Testing meter, rhythm, and tempo discriminations in pigeons

Rhythmic grouping and discrimination is fundamental to music. When compared to the perception of pitch, rhythmic abilities in animals have received scant attention until recently. In this experiment, four pigeons were tested with three types of auditory rhythmic discriminations to investigate their processing of this aspect of sound and music. Two experiments examined a meter discrimination in which successively presented idiophonic sounds were repeated in meters of different lengths in a go/no-go discrimination task. With difficulty, the birds eventually learned to discriminate between 8/4 and 3/4 meters constructed from cymbal and tom drum sounds at 180 beats per minute. This discrimination subsequently transferred to faster tempos, but not to different drum sounds or their combination. Experiment 3 tested rhythmic and arrhythmic patterns of sounds. After 40 sessions of training, these same pigeons showed no discrimination. Experiment 4 tested repetitions of a piano sound at fast and slow tempos. This discrimination was readily learned and showed transfer to novel tempos. The pattern of results suggests that pigeons can time periodic auditory events, but their capacity to understand generalized rhythmic groupings appears limited.     

Contextual Effects of Scene on the Visual Perception of Object Orientation in Depth

We investigated the effect of background scene on the human visual perception of depth orientation (i.e., azimuth angle) of three-dimensional common objects. Participants evaluated the depth orientation of objects. The objects were surrounded by scenes with an apparent axis of the global reference frame, such as a sidewalk scene. When a scene axis was slightly misaligned with the gaze line, object orientation perception was biased, as if the gaze line had been assimilated into the scene axis (Experiment 1). When the scene axis was slightly misaligned with the object, evaluated object orientation was biased, as if it had been assimilated into the scene axis (Experiment 2). This assimilation may be due to confusion between the orientation of the scene and object axes (Experiment 3). Thus, the global reference frame may influence object orientation perception when its orientation is similar to that of the gaze-line or object.     

Effects of stimulus manipulations on visual categorization in pigeons

Four pigeons were previously trained [Lazareva, O.F., Freiburger, K.L., Wasserman, E.A., 2004. Pigeons concurrently categorize photographs at both basic and superordinate levels. Psychon. Bull. Rev. 11, 1111-1117] to classify color photographs into either their proper basic-level category (cars, chairs, flowers, or people) or a superordinate-level category (nominally natural or artificial). In Experiment 1, the same pigeons were shown either reflected or inverted versions of the training stimuli. Reflection had no effect on pigeons' classification behavior, whereas inversion impaired discrimination of all stimulus categories, except flowers, on the basic-level and superordinate-level tasks. Pixel matching analysis revealed that pattern matching played at most a minor role in the birds' categorization behavior. In Experiment 2, the pigeons were shown test stimuli that were either blurred or quartered and scrambled. Blurring impaired discrimination of cars, but had no effect on discrimination of people and flowers; scrambling impaired discrimination of people and flowers leaving discrimination of cars and chairs unaffected. These results suggest that categorization of flowers and people may be controlled primarily by the overall shape of the object rather than by local features, whereas categorization of cars and chairs may rely primarily on local features rather than the overall shape of the object.     

A comparison of intradimensional and extradimensional shift learning in pigeons

In each of three experiments pigeons were trained on a simultaneous discrimination between stimuli that differed in both colour and orientation. For half the birds the colour dimension was relevant and for half orientation was relevant (i.e., differences along that dimension were correlated with reward and nonreward). All birds were then shifted to a second discrimination between new colours and orientations. For half this constituted an intradimensional shift in that the previously relevant dimension remained relevant; for the remainder the previously irrelevant dimension was made relevant (an extradimensional shift). Contrary to the predictions of attentional theory, the two types of shift were learned with equal ease.     

