Copyright 1992 by the American Psychological Association, Inc.

Journal of Comparative Psychology 1992, Vol. 106, No. 3,295-305

Proficient Performance of a Conjunctive, Recursive Task by an African Gray Parrot (Psittacus erithacus)

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Irene M. Pepperberg Department of Ecology and Evolutionary Biology, University of Arizona The comprehension skills of an African gray parrot (Psittacus erithacus), Alex, were tested on a task that included a conjunctive condition. For each trial, Alex was shown different collections of 7 items, each collection chosen from among 100 objects of various combinations of shapes, colors, and materials, and he was asked to provide (vocally) information about the specific instance of one category of an item that was uniquely defined by the conjunction of two other categories (e.g., "What color is the [object defined by shape and material]?"). Other objects exemplified one, but not both, of these defining categories. Alex responded with an accuracy of 76.5%, which indicated that he understood all the elements in the question, including the conjunctive condition, and that he used these elements to guide his search for the one object in the collection that provided the requested information.

Use of Conjunctive Tasks to Study Animal Intelligence

Conjunctive tasks, as defined by Thomas (1980), evaluate a more complex form of intelligence than that required, for example, for discriminations based on a specific collection of dimensions (e.g., "red, square"). According to Thomas (1980), a conjunctive task requires use of a logical operation (and) to connect any number of affirmative concepts. Thus a subject that successfully performs a conjunctive task not only evaluates stimuli with respect to a large number of different dimensions but also understands that evaluation is based on the process of combining and recombining concepts. Moreover, because a conjunctive task requires that information be stored about multiple concepts, the task also tests a subject's capacity for processing various amounts of information. I therefore chose a conjunctive task (as defined by Thomas, 1980) to evaluate further the abilities of an African gray parrot (Psittacus erithacus) who had successfully completed other complex tasks (e.g., Pepperberg 1990a, 1990b).

Problems in the Use of Conjunctive Tasks Conjunctive tasks are not often used in animal research, possibly because the extent of cognitive ability they can assess (i.e., their power) is not fully appreciated. This lack of appreciation of power and use may have arisen because administering a task that is truly conjunctive can be difficult. Specifically, the conjunctive label is often misapplied to three other types of tasks. These other tasks may or may not be simpler than, but in any case are distinctly different from, tasks that involve conjunction (see Thomas, 1980). Tasks that require a subject to associate multiple different, specific signs for each discriminative stimulus are, according to Thomas (1980), misidentified as conjunctive. Subjects in such studies learn to respond, for example, to "A and B, not A and C" (e.g., Rescorla, 1981; Wells & Deffenbacher, 1967). Such specific responses do not demonstrate sensitivity to the abstract (and flexible) logical combinatorial concept basic to conjunction (Thomas, 1980). Conjunctive tasks may also be confounded with the task of decoding information about compound stimuli. Conjunctive tasks test whether a subject can process questions about various combinations of several abstract categories. In contrast, tasks that involve compound stimuli generally examine how combining two or more specific attributes affects the subject's accuracy in discriminating among exemplars (see Langley & Riley, 1988). Finally, some studies that have purported to test conjunction may instead have tested conditional discrimination. The basis for choosing a triangle when the exemplars are on a red tray or a square when the tray is green may be "for a reward, chose triangle IF red" as well as "for a reward, respond to triangle AND red" (see Thomas, 1991). To be categorized as conjunctive, the task must ensure that the condition red is not the criterion for the choice of the triangle. Conditional tasks thus involve sequential processing to test the relationship

This research was supported by National Science Foundation Grants BNS 86-16955, BNS 88-20098, and BNS 91-96066 and by the National Science Foundation Research Experiences for Undergraduates Program. I thank Pam Banta, Ellen Birkebile, Robyn Bright, Susan Koenig, Jane Lewis, Melissa McGowen, Stephanie Moore, Steve Queen, Jeff Starcheski, and Rebecca Zweifel for assistance as secondary trainers and Ronald J. Schusterman, Thomas Zentall, Anthony Wright, and two unknown reviewers for their comments on an earlier version of this article. I also thank Susan Brown, Greg Harrison, Scott McDonald, and Richard Nye, without whose veterinary care Alex would not have survived to complete this study, and Ernie and Lisa Colaizzi, the Chicago chapter of the American Federation of Aviculture, the veterinarians, and Julia Weertman for their financial assistance with the expenses associated with this medical care. Correspondence concerning this article should be addressed to Irene M. Pepperberg, Department of Ecology and Evolutionary Biology, BioScience West, University of Arizona, Tucson, Arizona 85721.

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between one of generally two initial conditions and a choice of subsequent action. Conjunctive tasks instead test how combinations and recombinations of any number of initial conditions (which themselves can be processed in any order) affect a choice. These problems may be avoided if conjunction is added to a recursive task. Understanding how the combination of conjunction and recursion achieves this objective is, however, possible only when the distinctions between recursion and conjunction are appreciated (Premack, 1986). I therefore briefly review the type of processing required by a recursive task (see Pepperberg, 1990a, for details) and then describe the effect of adding a conjunctive condition.

Description of a Recursive Task to Be Used With a Conjunctive Condition A recursive task is hierarchical: The subject must divide the task into parts and apply the appropriate rule (the same one or a different one) first to solve each part and then, in turn, to the solutions of each part (see Premack, 1986). For example, a subject can be given several objects that each differ in color, shape, and material and be asked "What material is the object of [a given shape]?", "What color is the object of [a given material]?", "What material is the object of [a given color]?", or "What shape is the object of [a given material]?" (see Pepperberg, 1990a). To respond, the subject must (a) comprehend the symbols that represent all possible actions (e.g., fetch vs. touch; see Herman, 1987; Schusterman & Gisiner, 1988) or object attributes (e.g., shape vs. number) that will guide its response, (b) comprehend additional symbols to determine the subset of information to which it will selectively attend (e.g., exemplars that are blue) in the context of any possible collection of objects (Granier-Deferre & Kodratoff, 1986), and finally (c) determine its response and encode this response into an appropriate physical motion or verbal representation of an object or attribute. The subject demonstrates its competence by reporting on only a single aspect (e.g., color, shape, or material) of or performing one of several possible actions (fetching or touching) on the one designated object in the collection. Recursive tasks can also be evaluated by examining how they differ from other tasks (Pepperberg, 1990a). Recursive tasks cannot be solved by responding with respect to a single set of criteria (e.g., match-to-sample on the basis of color) or by performing an action determined by a relatively simple 1:1 correlation ("Pick up [a given object]"). The tasks are not based on responses to single questions (e.g., "What's this?") for even a large number of different exemplars or to chaining two independent responses to different objects ("Do [first given action] to [first given object] and [second given action] to [second given object]"; Premack, 1986). Although recursive tasks are related to conditional tasks (e.g., "If tray is red, do match-to-sample; if tray is black, do oddity"), both the number of concepts involved and options for response are considerably greater; for example, a recursive task requires the subject to process additional information as to whether the match was, for example, to be on the basis of color, shape, or material (see Thomas, 1980).

