Effects of adding a second reinforcement alternative: implications for Herrnstein's interpretation of r(e)

Herrnstein's hyperbola describes the relation between response rate and reinforcer rate on variable-interval (VI) schedules. According to Herrnstein's (1970) interpretation, the parameter r(e) represents the reinforcer rate extraneous to the alternative to which the equation is fitted (the target alternative). The hyperbola is based on an assumption that extraneous reinforcer rate remains constant with changes in reinforcer rate on the target alternative (the constant-r(e) assumption) and that matching with no bias and perfect sensitivity occurs between response and reinforcer ratios. In the present experiment, 12 rats pressed levers for food on a series of 10 VI schedules arranged on the target alternative. Across conditions, six VI values and extinction were arranged on a second alternative. Reinforcer rate on the second alternative, r2, negatively covaried with reinforcer rate on the target alternative for five of the six VI values on the second alternative, and significant degrees of bias and undermatching occurred in response ratios. Given covariation of reinforcer rate on the second and target alternatives, the constant-r(e) assumption can be maintained only by assuming that reinforcer rate from unmeasured background sources, rb, covaries with reinforcer rate on the second alternative such that their sum, r(e), remains constant. In a single-schedule arrangement, however, r(e) equals rb and thus rb is assumed to remain constant, forcing a conceptual inconsistency between single- and concurrent-schedule arrangements. Furthermore, although an alternative formulation of the hyperbola can account for variations in bias and sensitivity, the modified equation also is based on the constant-r(e) assumption and therefore suffers from the same logical problem as the hyperbola when reinforcer rate on the second alternative covaries with reinforcer rate on the target alternative.     

Pregnancy as a stressful life event

Pregnancy and childbirth typically are associated with positive emotions and with motherhood, but the reality is that this is not the case for all women or for all pregnancies. This review addresses a different aspect of these reproductive events, focusing on stressful circumstances surrounding pregnancy, as well as times when the pregnancy itself becomes a stressful life event. Pregnancy-related topics that tend to receive less attention will be emphasized. These include issues related to infertility; unplanned pregnancy; stress associated with testing and diagnosis of common medical complications; peripartum cardiomyopathy; fear of childbirth; and pregnancy loss as a risk factor for psychopathology. Epidemiologic information will be presented, as will relevant psychosocial factors related to each phenomenon. Healthcare providers should be sensitive to the distress and anxiety experienced by many women and their families as a consequence of these adverse events and the stressful challenge of any consequential decision-making, as well as stressors in their broader life context that can further exacerbate their distress, and make mental health referrals as appropriate.     

Does comorbid attention-deficit/hyperactivity disorder impact the clinical expression of pediatric obsessive-compulsive disorder?

What is the impact of attention-deficit/hyperactivity disorder (ADHD) on the phenotypic expression of pediatric obsessive-compulsive disorder (OCD). We examined phenotypic features, and functional and clinical correlates in youths with OCD, with and without comorbid ADHD, from a large sample of consecutively referred pediatric psychiatry patients. Although comorbid ADHD had no meaningful impact on the phenotypic expression or clinical correlates of OCD, it was associated with higher rates of compromised educational functioning compared with other OCD youths. Our findings suggest that the OCD phenotype runs true and is not impacted by comorbid ADHD in youths diagnosed with both OCD and ADHD. In such affected youths, both disorders contribute to morbid dysfunction and require treatment. More work is needed to determine whether OCD plus ADHD represents a developmentally and etiologically distinct form of the OCD syndrome.     

ALTERING SHOPPERS' SUPERMARKET PURCHASES TO FIT NUTRITIONAL GUIDELINES: AN INTERACTIVE INFORMATION SYSTEM

This study reports the results of one effort to help supermarket shoppers alter food purchases to make purchases (and meals) that are lower in fat and higher in fiber. A prototype interactive information system using instructional video programs, feedback on purchases with specific goals for change, weekly programs, and the ability to track user interactions and intended purchases was evaluated. The major dependent measure was users' actual food purchases as derived from participants' highly detailed supermarket receipts. After a 5- to 7-week baseline phase, participants were randomly assigned to an experimental or control condition for the 7- to 8-week intervention phase. A follow-up phase began 5 to 8 weeks after participants completed the intervention and discontinued use of the system. The results indicated that experimental participants, when compared to control participants, decreased high fat purchases and increased high fiber purchases during intervention, with evidence for some maintenance of effect in follow-up. Plans for increasing the use and impact of the system are discussed.     