Pigeons and humans are more sensitive to nonaccidental than to metric changes in visual objects

Humans and macaques are more sensitive to differences in nonaccidental image properties, such as straight vs. curved contours, than to differences in metric properties, such as degree of curvature [Biederman, I., Bar, M., 1999. One-shot viewpoint invariance in matching novel objects. Vis. Res. 39, 2885-2899; Kayaert, G., Biederman, I., Vogels, R., 2003. Shape tuning in macaque inferior temporal cortex. J. Neurosci. 23, 3016-3027; Kayaert, G., Biederman, I., Vogels, R., 2005. Representation of regular and irregular shapes in macaque inferotemporal cortex. Cereb. Cortex 15, 1308-1321]. This differential sensitivity allows facile recognition when the object is viewed at an orientation in depth not previously experienced. In Experiment 1, we trained pigeons to discriminate grayscale, shaded images of four shapes. Pigeons made more confusion errors to shapes that shared more nonaccidental properties. Although the images in that experiment were not well controlled for incidental changes in metric properties, the same results were apparent with better controlled stimuli in Experiment 2: pigeons trained to discriminate a target shape from a metrically changed shape and a nonaccidentally changed shape committed more confusion errors to the metrically changed shape, suggesting that they perceived it to be more similar to the target shape. Humans trained with similar stimuli and procedure exhibited the same tendency to make more errors to the metrically changed shape. These results document the greater saliency of nonaccidental differences for shape recognition and discrimination in a non-primate species and suggest that nonaccidental sensitivity may be characteristic of all shape-discriminating species.     

Toward a framework for the evaluation of feature binding in pigeons

Pigeons were trained in a new procedure to test for visual binding errors between the dimensions of color and shape. In Experiment 1, pigeons learned to discriminate a target compound from 15 non-target compounds (constructed from four colors and shapes) by choosing one of two hoppers in a two-hopper choice task. The similarity of the target to non-target stimuli influenced choice responding. In Experiment 2, pigeons learned to detect a target compound when presented with a non-target compound within the same trial under conditions of simultaneity and sequentiality. Non-target trials were arranged to allow for the testing of binding errors (i.e., false identifications of the target on certain non-target trials). Transient evidence for binding errors in two of the birds occurred at the start of two-item training, but decreased with training. The experiments represent an important step toward developing a framework for the evaluation of visual feature binding in nonhumans.     

Effects of stimulus size and spatial organization on pigeons’ conditional same-different discrimination

In two experiments, we explored the effects of varying the size and the spatial organization of the stimuli in multi-item arrays on pigeons’ same-different discrimination behavior. The birds had previously learned to discriminate a simultaneously presented array of 16 identical (Same) visual items from an array of 16 nonidentical (Different) visual items, when the correct choice was conditional on the presence of another cue: the color of the background (Castro et al., in press). In Experiment 1, we trained pigeons with 7-item arrays and then tested them with arrays containing the same item, but in a variety of sizes. In Experiment 2, we tested the birds with the items grouped in novel locations: the top, the bottom, the left, or the right portions of the display area, which generated different vertical and horizontal alignments. Accuracy scores revealed virtually perfect stimulus generalization across various item sizes and spatial organizations. Reaction times revealed that the birds perceived different sizes of a single icon as the same stimulus (Experiment 1) and that the birds processed vertical arrangements faster than horizontal arrangements (Experiment 2). These results suggest that the pigeons noticed both physical and spatial changes in the stimuli (as shown by their reaction times), but that these changes did not disrupt the birds’ discriminating the sameness or differentness of the multi-item arrays (as shown by their accuracy scores).     

Pigeons do not perceptually complete partly occluded photos of food: an ecological approach to the "pigeon problem"

Humans routinely complete partly occluded objects to recognize the whole objects. However, a number of studies using geometrical figures and even conspecific images have shown that pigeons fail to do so. In the present study, we tested whether pigeons complete partially occluded objects in a situation simulating a natural feeding context. In Experiment 1, we trained pigeons to peck at any photograph of food and not to peck at any containing a non-food object. At test, we presented both photos of food partly occluded by pigeon's feather and photos simply truncated at the same part. We predicted that if the pigeons perceptually completed the occluded portion, then they would discriminate the photos of occluded food better than the truncated photos. The result was that the pigeons pecked at the truncated photos earlier than the occluded photos. Placing the occluder next to all of the stimuli in Experiment 2 or substituting indented lozenge for the feather in Experiment 3 did not affect the results. Thus, even in a simulated ecologically significant situation, pigeons continued to not show evidence of perceptual completion.     

