Memory variance in the peak procedure of timing in pigeons.

Pigeons were rewarded on a fixed interval (FI) schedule. On occasional unrewarded tests, they usually showed a break–run–break pattern of responding. Across trials, the start of the run correlated positively with the end, suggesting variance across trials in (1) clock speed, (2) the delay to start the clock, or (3) a single criterion time used on a trial. If variance in criterion time exists, then a task in which the start and the end of the run are based on independent criterion times should produce a reduced start–end correlation. In 2 such tasks, the start–end correlation dropped to near zero, although other correlations were comparable to those found in the standard FI task. This provides evidence for variance across trials in a single criterion time used on a trial. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Using the peak procedure to measure timing and counting processes in pigeons.

In 4 experiments, it was shown that the peak procedure can be used to study timing and counting in pigeons. In Experiment 1, pigeons were trained to peck at a green key that briefly flashed red every second. After training under a fixed interval 20 s/fixed number 20 flashes schedule of reinforcement, time and number were dissociated on empty test trials by varying the flash rate. The peak-time curves for different flash rates suggested that pigeons were using a strategy of responding to the first dimension, time or number, that crossed a threshold for initiating and terminating response. Experiments 2 and 3 showed that pigeons could be trained to time or count on empty trials by reinforcing response to only time or number. It was found in Experiment 4 that the set to time or count transferred to a new fixed interval 30 s/fixed number 30 flashes schedule of reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial peak shift and generalization in pigeons.

How pigeons generalize across spatial locations was examined in the 4 experiments reported in this article. During training, a square was presented at a fixed height at 1 of 2 horizontal locations on a monitor screen. One location (S+ ) signaled reward, whereas the other one (S–) signaled no reward. The birds were then tested occasionally with a range of locations. After training with S+ only, the generalization gradient peaked at S+ and was approximately Gaussian in shape. After training with equal numbers of S+ and S– trials, response rates were higher on the S+ side of the distribution. This asymmetry diminished over testing. When the S+ and S– were close together, the peak of responding was shifted on initial generalization tests. Generalization gradients along the orthogonal vertical dimension were approximately exponential in shape. This is the first demonstration of generalization and peak shift in the spatial domain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contextual stimulus control over operant responding in pigeons.

Gave pigeons (N = 48) 17 days of single stimulus (S) training with a house light and tone context. Ss were then given 20 days of discrimination training with a 555-nm green response key (S+) and a line (S-). For Group 1 the light and tone were paired with S+ (S+/context), for Group 2 they were paired with S- (S-/context), and for Group 3 they were paired with both (no context change, or NCC). For each group a matched control group experienced the same stimulus configurations without the prior single stimulus training. Then all groups were tested for wavelength generalization. Of the 3 experimental groups, the S+/context group acquired the discrimination the fastest, the S-/context group started poorly but eventually mastered the discrimination, and the NCC group never mastered it. The experimental groups yielded flatter wavelength gradients than did their matched controls, which suggests blocking by the contextual stimuli. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of lesions of the ascending 5-hydroxytryptaminergic pathways on timing behaviour investigated with the fixed-interval peak procedure

Twelve rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei; 12 rats received sham lesions. The rats were then trained for 60 sessions under a discrete-trials fixed-interval schedule (peak procedure). In half the trials, a reinforcer became available 40 s after trial onset, and the trial was terminated upon reinforcer delivery; the remaining trials were 120 s in duration, and reinforcement did not occur in these trials. Performance during the 120-s trials was characterized by increasing response rate during the first 40 s of the trial, declining response rate between 40 s and 80 s, and a secondary increase in response rate during the final 40 s of the trial. The lesioned group showed a broader "spread" of the response rate function than the control group (time between attainment of 70% of the peak response rate and subsequent decline of response rate below this level); however, the peak response rate and the time from trial onset until attainment of the peak response rate did not differ significantly between the groups; the spread/peak-time ratio was significantly greater in the lesioned group than in the control group. The levels of 5-hydroxytryptamine (5HT) and 5-hydroxyindoleacetic acid in the parietal cortex, hippocampus, amygdala, nucleus accumbens and hypothalamus were markedly reduced in the lesioned group, but the levels of noradrenaline and dopamine were not significantly affected by the lesion. The results confirm the involvement of 5HTergic function in timing behaviour.     

