O1. Thus, two hierarchical associations should have formed: (S1-O1)-R1→O2 whereas (S2-O2)-R2→O1. If specific (S-O)-R associations control performance then devaluing O1 should reduce R1 relative to R2. Rescorla found, however, that devaluing O1 reduced R2 relative to R1 suggesting that R-O rather than S-O associations exerted greater control over performance and, therefore, that (S-O)-R hierarchical associations likely play little if any role in this form of discrimination. To date there has not been any direct evidence to decide between the S-(R-O), the (S-R)-O and the S-R-O ternary accounts. One way in which these latter two structures might be thought to differ from the former is in the contribution of S–R associations to task solution. On both the (S-R)-O and the ternary account, of course, S-R associations are a necessary component of the underlying associative structure. As a consequence, a diminished capacity to form S-R associations might be expected to produce a deficit in performance. If, on the other hand, S-(R-O) associations governed performance, then a reduced capacity to form S-R associations would be expected to leave performance intact. Indeed, any tendency to form S–R associations might be expected to interfere with accurate performance as a result of competition between S-R and S-(R-O) associations. That is, when the rat is faced with a choice between, say, R1 and R2 during S1 presentations, S-R associations would produce a tendency to increase the performance of both actions (i.e. both R1 and R2), which would compete with the hierarchical S1-(R1-O1) and S1-(R2-O2) associations that promote discriminative control (i.e. R1 during S1 and R2 during S2). Thus, from this perspective, a diminished ability to form S-R associations should either have no effect or, by removing a source of interference, improve performance on this task. In this context, recent evidence suggesting that either lesions or pharmacological inactivation of the dorsolateral striatum (DLS) attenuates the ability of rats to form stimulus-response associations is of considerable interest (Yin, Knowlton, & Balleine, 2004, 2006). One area in which S–R associations are thought to play a central role is in the control of habitual instrumental performance after overtraining (Dickinson, 1985). Although undertrained actions are sensitive to outcome devaluation and to degradation of the response-outcome contingency, overtrained instrumental actions are not and persist when either the value of the outcome or the causal status of the instrumental action is changed (Dezfouli & Balleine, 2012). Furthermore, in a recent study we found evidence that correctly choosing between actions based on discriminative cues, in a task in which a simple SD-R association provided an optimal solution, was strongly attenuated by inactivation of the DLS (Balleine, Liljeholm, & Ostlund, 2009; see also McDonald & White, 1993). Based on these findings, different predictions can be made about the likely effect of DLS lesions during a biconditional discrimination task. If accurate performance on this task requires the formation of S-R associations, then lesions of the DLS might be anticipated to attenuate performance on a biconditional task. If, however, solving the biconditional task requires the formation of hierarchical S-(R-O) associations then DLS lesions should not produce a deficit in performance. Indeed, by removing a potential source of interference, lesioning the DLS might well be anticipated to facilitate task performance relative to sham controls. In contrast to these effects of DLS manipulation, lesions of an adjacent medial region of dorsal striatum, the dorsomedial striatum (DMS), do not affect these measures of S-R learning but, rather, appear to influence the ability of animals to form response-outcome associations (Balleine & Doherty, 2010). Thus, in undertrained animals, lesions or inactivation of the posterior DMS (pDMS) abolish sensitivity to both outcome devaluation and contingency degradation (Shiflett, Brown, & Balleine, 2010; Yin, Ostlund, Knowlton, & Balleine, 2005). Given that both the ternary and hierarchical accounts of biconditional discrimination performance rely upon animals being able to learn R-O associations, both of these accounts predict that lesions of the pDMS will attenuate performance. The aim of the current study was to test these predictions. Experiment 1 compared the effect of DLS and pDMS lesions on a biconditional discrimination task similar to that employed by Colwill and Rescorla (1990 – Experiment 2). In Experiment 2 we conducted a similar assessment except that we trained the rats on a more difficult version of the task than that employed in Experiment 1.

Overshadowing of geometry learning by discrete landmarks in the water maze: effects of relative salience and relative validity of competing cues.

Abstract: The effects of stimulus salience and cue validity in the overshadowing of geometric features of an enclosed arena by discrete landmarks were investigated in rats using the water maze paradigm. Experiment 1 established that in a rhomboid-shaped arena, the acute corner was more salient than the obtuse corner. In Experiment 2, rats were trained to find a submerged platform either in one of the acute, or obtuse, corners. In addition to the information provided by corner angle, the platform was also signaled by the presence of a spherical landmark suspended above the platform for rats in the experimental group. The landmark was a more valid cue for predicting the location of the platform than the angle of the corner. This training resulted in overshadowing of learning about the angle of the corner by the presence of the landmark. The final experiment extended this result by showing that when the predictive validities of the angle and the landmark were matched in the experimental group, learning about geometry was still overshadowed by the presence of landmarks, but only in animals that were trained with the platform at an obtuse, but not acute, corner. These results uniquely demonstrate that learning about geometry can be overshadowed by discrete landmarks, and also that whether overshadowing is observed depends on the stimulus salience and the relative validity of the competing cues. These findings imply that learning based on geometric cues follows the same basic rules that apply to a wide range of other learning paradigms.