Successive two-item same-different discrimination and concept learning by pigeons

Four pigeons were trained in a successive same/different procedure involving the alternation of two stimuli per trial. Using a go/no-go procedure, two different or two identical color photographs were alternated, with a brief, dark, inter-stimulus interval, on a computer screen for 20s. Pigeons learned to discriminate between same (S+) and different (D-) sequences with moderate to large contrasts between successive pictures. Analyses of pecking behavior within single trials revealed this discrimination emerged at the earliest possible point in the sequence (i.e. by the presentation of the second item). Pigeons transferred to novel color and gray-scale pictures, and showed savings in tests with novel video stimuli. These results suggest that same/different discrimination and concept formation can be acquired with successively presented pairs of stimuli by pigeons. When combined with results using simultaneous same/different presentations, these findings further support a qualitative similarity among birds and primates in their capacity to judge certain types of stimulus relations.     

Effect of between-category similarity on basic level superiority in pigeons

Children categorize stimuli at the basic level faster than at the superordinate level. We hypothesized that between-category similarity may affect this basic level superiority effect. Dissimilar categories may be easy to distinguish at the basic level but be difficult to group at the superordinate level, whereas similar categories may be easy to group at the superordinate level but be difficult to distinguish at the basic level. Consequently, similar basic level categories may produce a superordinate-before-basic learning trend, whereas dissimilar basic level categories may result in a basic-before-superordinate learning trend. We tested this hypothesis in pigeons by constructing superordinate level categories out of basic level categories with known similarity. In Experiment 1, we experimentally evaluated the between-category similarity of four basic level photographic categories using multiple fixed interval-extinction training (Astley and Wasserman, 1992). We used the resultant similarity matrices in Experiment 2 to construct two superordinate level categories from basic level categories with high between-category similarity (cars and persons; chairs and flowers). We then trained pigeons to concurrently classify those photographs into either the proper basic level category or the proper superordinate level category. Under these conditions, the pigeons learned the superordinate level discrimination faster than the basic level discrimination, confirming our hypothesis that basic level superiority is affected by between-category similarity.     

朝向和对比度同时快速变化条件下的分辨能力

在自然的视觉中,投射到视网膜上的视觉图像总是在不停地变化,而人类的感知系统依然可以准确高效地识别物体.因此,人类的感知系统有相应的快速处理机制以应对这种动态变化．然而,前人的实验都是在相对稳定的刺激条件下研究人类被试的感知系统对一个刺激参数的反应,比如在固定对比度下测试朝向分辨能力,或在固定朝向测定对比度分辨能力,而朝向和对比度同时变化时,人类对这两个参数的分辨能力仍然缺乏研究．因此,在本实验中,我们使用朝向和对比度同时变化的刺激,研究了人类被试对朝向和对比度的分辨能力．结果表明,在这种动态变化的条件下,被试对朝向和对比度的分辨阈值都有显著性的降低．而且,朝向分辨阈值降低的幅度与在固定对比度参数条件下的分辨阈值成负相关,即在固定对比度条件下朝向分辨阈值较高的被试,在朝向和对比度同时变化条件下,其朝向分辨阈值降低的幅度相对要大,朝向分辨能力也就相对地提高更大．对比度分辨能力也呈现同样的规律．这些结果说明,朝向和对比度的同时变化提高了被试对朝向和对比度的分辨能力,一个参数变化时其分辨能力越低的被试,两个参数变化时其分辨能力提高的幅度就越大．揭示了视觉系统处理这种多刺激参量信息变化的能力和机制,对人类视觉系统在真实的视觉过程中如何处理朝向和对比度信息提供了认识．     

Wie klassifizieren Javaneraffen (Macaca fascicularis) natürliche Muster?

How do Crab-eating Monkeys (Macaca fascicularis) Perceive and Classify Realistic Visual Patterns? The process by which crab-eating monkeys perceive and classify stimuli functionally relevant to their feeding behaviour was investigated. The visual patterns consisted of realistic drawings of insects and parts of plants.