Rapid acquisition of choice and timing in pigeons.

Pigeons were trained on a concurrent-chains procedure in which the initial link associated with the shorter terminal-link delay to food changed unpredictably across sessions. In the minimal-variation condition, delays were always 10 s and 20 s, whereas in the maximal-variation condition delays were generated pseudorandomly for each session. On some terminal links, food was withheld to obtain measures of temporal control. Measures of choice (log initial-link response ratios) and timing (start and stop times on no-food trials) showed temporal control and stabilized within the 1st half of each session. In the maximal-variation condition, choice was a nonlinear function of the log delay ratio, consistent with a categorical discrimination but contrary to models based on the matching law. Residuals from separate regressions of log response and log start and stop time ratios on log delay ratios were positively correlated. Overall, results support cognitive models that assume that initial-link choice is based on an all-or-none decision process, and that choice and timing are mediated by a common representation of delay. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of differential sample responding in the differential outcomes effect involving delayed matching by pigeons.

The role of differential sample responding in the differential outcomes effect was examined. In Exp 1, pigeons were trained on a one-to-many matching task with differential sample responding required. Differential outcomes were associated with samples and comparisons, with comparisons only, or with neither samples nor comparisons. Slopes of delay functions for trials with pecked versus nonpecked samples suggested use of a single-code-default strategy in the nondifferential-outcomes group but not in the differential-outcomes groups. In Exp 2, differential sample responding and differential outcomes were manipulated independently. Again, there were significant differences in the relative slopes of the delay functions. Results suggest that differential outcomes exert their effect independently of differential sample responding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prediction of the peak shift in pigeons from gradients of excitation and inhibition.

Obtained stimulus generalization gradients of excitation and inhibition from 2 groups of 5 Silver King pigeons each along the hue dimension. A predicted postdiscrimination gradient (PDG) was computed from the algebraic summation of these gradients. This predicted gradient was compared with the actual PDG obtained from a 3rd group of 5 Ss. The PDG computed from the gradients of excitation and inhibition predicted the peak shift found in the actual PDG, but there was a greater distribution shift in the actual than the predicted PDG. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The randomization procedure in the study of categorization of multidimensional stimuli by pigeons

Pigeons categorized rectangles varying in both height and width in an adaptation of a method used by Ashby and colleagues for the cognitive and neuropsychological analysis of human decision bounds for ill-defined categories. Optimal decision bounds were defined in a stimulus space in which the point (x,y) corresponded to a rectangle with width x and height y. Four tasks defined the following 4 optimal bounds: x = y, x = c, x = y + d, and (x-a)2 + (y-b)2 = r2, where a, b, c, d, and r were constants given by a task. Estimated decision bounds for individual pigeons conformed approximately to the optimal decision bound in each of the 4 tasks. The new method suggests a way to (a) integrate the disparate literature on ill-defined visual concepts and on optimal performances in nonhuman animals; (b) compare how humans and nonhuman animals categorize ambiguous, multidimensional configural stimuli; (c) model how nonhuman animals categorize naturalistic stimuli; and (d) infer that pigeons' categorizations of naturalistic stimuli may be remarkably close to optimal.     

Music discriminations by pigeons.

In Exp I, 2 White Carneaux pigeons responded at more than 80% correct in a single-operandum discrimination learning task when the S+ was a 1-min excerpt of Bach flute music and the S– was a 1-min excerpt of Hindemith viola music. In Exp II, 4 Ss responded at more than 70% correct when they were required to peck the left of 2 disks during presentations of any portion of a 20-min Bach organ piece and to peck the right disk during any portion of Stravinsky's Rite of Spring for orchestra. These discriminations were learned slowly. However, the Ss generalized consistently and independently of the instruments involved when presented with novel musical excerpts in Exp III. They preferred the left "Bach disk" when novel excerpts from Buxtehude and Scarlatti were introduced and the right "Stravinsky disk" when novel excerpts from Eliot Carter, Walter Piston, and another Stravinsky work were introduced. Seven college students responded similarly. Therefore, the pigeon's response to complex auditory events may be more like the human's than is often assumed. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rotational object discrimination by pigeons.

