Effects of anorectic drugs on food intake under progressive-ratio and free-access conditions in rats

The effects of two anorectic drugs, dexfenfluramine and phentermine, on food intake under different food-access conditions were examined. Experiment 1 compared the effects of these drugs on food intake under a progressive-ratio (PR) schedule and free-access conditions. Dexfenfluramine decreased food intake under both conditions, but the doses required to decrease intake under free-access conditions were higher than those required to reduce intake under the PR condition. Intermediate doses of phentermine sometimes increased breaking points, and higher doses decreased them. Phentermine decreased food intake at the same doses under both access conditions. Thus the potency of dexfenfluramine, but not phentermine, to decrease food-maintained behavior depended upon the food-access condition. Experiment 2 used a novel mixed progressive-ratio schedule of food delivery to study the duration of drug effects. Sessions consisted of five components separated by 3-hr timeouts. The ratio requirement reset at the beginning of each component and a new breaking point was obtained. Both dexfenfluramine and phentermine dose-dependently decreased breaking points early in the session. In some rats, compensatory increases in breaking point were observed. That is, breaking points later in the session increased over control levels, resulting in no change in the total number of food pellets earned for the session compared to control. The present findings suggest that the effects of some anorectic drugs depend upon the access conditions for food; increasing the effort to obtain food may enhance their ability to decrease food-maintained behavior.     

Matching: its acquisition and generalization

Choice typically is studied by exposing organisms to concurrent variable-interval schedules in which not only responses controlled by stimuli on the key are acquired but also switching responses and likely other operants as well. In the present research, discriminated key-pecking responses in pigeons were first acquired using a multiple schedule that minimized the reinforcement of switching operants. Then, choice was assessed during concurrent-probe periods in which pairs of discriminative stimuli were presented concurrently. Upon initial exposure to concurrently presented stimuli, choice approximated exclusive preference for the alternative associated with the higher reinforcement frequency. Concurrent schedules were then implemented that gave increasingly greater opportunities for switching operants to be conditioned. As these operants were acquired, the relation of relative response frequency to relative reinforcement frequency converged toward a matching relation. An account of matching with concurrent schedules is proposed in which responding exclusively to the discriminative stimulus associated with the higher reinforcement frequency declines as the concurrent stimuli become more similar and other operants-notably switching-are acquired and generalize to stimuli from both alternatives. The concerted effect of these processes fosters an approximate matching relation in commonly used concurrent procedures.     

Sustained change blindness to incremental scene rotation: a dissociation between explicit change detection and visual memory

In a change detection paradigm, the global orientation of a natural scene was incrementally changed in 1 degree intervals. In Experiments 1 and 2, participants demonstrated sustained change blindness to incremental rotation, often coming to consider a significantly different scene viewpoint as an unchanged continuation of the original view. Experiment 3 showed that participants who failed to detect the incremental rotation nevertheless reliably detected a single-step rotation back to the initial view. Together, these results demonstrate an important dissociation between explicit change detection and visual memory. Following a change, visual memory is updated to reflect the changed state of the environment, even if the change was not detected.     

Large errors, but no depth compression, in walked indications of exocentric extent

Observers can sight a target 20 m away or more and then walk to it accurately without vision. In contrast to this good performance, this article shows that walked indications of the exocentric separation of two locations exceed the required values by over 70% when vision is obscured. Significantly, these large errors are coupled with a robust lack of depth foreshortening, even under conditions in which visual matches and verbal estimates of extent exhibit strong evidence of depth compression. This article presents evidence that the overshooting errors are due largely to recalibration of locomotor control produced by prolonged exposure to nonvisual walking. The robust lack of depth foreshortening, meanwhile, could reflect a corresponding isotropy in the spatial representation controlling the walking response. More research is needed to confirm this interpretation, however.     

Responsivity to two odorants, androstenone and amyl acetate, and the affective impact of odors on interpersonal relationships

Substantial variation exists in the importance of olfaction in influencing individuals' preferences, yet the sources of this variation remain elusive. The authors explored responsivity to 2 odorants as 1 potential source. Participants (N = 258) completed the Affective Impact of Odor Scale and were assessed for responsivity to the putative human pheromone androstenone and amyl acetate. Results showed a significant relationship between odorant responsivity and self-reports of the influence of odors. People able to smell androstenone more commonly reported odors as having a negative effect on interpersonal relationships than did people anosmic to androstenone, whereas responsivity to amyl acetate was associated with positive effects of odors on relationships. Responsivity to certain odorants may be an important factor affecting human social interactions.     

A meta-analytic review of prospective memory and aging

A meta-analysis of prospective memory (PM) studies revealed that in laboratory settings younger participants outperform older participants on tests of both time- and event-based PM (rs=-.39 and -.34, respectively). Event-based PM tasks that impose higher levels of controlled strategic demand are associated with significantly larger age effects than event-based PM tasks that are supported by relatively more automatic processes (rs=-.40 vs. -.14, respectively). However, contrary to the prevailing view in the literature, retrospective memory as measured by free recall is associated with significantly greater age-related decline (r=-.52) than PM, and older participants perform substantially better than their younger counterparts in naturalistic PM studies (rs=.35 and.52 for event- and time-based PM, respectively).     

The developing constraints on parsing decisions: the role of lexical-biases and referential scenes in child and adult sentence processing

Two striking contrasts currently exist in the sentence processing literature. First, whereas adult readers rely heavily on lexical information in the generation of syntactic alternatives, adult listeners in world-situated eye-gaze studies appear to allow referential evidence to override strong countervailing lexical biases (Tanenhaus, Spivey-Knowlton, Eberhard, and Sedivy, 1995). Second, in contrast to adults, children in similar listening studies fail to use this referential information and appear to rely exclusively on verb biases or perhaps syntactically based parsing principles (Trueswell, Sekerina, Hill, and Logrip, 1999). We explore these contrasts by fully crossing verb bias and referential manipulations in a study using the eye-gaze listening technique with adults (Experiment 1) and five-year-olds (Experiment 2). Results indicate that adults combine lexical and referential information to determine syntactic choice. Children rely exclusively on verb bias in their ultimate interpretation. However, their eye movements reveal an emerging sensitivity to referential constraints. The observed changes in information use over ontogenetic time best support a constraint-based lexicalist account of parsing development, which posits that highly reliable cues to structure, like lexical biases, will emerge earlier during development and more robustly than less reliable cues.     

Daily marital interactions and positive affect during marital conflict among newlywed couples

The mundane and often fleeting moments that a couple experiences in their everyday lives may contribute to the health or deterioration of a relationship by serving as a foundation to major couple events such as conflict discussions and caring days. This study examines the role of playfulness and enthusiasm in everyday life to the use of humor and affection during conflict. Using observational methods, we studied 49 newlywed couples in a 10-minute dinnertime interaction and in a 15-minute conflict discussion. The conflict discussion was coded using the Specific Affect Coding System (SPAFF; Gottman, Coan, & McCoy, 1996), and a new observational system was developed to capture dinnertime interactions in a seminatural setting. We analyzed the data using path analysis and found a stronger path model when the direction of correlation moved from daily moments to the conflict discussion. These findings provide preliminary support for the importance of daily moments in couple relationships, but this research was strictly observational and therefore correlational, so further research is necessary to determine direction of causation.