In search of the feedback function for variable-interval schedules

Finding a theoretically sound feedback function for variable-interval schedules remains an important unsolved problem. It is important because interval schedules model a significant feature of the world: the dependence of reinforcement on factors beyond the organism's control. The problem remains unsolved because no feedback function yet proposed satisfies all the theoretical and empirical requirements. Previous suggestions that succeed in fitting data fail theoretically because they violate a newly recognized theoretical requirement: The slope of the function must approach or equal 1.0 at the origin. A function is presented that satisfies all requirements but lacks any theoretical justification. This function and two suggested by Prelec and Herrnstein (1978) and Nevin and Baum (1980) are evaluated against several sets of data. All three fitted the data well. The success of the two theoretically incorrect functions raises an empirical puzzle: Low rates of reinforcement are coupled with response rates that seem anomalously high. It remains to be discovered what this reflects about the temporal patterning of operant behavior at low reinforcement rates. A theoretically and empirically correct function derived from basic assumptions about operant behavior also remains to be discovered.     

Equivalence of two manufacturers’ precision food pellets for rats

Precision food pellets made from purified ingredients by two different manufacturers (P. J. Noyes Company, Inc. and Bio-Serv, Inc.), and advertised as dust-free and nutritionally complete, were compared as reinforcers of leverpressing in rats. Single schedules (a variable interval [VI] of 30 sec and a fixed ratio of 20) were used to compare ability to maintain moderate and high response rates, and concurrent VI schedules were used to assess preference. The two pellets maintained equivalent moderate and high response rates on the single schedules. In the concurrent schedules, 3 out of 4 rats showed a small preference for the Bio-Serv pellets. Although both pellets performed adequately in normal humidity, high humidity caused the Bio-Serv pellets to soften and occasionally to be crushed in the pellet dispenser. Their softness may have been the reason they were preferred. The two pellets can be regarded as generally equivalent, except in high humidity. The only experiments in which they might not be used interchangeably are those involving choices between different reinforcers.     

Performances on ratio and interval schedules of reinforcement: Data and theory

Two differences between ratio and interval performance are well known: (a) Higher rates occur on ratio schedules, and (b) ratio schedules are unable to maintain responding at low rates of reinforcement (ratio “strain”). A third phenomenon, a downturn in response rate at the highest rates of reinforcement, is well documented for ratio schedules and is predicted for interval schedules. Pigeons were exposed to multiple variable-ratio variable-interval schedules in which the intervals generated in the variable-ratio component were programmed in the variable-interval component, thereby “yoking” or approximately matching reinforcement in the two components. The full range of ratio performances was studied, from strained to continuous reinforcement. In addition to the expected phenomena, a new phenomenon was observed: an upturn in variable-interval response rate in the midrange of rates of reinforcement that brought response rates on the two schedules to equality before the downturn at the highest rates of reinforcement. When the average response rate was corrected by eliminating pausing after reinforcement, the downturn in response rate vanished, leaving a strictly monotonic performance curve. This apparent functional independence of the postreinforcement pause and the qualitative shift in response implied by the upturn in variable-interval response rate suggest that theoretical accounts will require thinking of behavior as partitioned among at least three categories, and probably four: postreinforcement activity, other unprogrammed activity, ratio-typical operant behavior, and interval-typical operant behavior.     

Optimality And Concurrent Variable-interval Variable-ratio Schedules

Despite claims to the contrary, all leading theories about operant choice may be seen as models of optimality. Although melioration is often contrasted with global maximization, both make the same core assumptions as other versions of optimality theory, including momentary maximizing, hill climbing, and the various versions of optimal foraging theory. The present experiment aimed to test melioration against more global optimality and to apply the visit-by-visit analysis suggested by foraging theory. Rats were exposed to concurrent schedules in which one alternative was always variable-ratio 10 and the other alternative was a variable-interval schedule. Although choice relations varied from rat to rat, the overall results roughly confirmed the matching law, a result often taken to support melioration. Pooling the data across sessions and across rats, however, resulted in no increment in unsystematic variance, lending support to the contention by Ziriax and Silberberg (1984) that the choice relation is partly constrained. When the data were analyzed at the level of visits, the results either disconfirmed predictions of melioration or showed regularities about which melioration is silent. Instead, performance tended toward a rough optimization, in which responding favored the variable ratio, but with relatively brief visits to the variable interval. There were no asymmetries in travel or variability that would indicate that different processes were involved in generating visits at the two different schedules. The findings point toward a more global optimality model than melioration and demonstrate the value of per-visit analysis in the study of concurrent performances.     

