Stages of category learning in monkeys (Macaca mulatta) and humans (Homo sapiens).

Smith and Minda (1998) and Blair and Homa (2001) studied the time course of category learning in humans. They distinguished an early, abstraction-based stage of category learning from a later stage that incorporated a capacity for categorizing exceptional category members. The present authors asked whether similar processing stages characterize the category learning of nonhuman primates. Humans (Homo sapiens) and monkeys (Macaca mulatta) participated in category-learning tasks that extended Blair and Homa’s paradigm comparatively. Early in learning, both species improved on typical items more than on exception items, indicating an initial mastery of the categories’ general structure. Later in learning, both species selectively improved their exception-item performance, indicating exception-item resolution or exemplar memorization. An initial stage of abstraction-based category learning may characterize categorization across a substantial range of the order Primates. This default strategy may have an adaptive resonance with the family resemblance organization of many natural-kind categories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rules and resemblance: Their changing balance in the category learning of humans (Homo sapiens) and monkeys (Macaca mulatta).

In an early dissociation between intentional and incidental category learning, Kemler Nelson (1984) gave participants a categorization task that could be performed by responding either to a single-dimensional rule or to overall family resemblance. Humans learning intentionally deliberately adopted rule-based strategies; humans learning incidentally adopted family resemblance strategies. The present authors replicated Kemler Nelson’s human experiment and found a similar dissociation. They also extended her paradigm so as to evaluate the balance between rules and family resemblance in determining the category decisions of rhesus monkeys. Monkeys heavily favored the family resemblance strategy. Formal models showed that even after many sessions and thousands of trials, they spread attention across all stimulus dimensions rather than focus on a single, criterial dimension that could also produce perfect categorization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Implicit and explicit category learning by macaques (Macaca mulatta) and humans (Homo sapiens).

An influential theoretical perspective differentiates in humans an explicit, rule-based system of category learning from an implicit system that slowly associates different regions of perceptual space with different response outputs. This perspective was extended for the 1st time to the category learning of nonhuman primates. Humans (Homo sapiens) and macaques (Macaca mulatta) learned categories composed of sine-wave gratings that varied across trials in bar width and bar orientation. The categories had either a single-dimensional, rule-based solution or a two-dimensional, information-integration solution. Humans strongly dimensionalized the stimuli and learned the rule-based task far more quickly. Six macaques showed the same performance advantage in the rule-based task. In humans, rule-based category learning is linked to explicit cognition, consciousness, and declarative reports about the contents of cognition. These results demonstrate an empirical continuity between human and nonhuman primate cognition, suggesting that nonhuman primates may have some structural components of humans’ capacity for explicit cognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The comparative psychology of same-different judgments by humans (Homo sapiens) and monkeys (Macaca mulatta).

The authors compared the performance of humans and monkeys in a Same-Different task. They evaluated the hypothesis that for humans the Same-Different concept is qualitative, categorical, and rule-based, so that humans distinguish 0-disparity pairs (i.e., same) from pairs with any discernible disparity (i.e., different); whereas for monkeys the Same-Different concept is quantitative, continuous, and similarity-based, so that monkeys distinguish small-disparity pairs (i.e., similar) from pairs with a large disparity (i.e., dissimilar). The results supported the hypothesis. Monkeys, more than humans, showed a gradual transition from same to different categories and an inclusive criterion for responding Same. The results have implications for comparing Same-Different performances across species--different species may not always construe or perform even identical tasks in the same way. In particular, humans may especially apply qualitative, rule-based frameworks to cognitive tasks like Same-Different. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prototype abstraction by monkeys (Macaca mulatta).

The authors analyze the shape categorization of rhesus monkeys (Macaca mulatta) and the role of prototype- and exemplar-based comparison processes in monkeys' category learning. Prototype and exemplar theories make contrasting predictions regarding performance on the Posner-Homa dot-distortion categorization task. Prototype theory--which presumes that participants refer to-be-categorized items to a representation near the category's center (the prototype)--predicts steep typicality gradients and large prototype-enhancement effects. Exemplar theory--which presumes that participants refer to-be-categorized items to memorized training exemplars-predicts flat typicality gradients and small prototype-enhancement effects. Across many categorization tasks that, for the first time, assayed monkeys' dot-distortion categorization, monkeys showed steep typicality gradients and large prototype-enhancement effects. These results suggest that monkeys--like humans--refer to-be-categorized items to a prototype-like representation near the category's center rather than to a set of memorized training exemplars. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of inferential order judgments in humans (Homo sapiens) and rhesus monkeys (Macaca mulatta).