Effect of Adding a Conjunctive Condition to a Recursive Task Three effects must be considered when conjunction is added to a recursive task: (a) how a conjunctive condition affects the recursive complexity of the task, (b) how recursion can help ensure that the task is conjunctive, and (c) how adding a conjunctive condition affects the overall complexity of a task. Adding conjunction need not alter the recursive complexity of a task. A recursive task without conjunction defines the target by a single category, for example, "What shape is the object that is wood?" The conjunctive condition adds features, for example, "What shape is the object that is wood and blue?" The subject could, however, search for blue and wood simultaneously, that is, use parallel rather than sequential processing (see Langley & Riley, 1988). Parallel processing does not require an additional recursive step, and the recursive complexity of the task thus need not necessarily increase with the addition of the conjunctive condition. Combining conjunction and recursion can lessen the possibility of confounding the task with others that evaluate nonconjunctive capacities. First, because trials in a recursive task can involve series of unique collections of different objects (e.g., subsets of a large collection of exemplars that each vary with respect to color, shape, and object label) and one of several different possible commands that concern the attributes of these objects, the subject cannot be responding to any single set of stimulus attributes (see Granier-Deferre & Kodratoff, 1986; Pepperberg, 1990a). Second, a conjunctive, recursive task is not about decoding specific elements of a given compound stimulus but rather about responding to (i.e., processing information about) successive combinations of concepts. On one trial, for example, the subject must label the shape of an object defined by its color and material and on the next trial label the material of an object defined by shape and color. Third, the structure of a recursive task lessens the likelihood that the problem will be solved as a conditional discrimination. Assume, for example, that a subject answers a question about the shape of an object that is green and wood by the apparently conditional process "If I find several green objects, then I'll choose the wooden one." The subject has not, however, used a conditional process, for the condition green is not the exclusive reason for the choice of wood. The structure of the task requires a number of green nonwooden and nongreen wooden objects from which to choose, and neither the condition green nor wood alone is sufficient for a correct response. To be correct, the subject must combine (conjoin) the instances of color and material. In sum, the potential problems inherent in a test for conjunctive understanding are considerably lessened when such a test is administered in connection with a recursive task. Finally, the overall complexity of a recursive task increases when the conjunctive condition is added. The subject now must not only process the information needed to solve the standard recursive task described above but also understand how different recombinations of categories affect its search for the targeted object. Moreover, the subject must store additional information about abstract categories to complete the search; that is, additional memory is required.

PROFICIENCY IN A CONJUNCTIVE, RECURSIVE TASK BY A PARROT

Advantages in the Use of Conjunctive Tasks in CrossSpecies Comparisons Conjunctive tasks, because of their abstract nature, can be adapted to many conditions and thus provide data on the cognitive capacities of various animals (Thomas, 1980). Such tasks have been given to several mammalian species: squirrel monkeys (Saimiri sciureus; Burdyn & Thomas, 1984), dolphins (Tursiops truncatus; Herman, 1987), and sea lions (Zalophus californianus; Schusterman & Gisiner, 1988). This study provides data for an avian subject, an African gray parrot.

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the one object of 7 that was the specific target of the search, and (c) information that designated (in the form of a different category label, e.g., color rather than shape or material) the particular category from which the response must be chosen. (This last piece of information could, of course, be deduced from other information; i.e., the question involved the only category for which specific information was not given.) To respond correctly, Alex had to process each type of information without error, then recognize and encode as a vocal label (e.g., "blue") the information about the appropriate instance of the targeted category. Some or all of these behaviors occurred as separate steps, each step adding to the complexity of the task (see Premack, 1983).

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Training Procedures Method Experimental Design Subject. The experimental subject, an African gray parrot (Psittacus erithacus) named Alex, resides in a laboratory (details in Pepperberg, 1981), where he has been the focus of studies on interspecies communication and animal cognition since June 1977.' When this experiment began, Alex could produce English labels for numerous colors (rose [red], green, blue, yellow, gray, purple, and orange), shapes (2-, 3-, 4-, 5-, and 6-corner), and materials (cork, wood, hide [rawhide], rock [Playdoh forms], paper, chalk, and wool), and could label various items of metal (chain, key, grate, tray, and truck [toy cars]), wood (peg wood [clothes pin] and block), and plastic or paper (cup and box; Pepperberg, 1987b, 1990a, 1990b). He could use these labels to identify, request, and refuse items and to respond to questions about abstract categories of color, shape, material, relative size, and quantity for more than 100 different objects, including those that differed somewhat from training exemplars (Pepperberg, 1978, 1981, 1983, 1987a, 1987b, 1987c, 1988b, 1988c, 1990a; Pepperberg & Brezinsky, 1991). Task. The task was an extension of that used in the prior recursion study (Pepperberg, 1990a). As before, the task differed from those used with mammals in several ways. First, Alex worked in the vocal mode. Second, each trial was presented intermittently during training and testing of other unrelated topics (e.g., numerosity or photograph recognition; see Discussion in Pepperberg, 1990a) so that Alex was exposed to numerous possible exemplars and questions during each session (see Premack, 1976, p. 132). Alex's responses were thus based on his entire repertoire (>80 vocalizations, including labels for foods, quantity, and locations). Such a protocol also minimized errors caused by proactive interference by separating the types of stimuli and responses (see Schusterman, Gisiner, & Hanggi, 1988). Third, unlike some earlier tasks (e.g., those in which monkeys associated "triangularity-sameness" and "heptagonality-difference"; Burdyn & Thomas, 1984; Thomas, 1991), the present task was less likely to be solved conditionally (see earlier discussions). In each trial of the task, Alex was shown a different collection of 7 exemplars and asked to label the specific instance of one category of an item that was uniquely defined by instances of two other categories. Each collection was chosen from among 100 objects of various combinations of shapes, colors, and materials; for each 7-item display, he was asked one of three possible vocal questions: "What color is [the object designated by a given shape and a given material]?", "What shape is [the object designated by a given color and a given material]?", or "What object is [designated by a given color and a given shape]?" Every question contained three types of information: (a) information about the topic under study (e.g., an attribute of one item in a collection vs. the quantity of the collection), (b) information that designated (by conjoining labels for particular instances of two categories, e.g., "wood and green" rather than "blue and 3-corner")