Magazine approach during a signal for food depends on Pavlovian, not instrumental, conditioning.

Abstract: In the conditioned magazine approach paradigm, rats are exposed to a contingent relationship between a conditioned stimulus (CS) and the delivery of food (the unconditioned stimulus, US). As the rats learn the CS-US association, they make frequent anticipatory head entries into the food magazine (the conditioned response, CR) during the CS. Conventionally, this is considered to be a Pavlovian paradigm because food is contingent on the CS and not on the performance of CRs during the CS. However, because magazine entries during the CS are reliably followed by food, the increase in frequency of those responses may involve adventitious ("superstitious") instrumental conditioning. The existing evidence, from experiments using an omission schedule to eliminate the possibility of instrumental conditioning (B. J. Farwell & J. J. Ayres, 1979, Stimulus-reinforcer and response-reinforcer relations in the control of conditioned appetitive headpoking (goal tracking) in rats. Learning and Motivation, 10, 295-312; P. C. Holland, 1979, Differential effects of omission contingencies on various components of Pavlovian appetitive conditioned responding in rats. Journal of Experimental Psychology: Animal Behavior Processes, 5, 178-193), is ambiguous: rats acquire magazine CRs despite the omission schedule, demonstrating that the response does not depend on instrumental conditioning, but the response rate is greatly depressed compared with that of rats trained on a yoked schedule, consistent with a contribution from instrumental conditioning under normal (nonomission) schedules. Here we describe experiments in which rats were trained on feature-positive or feature-negative type discriminations between trials that were reinforced on an omission schedule versus trials reinforced on a yoked schedule. The experiments show that the difference in responding between omission and yoked schedules is due to suppression of responding under the omission schedule rather than an elevation of responding under the yoked schedule. We conclude that magazine responses during the CS are largely or entirely Pavlovian CRs.

Pavlovian-to-instrumental transfer: paradoxical effects of the Pavlovian relationship explained.

Abstract: Four experiments with rats examined the origin of outcome-selective Pavlovian-to-instrumental transfer (PIT). Experiment 1 used a standard procedure, where outcomes were embedded within extended conditioned stimuli (CSs), to demonstrate the basic effect: Pavlovian stimuli augmented instrumental lever presses that had been paired with the same outcomes. Experiments 2 and 3 showed that after instrumental conditioning, whereas a conditioned stimulus (CS) trained using a backward conditioning procedure produced outcome-selective PIT, forward conditioning with a CS did not. These results are consistent with the idea that backward conditioning results in the outcome provoking its associated instrumental response during the CS and thereby allows a stimulus–response association to be acquired that directly generates outcome-selective PIT at test. Experiment 4 provided direct support for the assumptions that underlie this stimulus-response analysis. These results, and other paradoxical effects of the Pavlovian relationship, are incongruent with accounts of outcome-selective PIT that rely on a stimulus-outcome-response chain.

Categorization of Photographic Images by Rats Using Shape-Based Image Dimensions

Abstract: Strong interest exists in developing a rodent model of visual cognition to conduct research into the neural mechanisms of visual categorization. Yet, doubt remains as to whether rats perform visual categorization tasks as do humans and nonhuman primates. Here, we trained eight rats on two visual categorization tasks using photographs of eight objects from each of four basic-level categories: chairs, flowers, cars, and humans. In Experiment 1, rats learned to categorize chairs versus flowers; in Experiment 2, rats learned to categorize cars versus humans. After rats learned each discrimination, we tested them with eight novel pictures from each of the categories. The rats performed at reliably above-chance levels during these generalization tests. To determine which dimension(s) of the stimuli controlled the rats' behavior, we conducted regression analyses using several image dimensions. The chair versus flower discrimination was mainly controlled by the convexity of the stimuli, whereas the car versus human discrimination was mainly controlled by the aspect ratio of the stimuli. These results demonstrate that rats can categorize complex visual objects using shape-based properties of photographs.

The effects of the previous outcome on probabilistic choice in rats.

