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Human Models of Animal BehaviorAuthor(s): Russell M. ChurchSource: Psychological Science, Vol. 4, No. 3 (May, 1993), pp. 170-173Published by: Sage Publications, Inc. on behalf of the Association for Psychological ScienceStable URL: http://www.jstor.org/stable/40062532 .

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HUMAN MODELS OF ANIMAL BEHAVIOR

Russell M. Church Brown University

PSYCHOLOGICAL SCIENCE

Symposium on Animal Cognition

Abstract - Similarities between the behavior of humans and other animals in analogous tasks suggest that similar cognitive processes are involved. Hu- man studies provide an efficient way to collect data with low variability, and animal studies provide a way to collect a large amount of data under controlled conditions , study a wide range of manipulations, limit the range of plausible explanations, and develop explanations in terms of brain mechanisms. Examples are taken from studies of timing that used similar procedures for humans and other animals.

How similar are the brains of a rat and a human being? If asked to comment on their differences, most of us would have no difficulty doing so. One is small and has a relatively smooth surface; the other is much larger and has a convo- luted surface. Most of us would be able to describe an enormous number of differences, and an expert would know many more. But if asked to comment on the similarities between the brains of a rat and a human being, we would have no difficulty doing that either. Obvi- ously, both have a neocortex and cere- bellum, and many other parts are to be found in both brains (hippocampus, thal- amus, basal ganglia, and so forth). At a more molecular level, we might comment on the similarity of the structure of the brains of rats and human beings - the types of cells, axons, dendrites, and syn- apses.

Just as it is possible to compare the brains of rats and human beings with emphasis on either their similarities or their differences, it is also possible to compare the behavior of rats and human beings with emphasis on either their similarities or their differences. In neither case is it more correct to be impressed by one or

the other. For some purposes, the similarities are important, and for others, the differences. This article describes some very specific, quantitative similarities between the behavior of humans and other animals in analogous timing tasks; these results suggest that similar cognitive processes are involved. This discus- sion leads to a proposed strategy for research: the development of human models of animal behavior.

EMPHASIS ON DIFFERENCES BETWEEN HUMAN BEINGS AND

OTHER ANIMALS

The validity of any human model of animal behavior depends on the exis- tence of some general principles of perception, learning, motivation, emotion, or attention that apply to both human and animal subjects.

The first line of defense against the development of general principles is to claim that individual differences overwhelm similarities. When possible, it is desirable to analyze individuals sepa- rately and test the extent to which the same functional relationships occur in different individuals. There may be individual differences in average level and in the magnitude of a functional relation- ship, but it is rarely claimed that individuals differ in the form of a functional re- lationship.

The second line of defense is to claim that species differences overwhelm similarities. Some researchers are particu- larly interested in behavior that distin- guishes one species from another, con- straints in behavior, or correlations between the ecology and behavior of closely related species. The success or failure of these endeavors is logically un- related to the success or failure of the attempt to describe general psychological principles that apply to many species. Nonetheless, such researchers may ar- gue against well-established similarities by citing well-established differences.

The third line of defense is to claim that there are qualitative differences be-

tween human beings and other animals that preclude any meaningful compari- sons. Some psychologists agree with Descartes that lower animals are simple machines but people are machines with souls, although they would now use one of the modern synonyms for soul. Per- haps books with titles like Human Mem- ory, Human Information Processing, Human Problem Solving, and Human Motor Control contain the word human simply to reflect the limited content of the books. But probably the word is also used as a badge of honor. Much of modern cognitive psychology is designed to apply to human subjects, and perhaps in- telligent machines, but not to lower animals. There is no special virtue in finding principles that apply only to a single species, even our own. Human psychology is enriched, not diminished, by its similarity to animal psychology.