General training procedures: Model/rival approach, intrinsic rewards. Because details of the training procedures and the rationale for their use have been described previously (Pepperberg, 1981, 1983, 1987a, 1987c, 1988b, 1988c), only a summary (which follows Pepperberg, 1990a) will be given here. The primary technique, called the model/rival approach, uses humans to demonstrate referential, contextual use of each vocalization in the targeted task. Alex watches one human act as a trainer and a second human act as a trainee. The trainer questions the trainee about targeted objects, gives praise and reward for correct answers, and shows disapproval for incorrect answers (errors similar to those that Alex was making at the time). The trainee is both a model for the bird's responses and a rival for the trainer's attention. Frequent reversal of the roles of model/rival and trainer demonstrate the interactive nature of the system, and Alex is encouraged to participate in these vocal exchanges. For his correct responses, Alex receives intrinsic rewards, that is, the object or collection about which he has been queried (Pepperberg, 1978, 1981, 1987a, 1987b, 1988b; note Greenfield, 1978). Such a protocol provides the closest possible association of each object or action and the label or concept to be learned. To motivate Alex to work with objects in which he has little interest, we also allow him to discard this reward and request an alternative ("I want X"; see Pepperberg, 1987a, 1987b, 1988c). Because he has been trained to preface requests with "I want..." and to use object labels alone (e.g., "green key") for identifications (Pepperberg, 1988c), we can separate an inappropriate response from a request for a preferred item: A vocalization like "cork" to a collection of keys is considered an error, whereas "I want cork" is taken as a valid (if interruptive) request. After Alex produces correct responses with respect to the targeted objects and receives or rejects them, his requests for an alternative are accommodated. Training on the conjunctive comprehension task. Training on comprehension followed the basic procedures with respect to personnel and technique. Beginning in October 1986, Alex was trained on a comprehension task that did not include conjunction (see Pepperberg, 1990a). Training sessions occurred 2-4 times each week and lasted from 5 min to 1 hr, depending on the length of Alex's attention span in a given session (see Behaviors During Training). Beginning in November 1986, one question that included conjunction was added to one training session each week. Three students and I were 1

Questions often arise about the replicability of a study that uses a single subject. If a single subject in a study reliably demonstrates a capacity, the implication is that this aptitude is within the capacity of the species (Pack, Herman, & Roitblat, 1991; Pepperberg & Funk, 1990; Triana & Pasnak, 1981; Wright, Cook, Rivera, Sands, & Delius, 1988). Of course, negative results for a single individual cannot prove the lack of aptitude for the species as a whole.

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the trainers. Training ended in February 1987, when testing began on the comprehension task that did not involve conjunction. The specifics of the training procedure were therefore identical to those reported in Pepperberg (1990a): During training, items of different colors, shapes, and materials were placed on the green feltcovered tray that had been used for the studies on numerical concepts (Pepperberg, 1987b) and object permanence (Pepperberg & Kozak, 1986). To ensure further that the tray would not become associated solely with the comprehension task, we varied the number of items on the tray from 2 to 7 and continued to ask questions of "How many?" as well as questions about the colors, shapes, or materials of specific exemplars. We recorded which objects were included in each training trial so that neither the same collection nor the same question would occur during testing.

Behaviors During Training As in the previous recursion study (Pepperberg, 1990a), Alex often did not attend to the initial formal training. He labelled and grabbed favored objects before we asked questions, or he responded to many questions with either the label "green" (while pulling at the green wool tray liner) or "tray" (while biting at the tray itself). Such behavior was likely caused by a certain lack of novelty in the task. Although the combinations of objects for each task in this experiment were novel, the objects themselves were, by necessity, well-known.2 When familiar objects were repeatedly used as intrinsic rewards in previous studies, Alex responded in similarly disruptive ways (Pepperberg, 1983, 1987a, 1987c, 1988b; reports of "boredom" behavior in other animal subjects are in Davis, 1984; Davis & Bradford, 1986; Moran, Joch, & Sorenson, 1983; Putney, 1985). In contrast, when transfer trials incorporated novel (i.e., conceivably more interesting) objects, Alex's attention span increased, and his accuracy improved (Pepperberg, 1987a). To prevent disruptive behavior from interfering with subsequent training, my students and I used strategies developed in the earlier study (Pepperberg, 1990a). First, we continued to intersperse trials with other tasks. Second, we emphasized that a correct response would allow Alex to request any favored exemplar or activity. Third, we altered the syntactic form of our questions in a random manner from trial to trial to provide additional novelty; for example, examiners decided at the time of the trial whether they would phrase the question as "What color is the 3-corner key?" or as "Three-corner key, what color?" and whether, if Alex interrupted with a request or made an error, they would alter or retain the form.3 Syntactic alterations may not only have forced Alex to attend more closely but may also have helped avoid retroactive interference effects—in which the information in the second label or category interferes with that of the first. (See Schusterman & Gisiner, 1988; Schusterman et al., 1988, for discussions of retroactive interference effects in comprehension studies with marine mammals.) Fourth, when Alex reverted to disruptive behaviors during testing, we stopped testing for periods of days, weeks, even a year, so that the task itself would have some novelty.

Testing Procedures Criterion prior to testing. Our criterion for deciding when to initiate formal testing was identical to that used in the earlier comprehension study (Pepperberg, 1990a). The criterion was based on the efficacy of our training techniques in eliminating Alex's interruptive behaviors. We thus required that his responses on three consecutive sessions not include irrelevant responses of "tray" or "green" or his grabbing of preferred items before testing began.

General test procedures. Test sessions of a single comprehension question were held on average 1-4 times each week during JanuaryApril 1988, June-July 1989, June-July 1990, and March-April 1991." The following is a summary of the rationale for the test procedures. Details are in Pepperberg (1981, 1990a). Tests were designed to avoid a trainer's expectation of a certain type of answer. A trainer who, for example, administers a series of number-related questions might unconsciously accept an indistinct (and by our criteria, incorrect) response of "gree" (a combination of "green" and "three") for "three." Two precautions were therefore taken so that a trainer could not predict which questions (or answers) would appear on a given day. First, tests covered all topics that Alex had mastered. To construct a test, therefore, the principal trainer listed all of the possible questions and objects to be tested for all of the topics under examination (e.g., number competency or questions on same-different). The principal trainer covered the list and gave it to a student not involved in testing, who would then randomly order all the questions on the list. Each test included only one question on each topic. Second, questions were presented intermittently during training sessions5 on current (and thus unrelated) topics (e.g., photograph recognition and two studies related to counting) over the course of several days until all the questions on the test were presented. The opportunity for a particular object (or collection of objects) in this series thus might occur only once per week. Only those students who were working as trainers on novel topics were allowed to act as examiners. Questions were thus asked by students who had not been involved in training the comprehension procedure, a system that further lessened the possibility of trainer-induced cuing (Pepperberg, 1981). Multiple-topic tests not only avoid expectation cuing on the part of the trainer and increase the general complexity of the task but prevent results from being affected by expectation cuing on the part of the subject: Questions with a restricted range of answers could enable a subject to perform somewhat better than would otherwise be justified by its actual knowledge of the topic (see Discussion in Pepperberg, 1990a). Our procedure ensured that Alex was never tested exclusively on a single topic (e.g., number labels) in one session nor tested successively in one session on the same question ("What's same?") or on questions that had one particular correct response (e.g., "color"). A question was repeated in a session only if Alex's initial 2

Familiar objects were used because Alex had to be able to label all the attributes, and all combinations of attributes for these exemplars (colors, shapes, and materials) had been used in other studies. Training labels for new attributes (e.g., pink) would have confounded other concurrent studies (e.g., Pepperberg 1987a, 1987b) for which we needed attributes that Alex could not label. 3 The interactive nature and fast pace of the testing would be disrupted if examiners paused between queries to consult a table to see how they should proceed within a trial. Although data about which form of questioning was more effective would have been interesting, the point of the task was not to examine Alex's syntactic processing ability—as is the case with studies on marine mammals. 4 Testing was stopped between May 1988 to May 1989 and August 1989 to May 1990 because Alex reverted to his disruptive behaviors (see Behaviors During Training). The hiatus in testing between August 1990 and February 1991 occurred because, first, Alex became seriously ill (aspergillosis) in September 1990 and, second, the laboratory was moved from Illinois to Arizona in late 1990. 5 Training sessions had to be in progress at least 5 min before a test question could be administered. Such a procedure ensured both that Alex was attending to his trainers and that the sessions would not be interrupted before several training trials had been completed. After this initial 5-min period, test questions could be given at any time.

