Choice in a variable environment: every reinforcer counts

Six pigeons were trained in sessions composed of seven components, each arranged with a different concurrent-schedule reinforcer ratio. These components occurred in an irregular order with equal frequency, separated by 10-s blackouts. No signals differentiated the different reinforcer ratios. Conditions lasted 50 sessions, and data were collected from the last 35 sessions. In Part 1, the arranged overall reinforcer rate was 2.22 reinforcers per minute. Over conditions, number of reinforcers per component was varied from 4 to 12. In Part 2, the overall reinforcer rate was six per minute, with both 4 and 12 reinforcers per component. Within components, log response-allocation ratios adjusted rapidly as more reinforcers were delivered in the component, and the slope of the choice relation (sensitivity) leveled off at moderately high levels after only about eight reinforcers. When the carryover from previous components was taken into account, the number of reinforcers in the components appeared to have no systematic effect on the speed at which behavior changed after a component started. Consequently, sensitivity values at each reinforcer delivery were superimposable. However, adjustment to changing reinforcer ratios was faster, and reached greater sensitivity values, when overall reinforcer rate was higher. Within a component, each successive reinforcer from the same alternative ("confirming") had a smaller effect than the one before, but single reinforcers from the other alternative ("disconfirming") always had a large effect. Choice in the prior component carried over into the next component, and its effects could be discerned even after five or six reinforcement and nonreinforcement is suggested.     

A social learning therapy programme with an autistic child

Undergraduates were trained in a predominantly operant conditioning therapy aimed at acquiring a measure of control over the behaviour of an autistic child in the setting of a day-care centre. Objective measures of therapist-control prior to therapy showed that the workers initially had no influence whatever on the child. Post-measures indicated that both therapists had achieved a markedly greater degree of control. Controls for mere familiarity and for generalization to workers other than the therapists led to the conclusion that, during the programme, the child had become significantly more responsive to adults in general. The case study material, gleaned from the daily reports by means of which the author monitored the treatment, demonstrated many specific instances of behaviour-change, including the apparent desensitization of various fears. In view of the fact that the treatment setting was far from ideal for this approach, the positive results were regarded as strong support for the suitability of operant conditioning techniques for manipulating psychotic behaviour in children.     

Preference for multiple versus mixed schedules of reinforcement

Five pigeons were trained in a concurrent-chain procedure. In the initial links, equal nonindependent variable-interval schedules were available concurrently on two keys. Completing the schedule on either key led to exclusive presentation of one of two further variable-interval schedules for a fixed period of time. During these terminal links, as many reinforcers as were scheduled could be obtained. If the response producing this terminal link occurred on one key, differential stimuli signaled which variable-interval schedule had been produced. If the response producing the terminal link occurred on the other key, no such differential stimuli were available. Once the fixed period of time elapsed, the initial links were reinstated. In Experiment 1, the period of time for which the terminal links were available was always 10 s and the absolute duration of the initial links was varied. Subjects preferred the alternative leading to the multiple schedule when the initial-link duration was short, but preferred the alternative leading to the mixed schedule when the initial-link durations were longer. In Experiment 2, both the initial-link duration and the duration of the terminal links were varied. The effect of initial-link duration was identical to that in Experiment 1 and there was no systematic effect of varying the terminal-link duration.     

Brain size and cognitive ability: Correlations with age,sex, social class,and race

Using data from magnetic resonance imaging (MRI), autopsy, endocranial measurements, and other techniques, we show that (1) brain size is correlated with cognitive ability about .44 using MRI; (2) brain size varies by age, sex, social class, and race; and (3) cognitive ability varies by age, sex, social class, and race. Brain size and cognitive ability show a curvilinear relation with age, increasing to young adulthood and then decreasing; increasing from women to men; increasing with socioeconomic status; and increasing from Africans to Europeans to Asians. Although only further research can determine if such correlations represent cause and effect, it is clear that the direction of the brain-size/cognitive-ability relationships described by Paul Broca (1824–1880), Francis Galton (1822–1911), and other nineteenth-century visionaries is true, and that the null hypothesis of no relation, strongly advocated over the last half century, is false.     

