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Pica: Some Suggestions for Future Research (1987)

Pica: Some Suggestions for Future Research (1987)

©1987, 2013 by Dallas Denny

Source: Denny, Dallas. (1987). Pica: Some suggestions for future research. Paper for Department of Special Education, George Peabody College of Vanderbilt University.

This was one of my papers for qualifying exams.


Pica: Some Suggestions for Future Research

By Dallas Denny

For General Qualifying Examinations

Department of Special Education

George Peabody College of Vanderbilt Uninersity

8 June, 1987



Pica is the ingestion of substances ordinarily considered to be non-edible. Some authors have included the compulsive or inappropriate eating of food, coprophagy, and body-mouthing in their definitions of pica. In the past 15 years, studies have demonstrated the effectiveness of a variety of behavioral techniques for controlling pica behavior. Pica studies need to take a new direction. Some directions for future research are suggested. There is a need for a consensus on a definition of pica and on ethical issues, such as seeding of environments and prevention of the pica response by experimenters. Additionally, etiological and developmental studies are needed, as are comparisons of pica in normally developing children and individuals who exhibit pathological pica. Also, issues of generalization and maintenance should be thoroughly addressed.


Pica is the term used to refer to the ingestion of substances ordinarily considered to be non-edible. In normally developing infants, pica is common, but beyond the age of about 12-18 months, pica is considered to be pathological (Singh, 1983). Among institutionalized adults with mental retardation, between 14 and 26 percent of the population may engage in pica (Danford & Huber, 1982; Kruck, 1987; Lofts & Allen, 1985), depending upon whether pica is limited to ingestion of non-nutritive substances or whether food pica, mouthing of body parts, and coprophagy are included in the definition. Substances which are commonly ingested by persons with mental retardation include but are by no means limited to strings, rags, screws, dirt, grass and leaves, insects, paint, and feces (Danford & Huber, 1982). Pica is a health-threatening and in some cases a life-threatening behavior. Ingestion of toxic substances such as lead can lead to behavioral toxicity (Byers, 1959 Vessal, Ronaghy, Zarabi, 1975). Pica can increase the incidence of intestinal parasites (Foxx & Martin, 1975), cause mineral deficiencies (Crosby, 1971), or require surgical intervention for gastrointestinal blockage (Ausman, Ball; Alexander, 1974).

A variety of treatments have evolved for pica. These include mechanical devices which make it physically impossible to pick up and ingest substances (Lofts, 1986), administration of vitamins and minerals (Lofts, 1986), and applied behavior analysis (reviewed by Singh, 1983).

Although restraining devices can eliminate any possibility of engaging in pica behavior, their noncontingent use does not generalize to times when they are not applied, and their long-term use can lead to physical problems and interfere with socialization (Lovaas & Simmons, 1969). To date, there has not been a clear demonstration of a causal relationship between serum levels of any vitamin or mineral and frequency of pica behavior. For these reasons, the major focus of this paper will be to briefly summarize more than a decade of applied behavior analytic studies of pica and to suggest directions in which future research might proceed.

Behavior analytic studies of pica assume that pica behavior is maintained by its consequences and that changing the consequences of pica can lead to changes in its frequency. Various researchers have demonstrated that pica can be controlled by a variety of techniques and combinations of techniques including contingent visual screening (Singh & Bakker, 1983), overcorrection (Foxx & Martin, 1975; Mulick, Barbour, Schroeder, & Rojann, 1980), contingent verbal reprimand + brief physical restraint (Bucher, Peykdal, & Albin, 1976), and noncontingent provision of food (Quinn, Fitzgerald, Hinze, & Favell, 1987; White & Favell, 1987).

It is important that we now address problems which have been created by and uncovered by existing pica research. The first and perhaps most serious problem is definitional. Albin (1977), noted that different researchers defined pica in different ways. The DSM-III (Spitzer & Cantwell, 1980) defines pica as the ingestion of non-nutritive or inedible substances. The compulsive eating of objects which are generally considered to be edible, but which are ingested in non-conventional or inappropriate circumstances (e.g., the eating of food picked up from the floor or gathered from trash receptacles)—what Danford & Huber (1982) call food pica—is excluded by this definition, as are coprophagy and mouthing of body parts. Although some authors have used the DSM-III definition of pica (c.f. Singh & Winton, 1983), others have included food pica in their definitions (e.g. Foxx & Martin, 1975). Others have included coprophagy (Bucher, Reykdahl, & Albin, 1976) or mouthing of body parts (Paniagua, Braverman, & Capriotti, 1986) in their definition of pica. The ten years since the problem was pointed out by Albin has not resulted in a common definition of pica. It is important that workers in the field come to some consensus about what pica is. Is it exclusively the ingestion of non-edible substances? Should the eating of food items picked up from the floor be classified as pica? Different definitions of pica make comparisons across studies difficult (Albin, 1977).

The relationship of pica to other behaviors, in particular the inappropriate behaviors of scavenging, self-stimulatory behavior, and self-injurious behavior, has never been adequately addressed. Bluestone (1985) was able to successfully decelerate pica behavior of a single individual by interfering with antecedent scavenging behavior. Bluestone’s study, however, has not been replicated, and the relationship of pica to other inappropriate behaviors is not known. The relationship between pica and other behaviors can and should be determined empirically, by carefully controlled studies.