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PROFICIENCY IN A CONJUNCTIVE, RECURSIVE TASK BY A PARROT answer was incorrect (Pepperberg, 1981, 1983, 1987a, 1987b, 1987c, 1988b). Furthermore, use of secondary trainers who had not been involved in training the comprehension procedure lessened the possibility that Alex would associate the comprehension task with particular humans (Pepperberg, 1981). Conjunctive test procedure. The test procedure was, except for the conjunctive condition, identical to that used in the previous comprehension study (Pepperberg, 1990a). Details are repeated here for the reader's convenience. A comprehension trial began when the secondary trainer allowed Alex to touch his tongue to each of the exemplars that would constitute the collection. This step enabled Alex to distinguish certain materials that often appeared visually similar (e.g., Playdoh and rawhide forms). The trainer then scattered these objects onto the surface of the tray. Only if an object was obscured by the placement of other objects was the arrangement altered in any way. Each object was generally spaced less than 5 cm from the other nearest object. So that Alex could not tell which question was to be asked from the composition of objects on the tray, all trials contained seven objects, including shape trials for which there were only five labelable choices. All objects varied in color, shape, and material, although several objects did, as was noted earlier, independently embody one of two of the defining categories. Chance was calculated on the number of possible answers, not the number of objects. The number of times a collection was presented to Alex depended on his accuracy, which was determined as in previous studies (e.g., Pepperberg, 1990a): When the secondary trainer questioned the bird, the principal trainer was present but sat in a corner of the room with her back to the bird. She never asked the question nor did she know what was being presented. After Alex responded to the secondary trainer, the principal trainer repeated what she heard the bird say. Her interpretation of Alex's response was unlikely to have been influenced by her hearing the type of question: Subsequent transcriptions of contextless tapes of Alex's responses in a session agreed with the original evaluations to within 98.2%.6 If Alex gave the correct response (the appropriate label), then he was praised and given the object to which the question referred or allowed to request an alternative. There were then no additional presentations of the same material during that test; that is, there was only a single, first-trial response. If the identification was incorrect or indistinct, the examiner removed the tray of objects, turned his or her head, and emphatically said "No!" Only under this condition were the test materials immediately, repeatedly presented, and presentation continued until a correct identification was made; errors were recorded.7

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lation compared the results to what would have happened had Alex randomly selected an object to label. The other calculation assumed that Alex selected an object based on one but not both targeted properties, that is, as though he did not use the conjunctive condition. Such multiple calculations allow performance to be evaluated at different levels of complexity. In order to compare Alex's results to values based on a random choice of exemplar, his performance must be evaluated separately for each topic. Such statistical separation was necessary because chance values were based on the number of possible responses to the targeted category rather than to all categories (see Herman, Richards, & Wolz, 1984; Pepperberg, 1990a; Schusterman & Gisiner, 1988). For questions regarding color and material, chance was taken as 1 of 7, because there were seven possible responses—seven colors or seven labelable objects on the tray. A chance value of 1 of 5 was used for shape trials even though there were seven objects, because the number of labelable shapes was five. Chance values of 1 of 5 and 1 of 7 were conservative in that they ignored the possibility that Alex could have produced any of his labels (e.g., those for objects not on the tray or for food items, which were never included in a test). First-trial scores for questions about color and material were, respectively, 7 of 11 (63.6%) and 9 of 11 (81.1%); on a binomial test with chance value of 1 of 7, significance values were, respectively, p < .0003 and p < .0001. For questions about shape, firsttrial scores were 10 of 12 (83.3%); on a binomial test with chance value of 1 of 5, the significance value was p < .0001. Chance values could also be calculated not from a random choice of exemplar but from a choice based on one of the categories. On each trial, four of the objects exemplified one of the targeted categories, four exemplified the other targeted category, and only one object exemplified both. If Alex chose randomly after identifying one categorical subset, chance would be 1 of 4 for trials of color and material, and significance values were, respectively, p = .0064 and p = .0001. For five trials on shape, two of the four objects in one subset could not be labeled, so chance would be 1 of 2; on such trials Alex's score was 5 of 5, p = .0312. For the seven other trials on shape, one of the four objects in each subset was unlabelable,

Results Calculated with respect to first-trial performance, Alex's accuracy for a recursive task that included a conjunctive condition was 26 of 34, or 76.5%. For comparison, his accuracy for first trials on a nonconjunctive, recursive task was 39 of 48, or 81.3% (Pepperberg, 1990a). These scores did not differ to any statistically significant extent at the .05 confidence level based either on the test for differences in proportions or a chi-square test, x2( 1, N = 82) = 0.2709. The addition of the conjunctive condition thus did not affect Alex's accuracy. Because Alex was already familiar with the recursive task, and the addition of the conjunctive task was unlikely to have increased the complexity of the recursive task itself, the scores reflect Alex's competence on the conjunctive condition. First-trial scores were also calculated for each question topic (see Table 1), and the statistical significance of the results was calculated with two different criteria for chance. One calcu-

6 This percentage represented 106 matches of 108 vocalizations. Of the two mismatches, one involved transcribing Alex's production of the sound "sun" as "kuh" (n.b., a separate, concurrent task involves Alex's learning to sound out individual phonemes, so that such productions of single sounds do occasionally occur), and the second occurred because the "wanna," from "wanna go back," was inadvertently cut out of the tape. As a control, a live and a tape transcription was made of a student, new to the laboratory, who responded to the same types of questions as Alex. The principal trainer's two transcriptions of his vocalizations matched to within 95.8% (68 of 71). 7 Occasionally the examiner rather than Alex erred: In about 1 in 20 trials (particularly during student exam periods), an examiner erred and scolded Alex for a correct response. Alex repeated his correct response, despite our procedures, which encouraged a loseshift strategy. The examiner then recognized her error, and the bird got his reward. Note that although this is not a formal blind test, it produced the same results.