A review of observer reactivity in adult-child interactions

The present article reviews studies which have examined the question of observer reactivity in adult-child interactions. Seventeen studies were located. Studies were classified according to the paradigm used to examine reactivity, the setting in which the study was conducted, the identification of the child as a behavior problem, and the occurrence and direction (i.e., increases or decreases in the observed behavior) of reactivity. The results indicated that the awareness paradigm has been employed most frequently, the laboratory has been the primary setting utilized, and problem and nonproblem children have been employed with approximately equal frequency. Reactivity was reported in about three-fourths of the studies. For adults positive and neutral verbal and physical behaviors were more reactive than negative behaviors. The positive and neutral behaviors typically increased in the observer's presence. For children conclusions are not warranted at this time as too few studies have examined children's behavior.Preparation of this article was supported in part by NIMH Grant MH28859-01.     

Children's sensitivity to circular explanations

The ability to evaluate the quality of explanations is an essential part of children's intellectual growth. Explanations can be faulty in structural ways such as when they are circular. A circular explanation reiterates the question as if it were an explanation rather than providing any new information. Two experiments (N=77) examined children's preferences when faced with circular and noncircular explanations. The results demonstrate that a preference for noncircular explanations is present, albeit in a fragile form, by 5 or 6 years of age and that it appears robustly by 10 years of age. Thus, the ability to evaluate the quality of explanations based on structural grounds appears to develop rapidly during the elementary school years.     

DYNAMICS OF CHOICE: RELATIVE RATE AND AMOUNT AFFECT LOCAL PREFERENCE AT THREE DIFFERENT TIME SCALES

To examine extended control over local choice, the present study investigated preference in transition as food‐rate ratio provided by two levers changed across seven components within daily sessions, and food‐amount ratio changed across phases. Phase 1 arranged a food‐amount ratio of 4:1 (i.e., the left lever delivered four pellets and the right lever one pellet); Phase 2 reversed the food‐amount ratio to 1:4, and in Phase 3 the food‐amount ratio was 3:2. At a relatively extended time scale, preference was described well by a linear relation between log response ratio and log rate ratio (the generalized matching law). A small amount of carryover occurred from one rate ratio to the next but disappeared after four food deliveries. Estimates of sensitivity to food‐amount ratio were around 1.0 and were independent of rate ratio. Analysis across food deliveries within rate‐ratio components showed that the effect of a small amount was diminished by the presence of a large amount—that is, when a larger amount was present in the situation (three or four pellets), the value of a small amount (one or two pellets) became paltry. More local analysis of visits to the levers between food deliveries showed that postfood visits following a large amount were disproportionately longer than following a small amount. Continuing food deliveries from the same source tended to make visits less dependent on relative amount, but a discontinuation (i.e., food from the other lever) reinstated dependence on relative amount. Analysis at a still smaller time scale revealed preference pulses following food deliveries that confirmed the tendency toward dependence on absolute amount with continuing deliveries, and toward dependence on relative amount following discontinuations. A mathematical model based on a linear‐operator equation accounts for many of the results. The larger and longer preference following a switch to a larger amount is consistent with the idea that local preference depends on relatively extended variables even on short time scales.     

Negative consequences of community group participation for women's mental health and well‐being: Implications for gender aware social capital building

Participation in community groups is argued to be an important way to create health‐promoting social capital. However, relatively little attention has been paid to the ways in which gender affects the health promotion potential of participation. This paper reports on a qualitative study of women's experiences of participation in a diverse range of community groups, and considers how such involvement can potentially have a negative impact upon mental well‐being. In‐depth interviews were conducted with 30 women in Adelaide, South Australia. Women's accounts of their group involvement reflected that their identities as mothers were particularly important in shaping their participation. Some women reported difficulties in combining group involvement with their family responsibilities. Stress attached to negotiating social interaction within groups was also raised as an issue. It was found that participation can reinforce gender inequality and potentially have severe negative consequences for mental health, issues that need to be considered alongside the potential health benefits. The findings are considered in light of Bourdieu's critical conceptualization of social capital. Copyright © 2008 John Wiley & Sons, Ltd.     

Christian and Muslim Anti-Semitic Beliefs

One hundred Muslims and one hundred Christians were administered a battery of tests to determine the nature and extent of anti-Semitic beliefs. The two groups differed considerably in terms of rationale, level, and course of anti-Semitic beliefs. Specifically, differences may be explained via dimensions of personal and social identity. The implications for emotional development and its role in understanding prejudices are discussed.