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Pergamon 0005-7916(95)00036-4 d. Behav. lher. & Exp. Psychiat. Vol. 26, No. 3, pp. 209-214, 1995. Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0005 7916/95 $9.50 + 0.00 ON THE BATTLE BETWEEN BEHAVIOR AND COGNITION: LESSONS FROM PHYSICISTS AND PRAGMATISTS PATRICK W. CORRIGAN University of Chicago Summary -- Despite several decades of empirical research that has supported the utility of cognitive research and therapy, behaviorists continue to battle with cognitivists on epistemological grounds. Therefore, I seek to resolve this battle by reviewing epistemological lessons learned from two other disciplines, Physics and Pragmatism, Paradigm shifts in Physics taught us that formal models of phenomena and causality have just as valuable a role in a science of human behavior as models based on efficient cause and direct observation. Cognitive models have proven their worth as formal models of psychology. Pragmatism has taught us that accountability - - to the researcher and theorist, to the clinical professional, and to the consumer of care - - needs to be a renewed value in evaluating psychological models. Carefully controlled empirical research has shown cognitive models to have ably met these goals. Therefore, cognition meets epistemological criteria, other than those touted by behaviorists, which commend it as an important model for human psychology. The battle between cognitive and behavioral models has been maintained, in large part, by certain epistemological assumptions of a behavioral psychology. Other sciences and epistemologies, through the course of their history, have struggled with changing the philosophical paradigms on which they rest. Lessons from two such disciplines, Physics and Pragmatism, are reviewed. They are unlikely bedfellows; Physics has served as the paragon of hard science while Pragmatism is a short lived philosophy which has significantly influenced clinical psychology. Their lessons, however, have broadened our understanding of the principles that form the methodological base from which behavioral and cognitive models are examined. This broadening is meant to resolve the battle between the two models. A synopsis of the battle. An early and obvious blow in the battle between cognition and behavior was dealt by Skinner (1953) in his renunciation of the "black box", instead promoting the essential importance of directly observed behavior. Prior to his time, prominent psychologists bad been using relatively private strategies for studying psychological phenomena; e.g., the introspective methods of Wundt (1902), the concern with Freud's unconscious (Freud, 1965), or the idealistic psychology of Gestaltists (Kohler, 1947). Products of these schools often read like philosophical works and suffered the critiques that nonempirical pursuits endure. The battle was rejoined in earnest after Bandura's (1971) formulation of social learning theory. Fearing that Bandura may be reintroducing the black box into a now rigorous science of human behavior, several behaviorists countered with sophisticated (and perhaps overly intricate) explanations of vicarious learning based on directly observed behavior (Baer & Sherman, 1964; Gewirtz & Stingle, 1968). Clearly, the criterion of observed behavior has served Psychology well by exceeding some of the vagaries promoted by early investigators. The Requests for reprints should be addressed to Patrick W. Corrigan, University of Chicago Center for Psychiatric Rehabilitation, 7230 Arbor Drive, Tinley Park, IL 60477, U.S.A. 209

On the battle between behavior and cognition: Lessons from physicists and pragmatists

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Pergamon

0005-7916(95)00036-4

d. Behav. lher. & Exp. Psychiat. Vol. 26, No. 3, pp. 209-214, 1995. Copyright © 1995 Elsevier Science Ltd

Printed in Great Britain. All rights reserved 0005 7916/95 $9.50 + 0.00

ON THE BATTLE BETWEEN BEHAVIOR AND COGNITION: LESSONS FROM PHYSICISTS AND PRAGMATISTS

PATRICK W. CORRIGAN

University of Chicago

Summary - - Despite several decades of empirical research that has supported the utility of cognitive research and therapy, behaviorists continue to battle with cognitivists on epistemological grounds. Therefore, I seek to resolve this battle by reviewing epistemological lessons learned from two other disciplines, Physics and Pragmatism, Paradigm shifts in Physics taught us that formal models of phenomena and causality have just as valuable a role in a science of human behavior as models based on efficient cause and direct observation. Cognitive models have proven their worth as formal models of psychology. Pragmatism has taught us that accountability - - to the researcher and theorist, to the clinical professional, and to the consumer of care - - needs to be a renewed value in evaluating psychological models. Carefully controlled empirical research has shown cognitive models to have ably met these goals. Therefore, cognition meets epistemological criteria, other than those touted by behaviorists, which commend it as an important model for human psychology.

