Encoding of spatial information in images of an outdoor scene by pigeons and humans

Pigeons and adult humans searched for a 2-cm² unmarked goal in digitized images of an outdoor scene presented on a touch-screen monitor. In Experiment 1, the scene contained three landmarks near the goal and a visually rich background. Six training images presented the scene from different viewing directions and distances. Subsequent unreinforced tests in which landmark or background cues were removed or shifted revealed that pigeons’ search was controlled by both proximal landmarks and background cues, whereas humans relied only on the proximal landmarks. Pigeons’ search accuracy dropped substantially when they were presented with novel views of the same scene, whereas humans showed perfect transfer to novel views. In Experiment 2, pigeons with previous outdoor experience and humans were trained with 28 views of an outdoor scene. Both pigeons and humans transferred well to novel views of the scene. This positive transfer suggests that, under some conditions, pigeons, like humans, may encode the three-dimensional spatial information in images of a scene.     

Distances and directions are computed separately by honeybees in landmark-based search

Honeybees were trained with two landmarks at some angle (e.g., 120°) apart from the target. On crucial unrewarded tests, only a single landmark was present. If distances and directions to landmarks are computed separately (independent averaging), the search distance to the landmark should equal the landmark-target distance found in training. If entire vectors are averaged, the search distance should be much shorter. Three experiments with short target-landmark distances showed results in between the predictions of the two hypotheses. A fourth experiment used longer target-landmark distances and isolated double peaks on single-landmark tests: one predicted by the independent averaging hypothesis, and one very close to the landmark. The near peak is interpreted as arising from approach and exploration of a landmark in a new location, and not from searching.     

Factors affecting conditional discrimination learning by pigeons: II. Physical and temporal characteristics of stimuli

Four experiments were performed to determine the stimulus characteristics that favor the development of conditional stimulus control in the single reversal paradigm with pigeon subjects. In Experiment 1, pigeons were trained on a successive discrimination between tone frequencies ranging from 350 to 3500 Hz in a particular houselight context condition (houselight-on or -off). The subjects then were trained on the reversal of the tone discrimination in the alternative context. Subsequent tone-frequency generalization testing in the two contexts indicated that they had failed to gain conditional control over the pigeons’ discriminative performance. Such control was obtained in Experiment 2, in which the two problems were alternated daily for 32 sessions of training. The gradients then peaked at the appropriate S+ value in each context. In Experiment 3, the key colors (blue vs. red) served as contexts while pigeons learned a successive discrimination in which the discriminative cues were houselight-on versus houselight-off conditions. This was followed by a reversal of the discrimination in the alternative key-color context condition. The key colors were effective conditional cues in this situation. In a previous experiment (Thomas, McKelvie, & Mah, 1985), key color had been ineffective as a conditional cue when the discriminative cues were lines superimposed on the colored background. In Experiment 4, key color was effective when the color and lines were presented on a single key as in the earlier experiment, but were sequenced such that the onset of the key color preceded and then overlapped the presentation of the lines. We concluded that conditional discriminations are easiest for pigeons when visual cues are used, but the conditional and discriminative cues must be presented in such a way that they do not combine to form a psychological compound.     

The Spatial Coding Strategies of One-Year-Old Infants in a Locomotor Search Task

The ability of 1-year-old infants to remember the location of a nonvisible target was investigated in 3 experiments. Infants searched for a toy hidden in one of many possible locations within a circular bounded space. The presence, number, and spatial arrangement of local cues or "landmarks" within this space were varied. The results of Experiment 1 showed that search performance was highly successful when a landmark was coincident with the location of the toy ("direct"), but less successful when a landmark was adjacent to the target location ("indirect"). The results of Experiment 2 suggested that search with an indirect landmark may be more fragile than search with no landmarks at all. In Experiments 3a and 3b, 2 different configurations of indirect landmarks were employed; search performance was equally poor with both of these and was inferior to search with no landmarks. It is concluded that infants of this age are able to associate a nonvisible target with a direct landmark and are able to code the distance and direction of a target with respect to themselves or with respect to the larger framework. However, there was no evidence that they can code the distance and direction of a target relative to another object. The difficulty of coding with indirect landmarks is interpreted in terms of cognitive complexity and conflict between spatial strategies.     

