Retrospective coding in pigeons' delayed matching-to-sample.

In Exp I, 2 groups of 6 White Carneaux pigeons initially learned 0-delay matching-to-sample with identical comparison stimuli (vertical and horizontal lines) but with different sample stimuli (red and green hues or vertical and horizontal lines). Longer delays were then introduced between sample offset and comparison onset to assess whether Ss were prospectively coding the same events (the correct line comparisons) or retrospectively coding different events (their respective sample stimuli). The hue-sample group matched more accurately and showed a slower rate of forgetting than the line-sample group. In Exp II, 20 mixed-breed pigeons were trained (1) with either hues or lines as both sample and comparison stimuli or (2) with hue samples and line comparisons or vice versa. Subsequent delay tests revealed that the hue-sample groups remembered more accurately and generally showed slower rates of forgetting than the line-sample groups. Comparison dimension had little or no effect on performance. Data suggest that pigeons retrospectively code the samples in delayed matching-to-sample. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquired equivalence and distinctiveness in matching to sample by pigeons: Mediation by reinforcer-specific expectancies.

Assessed the ability of a reinforcer to mediate an association between 2 stimuli that independently predict the occurrence of that reinforcer (acquired equivalence of cues). In Exp I, 12 male White Carneaux pigeons were trained on shape (plus and circle) and color (red and green) matching-to-sample tasks. Correct responses were systematically reinforced with corn on some trials and wheat on others to establish associations between 1 stimulus from each task and a "common" outcome. Following training, Ss were transferred to a symbolic matching-to-sample task wherein a stimulus from one training task was presented as the sample, and the stimuli from the other training task were presented as comparisons. In the 1st session, experimental Ss made significantly more correct responses than controls (i.e., Ss "matched" stimuli previously associated with a common outcome). Exp II with 18 Ss replicated this acquired equivalence effect and controlled for food preference. Delayed matching-to-sample training demonstrated enhanced memory performance for Ss exposed to different reinforcement contingencies, but this effect was confined to the shape task. Results indicate that a reinforcer can serve as the basis for organizing otherwise unpaired predictive cues in memory and that animals will selectively use differential expectancies as cues for solving complex discrimination tasks, depending on the difficulty of the discrimination. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Training and Stroop-like interference: Evidence for a continuum of automaticity.

Three experiments varied the extent of practice in an analog of the Stroop color-word task. The experiments involved 4 phases: baseline naming of 4 familiar colors; training in consistently naming 4 novel shapes by using the names of the same 4 colors; naming the colors when they appeared in the form of the shapes; and naming the shapes when they appeared in color. In Exp 1, with up to 2 hr of training in shape naming, colors were named much faster than shapes. Interference was observed only in Phase 4. In Exp 2 (5 hr of training) shape naming sped up, but was still slower than color naming. There was symmetrical interference in Phases 3 and 4 that persisted 3 mo without further training. Exp 3 extended practice to 20 hr, by which time shape and color naming were equally rapid. After 20 hr, interference appeared only in Phase 3, reversing the original asymmetry. The overall pattern is inconsistent with a simple speed of processing account of interference. Implications of the alternative idea of a continuum of automaticity—a direct consequence of training—are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory mechanisms in pigeons: Evidence of base-rate neglect.

In delayed matching to sample, once acquired, pigeons presumably choose comparisons according to their memory for (the strength of) the sample. When memory for the sample is sufficiently weak, comparison choice should depend on the history of reinforcement associated with each of the comparison stimuli. In the present research, pigeons acquired two matching tasks in which Sample S1 was associated with one comparison from each task, C1 and C3, whereas Sample S2 was associated with Comparison C2, and Sample S3 was associated with Comparison C4. As the retention interval increased, the pigeons showed a bias to choose the comparison (C1 or C3) associated with the more frequently occurring sample (S1). Thus, pigeons were sensitive also to the (irrelevant) likelihood that each of the samples was presented. The results suggest that pigeons may allow their reference memory for the overall sample frequency to influence comparison choice, independent of the comparison stimuli present. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorical discrimination and generalization in pigeons: All negative stimuli are not created equal.