The ba t t l e b e t w e e n c o g n i t i v e and b e h a v i o r a l mode l s has been ma in ta ined , in large part , by c e r t a i n e p i s t e m o l o g i c a l a s s u m p t i o n s o f a b e h a v i o r a l p s y c h o l o g y . O t h e r s c i e n c e s and epistemologies, through the course of their history, have s t ruggled with changing the ph i losophica l paradigms on which they rest. Lessons from two such d i sc ip l ines , Phys i c s and P ragma t i sm , are reviewed. They are unl ikely bedfel lows; Physics has served as the paragon of hard science while Pragmatism is a short l ived philosophy which has significantly influenced clinical psychology. Their l e s s o n s , h o w e v e r , h a v e b r o a d e n e d ou r u n d e r s t a n d i n g o f the p r i n c i p l e s that fo rm the methodologica l base from which behavioral and cognit ive models are examined. This broadening is meant to reso lve the ba t t le be tween the two models.

A synopsis of the battle. An early and obvious blow in the battle between cognition and behavior was dealt by Skinner (1953) in his renunciation of the "black box", instead promoting the essential

importance of directly observed behavior. Prior to his time, prominent psychologists bad been using r e l a t i v e l y p r i v a t e s t r a t e g i e s fo r s t u d y i n g psychological phenomena; e.g., the introspective m e t h o d s o f W u n d t (1902) , the c o n c e r n wi th F r e u d ' s u n c o n s c i o u s ( F r e u d , 1965) , or the i d e a l i s t i c p s y c h o l o g y o f G e s t a l t i s t s ( K o h l e r , 1947). Products of these schools often read like philosophical works and suffered the critiques that nonempirical pursuits endure.

T h e b a t t l e was r e j o i n e d in e a r n e s t a f t e r Bandura ' s (1971) formulat ion of social learning theory. Fearing that Bandura may be reintroducing the b l a c k box into a now r i g o r o u s s c i ence o f human behavior , several behavior is ts countered with sophist icated (and perhaps overly intricate) e x p l a n a t i o n s o f v i c a r i o u s l e a r n i n g b a s e d on d i r ec t ly o b s e r v e d b e h a v i o r (Baer & She rman , 1964; Gewirtz & Stingle, 1968).

Clearly, the criterion of observed behavior has served Psychology well by exceeding some of the vaga r i e s p r o m o t e d by ear ly inves t iga to r s . The

Requests for reprints should be addressed to Patrick W. Corrigan, University of Chicago Center for Psychiatric Rehabilitation, 7230 Arbor Drive, Tinley Park, IL 60477, U.S.A.

209

210 PATRICK W. CORRIGAN

question, however, is whether the battle between behavioral and cognitive models is unnecessarily maintained by asserting that direct observation is the primary principle of a science of psychology. Perhaps there are additional principles by which a scientific approach to human behavior is judged, principles that permit a rapprochement between two models.

Lessons from Physicists

Physics exper ienced a s ignif icant shift in parad igms with the emergence of quantum mechanics and modern physics. In some ways, this shift corresponds with a change in focus on Aristotelian causality (Kuhn, 1971). The concept of efficient cause seemed to be adequate for classical physicists. Efficient causes accounted for the forces that impinge on relatively large and slow moving objects. Movement and force were attributed to the directly observable impact of one physical object on another. Subsequent questions about specific attributions were then resolved by directly examining the interactions of other bodies. Even the relatively newer physics - - electricity, magnet i sm, and the rmodynamics - - were understood in terms of Newtonian contact forces and, therefore, explainable via efficient causes.

The extent of efficient cause was challenged by works of Einstein, Schroedinger, Heisenberg, and Bohr at the turn of the century (Tipler, 1969). These physicists focused on relatively small and fast particles to address the physical problems of their era. Unfortunately, the models and principles of Isaac Newton were insufficient to the task; describing the direct interaction of observable bodies was not possible. Rather, comprehensive description required mathematical postulates and proofs; causality now depended on the form of the argument, not an efficient and physical interaction (Kuhn, 1971). Subsequent questions about an argument made by modern physicists were not resolved by examining the interactions of physical bodies on which fo rmulae rest. Rather , the soundness of the mathematics that forms modern theory served as the basis of epistemological validity.