Moral reasoning development and graduate education

The Defining Issues Test (DIT) of moral reasoning development was administered to 20 advanced and 20 first-year graduate students, plus 40 college graduates matched to the graduate groups on sex, age, and verbal ability. A two-way ANOVA design was used to infer whether graduate education, selection, maturation, or a combination of these effects is (are) associated with group differences on the DIT. Results suggest that differences found between the graduate students and college graduates can be accounted for by a combination of maturational and selection effects, contrary to the hypothesized effects of formal education.     

Preference for fixed-interval schedules: an alternative model

Pigeons were trained under concurrent chain schedules in which the initial links were equal aperiodic schedules and the terminal links were fixed-interval schedules. Choice proportions in the initial links were measured in 26 experimental conditions. The data showed the inadequacy of previous models of concurrent chain performance. A new model was suggested in which choice is a joint function of terminal-link times, overall reinforcement rates, and terminal-link entries. This model accounted for 94% of the variance in the present data and for substantial percentages of the variance in previously reported data. The model simplifies to matching between response ratios and obtained reinforcement rate ratios for simple concurrent schedule performance.     

Preference for fixed-interval terminal links in a three-key concurrent chain schedule

Pigeons were trained on three-key concurrent chain schedules in which the initial links were variable-interval schedules and the terminal links were fixed-interval schedules. In the first experiment, the initial links were all equal and the terminal-link schedule on one key only was varied. In the second part of the experiment, the terminal-link schedules were all fixed, but different, and the initial-link schedule on one key was varied. Relative response rates in the initial links did not match either the relative arranged, nor the relative obtained, terminal-link reinforcement rates. The relations between independent and dependent variables in three-key concurrent chains were similar to, but not identical with, those found in two-key chains comprising the same schedule types.     

A functional analysis of chained fixed-interval schedule performance

Three pigeons were trained on two-link chained fixed-interval fixed-interval schedules. Numbers of responses, time spent responding, and the total time spent in each component were measured. The data were analyzed according to the matching law for multiple and concurrent schedules. In most conditions, the ratio of response rates in the two links was a constant proportion of the ratio that would be predicted in a multiple schedule with the same components. Data on pauses during the interval schedules showed that, in most conditions, the pause duration was a linear function of the interval length, and greater in the initial link than in the terminal link. The experiment thus demonstrated a quantitative functional analysis of performance on a chained schedule.     

Preference for mixed-interval versus fixed-interval schedules: number of component intervals

Six pigeons were trained under a concurrent chains procedure so that preference for fixed-interval versus mixed-interval schedules with varying numbers of component intervals could be examined. The smallest and largest intervals in the terminal links were the same value as those used by Davison (1969). Relative choice in all cases approximated the relative means of the squares of the harmonic intervals to reinforcement in the terminal links, and no effect of number of component intervals was demonstrated. Mixed-interval versus fixed-interval choice could not be predicted from extant data on fixed-interval versus fixed-interval choice.     

A choice technique to assess the effects of selective punishment on fixed-ratio performance

The emission of a fixed number of responses by rats was followed by food reinforcement. This fixed number could be accumulated in any way from two continuously available but mutually incompatible response classes, bar pressing, and not bar pressing for a fixed time period. A preference for one response class was arranged by specifying different maximum reinforcement rates for the two classes. Under selective punishment conditions, the preferred response occasionally led to both food and electric shock, while the non-preferred response led only to food. Selective punishment effects were measured through changes in the preference to the two responses in the sequence. The actions of shock intensity, deprivation, the specification of the non-preferred response, and three drugs were investigated. The results were broadly similar to the work reported by Dardano and Sauerbrunn (1964), who found localized increases in interresponse times before punished responses in fixed-ratio schedules. Performance under this procedure was found to be stable and sensitive to each of the experimental variables examined.