Comparison of quantitative reasoning in nonhuman animals has suffered, on the one hand, from the methodological failure to do properly controlled studies of number (for review, recent examples and exceptions see refs 1, 2; 3, 4; and 5, 6 respectively), and on the other, from the conceptual failure to consider forms of quantitative reasoning other than number. An approach to mathematical reasoning may profit from the study of proportion, a continuous quantity, in addition to number, a discrete quantity. In the experiments reported here, an adult chimpanzee and four juveniles were tested for their knowledge of ‘proportion’ and ‘number’ with conceptual match-to-sample tasks. The juveniles failed but the adult successfully matched exemplars of the proportions 1/4, 1/2, 3/4 and 1, and the numbers 1, 2, 3 and 4, when the sample and alternatives were highly dissimilar physically (such as in shape, colour) and in other quantitative (for example mass, area, length) dimensions. The results reveal the presence of simple ‘proportion’ and ‘number’ concepts in a nonhuman primate.

approximately linear rate to 5.5°C. Control and exposure data were obtained between 3.9° and 5.3°C. A blower (100 ft3/min) provided airflow from above. The airflow, measured below the empty chamber with a hot-wire anemometer (Datametrics Airflow Multimeter Model 800 VTP), was approximately 6 m per minute in the region of the lever and increased to approximately 18 m per minute at the opposite side of the chamber. 10. Microwaves were transmitted to the horn via a coaxial cable to a coaxial-waveguide adapter. The feeder horn with a 6.5 by 7.5 cm rectangular aperture directed the microwaves toward the chamber floor 44.5 cm below with the E field parallel to the axis established by the response lever and infrared lamp. The designated power density specifies that value at the lever. A Narda Model 8315 probe calibrated against an NBS XD-I probe was used to map the field. With the back wall removed, the field was measured at the level of the lever at nine locations in a 10 by 10 cm grid with loci 5 cm apart covering the central area of the chamber. The distribution of power densities varied within 11 percent of the mean value. The field was also mapped with a smaller probe fabricated by J. Ali (U.S. Environmental Protection Agency) which enabled measurements to be made at loci close to the chamber walls. There was close correspondence between the two sets of measurements. The energy absorption rate per unit mass was estimated according to the relationship P = 4.186 CAT/t, where C is the tissue specific heat in calories per gram per degree Celsius (in this analysis, C = 0.83), AT is the temperature increase in degrees Celsius, t is the duration of exposure in seconds, and P is watts per kilogram [C. C. Johnson, J. Microwave Power 10, 249 (1975)]. A YSI 423 probe inserted 6 cm into the colon measured the temperature of a pentobarbitalanesthetized rat encased in a Styrofoam block during a brief exposure to microwaves [Lu et al. (11)]. Delta-t, the rate of temperature change, included a correction for the rate of temperature change immediately preceding the exposure. The absorption rate was approximately 8.4 W/kg at a power density of 41 mW/cm2, resulting in a specific absorption rate of 0.20 W/kg per milliwatt per square centimeter. 11. S.-T. Lu, N. Lebda, S. Michaelson, S. Pettit, D. Rivera, Radio Sci. 12(S), 147 (1977). 12. These data are the results of the second exposure session. After studying three rats, we found that the results from the first session were similar to but more variable than those from the second. Since such an outcome might be attributable to the novelty of the microwaves, an effect often seen during initial exposure to drugs and other stimuli, we decided to focus on the data from the second sessions of those three rats plus three others. The following are the means (standard errors in parentheses) of the proportion of time the heat lamp remained on at each power density for all six rats. For the first exposure session: 0 mW/cm2, 0.364 (0.017); 5 mW/ cm2, 0.333 (0.040); 10 mW/cm2, 0.324 (0.032); and 20 mW/cm2, 0.273 (0.029). For the second exposure session: 0 mW/cm2, 0.326 (0.009); 5 mW/cm2 0.298 (0.015); 10 mW/cm2, 0.264 (0.020); and 20 mW/cm2, 0.199 (0.011). Thus the two functions are similar, but the variability from the second session is less, as would be expected, after previous experience. 13. Serial correlation within individual rats was examined by the Durbin-Watson test [J. Neter and M. Wasserman, Applied Linear Statistical Models (Irwin, Homewood, Ill., 1974)], which confirmed the absence of an effect from the previous 15-minute exposure and the suitability of the linear regression model. 14. Using randomization tests [A. R. Feinstein, Clinical Biostatistics (Mosby, St. Louis, 1977)] we compared results for the six rats at each power density with all control periods, with only the preceding control period, and with the adjacent exposure to a different and nonzero power density. Two-sided P values were less than P = .003 except for 5 mW/cm2 against all zero exposures and 5 mW/cm2 against adjacent 10 mW/cm2 (P = .02). These results provide additional confirmation of the sensitivity of the procedure as well as an independent check of the regression analysis. 15. That interpretation is consistent with the conclusion reached in numerous studies of behavioral thermoregulation, including those of Weiss and Laties (7) and Carlisle (8). 16. See N. W. King, D. R. Justesen, and R. L. Clarke [Science 172, 398 (1971)] for an example of a different sensitive procedure. We did not attempt to determine the limits of the sensitivity in the present study; instead, we wanted to deter-

Communication about the location of a hidden incentive was studied in chimpanzee-human dyads, in which each member of a pair served alternately as “sender” and “recipient” of information. When the human cooperated with the chimpanzee in finding the goal, from the very beginning the chimpanzees were able to produce and comprehend behavioral cues which conveyed accurate locational information. When the human and chimpanzee competed for the goal, the chimpanzees learned both to withhold information or mislead the recipient, and to discount or controvert the sender's own misleading cues. The chimpanzee's ability to convey and utilize both accurate and misleading information, by taking into account the nature of the sender or recipient, provides evidence of a capacity for intentional communication in this nonhuman primate species.