Modern physicis ts also "crea ted" various constructs to account for the physical phenomena that corresponded with the mathematical proofs. For example, energy properties of light were explained by photons while interference patterns were described by waves. Interestingly, conflicting aspects of particle and wave properties added a certain indeterminacy or uncertainty to modern theories of light and particles (Heisenberg, 1966). For example, the Fourier Transform that describes light waves prevents the exact mapping of any single photon at time x. Uncertainty required use of probabilistic models, a foreign experience to most physicists of the times.

Behavioral and cognitive models seem to have traversed a similar path. Many of the questions of interest to behavioral theories were first addressed by direct observation and assumptions of efficient cause. The Law of Ef fec t suggests that performance of a behavior in a specific setting depends on the observable (and immediate) consequences to that behavior (Thorndike, 1913). Unfortunately, direct observation does not explain other important factors that affect the relationship between behavior and environment. For example, behavioral consequences-over-time also affect the pe r fo rmance of behaviors . The amalgam of reinforcers and punishers provided in various situations helps shape relatively intricate behaviors which are used in some settings and not in others. This amalgam suggests the construct of learning history, a construct which would seem to defy direct observation. The black box needs to be opened and examined to define factors that affect learning history.

Clearly, cognitive models that describe the black box are formal, comprised of structures, opera t ions , and products that explain how information is acquired and manipulated to form new constructs (Ingram & Kendall, 1986). Like the photons and waves of opt ical theory, information processing constructs are not directly observable. However, they are necessary to fully descr ibe phenomena of human psycho logy . Formal models in psychology are often filled out by using regression and factor analytic statistics, and then looking for the pattern of associations in

Behavior and Cognition 211

constructs (Corrigan, 1991). Behaviorists tend to critique correlational models like these; they are not causal because associations between cognitive and behavioral variables do not suggest that cogni t ion led to behav ior (Hawkins, 1992). Hawkins is guilty, however, of using Aristotelian efficiency as the standard of cause. Formal models of causality need not be hindered by concerns about the directionality of a relationship.

Others have struggled with defining formal models of psychology that demonstrate some rigor. Meehl and Cronbach (1955) argued that valid and meaningful psychological constructs show a convergent and divergent network of relationships with other psychological variables. Self-efficacy (Bandura, 1982, 1984), for example, converges with such disparate constructs as managing social comparison (Litt, 1988), handling phobic stimuli (Bandura, Reese & Adams, 1982), and changing smoking behav io r (Devins & Edwards, 1988). Note, however, that self-efficacy diverges from similar constructs like locus of control (Bandura, 1995), thereby suggesting that se l f - e f f i cacy is not mere ly an a l ternat ive representat ion of an already well established construct. These nomological networks are useful for descr ib ing why past behaviors occur , explaining why current activity is performed, or predicting which of future responses will happen. Se l f - e f f i cacy studies have showed that the construct explains current academic ability as well as predicts future performance (Brown, Lent & Larkin, 1989; Multon, Brown & Lent, 1991). Nomological networks support formal models that provide a broad range of exp lana t ion and prediction. Moreover, these networks serve as a heuristic for future research, outlining testable relationships between components of the model. Hypo theses genera ted by these models are consistent with good science because they are falsifiable (Popper, 1959).

It is hard to imagine any psychological model that escapes some formalistic influence. Even the objects of direct behavioral observation tend to be nested in some theory about the form of that behavior. For example, observing an actor raise his fist above his head might alternatively be

associated with pride (perhaps after a sporting accomplishment) or anger (perhaps as a result of a racial injustice). The meaning of these respective interpretations is based not only on the context of the behavior (sporting event or site of racial injustice) but also on the observer 's model of behaving in these contexts . Meaning and interpretation of events is a conundrum that has been tackled by various philosophies. Pragmatism, an early 20th century philosophy, was based on principles that seemed especially relevant to psychology in general and clinical approaches in particular.

Lessons from Pragmatists

The pragmatism of Charles Pierce (Gallie, 1952) was fundamenta l ly a ph i losophy of meaning, attempting to ground the intention of specific constructs in terms of their practical bearings; i.e., some empir ical ly conceivable consequences that matter to humanity. William James (1909) expanded on Pragmat i sm by focusing on the centrality of "practical bearings", meaning was found in experienced facts and plan of actions. "The whole function of philosophy ought to be to find out what definite difference it will make to you and me, at definite instants of our life, if this world formula or that world formula be the true one" (James, 1909, p. 123). His epistemology is closely intertwined with the practical value (or payoff) of an idea. Despite its intuitive appeal, several contemporaries of Pierce and James challenged its assertions. Bertrand Russell (1910) argued that basing the value of a specific belief on its practical consequences was flawed. Although abstract concepts, such as gravity in physics, seem to have conceptual value, how is this value measured? The relative merit of two concepts cannot be addressed without some index of payoff, indices which frequently are undeterminable.