Conditioned reinforcement and complex discrimination: Can conditioned reinforcing value be specific to a complex of three cues?

The present experiment is concerned with the nature of the cues that might acquire conditioned reinforcing value, and the ways in which such cues might interact with one another. Red and green colored keylights were differentially paired with food dependent upon the houselight context (A or B) and the trial type (training or choice/forced). The duration of the colored keylights was varied between groups in an attempt to manipulate the effectiveness of the short-term memory of trial-type cues at the trial’s end. The red and green stimuli were of 30 sec duration for Group 30 and of 3 sec duration for Group 3. The results indicated that the choices of the pigeons in Group 30 were influenced by the houselight context present and by the keylight color. The choices of the pigeons in Group 3 seemed to be influenced by the houselight context present, the keylight color, and the memory of trial-type cues. Memory cues for trial antecedents were not overshadowed by presumably more salient external houselight stimuli for the pigeons in Group 3. Two alternative explanations for the results are discussed, and determined to be unlikely based on the results of an earlier experiment. The present results are related to a model of the conditioned reinforcing value of momentary stimuli and of transmission of conditioned reinforcing value.     

Surprise and change: Variations in the strength of present and absent cues in causal learning

It is said that “absence makes the heart grow fonder.” But, when and why does an absent event become salient to the heart or to the brain? An absent event may become salient when its nonoccurrence is surprising. Van Hamme and Wasserman (1994) found that a nonpresented but expected stimulus can actually change its associative status—and in the opposite direction from a presented stimulus. Associative models like that of Rescorla and Wagner (1972) focus only on presented cues; so, they cannot explain this result. However, absent cues can be permitted to change their value by assigning different learning parameters to present and absent cues. Van Hamme and Wasserman revised the Rescorla-Wagner model so that the α parameter is positive for present cues, but negative for absent cues; now, changes in the associative strength of absent cues move in the opposite direction as presented ones. This revised Rescorla-Wagner model can thus explain such otherwise vexing empirical findings as backward blocking, recovery from overshadowing, and backward conditioned inhibition. Moreover, the revised model predicts new effects. For example, explicit information about the absence of nonpresented cues should increase their salience (that is, their negative α value should be larger), leading to stronger associative changes than when no explicit mention is made of cue absence. Support for this prediction is detailed in a new causal judgment experiment in which participants rated the effectiveness of different foods’ triggering a patient’s allergic reaction. Overall, these and other findings encourage us to view human causal learning from an associative perspective.     

Counting absolute numbers of items,from 1 to 8, in pigeons

Pigeons were trained in a forced choice task with four alternatives to categorize arrays consisting of 1, 3, 5, or 8 dots. Before the pigeons chose a comparison stimulus, they were required to peck each dot sequentially. A single peck to a dot, which was defined as an indicating response, changed the color of the dot so that it was differentiated from those that remained to be counted. The pigeons successfully learned to categorize the numerical arrays and then displayed transfer to novel arrays consisting of two, four, six, or seven dots, in a manner according to the order of 1 < 2 < 3 < 4 < 5 < 6 < 7 < 8. Subsequent tests revealed that the pigeons discriminated the stimuli by relying on the number of indicating responses. They also utilized multiple information (surface area, time, and other confounded events), but this was of minor significance, and after training, the pigeons were able to disregard these cues.     

