Information entropy analysis of discrete aiming movements

Information entropy and mutual information were investigated in discrete movement aiming tasks over a wide range of spatial (20-160 mm) and temporal (250-1250 ms) constraints. Information entropy was calculated using two distinct analyses: (1) with no assumption on the nature of the data distribution; and (2) assuming the data have a normal distribution. The two analyses showed different results in the estimate of entropy that also changed as a function of task goals, indicating that the movement trajectory data were not from a normal distribution. It was also found that the information entropy of the discrete aiming movements was lower than the task defined indices of difficulty (ID) that were selected for the congruence with Fitts' law. Mutual information between time points of the trajectory was strongly influenced by the average movement velocity and the acceleration/deceleration segments of the movement. The entropy analysis revealed structure to the variability of the movement trajectory and outcome that has been masked by the traditional distributional analyses of discrete aiming movements.     

Sociodemographic factors,religiosity, academic performance,and substance use among first-year university students in South Africa

The purpose of this study was to identify the relationships among sociodemographic variables, family background, religiosity, course of study, academic performance, and substance use. The sample included 799 first-year students in the age range of 16 to 49 years (M age 20.1 yr., SD = 3.2) chosen at random from the University of the North in South Africa. A Model Core Questionnaire from the WHO on Substance use was administered. Analysis indicated that women smoked tobacco or cannabis and drank less than men, while women took more stimulants and other opiate type drugs than men. Low scores on religiosity was a predictor for past-month tobacco use alcohol use, binge drinking, cannabis use, and having a drinking or drug problem now. Being a member of a Protestant denominational church or a Roman Catholic was a predictor for past-month tobacco and alcohol use. A family history of drinking or drug problems and being a social science or humanities student were predictive for a current alcohol or drug problem. Economic status, education of parents. living arrangement. and rural-urban differences were not associated with substance use. Findings have implications for prevention programmes.     

Transsaccadic perception of saccade target and flanker objects

To account for location-dependent and location-independent preview benefits in transsaccadic object perception, J. M. Henderson (1994) and J. M. Henderson and M. D. Anes (1994) proposed a dual-route model in which both episodic object representations and long-term memory representations store information across a saccade. Four experiments are reported in which the dual-route model was assessed. Preview benefits for saccade target objects were found to be location independent, whereas preview benefits for flanker objects were location dependent. These results support a single-route, 2-stage model of transsaccadic object perception. First, preattentive object files are set up to parse a set of attentional and/or saccade targets from peripheral vision, causing location-dependent preview benefits. Second, 1 object is attentionally selected for further processing, activating long-term memory representations and resulting in location-independent preview benefits.     

The duration component of the stress effect in stuttering

The purpose of the present study was to investigate whether there is a relationship between stuttering on stressed syllables and the duration of these syllables. Sixteen adults who stutter read a text consisting of 226 syllables. The relative stress of each syllable was rated, and syllables were categorized into long- and short-stressed syllables, unstressed syllables and intermediate syllables lying in-between. In order to isolate effects caused by within-word position from those caused by linguistic stress, syllables in initial and in subsequent positions were analyzed separately. In both word position categories stressed syllables were stuttered more often than unstressed syllables. Stuttering frequency of intermediate syllables seems to be in-between stressed and unstressed syllables, just as their stress level is rated in-between. Results regarding the duration of stressed syllables do not allow final conclusions.

Educational objectives: The reader will learn about and be able to describe (1) language factors related with stuttering events, (2) the stress effect in adults who stutter, and (3) methods to control for its confounding variables.     

The contributions of color to recognition memory for natural scenes

The authors used a recognition memory paradigm to assess the influence of color information on visual memory for images of natural scenes. Subjects performed 5%-10% better for colored than for black-and-white images independent of exposure duration. Experiment 2 indicated little influence of contrast once the images were suprathreshold, and Experiment 3 revealed that performance worsened when images were presented in color and tested in black and white, or vice versa, leading to the conclusion that the surface property color is part of the memory representation. Experiments 4 and 5 exclude the possibility that the superior recognition memory for colored images results solely from attentional factors or saliency. Finally, the recognition memory advantage disappears for falsely colored images of natural scenes: The improvement in recognition memory depends on the color congruence of presented images with learned knowledge about the color gamut found within natural scenes. The results can be accounted for within a multiple memory systems framework.     

Missing data: our view of the state of the art

Statistical procedures for missing data have vastly improved, yet misconception and unsound practice still abound. The authors frame the missing-data problem, review methods, offer advice, and raise issues that remain unresolved. They clear up common misunderstandings regarding the missing at random (MAR) concept. They summarize the evidence against older procedures and, with few exceptions, discourage their use. They present, in both technical and practical language, 2 general approaches that come highly recommended: maximum likelihood (ML) and Bayesian multiple imputation (MI). Newer developments are discussed, including some for dealing with missing data that are not MAR. Although not yet in the mainstream, these procedures may eventually extend the ML and MI methods that currently represent the state of the art.