Despite its various philosophical shortfalls, Pragmatism is not anti-thetical to an empirical epistemology or behavioral psychology. In fact, much of what pragmatism offers is recommended by behavioral researchers . Skinner ' s call to

212 PATRICK W.

science was, in part, out of practical motivation, "But a science may also deal with the behavior of the individual, and its success in doing so must be evaluated in terms of its achievement rather than any prior contentions" (Skinner, 1953, p. 19). Pragmatism suggests several criteria for evaluating empirically-sound psychological models.

Most empirical investigations, especially of clinically meaningful phenomena, are now expected to show some level of accountability (Barlow, Hayes & Nelson, 1984). In others words, the value of research endeavors not only depends on its internal validity, but also its ability to address important life problems, an obvious goal of the pragmatist. Findings from a particular study should advance the conceptual underpinnings of an important behavior o r support the efficacy of a specific intervention vis-h-vis these behaviors. Moreover, the effects produced by experimental manipulations, or investigated interventions, need to be sizeable. Studies that yield significant findings at .05 may be meeting the requirements of inductive logic but may not represent any real change in behavior (Barlow, Hayes & Nelson, 1984; Bergin & Garfield, 1972; Cohen, 1979). Large effect sizes need to be evident in visual inspection of data from single subject designs (Barlow & Hersen, 1984) or in statistical tests that represent the change in group means from baseline (Cohen, 1977).

Cognitive models need to target important life problems with potent interventions to be accountable pragmatically. Research has shown that cognitive models of psychopathology have been helpful for describing the phenomenology of various severe mental illnesses. Information processing models have been especially fruitful for describing the course of schizophrenia (Nuechterlein & Dawson, 1984) and for understanding the specific impact of neurological disorders (Lezak, 1983). Cognitive schema have been useful for understanding recurring depression or anxiety in the absence of grief or stressors (Hartlage, Alloy, Vazquez & Dykman, 1993). Cognitive models have yielded some potent interventions for remediating life problems. Depression in particular, seems to respond well to

CORRIGAN

cognitive therapies, especially compared to behavioral interventions (Eifert & Craill, 1989; Dobson, 1989). More recently, cognitive rehabilitation, which targets various information processing deficits, seems to improve some of the difficulties of schizophrenia (Spaulding, 1994) and neuropsychological difficulties (Gouvier, Webster & Blanton, 1986).

Behavioral and cognitive models must not only be valuable for improving significant life problems, they need to be practical or user- friendly for both the clinical professionals and consumers who adopt them. This criterion is especially important in light of research which suggests that many empirically validated, behavioral innovations are not adopted by real- world clinicians (Bellack, 1986; Corrigan, 1991; Glynn, 1990). Clinical investigators have identified several barriers that impede the development and implementation of these interventions (Backer, Liberman & Kuehnel, 1986; Corrigan, Kwartarini & Pramana, 1992; Emerson & Emerson, 1987). In particular, interventions are frequently packaged in very complex formats which are not easy to replicate by practitioners (Barlow, 1981; Garfield & Kurtz, 1976). Alternatively interventions are written in language that is not readily understandable by consumers of services or that does not seem relevant to their problems.

Perhaps the most uniquely appealing aspect of cognitive models is their accessibility to consumers. For example, individuals who suffer depression quickly understand that defeating self- statements can exacerbate their dysphoria. It is relatively easy for them then to learn that making realistic, and somewhat optimistic, self-statements can serve as a buffer to depression. Moreover, cognitive models do not seem to be overly complex, so that professionals and paraprofessionals can learn them relatively easily and translate cognitive tenets into useful interventions. In fact, several manuals and texts have been written so that clinician or consumer might pick them up and run through a quick course in cognitive therapy to address an anxious or depressive episode (Bums, 1980; Ellis, 1988).