Pigeons exhibit higher accuracy for chosen memory tests than for forced memory tests in duration matching-to-sample

Following training to match 2- and 8-sec durations of feederlight to red and green comparisons with a 0-sec baseline delay, pigeons were allowed to choose to take a memory test or to escape the memory test. The effects of sample omission, increases in retention interval, and variation in trial spacing on selection of the escape option and accuracy were studied. During initial testing, escaping the test did not increase as the task became more difficult, and there was no difference in accuracy between chosen and forced memory tests. However, with extended training, accuracy for chosen tests was significantly greater than for forced tests. In addition, two pigeons exhibited higher accuracy on chosen tests than on forced tests at the short retention interval and greater escape rates at the long retention interval. These results have not been obtained in previous studies with pigeons when the choice to take the test or to escape the test is given before test stimuli are presented. It appears that task-specific methodological factors may determine whether a particular species will exhibit the two behavioral effects that were initially proposed as potentially indicative of metacognition.     

Attempts to condition homing pigeons to magnetic cues in an outdoor flight cage

An attempt was made to train 9 homing pigeons to respond to the presence or absence of bar magnets by turning either left or right after flying the length of a 20-ft outdoor flight cage. During initial training, color cues were placed in front of feeding stations on the left and right sides of the cage. The color cues were paired with magnetic cues by attaching either bar magnets or brass bars to the backs of the birds. The color cues were then deleted, leaving only the magnetic cues. Each pigeon received about 300 trials of color training followed by about 200 trials of magnet testing. When only magnetic cues remained, none of the pigeons were able to choose the correct feeder at greater than chance levels of probability.     

Discrimination and representation of relative numerosity in a bisection task by pigeons

We trained 4 pigeons in a numerical bisection task to discriminate between pairs of keylight flashes with a ratio of 1∶3 (2 vs. 6, 4 vs. 12, and 8 vs. 24) that were presented in a sample phase. Responses to the blue key were reinforced after a sequence of a larger number of flashes, and responses to the white key were reinforced after a sequence of a smaller number of flashes. The intervals between flashes in the sample phase were randomized to attenuate the covariation of temporal cues with flash number. Pigeons responded accurately in each of the discriminations, with typically 85%–90% correct responses. Transfer tests showed that the proportion of large responses increased with number and performance generalized to larger values outside the training ranges. Psychometric functions superposed when plotted on a relative scale, and estimates of Weber fractions were approximately constant, suggesting that variability was scalar. However, contrary to previous research in nonhumans, bisection points were located at the arithmetic, not geometric, mean. Hierarchical logistic regressions confirmed significant control over responding by number beyond that attributable to temporal cues. These results show that pigeons are able to respond accurately in a relative numerosity discrimination with successively presented visual stimuli, although the nature of the numerical representation and response rule remains unclear.     

Pigeons learn to answer the question “where did you just peck?” and can report peck location when unexpectedly asked

If pigeons are trained on matching-to-sample with differential responding required to the two samples, there is evidence that the differential responding can control comparison choice. We asked whether similar responding required at two different locations could also serve as the basis for comparison choice. Pigeons were pretrained to report the location that they had pecked. To reduce the likelihood that they could use the presence of differential proprioceptive cues at the time of their report, a common response was required between the location response and the comparison choice. They were then given experience with a conditional discrimination in which location of the comparison response varied randomly and was incidental to the choice of comparison. On test trials, after the pigeons had made their comparison choice, they showed a significant tendency to choose the appropriate test comparison when they were unexpectedly asked to report the location of their previous pecking response. These results have implications for the demonstration of episodic-like memory in pigeons because they suggest that pigeons have the capacity to recall, unexpectedly, specific details about their past experiences. 2007 Psychonomic Society, Inc.     