• 1 A new experimental approach was conceived: During the experimental sessions social interactions within the group were permitted while the learning behaviour of individual monkeys was analysed. The procedure consisted of the simultaneous discrimination tasks of four visual patterns and motoric responses (continuous reinforcement).
• 2 To prepare the functional analysis of their ability to classify environmental objects, tests were conducted in which the animals successively learned to answer visual stimuli with motoric responses. The monkeys learned not only to discriminate geometrical patterns from contrast and form cues but also to build specific associations between visual patterns and special motoric coordinations. When shown similar geometrical stimuli, the animals were able to generalise their recognition of invariant features (‘angularity’).
• 3 The monkeys learned very quickly to discriminate insects from parts of plants. This discrimination ability could be transferred immediately to other insect pictures. This learning process was linked with a memorized classification system of natural objects induced by environmental experience. A preference test for single cues resulted in a graded estimation of particular pattern components. Numerous variations of the insect pattern were shown to the animals. From the different choice frequency for single cues, a gradual continuum of cue relevance could be established (e. g. contrast and form were the most relevant cues). A direct dependence between the completeness of the insect ‘gestalt’ and its choice frequency was shown.

     

Transfer between views of conspecific faces at different ages or in different orientations by sheep

Sheep are able to discriminate photographs of conspecific faces. The present study investigates adult ewe's recognition of faces of the same animal between different ages or between different orientations. Twelve adult sheep were first trained to discriminate between faces of two unfamiliar animals, one of which was associated with a food reward. Transfer of discrimination from this pair to the same pair but at a different age, or in a different orientation, was then evaluated (transfer test), and compared with a new pair of the same condition (control test). Learned discrimination of a frontal view of unfamiliar 3-month-old lambs' faces improved subsequent discrimination of the same pair when they were 1-month-old in comparison to discrimination of new 1-month-old faces. Moreover, sheep that were trained to discriminate frontal views of unfamiliar adult individuals discriminated profile views of the same animals more accurately than that of novels. However, learned discrimination of the profile view of unfamiliar adult faces had no effect on subsequent discrimination of the frontal view of that same pair. These results suggest that to some extent sheep recognise faces of unfamiliar animals at different ages and in different orientations.     

Long-term Retention of Many Visual Patterns by Pigeons

Using a simultaneous discrimination procedure it was shown that pigeons were capable of learning to discriminate 100 different black and white visual patterns from a further 625 similar stimuli, where responses to the former were rewarded and responses to the latter were not rewarded. Tests in which novel stimuli replaced either the rewarded or nonrewarded stimuli showed that the pigeons had not only learned about the 100 positive stimuli but also about the 625 negative stimuli. The fact that novel stimuli enhanced discrimination performance when they replaced the many negative stimuli indicated that the pigeons had categorized the stimuli into two classes, familiar and less familiar. Long-term retention was examined after a 6-month interval. To begin with it seemed poor but a recognition test performed after the subjects had been retrained with a subset of the stimuli after an interval of 7 months confirmed that pigeons are capable of retaining in memory several 100 visual items over an extended period. It is proposed that the initial retrieval weakness was due to a forgetting of the contingencies between stimulus categories and response outcomes. Further tests involving variously modified stimuli indicated that while stimulus size variations had a negative effect on performance, orientation changes did not interfere with recognition, supporting the view that small visual stimuli are memorized by pigeons largely free of orientation labels. The experiment generally confirms that pigeons have the capacity of storing information about a large number of visual stimuli over long periods of time.     

Baboons (Papio papio) spontaneously process the first-order but not second-order configural properties of faces

A two-alternative forced-choice discrimination task was used to assess whether baboons (N=7) spontaneously process qualitative (i.e., first-order) or quantitative (i.e., second-order) variations in the configural arrangement of facial features. Experiment 1 used as test stimuli second-order pictorial faces of humans or baboons in which the mouth and the eyes were rotated upside down relative to the normal face. Baboons readily discriminated two different normal faces but did not discriminate a normal face from its second-order modified version. Experiment 2 used human or baboon faces for which the first-order configural properties had been distorted by reversing the location of the eyes and mouth within the face. Discrimination was prompt with these stimuli. Experiment 3 replicated some of the conditions and the results of experiment 1, thus ruling out possible effects of learning. It is concluded that baboons are more adept at spontaneously processing first- than second-order configural facial properties, similar to what is known in the human developmental literature.     