If A > B, and B > C, it follows logically that A > C. The process of reaching that conclusion is called transitive inference (TI). Several mechanisms have been offered to explain transitive performance. Scanning models claim that the list is scanned from the ends of the list inward until a match is found. Positional discrimination models claim that positional uncertainty accounts for accuracy and reaction time patterns. In Experiment 1, we trained rhesus monkeys (Macaca mulatta) and humans (Homo sapiens) on adjacent pairs (e.g., AB, BC, CD, DE, EF) and tested them with previously untrained nonadjacent pairs (e.g., BD). In Experiment 2, we trained a second list and tested with nonadjacent pairs selected between lists (e.g., B from List 1, D from List 2). We then introduced associative competition between adjacent items in Experiment 3 by training 2 items per position (e.g., B?C?, B?C?) before testing with untrained nonadjacent items. In all 3 experiments, humans and monkeys showed distance effects in which accuracy increased, and reaction time decreased, as the distance between items in each pair increased (e.g., BD vs. BE). In Experiment 4, we trained adjacent pairs with separate 9- and 5-item lists. We then tested with nonadjacent pairs selected between lists to determine whether list items were chosen according to their absolute position (e.g., D, 5-item list > E, 9-item list), or their relative position (e.g., D, 5-item list     

Flexible serial response learning by pigeons (Columba livia) and humans (Homo sapiens).

Experimental tasks designed to involve procedural memory are often rigid and unchanging, despite many reasons to expect that implicit learning processes can be flexible and support considerable variability. A version of the serial response time (SRT) task was developed, in which the locations of targets were probabilistically determined. Targets appeared in locations according to both a structured sequence and a cue validity parameter, and the time to respond to each target was measured. Pigeons (Columba livia) and humans (Homo sapiens) both showed response time facilitation at the highest tested value for cue validity, and the magnitude of that facilitation gradually weakened as cue validity was decreased. Both species showed evidence that response times were largely determined by the local predictabilities of individual cue locations. In addition, humans showed some evidence that explicit knowledge of the sequence affected response times, specifically when cue validity was 100%. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Prospective memory in the formation of learning sets by rhesus monkeys (Macaca mulatta).

In conventional discrimination learning-set formation, it is possible that rhesus monkeys (Macaca mulatta) learn to lay down prospective memories by anticipating the next trial and deciding in advance what choice will be made. To test this hypothesis, the authors administered discrimination problems with 24-hr intertrial intervals, predicting that these long intervals would disrupt or prevent the putative anticipation of the next trial. Confirming their expectation, the authors found no indication of learning-set formation under these conditions. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Perception of chirps by Sykes's monkeys (Cercopithecus albogularis) and humans (Homo sapiens).

Four Sykes's monkeys (Cercopithecus albogularis) and 4 humans (Homo sapiens) discriminated among 12 chirps presented in a repeating background paradigm. The test stimuli consisted of sets of 4 chirps recorded from Sykes's monkeys, red-tailed monkeys (C. ascanius), and small East African birds. Reaction times (RTs) were submitted to a multidimensional scaling analysis. All monkey listeners perceived the bird chirps as similar to each other and distinct from the monkey calls, whereas 3 of the 4 human listeners had difficulty distinguishing the bird chirps from the monkey calls. Both human and monkey subjects tended to perceive Sykes's and red-tailed monkey calls as very similar to one another, but the degree of perceived similarity was greatest for the monkey listeners. The data suggest that the perceptual map of these calls is influenced by their biological significance in nature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What meaning means for same and different: Analogical reasoning in humans (Homo sapiens), chimpanzees (Pan troglodytes), and rhesus monkeys (Macaca mulatta).