Sarah, an adult "language"-trained chimpanzee, made accurate same-different judgments on quantities of liquid and solid matter and conserved both types of quantity despite a transformation in an irrelevant property (shape). Control tests showed that she judged on the basis of inference rather than perceptual evaluation of the quantities. She failed to make accurate same-different judgments on the basis of number, and she was not tested for conservation of this type of quantity.

An adult chimpanzee was shown videotaped scenes of a human actor struggling with one of eight problems and was then shown two photographs, one of which depicted an action or an object (or both) that could constitute a solution to the problem. On seven of the eight problems, the animal consistently chose the correct photograph. This test problem-solving comprehension permits the animal's knowledge about problem-solving—its ability to infer the nature of problems and to recognize potential solutions to them—to be examined.

A series of paper-marking tests, modeled after tests widely applied to humans, was administered to Sarah, a "language"-trained chimpanzee (Pan troglodytes). The test format was simple, economical, and controlled for social cues. The ape successfully made same-similar-different judgments on pictures of familiar objects when up to four questions were presented at the same time. Performance remained satisfactory on same-different judgments of novel pictures of alphabetic characters. Throughout the series of tests, the subject showed a superiority on same judgments.

AbstractAn individual has a theory of mind if he imputes mental states to himself and others. A system of inferences of this kind is properly viewed as a theory because such states are not directly observable, and the system can be used to make predictions about the behavior of others. As to the mental states the chimpanzee may infer, consider those inferred by our own species, for example, purpose or intention, as well as knowledge, belief, thinking, doubt, guessing, pretending, liking, and so forth. To determine whether or not the chimpanzee infers states of this kind, we showed an adult chimpanzee a series of videotaped scenes of a human actor struggling with a variety of problems. Some problems were simple, involving inaccessible food – bananas vertically or horizontally out of reach, behind a box, and so forth – as in the original Kohler problems; others were more complex, involving an actor unable to extricate himself from a locked cage, shivering because of a malfunctioning heater, or unable to play a phonograph because it was unplugged. With each videotape the chimpanzee was given several photographs, one a solution to the problem, such as a stick for the inaccessible bananas, a key for the locked up actor, a lit wick for the malfunctioning heater. The chimpanzee's consistent choice of the correct photographs can be understood by assuming that the animal recognized the videotape as representing a problem, understood the actor's purpose, and chose alternatives compatible with that purpose.

Infant chimpanzees, after watching a small black-and-white closed-circuit television picture of a familiar caretaker walking out into an outdoor field and disappearing from sight, were more successful in finding the person than if they had been given no such cue; and their performance approximated that which obtained after they had seen the same scene normally, via direct perception.

The joint control of rate of key pecking in pigeons by stimulus-reinforcer and response-reinforcer relationships was studied in the context of a two-component multiple schedule of reinforcement. Food presentation was always associated with one component and extinction with the other. The stimulus-reinforcer relationship was manipulated by varying the relative durations of the two components. In the food-presentation component, a fixed rate of reinforcement, independent of rate of responding, was generated by a schedule referred to as "T*". One aspect of the response-reinforcer relationship, contiguity, was manipulated by varying the percentage of delayed reinforcers. With the multiple T* extinction schedule, stimulus-reinforcer and response-reinforcer relationships could be varied independently of one another. Rate of key pecking was sensitive to manipulations of both relationships. However, significant differential effects due to either the stimulus-reinforcer or response-reinforcer relationship were obtained only when the other relationship was weak: stimulus-reinforcer and response-reinforcer relationships interacted in the joint control of responding.

Fifteen pigeons were exposed to either response-independent or response-dependent schedules of water reinforcement, whereby water was injected directly into the unrestrained pigeons' mandibles. Key-contact responses were released by a lighted key correlated with water, but not by a lighted key uncorrelated with water. A negative response-reinforcer contingency suppressed autoshaped key-contact responses, resulting in responding directed away from the lighted key. In all pigeons, water injected directly into the mandibles elicited a consummatory fixed-action pattern of "mumbling" and swallowing. The lighted key correlated with water released a broader set of both appetitive and consummatory responses: approach to the lighted key, "bowing", "rooting", "mumbling", and swallowing. Key-contact responses were "rooting" and "mumbling" motions of the beak on the surface of the key. Views of autoshaping based on stimulus substitution or stimulus surrogation do not fully explain the origin of autoshaped responses not previously elicited by the reinforcer. The present findings are consonant with views of conditioning that emphasize the large degree of biological pre-organization in conditioned response patterns, and the importance of associative factors in the control of such patterns.