Computer program for quasi-random stimulus sequences with equal transition frequencies

C language routines are presented for the generation of randomized stimulus sequences constructed from multiple presentations of m stimuli satisfying sequential constraints with respect to the frequencies of the occurrence of n-gram subsequences. Applications are suggested for sequential experiments in which main effects for the present stimulus and the stimuli in the preceding (n?1)-length substring can be tested, as well as the interactions among stimuli at the various positions in the substrings.     

Fixed and optional stopping models for two-choice discrimination times

Several current models for choice- or discrimination-time experiments represent the stimulus as a sequence of independent and identically distributed observations. This paper develops and compares models based on two different stopping rules that a subject might use to terminate his sampling process and convert his perceptual evidence into an observable response. The fixed and optional stopping rules yield different predicted forms for the speed/accuracy tradeoff function and for the relation between mean and variance of response times. These predictions are developed in the general case and then specialized for certain conditions of symmetry, so that the expressions are easier to apply and to compare between models. A later section considers how changes in stopping criteria (either between or within experimental trials) affect predictions about mean response times for correct responses and errors, and then uses these ideas to relate the optional stopping rule for the Random Walk models to those of the Accumulator models. A final section considers specialized models for stimulus detection and intensity discrimination that assume Poisson-distributed sensory input, and relates these models to the present fixed stopping model.     

Reaction time to the onset and offset of electrocutaneous stimuli as a function of rise and decay time

Reaction times were obtained to the onset and offset of 70-cps electrocutaneous signals of five rise and decay times and five intensity levels. The results show that both onset and offset RTs increase linearly with increased rise and decay times. With fast rates of rise or decay, the onset produces faster RTs than the cessation of stimulation. The opposite effect is found when long rise and decay times are used. Interpretations of these results are given in terms of neural adaptation and accommodation.     

Reaction time to the onset and offset of electrocutaneous stimuli as a function of rise and decay time

Reaction times were obtained to the onset and offset of 70-cps electrocutaneous signals of five rise and decay times and five intensity levels. The results show that both onset and offset RTs increase linearly with increased rise and decay times. With fast rates of rise or decay, the onset produces faster RTs than the cessation of stimulation. The opposite effect is found when long rise and decay times are used. Interpretations of these results are given in terms of neural adaptation and accommodation.     

The impact of mental health problems and religiosity on African-American girls' HIV-risk

We investigated the relationship between religiosity, mental health problems, and two sexual risk behaviors-condom use and number of partners. Participants were 80 sexually active African American girls in psychiatric care and their caregivers. Results indicated differential relationships, depending on parent versus youth report. Mother's religiosity was positively related to girls' condom use and not to girls' number of partners. Controlling for other predictors in the models, mother's religiosity explained as much as 15% of the variance in girls' condom use. Whereas parent and adolescent reports of girls' depression/anxiety and rule-breaking were positively associated with number of partners, reports of aggression were associated with having fewer partners. Neither parent nor youth reports of girls' mental health problems were associated with condom use. Controlling for other predictors in the models, girls' mental health problems accounted for as much as 31% of the variance in number of partners. Findings underscore the importance of adopting an ecological framework to understand both the risk and promotive factors for sexual risk taking among troubled girls. The roles of specific aspects of psychopathology and religiosity in relation to sexual risk behavior among African American girls in psychiatric care are discussed.