Some scholars believe there is a qualitative difference in time perception between human beings and other animals. People have a concept of the past and the future as well as the present, but other animals live only in the present. Whitrow (1988) wrote, "All animals except man live in a continual present" (p. 71). Ac- cording to this view, animals are affected by past events but do not really remem- ber them, and animals are influenced by temporal regularities but do not really anticipate them. The behavior of an animal is determined by present conditions (including those left by previous events and regularities), and not by memories and anticipations. This analysis appears to be logically sound, but it is not partic- ularly helpful. The proposal is that the present behavior only of human beings, in contrast to other animals, is determined by memory of the past and antic- ipation of the future. This idea is supported by introspection and analogy, and a belief that language provides a window to the true causes of behavior, not dis- tracting rationalizations. There appears to be nothing that an animal could do to convince a skeptic that it has concep- tions of the past or the future except to talk about them. For people who are im-

Address correspondence to Russell M. Church, Department of Psychology, Box 1853, Providence, RI 02912; e-mail: Russell_Church@brown . edu .

170 Copyright © 1993 American Psychological Society VOL. 4, NO. 3, MAY 1993




Russell M. Church

pressed only by the differences between animal and human time perception, there is no value in comparative research. But other investigators of animal and human timing have found it useful to attempt to identify common problems and solutions (Gibbon & Allan, 1984).

The final line of defense is to recog- nize that, in some tasks, human and animal subjects may perform in a similar manner, but to claim that the similarities are uninteresting, are superficial, and reveal nothing about the uniquely human condition. If we know something about people, why would anyone care to know whether the same is true of other animals? Investigators who want to under- stand only people should study human subjects; investigators who want to un- derstand only animals should study animal subjects.

EMPHASIS ON SIMILARITIES BETWEEN HUMAN BEINGS AND

OTHER ANIMALS

An interest in evolution should not predispose an investigator to emphasize either differences or similarities. Dar- win's legacy includes evidence for im- pressive continuity of both body and mind among animal species, and experimental psychologists have attempted to identify principles of generality. Investi- gators of animal cognition have empha- sized similarities between human beings and other animals, although perhaps not enough different species (Cook, this issue). In contrast with the anthropocen- tric program described by Shettleworth (this issue), many of them have adopted a zoocentric approach in which the only behavior or process they would study in humans is one that is widely shared among other animals.

TIMING BY HUMAN BEINGS AND OTHER ANIMALS

Timing by human subjects and other animals is often quite similar when similar timing requirements are imposed. Two examples are given.

Stimulus Timing

A stimulus timing task may involve the categorization of stimuli into two cat-

egories based on the duration. Stubbs (1968) trained pigeons to make one response following stimuli shorter than some criterion duration and a different response following stimuli longer than that criterion. The two responses may be called "short" and "long." The mean probability of a long response increased as a function of the duration of the stimulus. Deluty and I, using rats, modified the procedure slightly by reinforcing a response on one lever following a short stimulus duration, reinforcing a response on another lever following a long stimulus duration, and not reinforcing any response following stimuli of intermediate durations (Church & Deluty, 1977). Al- though there was no differential reinforcement for responses following the stimuli of intermediate duration, the probability of a long response by each rat increased as a function of the duration of the stimulus. Figure 1 shows the mean probability of a long response for 8 rats trained under four stimulus ranges (1-4 s, 2-8 s, 3-12 s, and 4-16 s). The horizontal axis is shown as the ratio of the presented stimulus duration (f) to the point of subjective equality (Tl/2). The point of subjective equality is the stimulus duration that is equally likely to be classified as short or long, and it was

found to be approximately at the geometric mean of the extreme values (i.e., at approximately 2, 4, 6, and 8 s for the four stimulus ranges). The mean functions at the four ranges were approximately the same when expressed as relative time. This is called the superposition result, and it is an essential feature of scalar timing theory (Gibbon, 1991).

Allan and Gibbon (1991) used a similar procedure with human subjects. The major procedural difference was that in- structions were used, rather than differential reinforcement, to induce the subjects to make one response following a perceptually short stimulus and a different response following a perceptually long stimulus. The results from 1 subject are shown in Figure 2. The horizontal axis is scaled in relative time: the duration of the presented stimulus (r) to the point of subjective equality (Ty2). As in the case of the animals, the mean probability of a long response increased as a function of the duration of the stimulus, and the point of subjective equality was approximately at the geometric mean of the extreme values. The mean functions at different ranges (1.0-2.0 s, 1.0-1.5 s, 1.4-2.1 s, and 0.75-1.0 s) were approximately the same. This is another exam- ple of the superposition result.

