Hemispheric priming by meaningful and nonmeaningful symbols in language-trained chimpanzees (Pan troglodytes): Further evidence of a left hemisphere advantage.

Hemispheric priming was examined in 3 language-trained chimpanzees (Pan troglodytes) using a simple reaction time (RT) paradigm. Ss were required to hold down a response button until the occurrence of a response cue. A warning stimulus was presented to either the left visual field or the right visual field (RVF) before the response cue occurred. No warning stimulus was presented on control trials. The warning stimuli were geometric communicative symbols from 2 semantic categories: food and tools. A 3rd set of warning stimuli were familiar geometric symbols. Dependent measures included RT and the number of false-positive responses. RT data indicated an RVF advantage in priming when the warning stimuli were food or tool symbols. No significant visual half-field differences were found for familiar symbols, but a trend toward an RVF advantage was observed. These effects were enhanced when Ss responded with their left hand. False-positive data also indicated an RVF advantage for the food and tool warning stimuli. The data indicate that hemispheric asymmetries for processing communicative symbols are present in language-trained chimpanzees. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Communication, symbolic communication, and language: Reply to Seidenberg and Pettito.

Seidenberg and Petitto's (1987) assertion that Kanzi and Mulika's lexigram usage is not representational is evaluated by contrasting their abilities with Nim's. Kanzi and Mulika's data indicate that they (a) comprehend spoken English words; (b) can identify lexigram symbols when they hear these words; (c) can comprehend lexigram usage; (d) can use lexigrams when referents are absent and can, if asked, lead someone to the referent; and (e) that all these skills were acquired through observation, not conditioning. Nim evidenced no comprehension of signs and could not use signs when referents were absent. He was forced to sign and encouraged to imitate his teachers. Seidenberg and Petitto's negative experiences with Nim apparently led them to overgeneralize to all other apes, regardless of species, modality, or training history. Consequently, they unjustifiably disregard important components of Kanzi and Mulika's comprehension data which demonstrate that their lexical knowledge could not have been acquired in an instrumental fashion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhesus monkeys (Macaca mulatta), video tasks, and implications for stimulus-response spatial contiguity.

Recent reports (Iwai, Yaginuma, & Mishkin, 1986; Yaginuma & Iwai, 1986) have supported the earlier conclusion by Meyer, Treichler, and Meyer (1965) and by Stollnitz (1965) that the efficiency of primate learning is compromised to the degree that there is spatial discontiguity between discriminanda and the locus of response. The research reported in this article calls for a reconsideration of this conclusion. Two rhesus monkeys (Macaca mulatta) easily mastered precise control of a joystick to respond to a variety of computer-generated targets despite the fact that the joystick was located 9 to 18 cm from the video screen. We hold that stimulus–response contiguity is a significant parameter of learning only to the degree that the monkey visually attends to the directional movements of its hand in order to displace discriminanda as in the Wisconsin General Test Apparatus. If, instead, attention is focused on the effects of the hand's movement rather than on the hand itself, stimulus–response contiguity is no longer a primary parameter of learning. The implications of this work for mirror-guided studies are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Summation in the chimpanzee (Pan troglodytes).

In this research, we asked whether 2 chimpanzee (Pan troglodytes) subjects could reliably sum across pairs of quantities to select the greater total. Subjects were allowed to choose between two trays of chocolates. Each tray contained two food wells. To select the tray containing the greater number of chocolates, it was necessary to sum the contents of the food wells on each tray. In experiments where food wells contained from zero to four chocolates, the chimpanzees chose the greater value of the summed wells on more than 90% of the trials. In the final experiment, the maximum number of chocolates assigned to a food well was increased to five. Choice of the tray containing the greater sum still remained above 90%. In all experiments, subjects reliably chose the greater sum, even though on many trials a food well on the "incorrect" tray held more chocolates than either single well on the "correct" tray. It was concluded that without any known ability to count, these chimpanzees used some process of summation to combine spatially separated quantities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceived variability and symbol use: A common language-cognition interface in children and chimpanzees (Pan troglodytes).