Three experiments investigated categorical discrimination and generalization in pigeons. Multiple FI-extinction training was conducted with a pool of 48 different negative discriminative stimuli (12 slides each of people, flowers, cars, and chairs). The most errors were committed to negative stimuli (S–s) from the same category as the 12 positive stimulus (S+) slides. Such categorical generalization was stronger when the 12 S+s entailed 1 copy of 12 different slides (Exp 2) than when the S+s entailed 12 copies of 1 slide (Exp 1). In addition, reliable but incomplete loss of inhibitory control was observed to novel stimuli chosen from the same category as the S– slides (Exp 3). These results are consistent with perceptual theories of categorical coherence, according to which preexisting similarities among stimuli chiefly determine the acquisition and application of categories. (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)     

Orientation invariant pattern recognition by pigeons (Columba livia) and humans (Homo sapiens).

The orientation invariance of visual pattern recognition in pigeons and humans was studied using a conditioned matching-to-sample procedure. A rotation effect, a lengthening of choice latencies with increasing angular disparities between sample and comparison stimuli, was replicated with humans. The choice speed and accuracy of pigeons was not affected by orientation disparities. Novel mirror-image stimuli, rotation of sample shapes, a delayed display of comparison shapes, and a mixed use of original and reflected sample shapes did not lead to a rotation effect in pigeons. With arbitrarily different odd comparison shapes, neither humans nor pigeons showed a rotation effect. Final experiments supported the possibility that the complete absence of a rotation effect in pigeons is because they are relatively better than humans at discriminating mirror-image shapes compared with arbitrary shapes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sources of visual interference in delayed matching-to-sample with pigeons.

In 2 experiments, independent groups of pigeons were trained on an identity matching task involving line orientations as sample and comparison stimuli. An overhead houselight was illuminated continuously throughout each training session or was never illuminated during training sessions. During subsequent testing, the lighting conditions during the delay were the same as in training on some trials, but on other trials they were opposite those of training during either the entire delay (Exp 1) or during a portion of the delay (Exp 2). In Ss trained with the houselight off, turning the houselight on during the delay produced a large and enduring disruption in matching accuracy. In Ss trained with the houselight on, turning the houselight off during the delay produced only a moderate and temporary disruption in matching accuracy. In pigeons, as in monkeys, sustained retroactive interference effects obtain only when the level of illumination is increased during the delay interval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of temporal relations by pigeons.

In 4 experiments, pigeons were tested on a duration comparison task involving the successive presentation of two visual stimuli that varied in duration from trial to trial. Following presentation of the durations, 2 choice keys were lit, and reinforcement for choices was based on the temporal relation between durations of the pair. In Exp 1, the range of durations was varied over conditions. Responding changed as an orderly function of the ratio of the 2 durations. There was a decrease in discrimination accuracy as average duration increased over conditions. In Exp 2, Ss were transferred from a task involving spatially differentiated choices to one involving hue-differentiated choices. Performance was similar to that of Exp 1. In Exp 3, Ss were exposed to a single duration range that included many durations from the 4 ranges of Exp 1. Discrimination accuracy was comparable on 3 problem duration categories within this range and declined slightly for problems in the 4th and longest category. Manipulation of absolute reinforcement rate in Exp 4 resulted in no change in discrimination accuracy, suggesting that the decline in accuracy over conditions of Exp 1 could not be attributed to decreases in reinforcement rate that accompanied lengthier durations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Outcome expectancies as mediators for discriminative responding.

Attempted to identify the mechanism that underlies the differential outcome effect in acquisition and working memory in pigeons. Different outcomes were cued by 2 pairs of colors that also served as initial stimuli in 2 delayed conditional discriminations. The test stimuli were vertical and horizontal lines. Ss were 22 White Carneaux pigeons. The outcomes were arranged so that expectancies based on them would cue the same response patterns to the 2 test stimuli in both problems (consistent conditions) or opposite response patterns (inconsistent conditions). In Exp I, the 2 problems were trained concurrently; acquisition was faster and reached a higher level in the consistent conditions. In Exp II, transfer of a discrimination between pairs of initial stimuli was studied. Transfer based on consistent expectancies was almost perfect, but there was no transfer with inconsistent expectancies. Shifts from inconsistent to consistent training conditions improved performance, and those in the opposite direction worsened performance. It is concluded that expectancies act as mediating cues and control discriminative behavior directly, strengthening or replacing the cues provided by initial stimuli. (French abstract) (18 ref) (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)     

Matching to element and compound samples in pigeons: The role of sample coding.