Abstract: This study examined the effects of previous outcomes on subsequent choices in a probabilistic-choice task. Twenty-four rats were trained to choose between a certain outcome (1 or 3 pellets) versus an uncertain outcome (3 or 9 pellets), delivered with a probability of .1, .33, .67, and .9 in different phases. Uncertain outcome choices increased with the probability of uncertain food. Additionally, uncertain choices increased with the probability of uncertain food following both certain-choice outcomes and unrewarded uncertain choices. However, following uncertain-choice food outcomes, there was a tendency to choose the uncertain outcome in all cases, indicating that the rats continued to “gamble” after successful uncertain choices, regardless of the overall probability or magnitude of food. A subsequent manipulation, in which the probability of uncertain food varied within each session as a function of the previous uncertain outcome, examined how the previous outcome and probability of uncertain food affected choice in a dynamic environment. Uncertain-choice behavior increased with the probability of uncertain food. The rats exhibited increased sensitivity to probability changes and a greater degree of win–stay/lose–shift behavior than in the static phase. Simulations of two sequential choice models were performed to explore the possible mechanisms of reward value computations. The simulation results supported an exponentially decaying value function that updated as a function of trial (rather than time). These results emphasize the importance of analyzing global and local factors in choice behavior and suggest avenues for the future development of sequential-choice models.

Outcome value influences attentional biases in human associative learning: dissociable effects of training and instruction.

Abstract: Four experiments using human participants examined how learning about the value of an outcome with which a cue is associated influences attention to that cue. Experiment 1 demonstrated that participants learn more rapidly about cues that previously predicted high-value outcomes than those that predicted low-value outcomes, indicating an attentional bias that is based on the learned value of cues. Experiments 2 through 4 examined the nature of this bias by retrospectively manipulating the value of the outcomes involved through instructions to participants. Results demonstrate that learning about value through trial-by-trial training and through instruction both influence attention to the cues involved, but in different ways. We take these findings to suggest that the learning of attentional responses, just like more overt forms of instrumental action, can be influenced by both goal-directed and habit-like processes.

Extinction of reinstated or ABC renewed fear responses renders them resistant to subsequent ABA renewal.

Abstract: Three experiments used an ABA renewal paradigm to study deepening of response loss produced by extinction of reinstated or ABC renewed fear responses. In Experiment 1, rats were trained with two stimuli, S1 and S2, in context A and extinguished to S1 in context B and S2 in context C, shocked in B but not in C, and subjected to additional extinction of S1 in B and S2 in C. Rats froze less to S1 than S2 when subsequently tested in A. In Experiments 2 and 3, following training of S1 and S2 in A, one group received extinction of S1 in B and S2 in C followed by extinction of S1 in C and S2 in B. This group froze less to S1 in A or to S2 in a novel context, D, than a group always extinguished to S1 in B and S2 in C or a group extinguished to both S1 and S2 in B and C. These results show that additional extinction of a conditioned stimulus (conditional stimulus [CS]) exhibiting either reinstatement or ABC renewal renders that CS resistant to ABA renewal. They are consistent with theories that allow a role for context in extinction learning and that use error-correction mechanisms to update this learning.

Extinction arouses attention to the context in a behavioral suppression method with humans

Abstract: One experiment assessed predictions from the attentional theory of context processing (ATCP, J. M. Rosas, J. E. Callejas-Aguilera, M. M. Ramos-Alvarez, & M. J. F. Abad, 2006, Revision of retrieval theory of forgetting: What does make information context-specific? International Journal of Psychology & Psychological Therapy, Vol. 6, pp. 147-166) that extinction arouses attention to contextual stimuli. In a video-game method, participants learned a biconditional discrimination (RG+/BG-/RY-/BY+) either after extinction of another stimulus had occurred, or not. When contextual stimuli were relevant to solving the discrimination (i.e., all RG+/BG- trials occurred in one context and all RY-/BY+ in another), prior extinction of another stimulus facilitated the discrimination, as if extinction enhanced attention to the contexts. Results are discussed briefly in terms of ATCP and the model of N. A. Schmajuk, Y. W. Lam, & J. A. Gray (1996, Latent inhibition: A neural network approach, Journal of Experimental Psychology: Animal Behavior Processes, Vol. 22, pp. 321-349).

The fate of redundant cues in human predictive learning.

Abstract: In each of three experiments, a single group of participants received a sequence of trials involving pictures of a variety of foods presented individually or in pairs. Participants were required to predict in which trials the food would lead to a hypothetical allergic reaction. The different trials involved blocking, A+ AX+, and a simple discrimination, BY– CY+, in which each letter stands for a different food. Training trials were followed by a test in which participants were asked to predict how likely each kind of food would be followed by the allergic reaction. The principal purpose of the experiments was to determine how the redundant cue from blocking, X, would be judged relative to the redundant cue from the simple discrimination, Y. In contrast to predictions from currently influential theories of associative learning, X was regarded as a better predictor for the allergic reaction than Y.

Within-compound associations explain potentiation and failure to overshadow learning based on geometry by discrete landmarks.

