A program for fitting two-phase segmented-curve models with an unknown change point,with an application to the analysis of strategy shifts in a cognitive task

A program is described for fitting a regression model in which the relationship between the dependent and the independent variables is described by two regression equations, one for each of two mutually exclusive ranges of the independent variable. The point at which the change from one equation to the other occurs is often unknown, and thus must be estimated. In cognitive psychology, such models are relevant for studying the phenomenon of strategy shifts. The program uses a (weighted) least squares algorithm to estimate the regression parameters and the change point. The algorithm always finds the global minimum of the error sum of squares. The model is applied to data from a mental-rotation experiment. The program’s estimates of the point at which the strategy shift occurs are compared with estimates obtained from a nonlinear least squares minimization procedure in SPSSX.     

The effects of chronic sleep reduction on the performance of cognitive tasks sensitive to sleep deprivation

In four sleep loss experiments we aimed, first, to compare performance during long-term sleep reduction with performance during short-term total sleep deprivation, and second, to measure the effects of both methods of sleep loss on ability to ignore distracting irrelevant stimuli, using a finding embedded figures test (FEFT). Logical reasoning, auditory vigilance and finding embedded figures tasks were shown to be significantly sensitive to one night's sleep deprivation. However, in one sleep reduction study subjects reduced to a mean of 5.2 hours sleep per night for 4 weeks showed no performance deficits on logical reasoning. In a second sleep reduction study subjects reduced to a mean of 4.3 hours sleep per night for 4 nights, and subjects reduced to a mean of 5.3 hours sleep per night for 18 nights, showed no performance deficits on logical reasoning or auditory vigilance, despite their reports of severe increases in subjective sleepiness and reduced concentration. Both these sleep reduction groups, though, did show decrements on the FEFT, which we interpret in terms of dearousal increasing distractibility, which the sleep-reduced subjects could not overcome with effort, as they did with the other tests.     

Treating the Doll's House Marriage

The Doll's House, a common pitfall for family therapists, is an extremely unequal relationship in which one spouse's incompetence is required or encouraged by the other. This pattern of marriage is common in a sick population and is chosen by people with clear individual pathology. It may be stable and satisfying, but it is crisis prone. Doll's Houses are likely to be disrupted by the arrival of children, financial reverses, and, most important, the intrusion of another person upon whom the Doll is dependent and who sets out to equalize the marital relationship. A well-intentioned therapist with an intolerance for pathology can destroy the marriage. Therapy seems more successful when the therapist respects the basically unequal framework the couple has chosen and works toward greater understanding and respect for unique individual needs within that framework.     

The experimental determination of unique green in the spectrum

The notion is gaining currency that observers who are distributed normally with respect to commonly measured indices of color vision, may be bimodally distributed with respect to the spectral locus of unique green. Experimental conditions which can produce such deviations from a normal distribution are explored, and it is concluded that the “bimodality” results reported in the literature may reflect differential chromatic adaptation effects. Experimental conditions which guarantee a neutral state of adaptation yield spectral unique green loci that show no evidence of bimodality.     

The variance of the number of mutual choices in sociometry

The variance of the number of mutual dyads in a sociometric situation where each member of a group chooses independently and at random is derived for unrestricted numbers of choices per group member, as well as for a fixed number of choices. The distribution of the number of mutuals is considered.We are indebted to Robert Bush and Hartley Rodgers of Harvard University for helpful criticisms.     

Gender-related sexual attitudes: Some crosscultural similarities and differences

We tested the hypothesis that males differentiate love and sex more strongly than females, and that the magnitude of this gender difference is augmented in homosexuals and diminished in married heterosexuals. American and Swedish subjects sorted statements describing behaviors of love, sex, and services into two piles on the basis of perceived similarity. The results of all three studies were consistent with the predictions. In addition, the findings suggest that Americans differentiate love and sex more strongly than Swedes.     

Understanding the effects of sample size on the variability of the mean

In the first three experiments, we attempted to learn more about subjects' understanding of the importance of sample size by systematically changing aspects of the problems we gave to subjects. In a fourth study, understanding of the effects of sample size was tested as subjects went through a computerassisted training procedure that dealt with random sampling and the sampling distribution of the mean. Subjects used sample size information more appropriately for problems that were stated in terms of the accuracy of the sample average or the center of the sampling distribution than for problems stated in terms of the tails of the sampling distribution. Apparently, people understand that the means of larger samples are more likely to resemble the population mean but not the implications of this fact for the variability of the mean. The fourth experiment showed that although instruction about the sampling distribution of the mean led to better understanding of the effects of sample size, subjects were still unable to make correct inferences about the variability of the mean. The appreciation that people have for some aspects of the law of large numbers does not seem to result from an in-depth understanding of the relation between sample size and variability.     

CONSTRUCT VALIDITY OF TWO CATEGORIES OF ASSESSMENT CENTER DIMENSION RATINGS

The construct validity of assessment center final dimension ratings was examined within a nomological network of cognitive and personality measures. Four hundred forty-one employees of a large mid-western petroleum company were assessed on 11 dimensions in two broad categories and completed four tests. Results showed that several cognitive ability measures related more strongly to performance-style dimension ratings than to interpersonal-style dimension ratings, providing evidence for convergent and discriminant validity. Correlation analysis and factor analysis support the two a priori interpersonal- and performance-style categories. The results suggest that final dimension ratings possess construct validity and that assessors can differentiate between two broad categories of assessment dimensions.