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Table 1 Results and Errors for Comprehension Trials

Test Question

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What object is [item designated by color and shape label]? What shape is [item designated by color and object label]? What color is [item designated by shape and object label]?

which gave a chance value of 1 of 3; his score for these trials was 5 of 7, p= .0416. Because test questions were repeated until Alex responded correctly, I also report the number and type of errors for each question. In eight reported instances in which he initially erred (Table 1 and Appendix), he responded correctly on the second presentation. In two additional trials (one on color and one on material), however, Alex did not respond correctly on the second try. In these instances he produced instead each of the wrong possible answers from the appropriate category, repeated each wrong answer, then grabbed the tray liner and tossed all the exemplars to the floor. The probability (binomial test) of his producing, by chance, each wrong answer in turn is .0061; the probability of his repeating that behavior is even smaller (p < .0001). His consistent omission of the correct answer suggests that his errors were not caused by a failure to understand the task (see Behaviors During Training). These two trials were considered mistrials and are not included in the data. Other data demonstrate his understanding of which category was being targeted in the task. As in the earlier recursive study (Pepperberg, 1990a), the first single vocalization that Alex uttered was generally a label from the appropriate category, whether or not it was the correct instance of that category. With one exception (his response to Question 4; see Appendix), any other phrases he produced were either repetitions of parts of our questions (e.g., "What color?") or encoded requests for information or other objects or actions (e.g., "You tell me, what shape?" or "I want X"; see Pepperberg, 1987a, 1987c, 1988c) and were not scored as identification errors (see Pepperberg, 1988c). His response of a label from the appropriate category did not, however, necessarily imply that he was merely responding to the initial part of the question: As noted above, we often varied the order in which we presented the parts of the question, so that he was as likely to hear "What shape is the green wood?" as "Green wood, what shape?" As is usual in such studies, Alex's errors are of particular interest, because these errors tell us not only what he does and does not comprehend, but they may also tell us about the processes involved. Errors could arise from five sources: (a) confusion of labels that sound alike; (b) misunderstanding a label that directs the search; (c) problems with respect to perceptual boundaries, for example, differences in avian and human color perception; (d) an inability to comprehend the conjunctive condition, that is, to understand that information

Error Type

No.

Score

No.

9

11

81.1

Wrong object

2

10

12

83.3

Wrong shape

2

7

11

63.3

Alternate item cited Wrong color

1 3

from two categories must be used to determine the object of the search; or (e) correct selection of the targeted object, but then a mislabeling of the attribute in question. Because almost half of the errors in the previous recursion study involved either comprehension or production of labels that, at least to humans, sound similar (e.g., rock and block), such confounds were eliminated in this task. A collection might contain objects with similar labels (e.g., a 2-corner yellow rock and a yellow block), but questions about such a collection targeted other items (the shape of the yellow rawhide). As expected, no errors were based on auditory similarity. Errors from the second and fifth sources could not be distinguished (Pepperberg, 1990a). In previous studies, however, Alex's scores for labeling object attributes averaged 80% (Pepperberg, 1987c, 1990a, 1990b, 1990c), and his present scores were comparable. Thus, he likely mislabeled the attribute of an object after targeting it correctly. Of the eight errors, five may be attributed to perceptual rather than cognitive abilities. One error, on "What object... ?" (Question 6), involved rock (Playdoh) and hide, which are difficult even for humans to distinguish by sight. Alex does touch the objects before a trial, but forgetting the material of an object is not the same as failing to recognize it. Of four errors on "What color . . . ?", one (Question 28) involved a confound between red and orange and one (Question 19) between red and purple. Alex may not have perceived the color of these exemplars exactly as did his human trainers: Psittacine and human visual systems may differ in their color boundaries (see Bowmaker, 1986), and previous studies (Pepperberg, 1988a, 1990c) have suggested that errors on orange are most likely to be "rose" or "yellow" and errors on purple to be "blue" or "rose." Although this subset of Alex's errors could indeed be related to cognitive processing or chance behavior, alternative explanations are consistent with Alex's perceptual capacities. Discussion The data obtained in this task can be compared with that from previous studies on other species. The three main areas of comparison involve the cognitive capacities involved in the recursive part of the task, the effect of using a human-based symbolic communication code, and the capacities that are evaluated by the conjunctive part of the task. Because the first two areas have already been examined in detail (Pepperberg,

PROFICIENCY IN A CONJUNCTIVE, RECURSIVE TASK BY A PARROT

1986, 1990a; Pepperberg & Brezinsky, 1991), I confine my remarks to faculties evaluated by conjunction (note Thomas, 1980): flexibility in processing various types of information and capacity for processing various amounts of information.

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Flexibility in Processing Types of Abstract Information A properly designed conjunctive task requires a subject to use the logical operation and to relate conceptual categories (Thomas, 1980, 1991). Thus, to respond correctly a subject must (a) understand the abstract categories that are being represented, (b) recognize that any categories can be combined, and (c) demonstrate that the task is not being solved as a conditional discrimination. Alex's aptitude on a conjunctive task was at least as great as that of mammalian subjects. Alex's understanding of labels and abstract categories was demonstrated in previous studies (Pepperberg, 1983, 1987a, 1990b). Not only did he learn to identify specific colors, shapes, or materials of entirely novel objects but also that each such label is an instance of a particular category. Given two objects that were identical or varied with respect to one, several, or all attributes and queried "What's same?" or "What's different?", he learned to produce the labels for the categories to which the attributes belong (Pepperberg, 1987a) or to indicate if nothing was same or different (Pepperberg, 1988b). Such data provide evidence for the abstract nature of his concepts, for his understanding that objects in two different collections—one set that is blue and one set that is green— each have the same color does not depend on the specific colors but on understanding that color labels form a category. The questions in the present task continued to require that Alex understand categorical concepts. The task did not involve a search for a single specific collection of attributes, but unlike tasks often used with nonhuman primates and monkeys, Alex's task required simultaneous comprehension of several category and object labels and the meaning of entirely different categorical questions (e.g., "How many?" and "What's different?") in any given session (see Pepperberg, 1990a; note Burdyn & Thomas, 1984). Alex thus could not use the context of the question to anticipate the topic of the task or type of trial. Much like the research with marine mammals (see Herman, 1987;Schusterman&Gisiner, 1988), this study thus ensured that, to be correct, Alex had to comprehend all the conceptual elements in the question or command and base his responses on his entire repertoire of concrete and abstract labels. Alex was capable of understanding the logical operation and at a level comparable with mammals that have been tested, although the tasks differed somewhat for the different species. Chimpanzees learned to request multiple objects or actions (e.g., banana and apple or wash and give apple; Premack, 1976, pp. 243-244), and after learning red and dish, they understood the command "Insert apple (in) red dish" (Premack, 1976, p. 203). Monkeys can associate triangularity with choosing same and heptagonality with choosing different; such data suggest that the animals comprehend two conjunctive relations that are specific to a set of abstract concepts (Burdyn & Thomas, 1984) but do not demonstrate the generality that is necessary (Thomas, 1980) for complete under-