Fig. 1. Mean probability of a * 'long'

' response as a function of relative time for groups

of rats trained with various ranges of stimulus duration (1-4 s, 2-8 s, 3-12 s, and 4-16 s). Relative time is the ratio of stimulus duration to the point of subjective equality. Data are from Church and Deluty (1977).

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Human Models of Animal Behavior

Fig. 2. Probability of a "long" response as a function of relative time for 1 human subject trained with various ranges of stimulus duration (1.0-2.0 s, 1.0-1. 5s, 1.4-2.1 s, and 0.75-1.0 s). Relative time is the ratio of stimulus duration to the point of subjective equality. Data are from Allan and Gibbon (1991).

There appears to be more than a superficial similarity between the animal and human bisection results. The forms of the functions were similar- ogives that were approximately symmetrical on a logarithmic axis. In both cases, the point of subjective equality was approximately at the geometric mean, a general rule if the ratio of the short to long interval does not exceed about 4:1 (Siegel, 1986; Wearden, 1991). And in both cases, there was superposition of the functions when time was scaled in relative units. This is an important extension of the animal results because it shows that the superposition result can apply even when the ratio of the short to the long time is not constant.

The quantitative aspects of both the human and the animal data on stimulus timing tasks are well accounted for by the same scalar timing theory (Gibbon, 1991). This theory is usually expressed in terms of an information processing model with a clock, memory, and com- parison process. The clock is represented as a pacemaker that sends pulses to an accumulator, and the sum of the pulses in the accumulator is the representation of the stimulus duration. The information processing model becomes a quantitative theory when specific as- sumptions are made about distribution forms and values of several parameters (such as clock speed, a memory constant, and a decision threshold). Because the results of time estimation experiments with humans and other animals are similar, and because the same theory

provides an explanation of the data, it is plausible to conjecture that humans and other animals use similar cognitive processes for time estimation.

The main difference between the human and animal results is that the human subjects were more sensitive to small differences in time. The functions relating the probability of a long response to stimulus duration for individual subjects were smooth and steep. The mean We- ber fraction for the human subjects (Al- lan & Gibbon, 1991) was about .06, and the mean Weber fraction for the rats (Church & Deluty, 1977) was about .23. With some procedural modifications, the Weber fractions for rats can be reduced (Meek, 1985). Some improvement oc- curred when the difference between the extreme stimuli was reduced from a ratio of 4:1 (as in Church & Deluty, 1977) to a ratio of 3:2 (more comparable to Allan & Gibbon, 1991). Further improvement oc- curred when a postreinforcement signal was added following a correct response. Under the best conditions, the smallest Weber fraction obtained from rats was about .10.

Repetitive Responding

In a standard case of repetitive responding, thirsty rats given access to a tube attached to a water bottle are found to lick the tube at a fairly constant rate of about seven responses per second (Cor- bit & Luschei, 1969). By analogy, a person may be asked to tap in synchrony to

a metronome that is regularly occurring at some interval (such as 500 ms). Fig- ures 3 and 4 show the probability of a licking response as a function of time for a rat and the probability of a tapping response as a function of time for a human subject, respectively (Church, Broad- bent, & Gibbon, 1992).

Wing and Kristofferson (1973) described a two-process theory of repetitive responding in which there are two independent sources of variability: timer and motor. The particular function form is well fit by the assumption that the in- terpulse interval of the timer is distrib- uted as the difference of two independent random waiting times, and the motor variability is an independent random waiting time. In both the cases of a rat licking and a person tapping, the distribution of interresponse times is reliably better characterized by this process than by one containing more or fewer random waiting times. As in the case of time estimation, the correspondence of the de- tailed results of the repetitive responding of human and rat subjects suggests that there are more than superficial similarities between the cognitive processes used by humans and other animals en- gaged in this task. Perhaps similar mechanisms may be generating the results.