The etiology of pica is not known. We do not know why normally developing infants engage in pica behavior, or why some developmentally delayed persons engage in pica behavior after 18 months of age, whereas others do not. A careful developmental study of pica in normally developing children, much like Esther Thelen’s (1979, 1981) studies of rhythmic behavior in children, is needed, and indeed, should have been done long ago. Ethograms of the pica behavior of normally developing youngsters and developmentally delayed individuals could tell us much about the emergence, functionality, topography, maintenance, and eventual decline of pica. A thorough understanding of pica behavior in normally developing children would tell us much about pathological pica in adults. Similarly, comparisons of pica in children with and without delays would be enlightening.

There must also be some discussion about the ethical issues involved in pica research. There has been previous concern about the techniques of (a) seeding the environment and (b) prevention of ongoing pica behavior (Albin, 1977). Obviously, preventing individuals from swallowing potentially harmful objects is ethically defensible (and even ethically mandated), and seeding an environment may be desirable for practical reasons. However, both procedures may interfere with the validity of observations. That is, interventions made in such contrived environments may or may not generalize to the more natural environment. Although the ethical issues posed by these manipulations must be resolved by discussion, the effects of the procedures on the validity of research can and should be determined empirically.

Although most of the behavioral researchers who have studied pica have made attempts to study the generality of their behavioral treatments across stimulus and response classes (c.f. Mulick, et. al., 1980), thorough studies of stimulus generality, response generality, and maintenance (Cooper, Heron, & Heward, 1987) are needed. Only when it has been clearly demonstrated that behavioral interventions have generality to the everyday context of the individual’s life will generality have been adequately addressed.

Although some of the problems I have mentioned can be best addressed empirically, by future research, others will require discussion between concerned researchers and other professionals, in person, rather than in print. A conference on pica, or at least a symposium as part of a larger conference, would be an appropriate forum to discuss ethical and definitional issues.

The study of pica is in its infancy. Fortunately, behavioral researchers have provided simple, effective techniques to significantly reduce the frequency of pica behavior. With luck, the next decade will provide us with a clearer definition of pica and with many well-designed and relevant studies of this common, life-threatening behavior.


Albin, J. B. (1977). The treatment of pica (scavenging) behavior in the retarded: A critical analysis and implications for research. Mental Retardation, 15, 14-17.

Ausman, J., Ball, T. S., & Alexander, D. (1974). Behavior therapy of pica in a profoundly retarded adolescent. Mental Retardation, 12, 16-18.

Bluestone, M. A. (1985). Decreasing pica by targeting antecedent scavenging behaviors. Presented at the 93rd Annual Meeting of the American Psychological Association, Los Angeles, CA, August 23-27.

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Byers, P. K. (1959). Lead poisoning: A review of the literature and report on 45 cases. Pediatrics, 23, 585-603.

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Lovaas, O. I., & Simmons, J. Q. (1969). Manipulation of self-destruction in three retarded children. Journal of Applied Behavior Analysis, 2, 143-159.

Mulick, J. A., Barbour, R., Schroeder, S. R., & Rojahn, J. (1980). Overcorrection of pica in two profoundly retarded adults: Analysis of setting effects, stimulus and response generalization. Applied Research in Mental Retardation, 1, 241-252.

Paniagua, F. A., Braverman, C., & Capriotti, P. M. (1986). Use of a treatment package in the management of a profoundly mentally retarded girl’s pica and self-stimulation. American Journal of Mental Deficiency, 90(5), 550-557.

Quinn, L. T., Fitzgerald, J. R., Hiaze, C. B., & Favell, J. E. (1987). Treatment of pica using benign alternate sensory activities. Presented at the Twentieth Annual Gatlinburg Conference on Research and Theory in Mental Retardation and Developmental Disabilities, Gatlinburg, TN, March 26-28.

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Singh, N. N, & Winton, A. S W. (in press). Effects of a screening procedure on pica and collateral behaviors. Journal of Behavior Therapy and Experimental Psychiatry.

Singh, N. N., & Winton, A. S. W. (1983). Controlling pica by components of an overcorrection procedure. American Journal of Mental Deficiency, 90(1), 40-45.

Spitzer, P. L., & Cantwell, D. P. 1980. The DSM-III classification of the psychiatric disorders of infancy, childhood, and adolescence. Journal of the American Academy of Child Psychiatry, 19, 356-370,

Thelen, E. (1979). Rhythmical stereotypies in normal human infants. Animal Behaviour, 27. 699-715.

Thelen, E. (1981). Rhythmical behavior in infancy: An ethological perspective. Developmental Psvchology, 17(3), 237-257.

Vessal, K., Ronaghy, H. A., & Zarabi, M. (1975). Radiological changes in pica. American Journal of Clinical Nutrition, 28, 1095-1098.

White, J. S., & Favell, J. E. (1987). Analysis of the effect of three alternate sensory stimuli on pica behavior. Presented at the Twentieth Annual Gatlinburg Conference on Research and Theory in Mental Retardation and Developmental Disabilities, Gatlinburg, TN, March 26-28.