Abstract: In three experiments, rats were trained to locate a submerged platform in one of the base corners of a triangular arena above each of which was suspended one of two distinctive landmarks. In Experiment 1, it was established that these landmarks differed in their salience by the differential control they gained over behavior after training in compound with geometric cues. In Experiment 2, it was shown that locating the platform beneath the less salient landmark potentiated learning based on geometry compared with control rats for which landmarks provided ambiguous information about the location of the platform. The presence of the more salient landmark above the platform for another group of animals appeared to have no effect on learning based on geometry. Experiment 3 established that these landmark and geometry cues entered into within-compound associations during compound training. We argue that these within-compound associations can account for the potentiation seen in Experiment 2, as well as previous failures to demonstrate overshadowing of geometric cues. We also suggest that these within-compound associations need not be of different magnitudes, despite the different effects of each of the landmarks on learning based on geometry seen in Experiment 2. Instead, within-compound associations appear to mitigate the overshadowing effects that traditional theories of associative learning would predict.

The effect of stimulus distribution form on the acquisition and rate of conditioned responding: implications for theory.

Abstract: In four experiments rats were conditioned to an auditory conditioned stimulus (conditioned stimulus; CS) that was paired with food, and learning about the CS was compared across two conditions in which the mean duration of the CS was equated. In one, the CS was of a single, fixed duration on every trial, and in the other the CS duration was drawn from an exponential distribution, and hence changed from trial to trial. Higher rates of conditioned responding to the fixed than to the variable stimulus were observed, in both between- (Experiment 1) and within-subject designs (Experiments 2 and 3). Moreover, this difference was maintained when stimuli trained with fixed or variable durations were tested under identical conditions (i.e., with equal numbers of fixed and variable duration trials)—suggesting that the difference could not be attributed to performance effects (Experiment 3). In order to estimate the speed of acquisition of conditioned responding, the scaled cumulative distribution of a Weibull function was fitted to the trial-by-trial response rates for each rat. In the within-subject experiments specific differences in the pattern of acquisition to fixed and variable CS were shown; a somewhat different pattern was found when intertrial interval (ITI) was manipulated (Experiment 4). The implications of these findings for theories of conditioning and timing are discussed.

Active change detection by pigeons and humans.