Pigeons initially trained to match using element samples and element comparisons demonstrate reduced matching accuracy on trials in which the sample is a compound stimulus. Two interpretations of this phenomenon, the shared attention account and the coding decrement account, were assessed in 3 experiments with 8 Silver King pigeons. Exp I obtained the typical outcome of reduced matching accuracy to compound samples following training to match to element samples. However, in a 2nd group trained initially to match to compound samples, Ss matched more accurately on compound sample trials than on element sample trials. Sample duration was manipulated in Exp II, and Ss were tested on simultaneous and 0-sec delayed matching trials in Exp III. Neither manipulation influenced the magnitude of the element–compound difference in either group. It is concluded that the coding decrement interpretation best accounts for these and other findings on matching to element and compound samples in pigeons. This account holds that (a) pigeons do not decompose compound samples; (b) presentation of a familiar sample activates a code; and (c) a novel sample that is sufficiently similar to a sample that activates a code will also tend to activate that code. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Category discrimination of artificial polymorphous stimuli based on feature learning.

Pigeons and humans were trained to discriminate between sets of artificial stimuli defined by a 2-out-of-3 polymorphous concept. Stimuli containing any 2 of 3 positive or negative features were used for training. In Exp 1, pigeons showed complete transfer to stimuli with all 3 positive or negative features and even to stimuli that had 1 of the 3 features replaced with a novel feature. In contrast, humans failed to show transfer to those stimuli. By using a selective reversal procedure for pigeons, Exp 2 revealed that functional equivalence was not formed among either the stimuli or the features. Exp 3 examined how pigeons integrate information from several distinct features to determine the response to any given stimulus. An additive rule and a combination rule were suggested to account for category discrimination by pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition and transfer of visual texture discriminations by pigeons.

Two experiments investigated texture discrimination in pigeons. In a simultaneous conditional-discrimination procedure, pigeons were reinforced for pecking at a small target region of identically colored form elements embedded in a larger region of distractor elements. These regions differed in either color or shape or differed redundantly in both dimensions. Pigeons readily acquired these discriminations and showed substantial positive discrimination transfer to new displays composed from novel recombinations of training colors and shapes, novel colors and shapes, and novel spatial organizations. The global organization of these displays appeared to be chief property mediating performance. This suggests that pigeons have mechanisms for perceptually grouping regions of similar colors and shapes, and these mechanisms may be similar to the preattentive visual mechanisms proposed for human texture segregation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context as a conditional cue in operant discrimination reversal learning.

Five experiments with 68 pigeons investigated the conditions under which contextual stimuli gain conditional control in the discrimination reversal paradigm. In Exp I, Ss learned an operant discrimination in which the positive stimulus (S+) was 555 nm and the negative stimulus (S–) was 576 nm in one context (houselight off plus white noise [HLFN]) and then learned the reversal (S+ 576 nm; S– 555 nm) in another context (houselight on plus tone [HLNT]). Subsequent wavelength generalization testing revealed responding appropriate to each context: The gradients peaked at 555 nm in HLFN and at 576 nm in HLNT. In Exp II, separate groups experienced both visual and auditory context cues, only visual ones, or only auditory ones. The visual cues worked as well as the compound, but the auditory cues gained no conditional control. In Exp III, houselight illumination replaced by white light directly added to the colors serving as discriminative cues. Results suggest that houselight illumination does not gain conditional control by altering the brightness and saturation of the key colors. In Exp IV, HLNT and HLFN gained conditional control over discriminations based on different angles of a white line, but background key color did not. In Exp V, conditional control over a color discrimination was established by contexts consisting of black and white striped walls vs plain walls. Findings suggest that pigeons use diffuse visual cues to identify the place where food-reinforced learning has taken place. (16 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Range effects in successive discrimination.

