Mechanisms of same-different abstract-concept learning by rhesus monkeys (Macaca mulatta).

Experiments with 9 rhesus monkeys (Macaca mulatta) showed, for the first time, that abstract-concept learning varied with the training stimulus set size. In a sameldifferent task, monkeys required to touch a top picture before choosing a bottom picture (same) or white rectangle (different) learned rapidly. Monkeys not required to touch the top picture or presented with the top picture for a fixed time learned slowly or not at all. No abstract-concept learning occurred after 8-itern training but progressively improved with larger set sizes and was complete following 128-itern training. A control monkey with a constant 8-item set ruled out repeated training and testing. Contrary to the unique-species account, it is argued that different species have quantitative, not qualitative, differences in abstract-concept learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analogical reasoning and the differential outcome effect: Transitory bridging of the conceptual gap for rhesus monkeys (Macaca mulatta).

Monkeys, unlike chimpanzees and humans, have a marked difficulty acquiring relational matching-to-sample (RMTS) tasks that likely reflect the cognitive foundation upon which analogical reasoning rests. In the present study, rhesus monkeys (Macaca mulatta) completed a categorical (identity and nonidentity) RMTS task with differential reward (pellet ratio) and/or punishment (timeout ratio) outcomes for correct and incorrect choices. Monkeys in either differential reward-only or punishment-only conditions performed at chance levels. However, the RMTS performance of monkeys experiencing both differential reward and punishment conditions was significantly better than chance. Subsequently when all animals experienced nondifferential outcomes tests, their RMTS performance levels were at chance. These results indicate that combining differential reward and punishment contingencies provide an effective, albeit transitory, scaffolding for monkeys to judge analogical relations-between-relations. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Flexible learning and use of multiple-landmark information by pigeons (Columba livia) in a touch screen-based goal searching task.

Three touch screen-based experiments were conducted to investigate whether pigeons would learn to use configural information about a goal's location in relation to a multiple-landmark array. In Experiment 1, 4 pigeons (Columba livia) were trained to peck a computer monitor at a location that constituted the third vertex of a hypothetical triangle defined by 2 different landmarks. The landmarks appeared in 3 orientations during the training, and the pigeons' goal-searching ability easily transferred to the landmarks presented in 3 novel orientations. Each landmark was asymmetric, so we next examined whether the pigeons used (a) the small-scale, local orientation information that could be inferred from each landmark individually, or (b) the large-scale, configural information that could be inferred from the spatial arrangement of multiple landmarks taken as a whole. Even when each single landmark appeared by itself, the pigeons were able to locate the goal accurately, suggesting that the large-scale, configural information was not essential. However, when 1 landmark locally pointed to a location that was consistent with the triangular configuration and the other landmark locally pointed to a different location, the pigeons predominantly pecked at the configurally array-consistent location. These results suggest that the pigeons redundantly learned both the large-scale, configural strategy and the local, single-landmark strategy, but they mainly used the latter information, and used the former information solely to disambiguate conflicts when the 2 landmarks pointed toward different targets. Such flexible learning and use of redundant information may reflect the pigeons' adaptation to unstable wild environments during their evolutionary history. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Multiple-landmark piloting in pigeons (Columba livia): Landmark configuration as a discriminative cue.

Using the landmark-transformation technique, researchers have shown that pigeons (Columba livia) tend to encode a goal location relative to 1 landmark, even when multiple landmarks are in the vicinity of the goal. The current experiments examined pigeons' ability to use configural information from a set of landmarks by making the arrangement of 4 landmarks a discriminative cue to the location of buried seeds. Results showed that pigeons used information from the 3 consistently placed landmarks to search accurately when 1 landmark was displaced. Findings indicate that pigeons are able to search for a goal using information from multiple landmarks instead of just 1 and that landmark use by these birds may be more flexible than previously theorized. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monkeys (Macaca mulatta and Cebus apella) track, enumerate, and compare multiple sets of moving items.

Despite many demonstrations of numerical competence in nonhuman animals, little is known about how well animals enumerate moving stimuli. In this series of experiments, rhesus monkeys (Macaca mulatta) and capuchin monkeys (Cebus apella) performed computerized tasks in which they had to enumerate sets of stimuli. In Experiment 1, rhesus monkeys compared two sets of moving stimuli. Experiment 2 required comparisons of a moving set and a static set. Experiment 3 included human participants and capuchin monkeys to assess all 3 species' performance and to determine whether responding was to the numerical properties of the stimulus sets rather than to some other stimulus property such as cumulative area. Experiment 4 required both monkey species to enumerate subsets of each moving array. In all experiments, monkeys performed above chance levels, and their responses were controlled by the number of items in the arrays as opposed to nonnumerical stimulus dimensions. Rhesus monkeys performed comparably to adult humans when directly compared although capuchin performance was lower. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interpreting the effects of image manipulation on picture perception in pigeons (Columba livia) and humans (Homo sapiens).