Thus far, language- and token-trained apes (e.g., D. Premack, 1976; R. K. R. Thompson, D. L. Oden, & S. T. Boysen, 1997) have provided the best evidence that nonhuman animals can solve, complete, and construct analogies, thus implicating symbolic representation as the mechanism enabling the phenomenon. In this study, the authors examined the role of stimulus meaning in the analogical reasoning abilities of three different primate species. Humans (Homo sapiens), chimpanzees (Pan troglodytes), and rhesus monkeys (Macaca mulatta) completed the same relational matching-to-sample (RMTS) tasks with both meaningful and nonmeaningful stimuli. This discrimination of relations-between-relations serves as the basis for analogical reasoning. Meaningfulness facilitated the acquisition of analogical matching for human participants, whereas individual differences among the chimpanzees suggest that meaning can either enable or hinder their ability to complete analogies. Rhesus monkeys did not succeed in the RMTS task regardless of stimulus meaning, suggesting that their ability to reason analogically, if present at all, may be dependent on a dimension other than the representational value of stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social learning in pig-tailed macaques (Macaca nemestrina) and adult humans (Homo sapiens) on a two-action artificial fruit.

An artificial fruit (AF) was used to test for social learning in pig-tailed macaques (Macaca nemestrina) and adult humans (Homo sapiens). A monkey demonstrator opened the AF, showing alternative methods to 2 groups of cage mates. Video films of the monkey demonstrations were presented to adult humans. Compared with chimpanzees and children, the macaques watched the demonstrations significantly less and in a much more sporadic manner. They also produced only very weak and transitory evidence of social learning. In contrast, the adult humans performed as one might expect of optimum imitators, even producing evidence of components of a "ratchet effect." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Object permanence in orangutans (Pongo pygmaeus), chimpanzees (Pan troglodytes), and children (Homo sapiens).

Juvenile and adult orangutans (n?=?5; Pongo pygmaeus), chimpanzees (n?=?7; Pan troglodytes), and 19- and 26-month-old children (n?=?24; Homo sapiens) received visible and invisible displacements. Three containers were presented forming a straight line, and a small box was used to displace a reward under them. Subjects received 3 types of displacement: single (the box visited 1 container), double adjacent (the box visited 2 contiguous containers), and double nonadjacent (the box visited 2 noncontiguous containers). All species performed at comparable levels, solving all problems except the invisible nonadjacent displacements. Visible displacements were easier than invisible, and single were easier than double displacements. In a 2nd experiment, subjects saw the baiting of either 2 adjacent or 2 nonadjacent containers with no displacements. All species selected the empty container more often when the baited containers were nonadjacent than when they were adjacent. It is hypothesized that a response bias and inhibition problem were responsible for the poor performance in nonadjacent displacements. (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)     

Memory of auditory lists by rhesus monkeys (Macaca mulatta).

Monkey auditory memory was tested with increasing list lengths of 4, 6, 8, and 10 sounds. Five-hundred and twenty environmental sounds of 3-s duration were used. In Experiment 1, the monkeys initiated each list by touching the center speaker. They touched 1 of 2 side speakers to indicate whether a single test sound (presented from both side speakers simultaneously) was or was not in the list. The serial-position functions showed prominent primacy effects (good first-item memory) and recency effects (good last-item memory). Experiment 2 repeated the procedure without the list-initiation response and with a variable intertrial interval. The results of both experiments were similar and are discussed in relation to theories and hypotheses of serial-position effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relative use of proximity, shape similarity, and orientation as visual perceptual grouping cues in tufted capuchin monkeys (Cebus apella) and humans (Homo sapiens).

Recent experimental results suggest that human and nonhuman primates differ in how they process visual information to assemble component parts into global shapes. To assess whether some of the observed differences in perceptual grouping could be accounted for by the prevalence of different grouping factors in different species, we carried out 2 experiments designed to evaluate the relative use of proximity, similarity of shape, and orientation as grouping cues in humans (Homo sapiens) and capuchin monkeys (Cebus apella). Both species showed similarly high levels of accuracy using proximity as a cue. Moreover, for both species, grouping by orientation similarity produced a lower level of performance than grouping by proximity. Differences emerged with respect to the use of shape similarity as a cue. In humans, grouping by shape similarity also proved less effective than grouping by proximity but the same was not observed in capuchins. These results suggest that there may be subtle differences between humans and capuchin monkeys in the weighting assigned to different grouping cues that may affect the way in which they combine local features into global shapes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postural asymmetries and language lateralization in humans (Homo sapiens).