301

standing of conjunction. Tasks used with marine mammals (Herman, 1986, 1987; Herman et al., 1984; Schusterman & Gisiner, 1988; Schusterman & Krieger, 1984, 1986), in contrast, do fulfill Thomas's criterion, for such tasks demonstrate their subjects' abilities to respond to novel combinations of different types of information: Dolphins and sea lions respond not only to novel combinations of attribute and object labels but also to novel combinations of action and object labels. Alex's trials were most similar to those of marine mammals: His tasks used questions in which any two of three possible categories were combined, and anticipating which combination would be targeted was not possible. His three sets of questions (on color and shape, color and matter, and shape and matter), moreover, were not only intermixed with one another but also combined with those from all other studies including the nonconjunctive recursion task. Alex could not, for example, predict that a trial would involve conjunction simply because a number of objects had colors or materials in common, for he was simultaneously shown similar collections and asked such questions as "How many green toys?" He was required, instead, to recognize from the form and content of the questions those trials in which the conjunction of attributes was necessary, he then had to demonstrate an understanding of the conjunctive condition itself. Alex's flexibility with respect to processing novel combinations of different categories of information was therefore at least as great as that demonstrated by mammalian subjects. Use of a recursive task to study conjunction lessens the possibility that a subject is processing the information conditionally. In a task that combines recursion and conjunction, the subject must choose from among a number of items, each of which has at least one of the criterion attributes. An argument can, of course, be made that Alex answered a question about the color of the 4-corner paper by the process, "If I find some 4-cornered objects, then I'll give the color of the one that is paper." In such a case, however, he would be using the condition of shape not as the specific criterion by which to choose the color of the paper but merely as a way of limiting his set of choices. He could equally as well have begun by limiting his choices on the basis of material. His processing, although sequential, would not be conditional (see discussion in Thomas, 1980, p. 464).

Capacity to Process Varying Amounts of Information: Memory and Processing Time Many tasks require a subject to use two types of memory, what researchers have defined as reference memory and working memory (see Roitblat, 1987). Reference memory involves the stable rules of the task, whereas working memory involves the information that changes depending on the particular trial of the task. Recursive and conjunctive tasks each require an integration of these two types of memory, and their combination increases the demands on both types of memory. Specifically, joining a conjunctive condition to an existent recursive task, as is done in the present study, adds (a) the logical operation and to the reference memory and (b) additional categorical information to the working memory. Although the expected effect of adding to memory load is an

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302

IRENE M. PEPPERBERG

increase in the number of errors (for example, see discussion in Grant & MacDonald, 1986), neither Alex nor the marine mammals demonstrated any significant difference in accuracy with the addition of a conjunctive condition (see Schusterman &Gisiner, 1988).8 The ease with which novel combinations of different types of information are processed, and whether such processing occurs sequentially or in parallel, may also be reflected in the amount of time a subject takes to respond to a question, that is, the reaction time or latency to response. For example, a subject may be expected to respond more slowly as the number of signals used to define an object, and thus the amount of information to be processed, increases. As reported in several previous studies, however, Alex's readiness to respond to a given set of exemplars is correlated with his level of interest in obtaining these items rather than any other factor (Pepperberg, 1987a, 1987b, 1988b). Because the familiarity of the exemplars in the comprehension tasks precluded Alex's interest (see Behaviors During Training), latency of response could be neither meaningfully measured nor compared with those of mammals either in the present comprehension task or in the related task that did not involve conjunction (Pepperberg, 1990a). In sum, the data demonstrate that an African gray parrot can perform as accurately on a recursive task that includes a conjunctive condition as he had previously on one that did not; the data thus demonstrate his competence with respect to conjunction. Because the overall cognitive demands of the present task are comparable to the demands of tasks given to marine mammals, Alex's successful completion of such a task, moreover, suggests that various species may have similar capacities and flexibility for processing complex forms of information.

8 A sea lion (Schusterman & Gisiner, 1988), but not a dolphin (Herman, Richards, & Wolz, 1984), did show higher numbers of errors when relational tasks included conjunction. Such tasks, however, involve additional concerns not relevant to this study: Not only did the marine mammals' tasks involve a relational condition, but also the modifiers in the sea lion's task referred to object qualities (e.g., brightness), whereas the dolphin's modifiers involved positional cues that may actually have simplified the task (see discussion in Schusterman & Gisiner, 1988).

References Bowmaker, J. K. (1986, June). Avian color vision and the environment. Paper presented at the meeting of the International Ornithological Congress, Ottawa, Ontario, Canada. Burdyn, L. E., & Thomas, R. K. (1984). Conditional discrimination with conceptual simultaneous and successive cues in the squirrel monkey (Saimiri sciureus). Journal of Comparative Psychology, 98, 405-413. Davis, H. (1984). Discrimination of the number three by a raccoon (Procyon lotor). Animal Learning & Behavior, 4, 121-124. Davis, H., & Bradford, S. A. (1986). Counting behavior in rats in a simulated natural environment. Ethology, 73, 265-280. Granier-Deferre, C, & Kodratoff, Y. (1986). Iterative and recursive behaviors in chimpanzees during problem solving: A new descrip-