The effects of picture manipulations on humans' and pigeons' performance were examined in a go/no-go discrimination of two perceptually similar categories, cat and dog faces. Four types of manipulation were used to modify the images. Mosaicization and scrambling were used to produce degraded versions of the training stimuli, while morphing and cell exchange were used to manipulate the relative contribution of positive and negative training stimuli to test stimuli. Mosaicization mainly removes information at high spatial frequencies, whereas scrambling removes information at low spatial frequencies to a greater degree. Morphing leads to complex transformations of the stimuli that are not concentrated at any particular spatial frequency band. Cell exchange preserves high spatial frequency details, but sometimes moves them into the “wrong” stimulus. The four manipulations also introduce high-frequency noise to differing degrees. Responses to test stimuli indicated that high and low spatial frequency information were both sufficient but not necessary to maintain discrimination performance in both species, but there were also species differences in relative sensitivity to higher and lower spatial frequency information. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Perception of the standard and the reversed Müller-Lyer figures in pigeons (Columba livia) and humans (Homo sapiens).

The authors compared perception of the standard and reversed Müller-Lyer figures between pigeons (Columbia livia) and humans (Homo sapiens). In Experiment 1, pigeons learned to classify 6 lengths of target lines into "long" and "short" categories by pecking 2 keys on the monitor, ignoring the 2 brackets so placed that they would not induce an illusion. In the test that followed, all 3 birds chose the "long" key more frequently for the standard Müller-Lyer figures with inward-pointing brackets (>). The subjects' responses were accountable by neither overall lengths of the figures nor horizontal gaps between the 2 brackets. For the reversed figures, effects of the brackets were absent. These results suggested that the pigeons perceived the standard Müller-Lyer illusion but not the reversed one. Experiment 2 confirmed that humans perceived both types of the illusion. Pigeons and humans may perceive the same illusory figures in different ways. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning of discriminations is impaired, but generalization to altered views is intact, in monkeys (Macaca mulatta) with perirhinal cortex removal.

Rhesus monkeys (Macaca mulatta) were taught a large number of visual discriminations and then either received bilateral removal of the perirhinal cortex or were retained as unoperated controls. Operated monkeys were impaired in retention of the preoperatively learned problems. To test for generalization to novel views, the monkeys were required to discriminate, in probe trials, familiar pairs of images that were rotated, enlarged, shrunken, presented with color deleted, or degraded by masks. Although these manipulations reduced accuracy in both groups, the operated group was not differentially affected. In contrast, the same operated monkeys were impaired in reversal of familiar discriminations and in acquisition of new single-pair discriminations. These results indicate an important role for perirhinal cortex in visual learning, memory, or both, and show that under a variety of conditions, perirhinal cortex is not critical for the identification of stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeon (Columba livia) encoding of a goal location: The relative importance of shape geometry and slope information.

The ability to use the geometric shape of an environment as an orienting cue for goal location has been shown in many vertebrate groups. Experimentally, however, geometric spatial tasks are typically carried out on horizontal surfaces. The present study explored how learning a geometry task is affected by training on a surface extending in the vertical dimension—a slope. In a reference memory task, pigeons (Columba livia) were trained to locate a goal in an isosceles trapezoid arena. Learning on a slope proceeded more rapidly or with fewer errors than on a flat surface, presumably because of kinesthetic, vestibular, and visual information extractable from an inclined surface. Experiment 1 showed that, although the geometric shape of the arena was encoded, pigeons trained on a slope were guided by a goal representation based on the vertical and orthogonal axes of the slope to solve the task. Experiment 2 revealed that geometric learning was neither overshadowed nor facilitated by training on a slope. The data highlight a potentially important role for slope as an allocentric cue for goal location. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal integration as a function of signal and gap intensity in rats (Rattus norvegicus) and pigeons (Columba livia).