Behavior and Cognition 213

Summary

Like most paradigm shifts, expanding the tenets of classical mechanics and efficient cause to include formal cause and modern physics was difficult (Kuhn, 1970). Many of the physicists schooled in more traditional models found the new conceptualizations foreign and tended to dismiss them as irrelevant or epiphenomena. History suggests, however, that modern physics has catapulted our understanding of the world and yielded significant impact on practical products. This impact by no mean cancels classical ways of knowing physical phenomena, but augments them.

In a similar vein, psychology benefits from augmenting classical behavioral paradigms with the more formal models of cognition. The fruits of cognitive models seem to have significant pragmatic value. They are excellent heuristics for understanding deficits that result from various psychiatric problems. Cognitive models have also generated clearly useful intervention strategies.

The question should, therefore, move away from "what 's better, behavioral or cognitive models, efficient or formal models of causality?" A rapprochement between the two paradigms is here and needs to be acknowledged by those who persist in the battle. True, this rapprochement introduces methodological problems that are absent in the relatively simpler behavioral paradigm. But we cannot ignore the utility of cognitive models merely to satisfy the demands of those who insist on such a narrow epistemology built on direct observation and efficient cause. It is up to researchers and investigators to address the challenge of a combined behavioral and cognitive paradigm to meet the questions of human psychology as we approach the next century.

Acknowledgements - - Helpful reviews of earlier versions of this manuscript were provided by Heimir Geirsson & Stanley McCracken.

References

Backer, T., Liberman, R., & Kuehnel, T. (1986). Dissemination and adoption of innovative psychosocial interventions.

Journal of Consulting and Clinical Psychology, 54, 111-118.

Bandura, A. (1971). Social learning theory. Morristown, NJ: General Learning Press.

Bandura, A. (1982). The assessment and predictive generality of self-percepts of efficacy. Journal of Behavior Therapy and Experimental Psychiatry, 13, 195-199.

Bandura, A. (1984). Recycling misconceptions of perceived self-efficacy. Cognitive Therapy and Research, 8, 231- 255.

Bandura, A. (1995). Comments on the crusade against the causal efficacy of human thought. Journal of Behavior Therapy and Experimental Psychiatry, 26, 179-190.

Bandura, A., Reese, L., & Adams, N. E. (1982). Microanalysis of action and fear arousal as a function of differential levels of perceived self-efficacy. Journal of Personality and Social Psychology, 43, 5-21.

Barlow, D. H. (1981). On the relation of clinical research to clinical practice: current issues, new directions. Journal of Consulting and Clinical Psychology, 49, 147-155.

Barlow, D. H., Hayes, S. C., & Nelson, R. O. (1984). The scientist practitioner: research and accountability in clinical and educational settings. New York: Pergamon Press Inc.

Barlow, D. H., & Hersen, M. (1984). Single case experimental designs: strategies for studying behavior change (2nd edition). New York: Pergamon Press.

Baer, D. M., & Sherman, J. A. (1964). Reinforcement control of generalized imitation in young children. Journal of Experimental Child Psychology, 1, 37~J,9.

Bellack, A. S. (1986). Schizophrenia: behavior therapy's forgotten child. Behavior Therapy, 17, 199-214.

Bergin, A. E., Garfield, S. L., & Thompson, A. S. (1967). The Chicago Conference on clinical training and clinical psychology at Teachers College. American Psychologist, 22, 307-316.

Bergin, A. E., & Strupp, H. (1972). Changing frontiers in the science of psychotherapy. Chicago: Aldine.

Brown, S. D., Lent, R. W., & Larkin, K. C. (1989). Self- efficacy as a moderator of scholastic aptitude-academic performance relationships. Journal of Vocational Behavior, 35, 64-75.

Bums, D. (1980). Feeling good: the new mood therapy. New York: Signet.

Cohen, L. H. (1979). The research readership and information source reliance of clinical psychologists. Professional Psychology, 10, 780-786.

Cohen, J. (1977). Statistical power analysis for the behavioral sciences (rev. ed.). Orlando, FL: Academic Press, Inc.

Corrigan, P. W. (1991). Strategies that overcome barriers to token economies in community programs for severely mentally ill adults. Communi~ Mental Health Journal, 27, 17-30.

Corrigan, P. W., Kwartarini, W. Y., & Pramana, W. (1992). Barriers to the implementat ion of behavior therapy. Behavior Modification, 16, 132-144.