tive model inspired from the artificial intelligence approach. Cahiers de Psychologie Cognitive, 6, 483-500. Grant, D. S., & MacDonald, S. E. (1986). Matching to element and compound samples in pigeons: The role of sample coding. Journal of Experimental Psychology: Animal Behavior Processes, 12, 160171. Greenfield, P. M. (1978). Developmental processes in the language learning of child and chimp. Behavioral and Brain Sciences, 4, 573-574. Herman, L. M. (1986). Cognition and language competencies of bottlenosed dolphins. In R. J. Schusterman, J. A. Thomas, & F. G. Wood (Eds.), Dolphin cognition and behavior: A comparative approach (pp. 221-252). Hillsdale, NJ: Erlbaum. Herman, L. M. (1987). Receptive competencies of language-trained animals. In J. S. Rosenblatt, C. Beer, M.-C. Busnel, & P. J. B. Slater (Eds.), Advances in the study of behavior (Vol. 17, pp. 1-60). New York: Academic Press. Herman, L. M., Richards, D. G., & Wolz, J. P. (1984). Comprehension of sentences by bottlenosed dolphins. Cognition, 16, 129-219. Langley, C., & Riley, D. A. (1988, November). Feature versus conjunctive search in pigeons. Paper presented at the annual meeting of the Psychonomic Society, Chicago. Moran, G., Joch, E., & Sorenson, L. (1983, June). The response of meerkats (ISuricata suricattaj to changes in olfactory cues on established scent posts. Paper presented at the annual meeting of the Animal Behavior Society, Lewisburg, PA. Pack, A. A., Herman, L. M., & Roitblat, H. L. (1991). Generalization of visual matching and delayed matching by a California sea lion (Zalophus californianus). Animal Learning & Behavior, 19, 37-48. Pepperberg, I. M. (1978, March). Object identification by an African Grey parrot (Psittacus erithacus,). Paper presented at the midwestern meeting of the Animal Behavior Society, West Lafayette, IN. Pepperberg, I. M. (1981). Functional vocalizations by an African Grey parrot (Psittacus erithacus). Zeitschrift fur Tierpsychologie, 55, 139-160. Pepperberg, I. M. (1983). Cognition in the African Grey parrot: Preliminary evidence for auditory/vocal comprehension of the class concept. Animal Learning & Behavior, 11, 179-185. Pepperberg, I. M. (1986). Acquisition of anomalous communicatory systems: Implications for studies on interspecies communication. In R. J. Schusterman, J. A. Thomas, & F. G. Wood (Eds.), Dolphin cognition and behavior: A comparative approach (pp. 289-302). Hillsdale, NJ: Erlbaum. Pepperberg, I. M. (1987a). Acquisition of the same/different concept by an African Grey parrot (Psittacus erithacus): Learning with respect to color, shape, and material. Animal Learning & Behavior, 15, 423-432. Pepperberg, I. M. (1987b). Evidence for conceptual quantitative abilities in the African Grey parrot: Labeling of cardinal sets. Ethology, 75, 37-61. Pepperberg, I. M. (1987c). Interspecies communication: A tool for assessing conceptual abilities in the African Grey parrot (Psittacus erithacus). In G. Greenberg & E. Tobach (Eds.), Cognition, language, and consciousness: Integrative levels (pp. 31-56). Hillsdale, NJ: Erlbaum. Pepperberg, I. M. (1988a). [Color labeling by an African gray parrot]. Unpublished raw data. Pepperberg, I. M. (1988b). Comprehension of "absence" by an African Grey parrot: Learning with respect to questions of same/different. Journal of the Experimental Analysis of Behavior, 50, 553-564. Pepperberg, I. M. (1988c). An interactive modeling technique for acquisition of communication skills: Separation of "labeling" and "requesting" in a psittacine subject. Applied Psycholinguistics, 9, 3156. Pepperberg, I. M. (1990a). Cognition in an African gray parrot (Psit-

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PROFICIENCY IN A CONJUNCTIVE, RECURSIVE TASK BY A PARROT locus erithacus): Further evidence for comprehension of categories and labels. Journal of Comparative Psychology, 104, 41-52. Pepperberg, I. M. (1990b). Conceptual abilities of some nonprimate species, with an emphasis on an African Grey parrot. In S. T. Parker & K. Gibson (Eds.), Language and intelligence in apes and monkeys: A developmental approach (pp. 469-507). Cambridge, United Kingdom: Cambridge University Press. Pepperberg, I. M. (1990c). Referential mapping: A technique for attaching functional significance to the innovative utterances of an African Grey parrot Applied Psycholinguistics, 11, 23-44. Pepperberg, I. M., & Brezinsky, M. V. (1991). Acquisition of a relative class concept by an African gray parrot (Psittacus erithacus): Discriminations based on relative size. Journal of Comparative Psychology, 105, 286-294. Pepperberg, I. M., & Funk, M. S. (1990). Object permanence in four species of psittacine birds: An African Grey parrot (Psittacus erithacus), and llliger minimacaw (Ara maracana), a parakeet (Melopsittacus undulatus), and a cockatiel (Nymphicus hollandicus). Animal Learning & Behavior, 18, 97-108. Pepperberg, I. M., & Kozak, F. A. (1986). Object permanence in the African Grey parrot (Psittacus erithacus). Animal Learning & Behavior, 14, 322-330. Premack, D. (1976). Intelligence in ape and man. Hillsdale, NJ: Erlbaum. Premack, D. (1983). The codes of man and beast. Behavioral and Brain Sciences, 6, 125-176.

Premack, D. (1986). Gavagai! or the future history of the animal language controversy. Cambridge, MA: Bradford Books, MIT Press. Putney, R. T. (1985). Do willful apes know what they are aiming at? Psychological Record, 35, 49-62. Rescorla, R. A. (1981). Within-signal learning in autoshaping. Animal

Learning & Behavior, 9, 245-252. Roitblat, H. L. (1987). Introduction to comparative cognition. New York: Freeman. Schustennan, R. J., & Gisiner, R. (1988). Artificial language comprehension in dolphins and sea lions: The essential cognitive skills. The Psychological Record, 38, 311-348. Schusterman, R. J., Gisiner, R. C, & Hanggi, E. B. (1988, November). Priming short-term memory on a language task in sea lions. Paper presented at the annual meeting of the Psychonomic Society, Chicago. Schusterman, R. J., & Krieger, K, (1984). California sea lions are capable of semantic comprehension. The Psychological Record, 34, 3-23. Schusterman, R. J., & Krieger, K. (1986). Artificial language comprehension and size transposition by a California sea lion (Zalophus califomianus). Journal of Comparative Psychology, 100, 348-355. Thomas, R. K. (1980). Evolution of intelligence: An approach to its assessment Brain, Behavior, and Evolution, 17,454-472. Thomas, R. K. (1991, March). Misuse of conditional reasoning in animal research with special reference to the evolution of language. Paper presented at the annual meeting of the Southern Society for Philosophy and Psychology, Atlanta. Triana, E.( & Pasnak, R. (1981). Object permanence in cats and dogs. Animal Learning & Behavior, 9, 135-139. Wells, H., & Deffenbacher, K. (1967). Conjunctive and disjunctive concept learning in humans and squirrel monkeys. Canadian Journal of Psychology, 21, 301-308. Wright, A. A., Cook, R. G., Rivera, J. J., Sands, S. F., & Delius, J. D. (1988). Concept learning by pigeons: Matching-to-sample with trialunique video picture stimuli. Animal Learning & Behavior, 16, 436444.

Appendix Table A1 Details of the Trials Trial 1

2 3

4

5

6

7

Exemplars 2-corner rose hide, 3-corner purple rock, 3-corner orange wood, 3-corner blue paper, 3-corner yellow hide, 4-corner green hide, 5-corner gray hide circular rose paper, 2-corner gray paper, 3-corner yellow paper, 4-corner gray key, 5-corner gray wood, 6-corner gray hide, blue paper box 2-corner orange wood, 3-corner orange hide, 4corner orange wool, 4-corner purple rock, 4corner blue paper, 4-corner yellow key, orange truck 2-corner blue paper, 3-corner yellow hide, 3-corner gray paper, 3-corner orange wool, 3-corner purple key, 4-corner green paper, 5-corner rose paper circular rose hide, 2-corner purple wool, 3-corner purple key, 4-corner yellow hide, 5-corner orange hide, 6-corner purple hide, purple metal box circular green wood, 2-corner green hide, 2-corner yellow wool, 2-corner rose rock, 2-corner blue paper, 3-corner green key, green metal box 2-corner yellow paper, 3-comer green paper, 4corner rose paper, 4-corner blue key, 4-corner orange hide, 4-corner purple rock, 5-corner gray paper

Question What color is 3-corner hide?