The sensory basis of spatial memory in the rat

Rats were given three stages of training on an eight-arm, elevated radial maze with food reward at the end of each arm. In Stage 1, rats were allowed to choose freely among the arms from the beginning of a trial. In Stage 2, three initial forced choices were followed by a series of free choices. In Stage 3, the central platform of the maze was rotated with the rat on it between the initial forced choices and the free choices. Following testing on these three stages, the animals were divided into four groups and deprived of selected senses. One group was made blind, a second anosmic, a third blind and anosmic, and a fourth was left normal. The same three stages of testing that had been conducted preoperatively then were run again post-operatively. Throughout these tests, the possible use of auditory cues was tested by presenting white noise on alternate trials. Finally, two further tests were carried out, the multiple rotations test and the removal-replacement test. The results indicated that visual cues, but not olfactory or auditory cues, played a critical role in the rat’s ability to avoid previously entered alleys. There was evidence also that rats used internal cues from kinesthetic and/or vestibular receptors when visual cues were absent.     

How is radial arm maze behavior in rats related to locomotor search tactics?

Norway rats have been shown to depend on short-term spatial memory to find food on a radial arm maze (RAM), but what locomotor search tactics are involved in using this memory effectively? Four experiments distinguished tactics of distance minimizing, central-place search, trail following, thigmotactic search, and random search by using different configurations of a RAM placed flat on the floor of an arena. These search tactics make similar predictions on an elevated RAM but predict different outcomes on a floor RAM because the rats are free to approach the food from any direction. After initial trials dominated by exploration, rats traveled along arms to food, even when the resultant distance was up to three times the minimum distance. With no food present, rats also traveled along arms; with no arms up to present, they traveled along walls to food. It appears that both maze arms and arena walls engage mechanisms related to trail following in rats.     

Domestic pigeons (Columba livia) discriminate between photographs of individual pigeons

In two experiments, we examined the discrimination of photographs of individual pigeons by pigeons, using go/no-go discrimination procedures. In Experiments 1A and 1B, the pigeons were trained to discriminate 4 photographs of one pigeon from those of a number of pigeons. The subjects learned the discrimination, but their discriminative behavior did not transfer to new photographs taken from novel perspectives. When the pigeons were trained to discriminate between 20 photographs of five pigeons taken from four perspectives as the S+ and 20 photographs of five different pigeons as the S-, the subjects learned the discrimination, and this discriminative behavior partially transferred to new photographs taken from novel perspectives (Experiments 2A-2C). The results suggest that pigeons are able to discriminate among conspecific individuals, using stationary visual cues. This strengthens the assumption in evolutionary theory that animals can discriminate among individuals and encourages further investigation as to how this ability is used in various behaviors of animals.     

Stimulus stringing by pigeons: Conditional strings

Pigeons were trained to produce one serial list in the presence of a green background cue and another serial list in the presence of a red background cue when the items for both serial lists were presented on each trial. This demonstrated a combination of serial learning and conditional discrimination learning not previously shown in pigeons. Specifically, when presented with four geometric forms, A B C D, in random locations of a five-key display, the pigeons learned to peck A B C when the background was green and A B D when the background was red. Accuracy on the conditional string ranged from 73% to 85%. Transfer tests using different locations of the stimuli on the keys showed positive transfer, thus ruling out learning of specific locations as the basis of the accurate performance. Above-chance performance was maintained when the conditional colors were presented only on the key that did not contain one of the serial stimuli. The results are interpreted in terms of a chaining model that postulates that the sequential selections were controlled by cues produced by both onset of the trial and prior selections within the trial.     

Time-course of control by specific stimulus features and relational cues during same-different discrimination training

We trained 7 pigeons to discriminate visual displays of 16same items from displays of 16different items. The specific stimulus features of the items and the relations among the items could serve as discriminative stimuli. Unlike in most studies of same-different discrimination behavior, we gave a small number of probe tests during each session of acquisition to measure the time-course of control by the learning of specific stimulus features and relational cues. Both the specific stimulus features and relational cues exerted reliable stimulus control, with the specific stimulus features exerting more control during the final three fourths of same-different learning. These findings replicate research suggesting that pigeons encode both the specific stimulus features and relational cues, and for the first time document the time-course of control by each kind of cue.     