Abstract: Our continuous experience of a stable reality requires the coordinated integration of attention, perception, working memory, and long-term memory. How the brain accomplishes this apparently seamless integration has been of increasingly greater interest (Faw, 2003; Lamme, 2003; Naghavi & Nyberg, 2005; Tononi & Koch, 2008). The change detection task has been one widely used approach to assess this type of integration. In the change detection task, two different pictures are briefly shown in sequence, separated by a short visual mask (Rensink, 2002; Simons & Levin, 1997)., Studies using this approach have clearly demonstrated that we do not form complete representations of the entire visual input, often resulting in “change blindness” (Darriba, Pazo-Alvarez, Capilla, & Amenedo, 2012; Simons, Franconeri, & Reimer, 2000). Because of change blindness, a rather large change between the pictures is not detected until attention directly examines the changing portion of a display. Despite our stable experience of a continuous world, such findings suggest that little visual information is retained in memory from moment-to-moment. Non-human animals also appear to experience a stable world during their extended interactions with each other and the environment. Accordingly, they face the same issues as humans in sequentially integrating past and current experiences. It is thus natural to ask if and how they also detect and integrate change and constancy over time. If they do, are the attention, perception, and memory mechanisms involved the same as those found in humans? This seems to be the case for primates, as studies have revealed functionally similar change detection behavior in visual short term memory (VSTM) between rhesus monkeys and humans (Elmore, et al., 2011; Heyselaar, Johnston, & Pare, 2011). Only a few experiments have examined change detection in non-primate animals such as pigeons or directly compared their change detection abilities to those of humans. Wright et al. (2010) tested pigeons in a variant of the typical human change detection task. They showed the pigeons an array of two colored circles for 5 s. After a short 50 ms delay, a test array was presented in which the color of one of the two circles had changed. Pecking at the changed circle resulted in reinforcement. Following training with four colors in this two-item change detection task, the pigeons successfully transferred their discrimination to four novel colors. To evaluate whether this change discrimination was due to attentional capture or short-term memory for the stimuli, Wright et al. tested delays of up to 6.4 s between the initial and test arrays. The pigeons maintained performance above 70% accuracy with delays up to 1.6 s, and never dropped to chance at the longest delays. These results suggest pigeons were relying on working memory to mediate their detection of change, instead of attentional capture or other strictly perceptual mechanisms. Gibson, Wasserman, and Luck (2011) tested VSTM in pigeons and humans with eight-icon displays. After viewing an initial array of eight icons, members of each species were shown a briefly delayed test array where between zero and eight icons changed, thus requiring appropriate responses to “change” or “no change” choice options. Both species showed similar declines with fewer changes, and the pigeons were overall less accurate than humans. Based on a computational model, Gibson et al. suggested that humans store more items and have fewer memory errors than pigeons, but otherwise may share similar VSTM mechanisms. Recently, we examined change detection in pigeons using a different approach (Hagmann & Cook, 2011). Instead of presenting temporally separated sequences of discrete static images in order to isolate when a change had been detected, we used displays varied in their rate of continuous brightness change. Similar gradual techniques have been used to examine change blindness in humans (David, Laloyaux, Devue, & Cleeremans, 2006; Hollingworth & Henderson, 2004; Simons, et al., 2000). Using a grayscale stimulus that either changed slowly in brightness or was held at a constant brightness level, pigeons were trained in a go/no-go procedure to peck the display whenever a change in brightness was detected and to inhibit pecking when a constant stimulus was presented. The change condition consisted of continuously changing brightness values that oscillated at different rates between its dark and light extremes. The constant condition on any trial consisted of a randomly selected brightness value from the range of values tested on change trials. We found that the pigeons could detect changes in brightness over time and their detection ability varied directly as a function of rate of change. Fast rates of changes were the easiest to discriminate from constant trials, with decreasingly slower rates of change becoming monotonically more difficult to detect. At the slowest rates tested, detection almost certainly required a short-term memory for an earlier value of brightness that was compared to the current perception of brightness. The results suggested that pigeons can retrospectively integrate past experiences over approximately 20 to 30 seconds. Several lines of evidence suggested that perceptual mechanisms might have been used to detect rapidly changing displays and that working memory was used to compare values from different points in time when detecting slower rates of change. In the current paper, we examined a potential limitation in Hagmann and Cook’s (2011) approach. Go/no-go discriminations have a built-in asymmetry in their response contingences, with one class of stimuli indicated by pecking the display (the reinforced S+) and the other class reported by suppressing pecking to the display (the punished or extinguished S−). We have found that pigeons typically begin all trials by responding immediately upon stimulus presentation regardless of its reinforcement status and then gradually inhibit pecking to the S− condition over the course of a trial (Cook, Beale, & Koban, 2011; Cook & Roberts, 2007; Hagmann & Cook, 2010, 2011; Koban & Cook, 2009). Typically, S+ peck rates never change over a trial. As a result, the expressed discrimination between S+ and S− stimuli stems from the “active” inhibition of pecking behavior to the latter class rather than changes in peck rates to both classes. Because Hagmann and Cook’s pigeons were tested with the change condition as the S+ component in their go/no-go procedure, the birds were actively suppressing their peck rates only when stimuli were being experienced as constant. As a result, it could be argued that pigeons were in fact directly expressing their capacity to detect constancy, rather than change. Therefore, the pigeons may have only been indirectly reporting whether a change was present. To determine whether something is constant, however, inherently requires a much longer sample of time than directly reporting whether something has changed. In the latter case, you can respond immediately, and with more certainty, upon a change being detected. You can be certain things are constant and unchanging only after a sufficiently long time has passed and the possibility of change has been ruled out. Consequently, our previous assignment of the S+/S− conditions to change and constant conditions respectively may have underestimated how quickly pigeons can detect change. To examine whether the nature of the response and reinforcement assignment affected the measurement of change detection, we tested four pigeons in our continuous change detection task with the S+ and S− assignments for change and constancy reversed from those in Hagmann and Cook (2011). Here, the S+ condition in the go/no-go task was now assigned to be the constant condition and the S− condition was the change condition. Given the pigeons’ active suppression of pecking in the S− condition, they could now immediately report their detection of change by response cessation and thus provide a direct and potentially more sensitive measure of change detection than before. Reversing the reinforcement assignments additionally allowed us to examine whether the discrimination of change detection exhibited any asymmetry in responding similar in some sense to that found in feature-positive/feature-negative stimulus discriminations (Jenkins & Sainsbury, 1970; Sainsbury & Jenkins, 1967; Wasserman & Anderson, 1974). The added presence of a distinctive feature in the S+ or S− condition controls the relative ease of learning in such discriminations. One possibility is that changing events may be distinctive in a similar way, and thus might be more easily associated with reinforcement than constant events (e.g. Dittrich & Lea, 1993). Using this potentially more sensitive means of measuring change detection, the pigeons in the current experiment were tested similarly to those in Hagmann and Cook. Each 30-session phase of testing examined increasingly slower rates of change that necessitated longer working memory spans to differentiate any changes in the displays relative to constancy. The major question of interest of was whether the pigeons would show a similar or different ability to detect change given this procedure’s superior capacity to detect the birds’ immediate response to changing events. Humans were also tested using the same stimuli in an analogous task for comparison.

Does Constraining Field of View Prevent Extraction of Geometric Cues for Humans during Virtual-Environment Reorientation?