Examined the discrimination performance of 3 male white Carneaux pigeons, 2 male homing pigeons, and 2 female Oriental frill pigeons with a visual flicker-rate continuum, using a conventional successive discrimination procedure in 2 experiments. In Exp I, responses during the intermediate stimulus value were never reinforced, while responses during stimuli on either end of the continuum were reinforced periodically. In Exp II, responses during stimuli from one end of the continuum were never reinforced, while responses during stimuli from the other end of the continuum were reinforced periodically. Results from both experiments show that discrimination between unchanged positive and negative stimulus values is a function of the range over which the total stimulus set varies. These range effects are comparable to effects found in absolute judgment tasks in human and animal psychophysics. In addition, the range effects are not due to channel capacity but may depend instead on variability in judgment criteria. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of differential reinforcement of low rates (DRL) performance in pigeons (Columba livia) and crows (Corvus brachyrhynchos).

Compared the DRL performance of crows and pigeons in 3 experiments. In Exp I, 4 crows and 3 pigeons were studied under DRL schedules ranging from 10 to 120 sec. A standard pigeon test chamber, with minor modifications for the crow, was used. The crows performed much more successfully, obtaining many more reinforcers and making fewer responses per reinforcement. 2 crows continued to respond effectively up to DRL-120 sec. In Exp II, 3 crows were studied and limited hold requirements were added to the DRL schedules. Each crow showed improved temporal discrimination under this procedure, and the conditional probability curves appeared similar to those for rats. Exp III compared the performance of 3 crows and 3 pigeons under a DRL procedure in which the availability of reinforcement was signaled by a change in key-light color. Both species performed very successfully under this procedure, and the species differences observed in Exp I were essentially eliminated. Overall results suggest that crows can make accurate temporal discriminations in the absence of external cues, while pigeons are dependent on these stimuli for effective responding. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeon perception and discrimination of rapidly changing texture stimuli

The perception and discrimination of rapidly changing texture stimuli by pigeons was examined in a target localization task. Five experienced pigeons were rewarded for finding and pecking at a randomly placed odd target block of small repeated elements embedded in a larger rectangular array of contrasting distractor elements. On dynamic color test trials, the color of the target, distractor, or both of these regions changed at rates of 100, 250, 500, or 1000 ms per frame. The number of colors appearing within such trials also varied. Pigeons performed well above chance in all test conditions, with target-associated changes producing the best discrimination. The results suggest: (a) global relational information can exclusively guide target localization behavior, (b) pigeons can perceptually group and segregate colored textured differences quite rapidly (< or = 100 ms), and (c) pigeons may possess automatic search control processes that can be captured by stimulus-driven changes in the display.     

Evidence for common coding in many-to-one matching: Retention, intertrial interference, and transfer.

Two experiments indicated that pigeons commonly code samples associated with same comparison in many-to-one matching. Experiment 1 showed that retention was similar for pigeons matching four sample stimuli (two hues and two lines) to a different pair of comparisons (hues or lines). Accuracy was slightly higher with hue than with line samples, but this did not interact with delay. Alternative samples from each dimension and associatively different samples from the different dimensions both produced intertrial interference. In Experiment 2, pigeons learned new comparison associations to two samples from a prior many-to-one task. Later, their ability to match the remaining samples to the new comparisons was tested. Positive transfer occurred when samples previously paired with the same comparison replaced one another. Negative transfer occurred when opposing samples were interchanged. Apparently, the associatively related samples in many-to-one matching evoke similar representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of short-term memory codes on visual image processing: Evidence from image transformation tasks.

Three experiments showed that phonological recoding of visual stimuli in short-term memory affects coding in long-term memory (LTM) and therefore performance on tasks involving generation and manipulation of visual images of the stimuli. An image transformation task was devised. It consists of mentally subtracting a part of an image to discover in the remainder another object. In Exp 1, Ss were required to learn a set of easily nameable visual stimuli and then perform the subtraction task on images retrieved from LTM. Performance was significantly better when initial learning was accompanied by articulatory suppression (AS). Exp 2 confirmed that AS had no effect when the task was performed on an image of a just-presented stimulus. In Exp 3, the nameability of the stimuli was manipulated. The results replicated the effect of AS for items that were easy to name but showed no effect of AS for stimuli that were difficult to name. (PsycINFO Database Record (c) 2010 APA, all rights reserved)