Four experiments examined the discrimination of directional object motion by pigeons. Four pigeons were tested in a go/no-go procedure with video stimuli of geons rotating right or left around their central y-axis. This directional discrimination was learned in 7 to 12 sessions and was not affected by changes in object starting orientation, but did require the coherent ordering of the videos’ successive frames. Subsequent experiments found no or little transfer of this motion discrimination to novel objects. Experiments varying the speed of rotation and degrees of apparent motion per frame revealed that both factors strongly affected the discrimination. Finally, tests with partial occlusion of different portions of a rotating object suggested that the majority of the object was likely involved in determining rotational direction. These experiments indicate that pigeons can exclusively use motion cues to judge relative object motion. They also suggest the pigeons may have used a specific representation of the motion sequences of each object to make the discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Matching-to-sample abstract-concept learning by pigeons.

Abstract concepts--rules that transcend training stimuli--have been argued to be unique to some species. Pigeons, a focus of much concept-learning research, were tested for learning a matching-to-sample abstract concept. Five pigeons were trained with three cartoon stimuli. Pigeons pecked a sample 10 times and then chose which of two simultaneously presented comparison stimuli matched the sample. After acquisition, abstract-concept learning was tested by presenting novel cartoons on 12 out of 96 trials for 4 consecutive sessions. A cycle of doubling the training set followed by retraining and novel-testing was repeated eight times, increasing the set size from 3 to 768 items. Transfer performance improved from chance (i.e., no abstract-concept learning) to a level equivalent to baseline performance (>80%) and was similar to an equivalent function for same/different abstract-concept learning. Analyses assessed the possibility that item-specific choice strategies accounted for acquisition and transfer performance. These analyses converged to rule out item-specific strategies at all but the smallest set-sizes (3-24 items). Ruling out these possibilities adds to the evidence that pigeons learned the relational abstract concept of matching-to-sample. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Velocity-based motion categorization by pigeons.

To examine if animals could learn action-like categorizations in a manner similar to noun-based categories, eight pigeons were trained to categorize rates of object motion. Testing 40 different objects in a go/no-go discrimination, pigeons were first trained to discriminate between fast and slow rates of object rotation around their central y-axis. They easily learned this velocity discrimination and transferred it to novel objects and rates. This discrimination also transferred to novel types of motions including the other two axes of rotation and two new translations around the display. Comparable tests with rapid and slow changes in the objects' size, color, and shape failed to support comparable transfer. This difference in discrimination transfer between motion-based and property-based changes suggests the pigeons had learned motion concept rather than one based on change per se. The results provide evidence that pigeons can acquire an understanding of motion-based actions, at least with regard to the property of object velocity. This may be similar to our use of verbs and adverbs to categorize different classes of behavior or motion (e.g., walking, jogging, or running slow vs. fast). (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Dynamic object perception by pigeons.

Three experiments examined pigeon discrimination of computer-generated three-dimensional (3-D) projections of cube and pyramid objects. Four pigeons were tested using a go/no-go procedure involving static and dynamically rotating presentations of these stimuli. Transfer tests with different types of rotational and featural transformations suggested the pigeons may have used a 3-D representation of the objects as their primary means of performing the discrimination. The comparative implications for object and motion perception in animals are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The pattern of responding in the peak-interval procedure with gaps: An individual-trials analysis.

Humans and lower animals time as if using a stopwatch that can be “stopped” or “reset” on command. This view is challenged by data from the peak-interval procedure with gaps: Unexpected retention intervals (gaps) delay the response function in a seemingly continuous fashion, from stop to reset. We evaluated whether these results are an artifact of averaging over trials, or whether subjects use discrete alternatives or a continuum of alternatives in individual-trials: A Probability-of-Reset hypothesis proposes that in individual gap trials subjects stochastically use discrete alternatives (stop/reset), such that when averaged over trials, the response distribution in gap trials falls in between “stop” and “reset.” Alternatively, a Resource Allocation hypothesis proposes that during individual gap trials working memory for the pregap duration decays, such that the response function in individual gap trials is shifted rightward in a continuous fashion. Both hypotheses provided very good fits with the observed individual-trial distributions, although the Resource Allocation hypothesis generated reliably better fits. Results provide support for the usefulness of individual-trial analyses in dissociating theoretical alternatives in interval timing tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Testing models of delayed sequence discrimination in pigeons: The advance key procedure.