An experimental evaluation of a prototype public access nutrition information system for supermarkets

Located the Nutrition for a Lifetime System (NLS-1), a prototype interactive information system, in a large supermarket to help users decrease high-fat food purchases and increase high-fiber food purchases. Study participants were randomly assigned to control (n = 23; used the NLS-1 to enter food purchases only) or experimental (n = 26; viewed videodisc instructional programs, received prompts, made commitments, received feedback from the NLS-1) conditions. According to data entered in the NLS-1 and actual food shopping receipts, experimental participants significantly reduced higher fat purchases. Increases in higher fiber purchases favored the experimental group but were not significant.     

Presence of administrators differentially impacts eyewitness discriminability for same- and other-race identifications

Best practice guidelines recommend that eyewitness lineup administrators be blind to a suspect's identity, but no research has investigated whether the mere presence of a lineup administrator impacts eyewitness identification decisions. Informed by social facilitation theory, we predicted that the presence of an audience would differentially impact identification accuracy for same- and other-race identifications. Participants (N = 191) viewed same- and other-race lineups either with an audience or alone. Although the presence of an audience did not directly impact identification accuracy, significant indirect effects indicated that the audience provoked evaluation apprehension which hindered other-race identification accuracy and improved same-race identification accuracy. We suggest that using double-blind lineup procedures may not sufficiently protect eyewitness identification accuracy when making other-race lineup decisions in the presence of others.     

Feedback functions, optimization, and the relation of response rate to reinforcer rate

The present experiment arranged a series of inverted U-shaped feedback functions relating reinforcer rate to response rate to test whether responding was consistent with an optimization account or with a one-to-one relation of response rate to reinforcer rate such as linear system theory's rate equation or Herrnstein's hyperbola. Reinforcer rate was arranged according to a quadratic equation with a maximum at a unique response rate. The experiment consisted of two phases, during which 6 Long Evans rats lever pressed for food. In the first phase of the experiment, the rats responded on six fixed-interval-plus-quadratic-feedback schedules, and in the second phase the rats responded on three variable-interval-plus-quadratic-feedback schedules. Responding in both phases was inconsistent with a one-to-one relation of response rate to reinforcer rate. Instead, different response rates were obtained at equivalent reinforcer rates. Responding did vary directly with the vertex of the feedback function in both phases, a finding consistent with optimization of reinforcer rate. The present results suggest that the feedback function relating reinforcer rate to response rate imposed by a reinforcement schedule can be an important determinant of behavior. Furthermore, the present experiment illustrates the benefit of arranging feedback functions to investigate assumptions about the variables that control schedule performance.     

The roles of sequencing and verbal working memory in sentence comprehension deficits in Parkinson's disease

Studies of sentence comprehension deficits in Parkinson's disease (PD) patients suggest that language processing involves circuits connecting subcortical and cortical regions. Anatomically segregated neural circuits appear to support different cognitive and motor functions. To investigate which functions are implicated in PD comprehension deficits, we tested comprehension, verbal working memory span, and cognitive set-switching in a non-linguistic task in 41 PD patients; we also obtained speech measurements reflecting motor sequencing processes that may be involved in articulatory rehearsal within working memory. Comprehension of sentences with center-embedded or final relative clauses was impaired when they could not be understood from lexical semantic content alone. Overall comprehension error rates correlated strongly with impaired set-switching and significantly with reduced working memory span and speech motor sequencing deficits. Correlations with comprehension of different sentence structures indicate that these impairments do not represent a single deficit; rather, PD comprehension deficits appear to arise from several independent mechanisms. Deficits in cognitive set-switching or underlying inhibitory processes may compromise the ability to process relative clauses. Deficits in verbal working memory appear to impair comprehension of long-distance dependencies. Speech sequencing correlated with neither set-switching nor verbal working memory span, consistent with their being supported by independent, segregated cortico-subcortical circuits.