Secorbarbital and perceptual processing

Biological determinants of P300: the effects of a barbiturate on latency and amplitude

Polich & Kok (1995) (Biological Psychology, 41, 103-146) have recently argued that P300 is not only sensitive to specific 'cognitive' variables, but also to non-specific biological processes such as arousal. Fluctuations in arousal are said to be indexed by an inverse relationship between latency and amplitude. We tested this hypothesis with a drug that decreases arousal-the barbiturate secobarbital sodium. Twelve subjects performed a visual 80-20% oddball task at two levels of stimulus quality and after ingesting the drug (2.9 mg/kg body weight) or a placebo. Reaction time (RT) and P300 were collected simultaneously and the latter was analyzed on both a single trial and average basis. The RT results confirmed that secobarbital interacts with stimulus quality. Secobarbital slowed single trial P300 by about half as much as RT, and this slowing was additive with stimulus quality. Thus the two measures dissociated. Secobarbital did not influence P300 amplitude. Average P300 revealed the same pattern of results, although the size of the latency effects was somewhat attenuated. RT and P300 latency were more strongly correlated than P300 latency and amplitude. We propose that P300 latency reflected the slowing of stimulus evaluation produced by the depressant properties of the drug, and that fluctuations in arousal are not necessarily associated with a simple inverse relationship between P300 latency and amplitude.

Performance tests

This paper discusses the use of psychological performance tests to assess the effects of environmental stressors. The large number and the variety of performance tests are illustrated, and the differences between performance tests and other psychological tests are described in terms of their design, construction, use, and purpose. The stressor emphasis is on the effects of drugs since that is where most performance tests have found their main application, although other stressors, e.g., fatigue, toxic chemicals, are mentioned where appropriate. Diazepam is used as an example. There is no particular performance emphasis since the tests are intended to have wide applicability. However, vehicle-driving performance is discussed because it has been the subject of a great deal of research and is probably one of the most important areas of application. Performance tests are discussed in terms of the four main underlying models--factor analysis, general information processing, multiple resource and strategy models, and processing-stage models--and in terms of their psychometric properties--sensitivity, reliability, and content, criterion, construct, and face validity. Some test taxonomies are presented. Standardization is also discussed with reference to the reaction time, mathematical processing, memory search, spatial processing, unstable tracking, verbal processing, and dual task tests used in the AGARD STRES battery. Some comments on measurement strengths and appropriate study designs and methods are included.

Drugs and information processing in skilled performance

A concise review is presented of recent research on task aspects with respect to determining the effects of drugs on human information processing. It is concluded that progress in this area is hampered by lack of a theoretical basis to most behavioral tasks, preventing firm conclusions about the effects of drugs on either well-defined mental functions or on real-life performances. It is argued that the effects of drugs should only be tested in behaviorally well-researched tasks. Some proposals are discussed with an emphasis on perceptual-motor skills.

Dose effects of methaqualone on stimulus encoding in a memory scanning task

Three task variables, stimulus quality, memory set size and response type, were used in a Sternberg binary classification task to define stimulus encoding, short-term memory scanning, and response selection stages within a serial stage reaction process. Mean reaction times, and the slopes and intercepts of the function relating reaction time to memory set size, were used to test the hypothesis that performance deficits seen at two doses of methaqualone (2.9 mg/kg and 5.9 mg/kg), in the range formerly in common clinical use, were specific to the stimulus encoding stage of the reaction process. Mean reaction times were increased significantly by the methaqualone at both doses, but the effects of the two doses did not differ from one another. The intercept of reaction time as a function of set size showed significant main effects of methaqualone, stimulus quality, and response type, and a significant hyper-additive interaction of methaqualone with stimulus quality. At 2.9 mg/kg, the intercept was increased by methaqualone but only with degraded stimuli. At 5.9 mg/kg, the intercept was increased by methaqualone for both high and low quality stimuli. These results suggested a dose-dependent selective effect of methaqualone on the stimulus encoding stage of the reaction process.