In 2-event delayed sequence discrimination (DSD) training, one arrangement (temporal order) of 2 sample stimuli is the positive sequence and the remaining are the negative sequences for keypecking during a subsequent test stimulus. Three models of the DSD task were tested in 2 experiments with 8 White Carneaux pigeons. In Exp I Ss were allowed to terminate a trial by pecking the "advance key" during the sample stimuli or to let the test stimulus progress to the next trial. In the absence of a peck to the advance key, the trial continued to the completion of the test stimulus. In Exp II, Ss were forced to choose actively between advancing to the next trial and continuing through the current trial. Choice between the advance and continue keys was required with the occurrence of each of the successive sample stimuli and the test stimulus. Although the addition of forced choice resulted in more uniform effects, Ss were able to identify negative sample sequences with the occurrence of the 1st negative sample event in both experiments. Results support the prospective memory model but not the retrospective and hybrid models of temporal sequence recognition in the 2-event DSD task. (French abstract) (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bisection of temporal intervals by pigeons.

Two experiments investigated temporal bisection in 7 male White King pigeons using a procedure similar to that of D. A. Stubbs (see record 1976-27339-001), which measures the point in time at which the S switches from the shorter to the longer valued of 2 FI reinforcement schedules with a common starting point. Exp I substantiated Stubbs's findings of switching at the geometric mean of the 2 interval values and eliminated the possibility that Ss simply switched to the longer interval when the shorter one was perceived to have expired. The experiment also extended the range of values for which temporal intervals have been found to be bisected at their geometric mean. Exp II demonstrated that the usefulness of the present procedure for determining temporal bisection points is limited to cases in which the longer interval is no more than 4 times the duration of the shorter. Greater separation of the 2 durations produced a period of nonresponding during which the location of the switching or bisection point was totally ambiguous. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of stimulus compounds by pigeons.

Used a matching-to-sample (MTS) procedure to investigate short-term memory for compound visual stimuli in 10 mixed-breed pigeons. In Exp I, a symbolic MTS procedure was used. Three Ss were trained to match element samples, and 3 were trained to match compound samples. Findings indicate that the compound-trained group did not learn to match the compound samples in terms of element matching rules but rather processed them as unitary events. In Exp II, Ss were trained to match either element or compound samples in a true MTS task. Both groups were able to match elements and compounds in the transfer test. Findings show that at least some compound stimuli were represented in a unitary, nonanalytic fashion until the S was exposed to the elements of the compound in isolation from the compound. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prototype effects in categorization by pigeons.

In 4 experiments involving a total of 78 pigeons, Ss received a categorization task involving 6 simultaneous compounds in which the elements A, B, and C were more frequently paired with food than were the elements D, E, and F. Food was delivered after compounds ABF, AEC, and DBC but not after DEC, DBF, and AEF. Subsequent testing revealed a higher rate of responding during ABC than during any of the compounds that had signaled food and a lower rate of responding during DEF than during any of the compounds that had not signaled food. Exps 2, 3, and 4 further demonstrated that the rate of responding during test trials with ABC was faster than during a compound composed of 3 elements that had individually been paired with food. Results are more consistent with a configural than an elemental analysis of discrimination and categorization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Forgetting of visual discriminations by pigeons.

Three experiments examined the forgetting of visual discriminations by 48 Silver King pigeons. The problems consisted of feature discriminations, with dot displays as the discriminative stimuli, and involved a successive go/no-go pecking response. In all 3 experiments, Ss trained to refrain from pecking an S– display resumed pecking at this display after retention intervals. It is argued that these data represent the 1st direct demonstration of forgetting of a discrimination by pigeons. Exp I also showed that the amount of forgetting progressively increased, in a negatively accelerated fashion, over intervals of 1, 10, and 20 days. Also, more S– responses occurred during relearning a reverse discrimination than after relearning a nonreverse discrimination. In Exp II, acquisition was retarded and more forgetting occurred for discriminations that involved more highly similar stimuli. In Exp III, a change in contextual cues between acquisition and retention testing enhanced forgetting when the contextual cues present during original acquisition were conspicuous; when these cues were relatively inconspicuous, a change in context had no effect on forgetting. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)