Time discounting and time preference in animals: A critical review

Animals are an important model for studies of impulsivity and self-control. Many studies have made use of the intertemporal choice task, which pits small rewards available sooner against larger rewards available later (typically several seconds), repeated over many trials. Preference for the sooner reward is often taken to indicate impulsivity and/or a failure of self-control. This review shows that very little evidence supports this assumption; on the contrary, ostensible discounting behavior may reflect a boundedly rational but not necessarily impulsive reward-maximizing strategy. Specifically, animals may discount weakly, or even adopt a long-term rate-maximizing strategy, but fail to fully incorporate postreward delays into their choices. This failure may reflect learning biases. Consequently, tasks that measure animal discounting may greatly overestimate the true discounting and may be confounded by processes unrelated to time preferences. If so, animals may be much more patient than is widely believed; human and animal intertemporal choices may reflect unrelated mental operations; and the shared hyperbolic shape of the human and animal discount curves, which is used to justify cross-species comparisons, may be coincidental. The discussion concludes with a consideration of alternative ways to measure self-control in animals.     

Integration of stimulus dimensions in perception and memory: composition rules and psychophysical relations

A series of five experiments used the method of magnitude estimation to assess how height and width are integrated in perceptual and in memorial judgments of area. Separate groups of subjects estimated the areas of perceived or remembered rectangles produced by a symmetrical 4 X 4 factorial design of height and width. Additional independent groups of observers made area judgments, based on special mixes of perceptual and memorial information referring to the height and width components of the to-be-judged rectangles. Both perceptual and memory data obeyed the bilinear interaction prediction of the normative multiplicative model. The relation between perceived and actual area as well as the relation between remembered and actual area could both be described by a compressive power function, with the exponent being reliably smaller for remembered than for perceived area. These results seem to imply a principle of integration rule invariance across perceptual and memorial estimates of a given set of stimuli, in conjunction with characteristically different valuation operations.     

Factor analysis of MMPI-2 basic scales among college students

The MMPI-2 was administered to 288 college students (178 women and 110 men) between the ages of 18 and 34 years. Scores on the basic 13 (three validity and ten clinical) scales were correlated and subjected to principal component analyses separately for men and women. In each case, four factors were retained and subjected to varimax rotation. Coefficients of congruence were calculated for all possible pairs of factors across two samples of college students and the normative adults, separately for men and women, and across genders within each sample. Results indicated that the factorial structure of the MMPI-2 basic scales seemed to possess considerable uniformity across samples and genders, but not without some notable exceptions.     

Why we walk the way we do

By using inverse dynamics and forceplate recordings, this study established the principle of oscillating systems and the influence of gravity and body parameters on the programming of the gait parameters, step frequency and length. Calculation of the ratio of the amplitude of the center of mass (CM) and the center of foot pressure (CP) oscillations yielded an equation and established a biomechanical constant, the natural body frequency (NBF). NBF appears to be an absolute invariant parameter, specific to human standing posture and gait in terrestrial gravity, which influences the relative positions of CM and CP and whose value separates the frequency bands of standing posture from those for gait. This equation was tested by using the experimental paradigm of stepping in place and then used in calculating the magnitude of CM oscillations during gait. The biomechanical analysis of the experimental observations allows one to establish the relationships between body parameters and gravity and the central programming of locomotor parameters.     

Movement patterns of persons with HIV receiving treatment in public clinics in the Southern Health Region,Puerto Rico

A survey conducted among 187 HIV-infected patients from publicly supported HIV clinics in the Puerto Rican Southern Health Region (SHR) failed to substantiate health planners' concern that this group travels frequently to the US to receive medical services. Respondents were questioned about all places of residence and all sites of HIV treatment in the past 12 months. Movement was defined as being anywhere outside of the SHR for 2 weeks or longer. 7% of the sample had moved at least once in the past year; 4% had moved outside the SHR but within Puerto Rico, while 3% had been in the continental US. Compared to the heterosexual risk group, intravenous drug users and men who have sex with men were 7-8 times more likely to have moved. The attainment of at least a high school education was also significantly and independently associated with increased probability of movement. Medical care was not identified by any of these respondents as the primary reason for travel. 58% indicated they were in their current place of residence to be near family, friends, and relatives. Both the small sample size and the low socioeconomic status of respondents may have limited the ability of this study to identify the so-called "air bridge," however.     

Assessing the effectiveness of a multimedia-based lab for upper division psychology students

The efficacy of multimedia-based training in producing increased learning was evaluated. Two multimedia software packages were compared with live or videotaped lectures on the same material. Results differed by type of student (low or high initial knowledge) and type of program. Multimedia training programs may need to provide more aid to students with less initial knowledge in the training domain. In addition, the effects of multimedia may be subtle and therefore require rigorous evaluation.