Abstract: Environment size has been shown to influence the reliance on local and global geometric cues during reorientation. Unless changes in environment size are produced by manipulating length and width proportionally, changes in environment size are confounded by the amount of the environment that is visible from a single vantage point. Yet, the influence of the amount of the environment that is visible from any single vantage point on the use of local and global geometric cues remains unknown. We manipulated the amount of an environment that was visually available to participants by manipulating field of view (FOV) in a virtual environment orientation task. Two groups of participants were trained in a trapezoid-shaped enclosure to find a location that was uniquely specified by both local and global geometric cues. One group (FOV 50°) had visually less of the environment available to them from any one perspective compared to another group (FOV 100°). Following training, we presented both groups with a control test along with three novel-shaped environments. Testing assessed the use of global geometry in isolation, in alignment with local geometry, or in conflict with local geometry. Results (confirmed by a follow-up experiment) indicated that constraining FOV prevented extraction of geometric properties and relationships of space and resulted in an inability to use either global or local geometric cues for reorientation.

Perceptual learning with complex visual stimuli is based on location, rather than content, of discriminating features

Abstract: Exposure to complex checkerboards (comprising a common background, e.g., X, with unique features, e.g., A–D, that are placed in particular locations on the background) improves discrimination between them (perceptual learning). Such stimuli have been used previously to probe human perceptual learning but these studies leave open the question of whether the improvement in discrimination is based on the content or location of the unique stimuli. Experiment 1 suggests that perceptual learning produced by exposure to AX and BX transferred to stimuli that had new unique features (e.g., C, D) in the position that had been occupied by A and B during exposure. However, there was no transfer to stimuli that retained A and B as the unique features but moved them to a different location on the background. Experiment 2 replicated the key features of Experiment 1, that is, no transfer of exposure learning based on content but perfect transfer of exposure learning based on location using a design which allowed for independent tests of location- and content-based performance. In both the experiments reported here, superior discrimination between similar stimuli on the basis of exposure can be explained entirely by learning where to look, with no independent effect of learning about particular stimulus features. These results directly challenge the interpretation of practically all prior experiments using the same type of design and stimuli.

Extinction makes conditioning time-dependent.

Abstract: Two experiments explored whether forgetting of an association depended on previous extinction of a different association in rats. Experiment 1 found that when rats were conditioned and extinguished with flavor X, a subsequently acquired conditioned aversion to flavor Y was reduced by a 19-day retention interval, something that did not occur when X and the US were initially presented unpaired. Experiment 2 found that when rats received training and extinction in one of two tasks (conditioned aversion to sucrose in Experiment 2a, and running for water in a straight alley in Experiment 2b), subsequent learning of the alternative task was partially forgotten over the 19-day retention interval. These results are similar to those previously found when manipulating physical and conceptual contexts in rats and humans, respectively, and suggest that the passage of time may play a role similar to the one played by the change in physical or conceptual contexts on information retrieval.

Blocking and associability change.

Abstract: Blocking of learning about a conditioned stimulus (the "blocked" cue) occurs when it is trained alongside an additional stimulus (the "blocking" cue) that has been previously presented with the outcome. A number of theories (e.g., N. J. Mackintosh. 1975a. A Theory of Attention: Variations in the Associability of Stimuli With Reinforcement. Psychological Review, 82, 276-298; J. M. Pearce & G. Hall. 1980. A Model for Pavlovian Learning: Variation in the Effectiveness of Conditioned But Not Unconditioned Stimuli. Psychological Review, 87, 532-552) account for this attenuation in learning by proposing that attention paid to the blocked cue is restricted. In three experiments, we examined the associability of both blocked and blocking cues. In Experiment 1, rats were trained with a blocking protocol before being given a test discrimination composed of two components; one of these components required the use of the previously blocked cue as a discriminative stimulus, and the other component was soluble by using the blocking cue. To our surprise, the component that depended on the blocked cue was more readily solved than the component dependent on the blocking cue. The results of Experiments 2 and 3 suggest that this is due to the quantity of exposure that each stimulus received during initial training. Implications for theories of blocking, and more widely associative learning, are discussed.

Spontaneous object recognition memory is maintained following transformation of global geometric properties.

Abstract: Studies of spontaneous behavior to assess memory are widespread, but often the relationships of objects to contexts and spatial locations are poorly defined. We examined whether object-location memory was maintained following global, but not local, changes to the geometric shape of an arena. Rats explored two trial-unique objects in a distinctively shaped arena before being exposed to two identical copies of one of these objects in a different shape in a different physical location. Rats preferentially explored objects that were novel in relation to their local geometric context rather than identifying both locations as novel in the global geometric context.

Improved spontaneous object recognition following spaced preexposure trials: evidence for an associative account of recognition memory.

