A corollary of the law of effect predicts that the larger the reinforcement, the greater the rate of responding. However, an animal must eat more small portions than large portions to obtain the same daily intake, and one would predict, therefore, that when eating smaller portions an efficient animal would eat less (conserving time and energy) and/or respond faster (conserving time). The latter of these predictions was supported by the present experiments with free-feeding rats for which portion size (pellet size or duration of feeder presentation) and portion price within meals were varied. Response rate was a function of the unit price (responses/g) of food: Rats responded faster when portions were smaller or when prices were higher. Meal size and frequency were relatively unaffected by unit price, but were influenced by the price of meal initiation. The results are discussed in relation to the economic differences between traditional operant and free-feeding paradigms and to both traditional and more recent formulations of the law of effect.

Forty-eight male subjects who met the DSM-IV (APA, 1994) criteria for conduct disorder (CD) were assessed for psychopathy level using a modified version of the Psychopathy Checklist-Revised (PCL-R, Forth, Hart, & Hare, 1990). Rorschach variables associated with self-perception, affects, and object relations, early behavioral problems and history of violence were compared between psychopathic and nonpsychopathic CD adolescents. Psychopathic CD subjects were significantly more self-centered and violent than nonpsychopathic CD subjects. Decreased attachment and anxiety were found in both CD groups. Our study adds empirical support to the heterogeneity noted among CD adolescents (PCL-R), supports the utility of the Rorschach for detecting individual differences among CD subjects, and extends the empirical work of Gacono and Meloy (1994) to adolescent psychopathy.

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