Is hemispheric specialization for speech more closely related to left hemisphere specialization for manual skill and sequencing, as is usually supposed, or to control of asymmetries in whole body posture, as recent findings of right-handedness in nonhuman primates suggest? This question can be evaluated in the 10% of humans who have mixed handedness and footedness. Footedness entails postural asymmetry, and persons with mixed limb preferences often prefer the hand ipsilateral to the preferred foot in asymmetrical actions for which whole body postural adjustments are obligatory (e.g., throwing). The dichotic listening test, an indicator of language laterality, was administered to 4 groups of 48 persons with the 4 possible combinations of hand and foot preference. As in 2 past studies, language lateralization was somewhat more strongly related to postural asymmetries than to asymmetries in manual skill and sequencing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of duration ratios by pigeons (Columba livia) and humans (Homo sapiens).

Humans were trained on 2 versions of a 2-alternative, forced-choice procedure. First, Ss judged which of 2 successive stimulus durations was longer. Second, Ss judged whether the ratio of the 2 durations was less or greater than a criterion ratio (e.g., 2:1). Accuracy was significantly lower for the task in which the judgment was made according to the ratio of the 2 durations. This result is different than that obtained by J. G. Fetterman et al (1989), who trained pigeons on a similar pair of tasks and found that pigeons' performance was comparable for the 2 discriminations. Comparisons of the pigeon and human data suggest that humans were more accurate than pigeons when the judgment involved which duration was longer, but that accuracy was comparable for the ratio-based task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delayed figure reconstruction by a chimpanzee (Pan troglodytes) and humans (Homo sapiens).

A chimpanzee (Pan troglodytes) was trained to construct a copy of 3-element compound figures from a set of 9 elements. Delay intervals between sample offset and element presentation varied. The chimpanzee maintained accuracy at about 80% correct for a delay of 32 s, which was slightly higher than the mean of 4 human (Homo sapiens) Ss. Excellent visual reproductive memory in the chimpanzee as compared with that in humans was demonstrated. However, the nature of the reproductive memory was different in the 2 species in that humans better constructed meaningful figures, which represented food items, than meaningless ones, whereas the chimpanzee constructed these 2 types of figures with the same accuracy. This outcome suggests that the reproductive memory for meaningful figures of the chimpanzee may have been processed separately from symbolic processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Frequency ratio discrimination by zebra finches (Taeniopygia guttata) and humans (Homo sapiens).

We present the first evidence that songbirds can categorize stimulus sequences (note pairs) by frequency ratio (relative pitch) in an operant discrimination. Zebra finches (Taeniopygia guttata) and humans (Homo sapiens) were trained in a discrimination among 27 synthesized note pairs (9 S+ and 18 S– note pairs) with an operant go-no-go food-reward procedure. In the consistent-ratio discrimination groups, S+ note pairs had a common frequency ratio (1.12). In the jumbled-ratio discrimination group, S+ note pairs varied in frequency ratio (1.00, 1.12, and 1.26). Zebra finches and humans discriminated at least 8 of 9 consistent-ratio S+s, zebra finches discriminated 4 jumbled-ratio S+s, and humans discriminated few or no jumbled-ratio S+s. In this experiment, both species appeared to categorize note pairs by a consistent frequency ratio, but only zebra finches memorized several note pairs individually by rote. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Orientation invariant pattern recognition by pigeons (Columba livia) and humans (Homo sapiens).

The orientation invariance of visual pattern recognition in pigeons and humans was studied using a conditioned matching-to-sample procedure. A rotation effect, a lengthening of choice latencies with increasing angular disparities between sample and comparison stimuli, was replicated with humans. The choice speed and accuracy of pigeons was not affected by orientation disparities. Novel mirror-image stimuli, rotation of sample shapes, a delayed display of comparison shapes, and a mixed use of original and reflected sample shapes did not lead to a rotation effect in pigeons. With arbitrarily different odd comparison shapes, neither humans nor pigeons showed a rotation effect. Final experiments supported the possibility that the complete absence of a rotation effect in pigeons is because they are relatively better than humans at discriminating mirror-image shapes compared with arbitrary shapes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)