Abstract: Rodents' biased exploration of a novel object over a familiar object is taken as an indication of recognition memory. According to a general associative model of memory, the biased exploration is a consequence of reduced processing of the familiar object. A component of the reduction of stimulus processing is the result of the operation of Arena → Object associations that are best formed during widely spaced presentations of the stimulus. Results of extant experiments support this prediction but so, too, do accounts based on the effects of handling cues. We report an experiment in which handling cues are matched across stimulus-spacing treatments but that retain improved recognition memory with widely spaced stimulus presentation.

Asymmetry in the discrimination of length during spatial learning.

Abstract: The ability of rats to solve a discrimination between two objects that differ in length was investigated in five experiments. Using a rectangular swimming pool, Experiment 1 revealed it is easier to locate a submerged platform when it is near the center of a long rather than a short wall. For Experiments 2–4, the objects were black or white panels pasted onto the gray walls of a square pool, with two long panels pasted to two opposing walls and two short panels pasted to the remaining walls. The platform was easier to locate when it was placed near the middle of a long rather than a short panel. This effect was found when the long panels were twice (Experiments 2–4) or four times the length of the short panels (Experiment 4). Experiment 5 demonstrated that rats can solve a discrimination between panels of length 15 and 45 cm more readily than when they are 70 and 100 cm. The results are consistent with the claim that generalization gradients based on stimulus magnitude are steeper for stimuli that are weaker rather than stronger than the stimulus used for the original training.

Assessing the encoding specificity of associations with sensory preconditioning procedures.

Abstract: Three experiments examined the encoding specificity of associations using sensory preconditioning procedures in rats. In Experiment 1a, after exposure to two compounds (AX and BY), X (but not Y) was either followed by shock after a trace interval (Group Trace) or immediately followed by shock (Group Immediate). AX elicited less activity than BX (i.e., more fear) in Group Trace, but equivalent activity levels in Group Immediate. These results, replicated using a within-subjects design in Experiment 1b, indicate that the presence of A (on AX trials) generates fear because it associatively evokes X's memory into the same state as it was associated with the shock during (trace) conditioning. In Experiment 2, after exposure to AX and BY, X (but not Y) was immediately followed by shock. As in Experiment 1a, presentations of AX and BX elicited equivalent levels of fear, but there was more fear in the trace period after AX than in the trace period after BX. This finding suggests that during aversive conditioning, the associatively provoked memory of A was part of the conditioned complex, and that the trace of AX was more likely to activate this memory than was the trace of BX. (PsycINFO Database Record (c) 2013 APA, all rights reserved)

Modeling Human Sequence Learning Under Incidental Conditions

Abstract: This research explored the role that associative learning may play in human sequence learning. Two-choice serial reaction time tasks were performed under incidental conditions using 2 different sequences. In both cases, an experimental group was trained on 4 subsequences: LLL, LRL, RLR, and RRR for Group "Same" and LLR, LRR, RLL, and RRL for Group "Different," with left and right counterbalanced across participants. To control for sequential effects, we assayed sequence learning by comparing their performance with that of a control group, which had been trained on a pseudorandom ordering, during a test phase in which both experimental and control groups experienced the same subsequences. Participants in both groups showed sequence learning, but the group trained on "different" learned more and more rapidly. This result is the opposite that predicted by the augmented simple recurrent network used by F. W. Jones and I. P. L. McLaren (2009, Human sequence learning under incidental and intentional conditions, Journal of Experimental Psychology: Animal Behavior Processes, Vol. 35, pp. 538-553), but can be modeled using a reparameterized version of this network that also includes a more realistic representation of the stimulus array, suggesting that the latter may be a better model of human sequence learning under incidental conditions.

The Adaptive Analysis of Visual Cognition using Genetic Algorithms

Abstract: Two experiments used a novel, open-ended, and adaptive test procedure to examine visual cognition in animals. Using a genetic algorithm, a pigeon was tested repeatedly from a variety of different initial conditions for its solution to an intermediate brightness search task. On each trial, the animal had to accurately locate and peck a target element of intermediate brightness from among a variable number of surrounding darker and lighter distractor elements. Displays were generated from six parametric variables, or genes (distractor number, element size, shape, spacing, target brightness, distractor brightness). Display composition changed over time, or evolved, as a function of the bird’s differential accuracy within the population of values for each gene. Testing three randomized initial conditions and one set of controlled initial conditions, element size and number of distractors were identified as the most important factors controlling search accuracy, with distractor brightness, element shape, and spacing making secondary contributions. The resulting changes in this multidimensional stimulus space suggested the existence of a set of conditions that the bird repeatedly converged upon regardless of initial conditions. This psychological “attractor” represents the cumulative action of the cognitive operations used by the pigeon in solving and performing this search task. The results are discussed regarding their implications for visual cognition in pigeons and the usefulness of adaptive, subject-driven experimentation for investigating human and animal cognition more generally.