Associatively activated representations of food events resemble food outcome expectancies more closely than they resemble food-based memories

When Pavlovian stimuli activate representations of food, do these representations resemble memories of food consumed in the recent past or expectancies of food that is imminent? In Experiments 1A and 1B, this question was addressed by training pigeons on a symbolic matching-to-sample task involving different grains as memory cues or as expectancy cues for correct choices. Autoshaping trials involving these same grains were interspersed among matching-to-sample trials, as were test trials involving the substitution of autoshaping stimuli for cues in the matching-to-sample task. Control over choices transferred to autoshaping stimuli in both experiments, suggesting that associatively activated representations of food resemble both memories and expectancies. In Experiment 2, pigeons were trained on a symbolic matching-to-sample task in which food and no-food memory cues (i.e., the samples) were juxtaposed with no-food and food expectancy cues. Subsequently, autoshaping stimuli, which activated representations of food and no food, were substituted for the samples. Choices by the pigeons indicated that associatively activated representations of food-related events resemble expectancies more closely than they do memories.     

Path integration in cockroach larvae,Blattella germanica (L.) (insect: Dictyoptera): Direction and distance estimation

The question of how an insect finds its way between foraging areas and its shelter has been investigated in cockroaches,Blattella germanica. Our aim was to demonstrate that they integrate the characteristics of their outward trip to estimate direction and distance, which enable them to return to their shelter, relying on path integration mechanisms using kinesthetic cues. The return path pattern was characterized by a nearly linear oriented-to-the-goal trajectory, an arrest, and a systematic search at a much slower speed. The arrest position indicated that the insect’s home vector was back to zero and that it was the estimated shelter position. If the shelter failed to be at the arrest position, cockroaches started a nonrandom systematic search directed mainly around the arrest. They looped back and forth around the arrest position and increased the size of their loops with time. The pattern of this search seems to be an ubiquitous trait in insects.     

The influence of spatial irregularity upon radial-maze performance in the rat

In two experiments, we examined how the introduction of vertical or horizontal irregularities in the perfectly regular shape of a radial maze affected rats’ performances. The introduction of various tilts in each arm of an eight-arm radial maze had a slightly positive effect on accuracy. However, when intra- and extraraaze cues were dissociated by rotating the maze before maze completion, the rata relied preferentially on extramaze cues associated with the horizontal direction of the arms but not with the tilts. On the other hand, the rats showed poor performances when trained on a horizontally distorted maze (uneven angles between the arms instead of repeated 45° angles). The high number of errors was related to the neglect of particular arms, the disorganization of the patrolling sequences, and the tendency to chain the visit of five arms that formed a regular ahape. Other animals, trained in the same maze, displayed similar biases even after a pretraining phase with constrained choices. Results from the horizontally distorted maze confirm and extend data from the spontaneous alternation literature that choice behavior is influenced by rules of movement that favor large angle transitions and regular subdivisions of space. They also stress the relation between performance in the radial maze and spontaneous exploratory and foraging behaviors.     

Comprehending conflicting science-related texts: graphs as plausibility cues

When reading conflicting science-related texts, readers may attend to cues which allow them to assess plausibility. One such plausibility cue is the use of graphs in the texts, which are regarded as typical of ‘hard science’. The goal of our study was to investigate the effects of the presence of graphs on the perceived plausibility and situation model strength for conflicting science-related texts, while including the influence of readers’ amount of experience with scientific texts and graphs as a potential moderator of these effects. In an experiment mimicking web-based informal learning, 77 university students read texts on controversial scientific issues which were presented with either graphs or tables. Perceived plausibility and situation model strength for each text were assessed immediately after reading; reader variables were assessed several weeks prior to the experiment proper. The results suggest that graphs can indeed serve as plausibility cues and thus boost situation model strength for texts which contain them. This effect was mediated by the perceived plausibility of the information in the texts with graphs. However, whether readers use graphs as plausibility cues in texts with conflicting information seems to depend also on their amount of experience with scientific texts and graphs.