Four experiments investigated the processing of hierarchical stimuli by pigeons. Using a 4 alternative divided-attention task, 4 pigeons were food-reinforced for accurately identifying letters arranged as either hierarchical global- or local-relevant stimuli or as size-matched filled stimuli. Experiment 1 found that task acquisition was faster with local-relevant than global-relevant stimuli. This difference was not due to letter size. Experiment 2 demonstrated successful transfer to a novel irrelevant letter configuration. Experiments 3 and 4 tested pigeons' responses to conflict probe stimuli composed of equally discriminable relevant letters at each level. These tests revealed that all of the pigeons showed a cognitive precedence for local information early in processing, with the pigeons using different cues to initiate the processing of global information. This local advantage contrasts with previously reported results for humans and pigeons but is similar to that reported for nonhuman primates. Alternatives attempting to reconcile these contrasting comparative results are considered.

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 (

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

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