Generalization of feature- and rule-based learning in the categorization of dimensional stimuli: evidence for dual processes under cognitive control.

Abstract: Participants in 2 experiments classified face stimuli into 2 categories determined by the gender of the faces. Although the category rule was simple, the stimuli, created by morphing male and female faces, made the explicit identification of the rule difficult. Participants were classified as rule users or nonusers depending on whether they explicitly identified the gender rule on a postexperiment questionnaire. Nonusers displayed a generalization decrement to new category exemplars that were more obviously male and female but less similar to the trained exemplars. Rule users, instead, generalized their category judgments perfectly to new category members. However, when an exception to the rule was introduced, generalization decrement for stimuli related to the exception was evident in both groups. All participants displayed a near-perfect ability to reverse their category judgments, regardless of whether learning occurred in the presence or absence of the explicit gender rule. The results highlight a distinction between rule- and feature-based category learning but show that both processes are subject to cognitive control.

Contextual control of attentional allocation in human discrimination learning.

Abstract: In 3 human predictive learning experiments, we investigated whether the allocation of attention can come under the control of contextual stimuli. In each experiment, participants initially received a conditional discrimination for which one set of cues was trained as relevant in Context 1 and irrelevant in Context 2, and another set was relevant in Context 2 and irrelevant in Context 1. For Experiments 1 and 2, we observed that a second discrimination based on cues that had previously been trained as relevant in Context 1 during the conditional discrimination was acquired more rapidly in Context 1 than in Context 2. Experiment 3 revealed a similar outcome when new stimuli from the original dimensions were used in the test stage. Our results support the view that the associability of a stimulus can be controlled by the stimuli that accompany it.

Changing room cues reduces the effects of proactive interference in Clark's Nutcrackers, Nucifraga columbiana.

Abstract: To determine what factors are important for minimizing interference effects in spatial memory, Clark's Nutcrackers, Nucifraga columbiana were tested for their spatial memory for two serial lists of locations per day. In this experiment two unique landmark sets were either different between List 1 and List 2 or the same. We found that Nutcrackers were most susceptible to interference when the landmark sets were the same. This study suggests that repeatedly testing animal memory in the same room, with the same cues, can hamper recall due to interference.

Interval timing under variations in the relative validity of temporal cues.

Abstract: Two groups of pigeons were trained to respond on a white center key to a fixed-interval, 60-s schedule of reinforcement signaled by the onset of a side-key cue (S+ training). In additional training sessions, S+ trials alternated between S- trials in which a different side-key cue signaled nonreinforcement after 60 s (S+/S- training). For one group, S+/S- training sessions followed S+ training, and for the other group, S+/S- training preceded S+ training. Peak-time curves obtained from extended nonrewarded probe trials inserted among training trials showed loss of control by time during S+/S- training relative to S+ training. A follow-up experiment showed that this result was not caused by a difference in probability of reinforcement. We suggest that attention to time was weakened by the introduction of visual cues that were more valid predictors of trial outcomes.

Pigeons use low rather than high spatial frequency information to make visual category discriminations.

Abstract: Pigeons were trained to discriminate photographs of cat faces from dog faces. They were then presented with test stimuli involving high- and low-pass spatial frequency filtering. Discrimination was maintained with both types of filtered stimuli, though it was increasingly impaired the more information was filtered out, and high-pass filtering impaired discrimination more than low-pass filtering. The pigeons were then exposed to hybrid stimuli in which high-pass filtered dog faces were combined with low-pass filtered cat faces, and vice versa. Response to hybrid stimuli was determined more by the low spatial frequency content than by the high-frequency content, whereas humans viewing the same stimuli at corresponding viewing distance respond more strongly to the high-frequency content. These results are unexpected given that, compared with humans, pigeons' behavior tends to be controlled by the local details of visual stimuli rather than their global appearance.

Associative models of instrumental learning: a response to Dupuis and Dawson.

Abstract: Miller and Shettleworth (2007) used an associative model of instrumental choice to explain a confusing pattern of results in the geometry learning literature. Dupuis and Dawson (in press) identified a structural flaw in the Miller-Shettleworth (MS) model and suggested replacing it with an operant perceptron model which can correctly reproduce some experimental results that the MS model does not. Here we demonstrate that the error in the MS model can be easily corrected without altering any of the model's predictions by making it stochastic rather than deterministic. In addition, we show that the raw outputs of the perceptron model cannot be interpreted as discriminative choices in an instrumental task without first being normalized. We show that this additional step renders the results of the perceptron model identical to those of the MS model in exactly those cases in which it has been claimed to correctly predict results that the latter cannot.