COMPARATIVE ADVANTAGES OF HUMANS AND OTHER

ANIMALS AS EXPERIMENTAL SUBJECTS

In many cases, roughly equivalent results can be obtained from human subjects and other animals. Thus, it is possible to develop human models of animal

Fig. 3. Probability per millisecond of a lick response of 1 rat as a function of time since the last lick response. Data are from Church, Broadbent, and Gib- bon (1992).

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Russell M. Church

Fig. 4. Probability per 5 ms of a tap response of 1 human subject as a function of time since the last tap response. Data are from Church, Broadbent, and Gib- bon (1992).

behavior, but why would one want to do so?

Advantages of Human Subjects Studies with human subjects are often

more efficient than studies with animal subjects. They require fewer sessions and fewer subjects to obtain a particular level of performance, partly because in- structions to human subjects can bypass laborious training by differential reinforcement of animal subjects. In some cases, the amount of data collected per hour can be increased because trials can be massed without interfering with performance. Variability of performance is often lower for human subjects than for lower animals in corresponding tasks, so that the number of observations required for a particular estimate of a mean may be greatly reduced. Asymptotic performance of human subjects may be better than that of animal subjects. Finally, human subjects may be more sensitive than other animal subjects to small changes in time, so that the precision of research conclusions can be improved. Human subjects can be used for efficient para- metric studies and for the development of cognitive models. These are all practical advantages; the main theoretical ad- vantage of developing a human model of animal behavior is to extend the range of generality of the results.

Advantages of Animal Subjects The main practical advantages of us-

ing experimental animals are to increase

the experimental control and to do experiments that otherwise would not be possible. Animals are not easily bored, the range of possible manipulations is greater, and it is possible to develop explanations in terms of brain mechanisms. The main theoretical purpose of doing research with animals is to restrict the range of plausible explanations, espe- cially to exclude those involving language.

Exploration of New Results

The primary test of the value of a human model of animal behavior is whether the model leads to some new under- standing of animal behavior. In the case of human time production, there is evidence that the representation of time is not continuously variable. A person in- structed to tap in synchrony with a tone, and then to continue tapping at the same rate when there are no more tones, can do so quite accurately. In one experi- ment (Collyer, Broadbent, & Church, 1992), the mean interresponse interval (IRI) was approximately equal to the in- terstimulus interval (ISI) in the range of 175 to 825 ms. But an inspection of the small, highly systematic residuals was instructive. At some ISIs (typically about 250 and 500 ms), the IRIs were accurate, but below these privileged points they were too long, and above them they were too short. These results suggest some sort of multiple oscillator mechanism may underlie time production of human subjects. Multiple oscilla- tors are sufficient to code durations (Gal- listel, 1990), and a connectionist model with time represented by multiple oscil- lators can account for many results of timing experiments (Church & Broad- bent, 1990).

The results of the human studies that appear to require some sort of multiple oscillator mechanism suggest that a similar mechanism may be required to account for time production of other animals. The studies of human timing that reveal oscillatory processes serve to mo- tivate analogous animal studies. The animal studies are more time-consuming and difficult to conduct, but they do con-

tribute to knowledge. The proposal is to use efficient and precise studies with human subjects to develop a human model of animal behavior, and then to return to animal research for restricting the range of explanations, increasing experimental control, increasing the range of possible manipulations, and analyzing behavior in terms of brain mechanisms.

Acknowledgments- Preparation of this article was supported by a grant from the Na- tional Science Foundation (BNS91 10158).

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Church, R.M., & Broadbent, H.A. (1990). Alterna- tive representations of time, number, and rate. Cognition, 37, 55-81.

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Church, R.M., & Deluty, H.Z. (1977). The bisection of temporal intervals. Journal of Experimental Psychology: Animal Behavior Processes, 3, 216-228.

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