The acquisition and transfer of a "same-different" conditional discrimination using multidimensional visual texture stimuli was investigated in pigeons. Using a choice task, 4 pigeons were reinforced for discriminating different displays, created from aggregated differences in element color or shape, from uniform displays, in which all elements were identical. Discrimination of these 2 display types was readily acquired by the pigeons when they were required to locate and peck the contrasting target region of the different displays. The pigeons showed high levels of discrimination transfer to novel texture stimuli both during acquisition and in 2 subsequent transfer tests. The results suggest that pigeons may be able to learn a generalized same-different concept when promoted by the use of large numbers of multielement stimuli during training.Concepts are an essential part of human cognition, intelligence, and expression. With the growing interest in the cognitive abilities of nonhuman animals, a natural question is to what extent do animals use concepts in guiding their behavior (Herrnstein, 1990). Over the last 30 years, for instance, researchers have established abundant evidence for the formation and use of visually based object concepts by pigeons (Herrnstein & Loveland, 1964;Herrnstein, Loveland, & Cable, 1976;Wasserman, Kiedinger, & Bhatt, 1988). However, evidence for the use of more abstract concepts by pigeons, such as generalized "matching," "oddity," or "same-different" discriminations, has been far more difficult to obtain.Research on abstract concept learning in pigeons has for the most part focused on whether pigeons learn generalized matching or oddity rules in matching-to-sample and oddityfrom-sample discriminations. Although many studies have failed to find evidence of concept-based transfer in such conditional discriminations (Berryman, Cumming, Cohen,

The influence of dimensional organization on pigeon texture perception was examined in a simultaneous conditional discrimination procedure. Six experienced pigeons were reinforced for pecking at a small block of target elements randomly located within a larger array of distractor elements in each texture stimulus. Target/distractor differences in color, size, orientation, and combinations of these dimensions were examined. In Experiment 1, the influence of target/distractor similarity on performance was investigated by using different forms of unidimensional and conjunctively organized texture stimuli made of two and three dimensions. Targets infeature displays, in which the two regions consistently differed along a single dimension, were located more accurately than targets in conjunctive displays, where a combination of values from all dimensions defined each region. In Experiment 2, a tradeoff between response speed and accuracy was found in the pigeons' processing of conjunctive displays. In Experiment 3, the number of distractors differentially influenced the localization of feature and conjunctive targets. Overall, the pigeons' reactions to these feature and conjunctive stimuli paralleled those of humans, suggesting that functionally equivalent mechanisms may mediate the perceptual grouping, search, and discrimination of textured multidimensional stimuli in both species.Birds are highly visual animals. Like mammals, they form a major class of highly mobile, visually dominant, diurnal vertebrates. During their daily activities, birds behave as if they perceive an object-filled visual world similar to our own. If so, how do birds accomplish this remarkable perceptual feat, especially given the different organization and overall smaller size ofthe avian brain (Pearson, 1972)? We have been examining this larger comparative question by investigating the mechanisms underlying the perception and discrimination ofvisual textures by pigeons (

Two experiments examined the acquisition and transfer of a complex same-different discrimination by pigeons. With the use of a 2-alternative choice task, 5 pigeons were reinforced for discriminating odd-item Different displays, in which a contrasting target was present, from Same displays, in which all elements were identical. Four different types of same-different displays were concurrently tested. The display types differed in their configuration (texture vs. visual search organization), the nature of their elements (small and large colored shapes; pictures of birds, flowers, fish, and humans), and the processing demands required by their global-local element arrangement. Despite these differences, the pigeons learned to discriminate all 4 display types at the same rate and showed positive discrimination transfer to novel examples of each type, suggesting that a single generalized rule was used to discriminate all display types. These results provide some of the strongest evidence yet that pigeons, like many primates, can learn an abstract, visually mediated same-different concept.One of the most fundamental psychological discriminations of interest to psychologists for the last century has been the capacity of organisms to detect identity and nonidentity relations (Delius, 1994;Link, 1992, provides an excellent historical review). A popular and powerful means of studying these relations is through the use of the same-different task. In this task the subject is asked to respond same when two or more stimuli are identical and different if one or more of the stimuli are different from the others. This task has been successfully used in studying a wide range of issues in humans. In nonhuman animals, its use for the investigation of the perception and conceptualization of these relations has been far more limited, but it has been most successfully

The contributions of different monocular depth cues to performance of a scene perception task were investigated in 4 pigeons. They discriminated the sequential depth ordering of three geometric objects in computer-rendered scenes. The orderings of these objects were specified by the combined presence or absence of the pictorial cues of relative density, occlusion, and relative size. In Phase 1, the pigeons learned the task as a direct function of the number of cues present. The three monocular cues contributed equally to the discrimination. Phase 2 established that differential shading on the objects provided an additional discriminative cue. These results suggest that the pigeon visual system is sensitive to many of the same monocular depth cues that are known to be used by humans. The theoretical implications for a comparative psychology of picture processing are considered.

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 (-<100 ms), and (c) pigeons may possess automatic search control processes that can be captured by stimulus-driven changes in the display.The research described in this article is part of our ongoing efforts to understand the mechanisms of visual perception and cognition in pigeons, and their comparative relations to mammalian visual perception and cognition. Our overall goal is to discern the perceptual (Cook, 1992a) and decisional processes (Cook & Wixted, 1997) involved from the point when external visual information first impinges on the animal to its final behavioral reaction to this information. By looking in detail at each aspect of how pigeons accomplish complex visual discriminations, we hope to uncover the cognitive and neural mechanisms used by these visually sophisticated animals and to compare them with those mechanisms found in other types of animals, including humans.One way we have investigated these questions is by examining in detail how pigeons process and discriminate visual textures