Analysis of 2 chimpanzees' conversations with their teacher during a tool-use training task demonstrated that Ss used lexigrams, a humanly devised visual symbol system, selectively to encode perceived variability. Ss generally used their symbols to differentiate alternative possibilities or to represent change or novelty in a situation. In contrast, Ss tended to leave unsaid what was unchanging, repetitive, or the unique possibility in a situation. Perceived variability influenced not only which symbols were selected but also utterance length: A single dimension of variability in a situation led to single-lexigram utterances; multiple dimensions were associated with multilexigram utterances. Results indicate that the absence of formal grammatical structure in chimp language does not imply that utterances beyond 1 word in length are either rote strings or imitations. Ss' tendency to mention the variable while leaving the constant or redundant unsaid was supportive of the position that their use of a humanly devised symbol system is more than a series of CRs. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Addendum to "Summation in the chimpanzee (Pan troglodytes)."

Rumbaugh, Savage-Rumbaugh, and Hegel (1987) reported that two chimpanzees (Pan troglodytes) could select, with better than 90% accuracy, the greater of two paired quantities of chocolate chips. In that study, no one quantity of chocolates (from 0 through 5) was used in both pairs on a given trial. We investigated the effect of having one quantity in common (CQ) in both pairs. Whether the other quantities (OQs) of chocolates were both less than or greater than the CQ, summation still occurred. Accuracy was primarily a function of the ratios of sums to be differentiated. This finding substantiated the earlier conclusion that summation was based on both quantities of each pair and not on some simpler process such as the avoidance of the tray with the smallest single amount or selection of the tray with the single largest amount. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chimpanzee (Pan troglodytes) spatial problem solving with the use of mirrors and televised equivalents of mirrors.

Tested 2 highly experienced chimpanzees on mirror- and TV-guided tasks to examine their spatial problem-solving ability. Results show that by reaching through a hole in the wall of their home cage and by tracking the images of their hands and of an otherwise hidden target object (TO) in a mirror or closed-circuit TV screen, Ss were able to move their hands in the direction necessary to make contact with the TO. Ss also discriminated between live video images and tapes and performed effectively when TOs were presented in novel locations and when the video picture was presented at random in different orientations. It is reported that comparable performances in monkeys and nonprimates are unlikely since previous attempts to train rhesus monkeys and Macacca arctoides to perform similar tasks have been unsuccessful. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Assessing symbol usage versus symbol competency.

Responds to comments by S. Sugarman (see record 1984-22390-001) and C. A. Ristau (see record 1984-22382-001) on the present authors' (see record 1984-22384-001) article on chimpanzee language acquisition. The assumption that chimpanzees use their acquired symboling capacity in a manner different from that of human children is addressed. It is concluded that these differences are not significant in that they reflect the need, with ape Ss, to report data that are not open to criticisms of cuing, rather than real differences in communicative purpose. It is argued that a distinction must be made between the totality of an ape's symbol production and the ape's capacity to respond correctly in particular test settings. This separation reveals the inappropriateness of criticizing the tests of ape capacities as though such tests were the only extant behavioral evidence of symboling capacity. (6 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Can a chimpanzee make a statement?

Investigated, in 2 experiments conducted over a 7-yr period using 2 male chimpanzees, whether the gestural-referential complex can be developed. In Exp I, a test was designed to determine whether Ss could produce accurate requests for things they could not see and whether, as they produced these requests, they had an idea of the specific absent objects that corresponded to their symbolically encoded requests. In Exp II, a test was devised to eliminate all potential means of cuing and order strategies that might result in the S's selecting a symbol and giving the appropriate object without anticipating and planning the complete sequence in advance. Results demonstrate that the gestural-referential complex can be developed, with training, in the chimpanzee and that, consequently, naming with reference does appear. A review of the training that preceded the emergence of referential function in these chimpanzees suggests that symbolization is not a unitary skill but rather a combination of diverse productive and receptive skills. (57 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)