Responses yellow

What shape is the gray paper?

corner; 2-corner"

What object is 4-corner orange?

wool

What color is the 3-corner paper?

yellow wool; gray

What shape is the purple hide?

6-corner

What object is 2-corner green?

rock; hide

What color is the 4-comer paper?

yellow; rose

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IRENE M. PEPPERBERG

Table Al (Continued) Trial 8 9 10

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11

12 13

14

15

16

17 18 19

20

21 22

23 24

25

26

Exemplars

circular green wood, 2-corner green rock, 3-corner green hide, 4-corner rose rock, 5-corner purple rock, 6-corner blue rock, green chain 2-corner blue hide, 3-corner blue key, 4-corner blue rock, 4-corner rose paper, 4-corner purple wood, 4-corner orange hide, 5-corner blue wool 2-corner blue wool, 2-corner yellow hide, 2-corner gray wood, 2-corner purple paper, 3-corner orange wool, 4-corner rose wool, 5-corner green wool circular green rock, 2-corner green wood, 3-corner blue paper, 4-corner green paper, 5-corner orange paper, 6-corner green wool, yellow paper cup 2-corner yellow wood, 3-corner yellow rock, 6corner rose hide, 6-corner blue paper, 6-corner yellow key, 6-corner green wool, yellow block circular orange wood, 2-corner yellow wood, 3corner green wood, 5-corner gray wool, 5-corner rose hide, 5-corner blue paper, 5-corner purple wood circular green wood, 2-corner blue wool, 3-corner green key, 4-corner green wool, 5-corner orange wool, 6-corner green rock, rose wool string 2-corner orange paper, 4-corner orange rock, 5corner gray hide, 5-corner blue paper, 5-corner orange wood, 5-corner yellow wool, 6-corner orange key 2-corner rose hide, 3-corner orange key, 3-corner blue hide, 3-corner gray wood, 3-corner green wool, 5-corner yellow hide, 6-corner purple hide circular rose key, 2-corner gray paper, 3-corner gray key, 4-corner yellow key, 5-corner gray wool, 6-corner gray hide, 8-corner orange key 2-corner blue wood, 3-corner blue key, 3-corner purple rock, 3-corner orange paper, 3-corner yellow wool, 4-corner blue hide, blue truck circular orange wool, 2-corner yellow wool, 3corner green wool, 5-corner gray wood, 5-corner rose hide, 5-corner blue paper, 5-corner purple wool circular yellow wool, 2-corner green hide, 3-corner orange hide, 4-corner purple hide, 5-corner yellow hide, 6-corner yellow paper, yellow tubular rock 2-corner rose wool, 3-corner rose key, 6-corner green rock, 6-corner yellow hide, 6-corner rose paper, 6-corner purple wood, rose block green metal truck, yellow rubber truck, rose metal key, gray metal cup, orange metal box, purple paper, truck, blue plastic-covered metal nail circular yellow wood, 2-corner purple wood, 3corner rose key, 4-corner rose hide, 5-corner green wood, 6-corner rose wood, rose truck 2-corner purple wood, 3-corner purple key, 5corner green paper, 5-corner purple rock, 5corner orange wood, 5-corner yellow hide, purple chalk 3-corner purple hide, 4-corner green rock, 4-corner gray paper, 4-corner orange hide, 4-corner yellow wood, 5-corner blue hide, 6-corner rose hide circular blue paper, 2-corner blue hide, 3-corner blue rock, 4-corner yellow rock, 5-corner orange rock, 6-corner blue key, gray tubular rock

Question

Responses

What shape is the green rock?

2-corner

What object is 4-corner blue?

rock

What color is 2-corner wool?

blue

What shape is the green paper?

corner; 4-cornera

What object is 6-corner yellow?

key

What color is the 5-corner wood?

purple

What shape is the green wool?

3-; 4-corner

What object is 5-corner orange?

wood

What color is the 3-corner hide?

blue

What shape is the gray key?

3-corner

What object is 3-corner blue?

key

What color is the 5-corner wool?

rose; purple

What shape is the yellow hide?

5-corner

What object is 6-corner rose?

wool; paper

What is the color of the metal car [truck]?"

green

What shape is the rose wood?

6-corner

What object is 5-corner purple?

rock

What color is the 4-corner hide?

orange

What shape is the blue rock?

3-corner

305

PROFICIENCY IN A CONJUNCTIVE, RECURSIVE TASK BY A PARROT Table A1 (Continued) Trial 27

28 29

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30 31

32 33 34

Exemplars 2-corner orange rock, 2-corner gray paper, 2-corner purple wood, 2-corner rose hide, 3-corner purple key, 4-corner purple plastic key, 5-corner purple wool rose metal key, blue plastic key, purple wood key, gray metal cup, green metal box, orange metal truck, yellow paper key circular gray hide, 2-corner yellow rock, 3-corner orange hide, 4-corner purple hide, 5-corner yellow paper, 6-corner yellow hide, yellow block gray metal chain, yellow metal box, gray block, orange metal key, gray rock, gray paper, rose metal truck 2-corner orange wood, 2-corner blue hide, 2-corner purple paper, 2-corner yellow wool, 3-corner blue wool, 4-corner gray wool, 5-corner green wool circular rose key, 2-corner purple wood, 3-corner purple key, 4-corner green key, 5-corner gray key, 6-corner purple wool, tubular purple rock 3-corner blue key, 3-corner orange hide, 3-corner gray paper, 3-corner yellow wood, 5-corner blue rock, 6-corner blue wool, blue chalk circular blue wood, 2-corner purple wood, 3-corner orange hide, 4-corner orange key, 5-corner orange wood, 6-corner yellow wood, tubular orange rock

Question What object is 2-corner purple?

Responses wood

What color is the metal key?

orange; rose

What shape is the yellow hide?

6-corner

What object is gray metal?

chain

What color is the 2-corner wool?

yellow

What shape is the purple key?

corner; 3-corner

What object is 3-corner blue?

key

What shape is the orange wood?

3-; 5-corner

Note. All questions and exemplars were intermingled. Although Alex cannot label circular or tubular items, such exemplars were included so that he could not easily distinguish by the number of objects on the tray the shape-related questions (with five possible different responses) from the color- and object-related questions (with seven possible responses). Because Alex's label for red is "rose" and for gray or black is "gray," these labels are used in the table. His labels for different shapes are as follows: 2-corner = football-shaped; 3-corner = triangle; 4-corner = square; 5-corner = regular pentagon; and 6-corner = regular hexagon. His labels for different objects are as follows: hide = rawhide; rock = Playdoh; wool = pompon or shaped felt; and truck = toy car or truck. ' Alex now often initially responds to questions about shape with the vocalization "corner" followed without pause by the numbered label (e.g., "2-corner"). Because this pattern includes no pause (and thus no need for trainer intervention), such a response is not considered an error. b The student asking the question requested the color of the "car," a label that is not in Alex's repertoire. He did not answer until she corrected herself and requested the color of the "truck."

Received July 12, 1991 Revision received October 16, 1991 Accepted October 29, 1991 •