Previous data suggest that rats (Rattus norvegicus) and pigeons (Columba livia) use different interval-timing strategies when a gap interrupts a to-be-timed signal: Rats stop timing during the gap, and pigeons reset their timing mechanism after the gap. To examine whether the response rule is controlled by an attentional mechanism dependent on the characteristics of the stimuli, the authors manipulated the intensity of the signal and gap when rats and pigeons timed in the gap procedure. Results suggest that both rats and pigeons stop timing during a nonsalient gap and reset timing after a salient gap. These results also suggest that both species use similar interval-timing mechanisms, influenced by nontemporal characteristics of the signal and gap. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absolute pitch: Frequency-range discriminations in pigeons (Columba livia)--comparisons with zebra finches (Taeniopygia guttata) and humans (Homo sapiens).

Absolute pitch (AP) is the ability to classify individual pitches without an external referent. The authors compared results from pigeons (Columba livia, a nonsongbird species) with results (R. Weisman, M. Njegovan, C. Sturdy, L. Phillmore, J. Coyle, & D. Mewhort, 1998) from zebra finches (Taeniopygia guttata, a songbird species) and humans (Homo sapiens) in AP tests that required classification of contiguous tones into 3 or 8 frequency ranges on the basis of correlations between the tones in each frequency range and reward. Pigeons' 3-range discriminations were similar in accuracy to those of zebra finches and humans. In the more challenging 8-range task, pigeons, like zebra finches, discriminated shifts from reward to nonreward from range to range across all 8 ranges, whereas humans discriminated only the 1st and last ranges. Taken together with previous research, the present experiments suggest that birds may have more accurate AP than mammals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of artificial categories structured by family resemblances: A comparative study in people (Homo sapiens) and pigeons (Columba livia).

Adult humans (Homo sapiens) and pigeons (Columba livia) were trained to discriminate artificial categories that the authors created by mimicking 2 properties of natural categories. One was a family resemblance relationship: The highly variable exemplars, including those that did not have features in common, were structured by a similarity network with the features correlating to one another in each category. The other was a polymorphous rule: No single feature was essential for distinguishing the categories, and all the features overlapped between the categories. Pigeons learned the categories with ease and then showed a prototype effect in accord with the degrees of family resemblance for novel stimuli. Some evidence was also observed for interactive effects of learning of individual exemplars and feature frequencies. Humans had difficulty in learning the categories. The participants who learned the categories generally responded to novel stimuli in an all-or-none fashion on the basis of their acquired classification decision rules. The processes that underlie the classification performances of the 2 species are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Further analysis of perception of the standard Müller-Lyer figures in pigeons (Columba livia) and humans (Homo sapiens): Effects of length of brackets.

Nakamura, Fujita, Ushitani, & Miyata (2006) have shown that pigeons perceive the standard Müller-Lyer illusion. In this report, the authors examined effects of bracket sizes on perception of this illusion in pigeons (Columba livia) and humans (Homo sapiens). In Experiment 1, three pigeons were retrained to classify six lengths of target lines into “long” and “short” by pecking two keys on the monitor, ignoring the two brackets oriented toward the same direction. In the tests that followed, the standard Müller-Lyer figures of different bracket sizes were presented. All birds chose “long” more frequently for the figures having inward-pointing brackets (>), regardless of bracket sizes. The overestimation of the target lines of inward-pointing figures continued to increase in pigeons, whereas it decreased as the bracket size became longer in humans (Experiment 2). The results suggest that these two species perceive the standard Müller-Lyer illusion with long brackets in different ways. Perhaps pigeons might not perceive illusions induced by contrast with the surrounding stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeons (Columba livia) associate time intervals with symbols in a touch screen task: Evidence for ordinality but not summation.

The present experiments examined whether pigeons can sum symbols that are associated with various temporal consequences in a touch screen apparatus. Pigeons were trained to discriminate between two visual symbols that were associated with 0, 1, 2, 3, 4, or 5 s either of delay to 4 s of hopper access (delay group) or duration of hopper access (reward group). In Experiment 1, the pigeons in both groups learned to select the symbol associated with the more favorable outcome, and they successfully transferred this discrimination to novel symbol pairs. However, when tested with 2 pairs of symbols associated with different summed durations, they responded on the basis of a simple response rule rather than the sum of the symbol pair. In Experiment 2, the reward group was presented with four symbols at once and was allowed to successively choose one symbol at a time. All pigeons chose the symbols in order from largest to smallest. This indicates that pigeons formed an ordered representation of symbols associated with different time intervals, even though they did not sum the symbols. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrasting object-based and texture-based accounts of same/different discrimination learning with trial-unique stimuli.

