Computing Cohen’s kappa coefficients using SPSS MATRIX

This short paper proposes a general computing strategy to compute Kappa coefficients using the SPSS MATRIX routine. The method is based on the following rationale. If the contingency table is considered as a square matrix, then the observed proportions of agreement lie in the main diagonal’s cells, and their sum equals the trace of the matrix, whereas the proportions of agreement expected by chance are the joint product of marginals. The generalization to weighted kappa, which requires an additional square matrix of disagreement weights, both matrices having the same order, becomes possible by the use of the Hadamard product-that is, the elementwise direct product of two matrices.     

Simulation of complex survival distributions

This paper describes a method for generating sample survival distributions from a hypothetical population, as would be required for running Monte Carlo simulations. The method is based on the concept of a quincunx. Cases are entered into a life table and allowed to drop out or die during each interval with probabilities that mirror the hypothetical population. By repeating this process many times and tracking the results, the researcher is able to study the sampling distribution of effect size indices and test statistics, and can generate empirical estimates of power and precision for planned studies. Unlike other methods that are commonly used for this purpose, the model proposed here allows the researcher to define a population in which the hazard rates and/or attrition rates vary substantially from one time point to the next, as may be the case in clinical trials or studies of processing times. The method requires less than 100 lines of code and runs some 10,000 simulations per hour on a microcomputer.     

Human sensitivity to temporal proximity: The role of spatial and temporal speed gradients

Estimates of temporal proximity (sometimes called time-to-collision) from random-dot flow patterns are shown to be based upon retinal speed, rather than upon changes in dot density. Neither the spatial nor the temporal gradient of motion is essential to the task, but estimates can be made from either alone. Performance is unaffected by the addition of rotational motion, suggesting that observers axe capable of extracting the radial component of motion, which contains all the relevant information, from complex stimuli.     

Object recognition contributions to figure-ground organization: Operations on outlines and subjective contours

In previous research, replicated here, we found that some object recognition processes influence figure-ground organization. We have proposed that these object recognition processes operate on edges (or contours)detected early in visual processing, rather than on regions. Consistent with this proposal, influences from object recognition on figure-ground organization were previously observed in both pictures and stereograms depicting regions of different luminance, but not in randomdot stereograms, where edges arise late in processing (Peterson & Gibson, 1993). In the present experiments, we examined whether or not two other types of contours—outlines and subjective contours—enable object recognition influences on figure-ground organization. For both types of contours we observed a pattern of effects similar to that originally obtained with luminance edges. The results of these experiments are valuable for distinguishing between alternative views of the mechanisms mediating object recognition influences on figure-ground organization. In addition, in both Experiments 1 and 2, fixated regions were seen as figure longer than nonfixated regions, suggesting that fixation location must be included among the variables relevant to figure-ground organization.     

Measuring and predicting the effects of alcohol consumption on contrast sensitivity for stationary and moving gratings

Contrast sensitivity was measured for 12 healthy young males while sober, after ingestion of an alcohol placebo, and after ingestion of alcohol (95% grain alcohol; mean estimated blood alcohol level = .088%). Observations were made for both stationary gratings and gratings that traveled through a circular path and required pursuit eye movements. The significant alcohol-related reduction in contrast sensitivity was 2.6 times greater for moving (.29-log-unit reduction) than for stationary gratings (.11-log-unit reduction). The loss in contrast sensitivity for the moving gratings of high spatial frequency (12 cpd) was particularly severe (.37 log unit). Estimated blood alcohol level was correlated with the loss in contrast sensitivity for moving gratings (r = .61), but not with the loss for stationary gratings. Estimated blood alcohol level was strongly correlated with the difference between the loss in contrast sensitivity to moving and stationary gratings (r = .75). These results are consistent with reports that alcohol consumption degrades the ability to make pursuit eye movements. Subjects’ perceived intoxication level was not a reliable predictor of any index of visual performance.     

Two-month-old infants’ sensitivity to allophonic differences

The present study investigated 2-month-olds’ abilities to discriminate allophonic differences that are potentially useful in segmenting fluent speech. Experiment 1 investigated infants’ sensitivity to the kind of distinction that may signal the presence or absence of a word boundary. When tested with the high-amplitude sucking procedure, infants discriminated pairs of items, such as “nitrate” versus “night rate” and “nikrate” versus “nike rate.” By greatly reducing the potential contribution of prosodic differences to these contrasts, Experiment 2 evaluated whether the allophonic differences for /t/ and /r/ were sufficient for infants to distinguish the “nitrate” versus “night rate” pair. Infants distinguished “nitrate” from a cross-spliced version of “night rate,” which differed only in the allophones for /t/ and /r/ that it included. Thus, infants appear to possess one of the prerequisite capacities (i.e., the ability to discriminate allophonic distinctions) necessary to use allophonic information in segmenting fluent speech.     

Captives to the double standard

Pastoral Psychology -