Categorical perception of orientation in monkeys

Structural and functional substrates of orientation processing in monkeys have been clarified. However, orientation perception in monkeys has not been fully studied. In this study, the cognitive mechanism that controls monkeys' perception of orientation was evaluated. After the monkeys were trained to discriminate between a cardinal and an oblique orientation (e.g., 0 degrees and 30 degrees), their perceptual mechanisms underlying orientation discrimination were tested by using six orientations, ranging from 0 degrees to 150 degrees, including ones used in the discrimination training. Generalization tests showed that the monkeys who were trained with cardinal orientations (e.g., 0 degrees) as positive stimuli generalized their responses to the other cardinal orientation (e.g., 90 degrees). Similarly, the monkeys who were trained with oblique orientations (e.g., 30 degrees) as positive stimuli generalized their responses to all other oblique orientations (e.g., 60 degrees, 120 degrees, and 150 degrees). These findings indicated that the monkeys abstracted the quality of the cardinal/oblique category from the physical features of orientation stimuli although they were not trained to do so. Such an abstraction also suggested a discrepancy between a continuously and orderly arranged cortical map and a discontinuously categorized perception of orientation. The present findings provide insight into the learning-correlated plasticity of cortical orientation preference.     

Concept formation based on value relations evaluated with a matching-to-sample procedure

To study concept formation based on relations, adults were taught and tested on complex discriminations involving figures that varied in colors, forms, and orientations. In Experiment 1, participants learned to select figures with values A1 and B1 or values B1 and C1; thereafter, they consistently selected figures with values A1 and C1. Selections were based on the relations among the values, rather than on perceptual properties. Experiments 2 and 3 studied generalization with a matching-to-sample procedure: participants learned to select "yes" in the presence of the positive figures, such as A1B1, and "no" in the presence of the negative figures. Thereafter, all figures that resulted from combining three values of the three relevant dimensions were probed. Participants typically selected "yes" in the presence of the novel figures that had two or three values related to one another and selected "no" in the presence of the other figures. Finally, two participants learned a simple discrimination. They did not generalize responding to other figures with the same values; instead, their performance in the generalization test remained almost unaltered. Thus, the concept based on relations was not affected by the simple discrimination. These results showed some unique properties of the concept based on relations and challenge previous theories on concept formation.     

Object discrimination by pigeons: effects of object color and shape

Can nonhuman animals attend to visual stimuli as whole, coherent objects? We investigated this question by adapting for use with pigeons a task in which human participants must report whether two visual attributes belong to the same object (one-object trial) or to different objects (two-object trial). We trained pigeons to discriminate a pair of differently colored shapes that had two targets either on a single object or on two different objects. Each target equally often appeared on the one-object and two-object stimuli; therefore, a specific target location could not serve as a discriminative cue. The pigeons learned to report whether the two target dots were located on a single object or on two different objects; follow-up tests demonstrated that this ability was not entirely based on memorization of the dot patterns and locations. Additional tests disclosed predominate stimulus control by the color, but not by the shape of the two objects. These findings suggest that human psychophysical methods are readily applicable to the study of object discrimination by nonhuman animals.     

Pigeon's recognition of cartoons: effects of fragmentation, scrambling, and deletion of elements

J. Cerella [Pattern Recognit. 12 (1980) 1] and more recently S. Watanabe [Behav. Proc. 53 (2001) 3] demonstrated that pigeons showed no decrement in recognizing cartoons that were spatially scrambled, indicating that pigeons' discriminative responding is controlled by local features alone. In contrast Kirkpatrick-Steger et al. [J. Exp. Psychol. Anim. Behav. Proc. 24 (1998) 34] used line drawings as stimuli and demonstrated the importance of spatial organization for picture recognition by pigeons, confirming related findings reported in their previous studies. The present study revisited the recognition of cartoons by pigeons. In Experiment 1, pigeons were trained to discriminate cartoon people on a variety of background scenes. Subsequent tests revealed that discriminative performances with both familiar and novel instances decreased as the objects and object-like parts were progressively fragmented, indicating that search for the targeted cartoon people in the stimulus array might have enhanced the pigeons to attend to global aspects of cartoon people. Experiment 2 used line drawings of cartoon faces as stimuli and examined effects of scrambling and deletion of components. A set of components (eyes and eyebrows) exerted strong control over behavior and scrambling only moderately suppressed responding. The results suggest that pigeons use both global and local aspects, with different mixtures of these types of information depending on the particular perceptual context.     

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

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