Devins, G. M., & Edwards, P. J. (1988). Self-efficacy and smoking reduction in chronic obstructive pulmonary disease. Behavior Research and Therapy, 26, 127-135.

Dobson, K. S. (1989). A meta-analysis of the efficacy of cognitive therapy for depression. Journal of Consulting and Clinical Psychology, 57, 414-419.

Eifert, G. H. & Craill, L. (1989). The relationship between

214 PATRICK W. CORRIGAN

affect, behaviour, and cognition in behavioral and cognitive treatments of depression and phobic anxiety. Behaviour Change, 6, 96-103.

Ellis, A. (1988). How to stubbornly refuse to make yourself miserable about anything, yes, anything/New York: Carol Publishing.

Emerson, E., & Emerson, C. (1987). Barriers to the effective implementation of habilitative behavioral programs in an institutional setting. Mental Retardation, 25, 101-106.

Freud, S. (1965). Interpretation of dreams. New York: Avon Books.

Gallie, W. B. (1952). Pierce and pragmatism. New York. Garfield, S. L,, & Kurtz, R. (1976). Clinical psychologists in

the 1970s. American Psychologist, 31, 1-9. Gewirtz, J. L., & Stingle, K. G. (1968). Learning of generalized

imitation as the basis for identification. Psychological Review, 75, 374-397.

Glynn, S. (1990). The token economy: progress and pitfalls over 25 years. Behavior Modification, 14, 383-407.

Gouvier, D. G., Webster, J. S., & Blanton, P. D. (1986). Cognitive retraining with brain-damaged patients. In D. Wedding, A. M. Horton, Jr. & J. Webster (Eds.), The neuropsychology handbook: behavioral and clinical perspectives (pp. 278-324). New York: Springer.

Hawkins, R. M. F. (1992). Self-efficacy: a predictor but not a cause of behavior. Journal of Behavior Therapy and Experimental Psychiatry, 23, 251-256.

Hartlage, S., Alloy, L. B., Vazquez, C., & Dykman, B. M. (1993). Automatic and effortful processing in depression. Psychological Bulletin, 11,247-278.

Heisenberg, W. (1966). Philosophic problems of nuclear science. Greenwich: Fawcett.

Ingram, R. E., & Kendall, P. C. (1986). Cognitive clinical psychology: implications of an information processing perspective. In R. E. Ingram (Ed.), Information processing approaches to clinical psychology. New York: Academic Press.

James, W. (1909). The meaning of truth. New York. Kohler, W. (1947). Gestalt psychology. New York: Liveright. Kuhn, T. S, (1970). The structure of scientific revolutions (2nd

ed.). Chicago: University of Chicago Press. Kuhn, T. S. (1971). Concepts of cause in the development of

physics. In T. S. Kuhn (Ed.), The essential tension: selected studies in scientific tradition and change (pp. 21-30). Chicago: The University of Chicago Press.

Lezak, M. D. (1983). Neurological assessment (2rid ed.). New York: Oxford University Press.

Litt, M. D. (1988). Self-efficacy and perceived control: cognitive mediators of pain tolerance. Journal of Personality and Social Psychology, 54, 149-160.

Meehl, P. E., & Cronbach, L. J. (1955). Construct validity in psychological tests. Psychological Bulletin, 52, 281-302.

Multon, K. D., Brown, S. D., & Lent, R. W. (1991). Relation of self-efficacy beliefs to academic outcomes: a meta-analytic investigation. Journal of Counseling Psychology, 38, 30-38.

Nuechterlein, K. H., & Dawson, M. E. (1984). Information processing and attentional functioning in the developmental course of schizophrenic disorders. Schizophrenia Bulletin, 10, 160-202.

Popper, K. (1959). The logic of scientific discovery. New York: Basic Books.

Russell, B. (1910). "Pragmatism" and "William James' conception of truth," in Philosophical essays. London.

Skinner, B. F. (1953). Science and human behavior. New York: Macmillan.

Spaulding, W. D. (Ed.). (1994). Cognitive technology in psychiatric rehabilitation. Lincoln: University of Nebraska Press.

Thorndike, E. L. (1913). Educational psychology: the psychology of learning (Vol. 2). New York: Teachers College.

Tipler, P. A. (1969). Foundations of modern physics. New York: Worth Publishers.

Wundt, W. (1902). Principles of physiological psychology (Vol. 2). (E. B. Titchener, Trans.). New York: Macmillan.