The effects of EEG data transformations on the solution accuracy of principal component analysis.

Principal component analysis (PCA) is a commonly used multivariate procedure that reduces the dimensionality of a data set. When applied to quantitative electroencephalogram (qEEG) data, PCA produces components that may represent functional systems within the brain. Unfortunately, qEEG, like many other physiological measures, produce distributions that are positively skewed. In response, researchers often transform qEEG data prior to conducting a PCA, which does not require univariate or multivariate normality. Despite this, researchers continue to transform qEEG data with limited knowledge of how such transformations will affect the accuracy (precision) of their component solutions. The purpose of the present investigation was to examine the effects of several commonly used data transformation procedures on PCA solution accuracy.

Cyclic variations in sustained human performance.

Biological rhythms play a prominent role in the modulation of human physiology and behavior. [Smith, K., Valentino, D., & Arruda, J. (2003). Rhythmic oscillations in the performance of a sustained attention task. Journal of Clinical and Experimental Neuropsychology, 25, 561-570] suggested that sustained human performance may systematically fluctuate in a cyclic manner with periods of 1.5 min and 5.2 min. The current series of investigations sought to manipulate those periodicities by altering task difficulty, administering caffeine, and testing on a more ecologically valid task. Strong evidence of a 1.5 min periodicity was found across studies. Most participants did not demonstrate the 5.2 min periodicity. Moreover, the 1.5 min periodicity was resistant to task manipulations and appeared in similar levels across conditions in all three experiments. These rhythms may be indicative of an endogenous system that modulates sustained attention in humans. Evidence supporting this idea and implications of the research are discussed.

Language-dependent access to autobiographical memory in Japanese-English bilinguals and US monolinguals.

Japanese bilinguals retrieved autobiographical memories in response to 20 English and 20 Japanese cue words. US monolinguals were cued with 40 English words. All participants reported one earliest memory. Japanese bilinguals retrieved more memories and earlier memories when cued with Japanese words. They also retrieved more memories when the cue language matched either the language of memory encoding or the language of first thought. Although English cues elicited equivalent numbers of English and Japanese memories in the more fluent speakers of English, Japanese words elicited significantly larger numbers of Japanese memories in all Japanese-English bilinguals. The average age of cued autobiographical memories was significantly earlier for US than for Japanese students but age of the earliest memory did not differ.

The cognitive failures questionnaire revisited: dimensions and correlates.

The authors reexamined the factor structure of the Cognitive Failures Questionnaire (D. E. Broadbent, P. F. Cooper, P. Fitzgerald, & K. R. Parkes, 1982) and its correlates. The Cognitive Failures Questionnaire was designed to assess a person's likelihood of committing an error in the completion of an everyday task. A principal components factor analysis with varimax rotation yielded 4 internally consistent, interpretable factors. These factors were labeled Memory, Distractibility, Blunders, and (memory for) Names. This study lends partial support for the factor analytic solution proposed by L. K. Pollina, A. L. Greene, R. H. Tunick, and J. M. Puckett (1992). In addition, it extends previous findings by providing initial evidence for the construct validity of the factors established by correlating factor scores with measures of other related constructs (i.e., boredom proneness, attention deficit/hyperactivity disorder, Type A behavior pattern).