Same/different discrimination is a classic task for investigating relational learning in animals. Recent research suggests that pigeons can learn a trial-unique same/different discrimination, which eliminates the opportunity to memorize the training items (Brooks & Wasserman, 2008). The authors conducted three tests to elucidate the role that item-based comparison plays in this trial-unique discrimination. In the first, the authors tested the possibility that pigeons’ same/different discrimination was based on textural features of the displays by creating a single, unitary texture from same and different displays; pigeons failed to discriminate these unitary textural displays. In the second, the authors varied the number of items (mosaics) in the display and the authors reproduced the characteristic decline in performance associated with fewer items. In the third, the authors systematically increased the area of two mosaics to closely match the area occupied by increasing numbers of mosaics; the results obtained with two small items persisted even when the size of the mosaics was increased. These results clearly show that pigeons’ same/different discrimination was based on object-level variability and not on other properties of the displays. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ordinal judgments of symbolic stimuli by capuchin monkeys (Cebus apella) and rhesus monkeys (Macaca mulatta): The effects of differential and nondifferential reward.

Ordinal learning was investigated in capuchin monkeys (Cebus apella) and rhesus monkeys (Macaca mulatta). In Experiment 1, both species were presented with pairings of the Arabic numerals 0 to 9. Some monkeys were given food rewards equal to the value of the numeral selected and some were rewarded with a single pellet only for choosing the higher numeral within the pair. Both species learned to select the larger numeral, but only rhesus monkeys that were differentially rewarded performed above chance levels when presented with novel probe pairings. In Experiment 2, the monkeys were first presented with arrays of 5 familiar numerals (from the range 0 to 9) and then arrays of 5 novel letters (from the range A to J) with the same reward outcomes in place as in Experiment 1. Both species performed better with the numerals, suggesting that an ordinal sequence of all stimuli had been learned during Experiment 1, rather than a matrix of two-choice discriminations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Performance of pigeons (Columba livia) on maze problems presented on the LCD screen: In search for preplanning ability in an avian species.

The authors examined how pigeons (Columba livia) perform on 2-dimensional maze tasks on the LCD monitor and whether the pigeons preplan the solution before starting to solve the maze. After training 4 pigeons to move a red square (the target) to a blue square (the goal) by pecking, the authors exposed them to a variety of detour tasks having lines as a barrier. A preview phase was introduced, during which the pigeons were not allowed to peck at the monitor. Results of a set of experiments suggest that our pigeons successfully learned to solve these tasks, that they came to take an efficient strategy as the barriers became complex, and that they possibly preplan its solution, at least on familiar, well-practiced tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impairments in Spatial Generalization of Visual Skills After V4 and TEO Lesions in Macaques (Macaca mulatta).

The authors tested the spatial generalization of shape and color discriminations in 2 monkeys, in which 3 visual field quadrants were affected, respectively, by lesions in area V4, TEO, or both areas combined. The fourth quadrant served as a normal control. The monkeys were trained to discriminate stimuli presented in a standard location in each quadrant, followed by tests of discrimination performance in new locations in the same quadrant. In the quadrant affected by the V4 + TEO lesion, the authors found temporary but striking deficits in spatial generalization of shape and color discriminations over small distances, suggesting a contribution of areas V4 and TEO to short-range spatial generalization of visual skills. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of distinctive parts on recognition of depth-rotated objects by pigeons (Columba livia) and humans.

To explore whether effects observed in human object recognition represent fundamental properties of visual perception that are general across species, the authors trained pigeons (Columba livia) and humans to discriminate between pictures of 3-dimensional objects that differed in shape. Novel pictures of the depth-rotated objects were then tested for recognition. Across conditions, the object pairs contained either 0, 1, 3, or 5 distinctive pails. Pigeons showed viewpoint dependence in all object-part conditions, and their performance declined systematically with degree of rotation from the nearest training view. Humans showed viewpoint invariance for novel rotations between the training views but viewpoint dependence for novel rotations outside the training views. For humans, but not pigeons, viewpoint dependence was weakest in the 1-part condition. The authors discuss the results in terms of structural and multiple-view models of object recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of hippocampal lesions on the discrimination of structure and on spatial memory in pigeons (Columba livia).

Pigeons (Columba livia) were trained with a spatial structural discrimination, which was based on the spatial relationship among the components of a pattern, and a feature-binding structural discrimination, which was based on how different visual features within a pattern were combined. Neither discrimination was impaired by damage to the hippocampus and area parahippocampalis. The lesions impaired performance on a spatial working memory and a spatial reference memory task in open field. The results indicate an intact hippocampus is not essential for the solution of structural discriminations in pigeons and the hippocampus is important for processing some types of spatial information--that used in navigation, but not other types--that used in spatial structural discriminations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)