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The acquired immunodeficiency syndrome (AIDS) pandemic has highlighted the need for safeguards against the inadvertent transmission of Infectious disease in the psychophysiology laboratory. These Guidelines identify factors contributing to the risk of bloodborne disease transmission to subjects or technicians, and recommend procedures to minimize such risk, given current knowledge and techniques. The lowest risk is associated with the application of devices, such as surface electrodes, to non-abraded, intact skin. Such devices should be clean, but do not require disinfection. The potential risk of infection is higher when surface electrodes are applied to non-intact skin. Abrasion, or other breaks in the skin, can allow seepage of blood products carrying such pathogens as hepatitis B virus and the human Immunodeficiency virus that causes AIDS. Thus electrodes require high-level disinfection before reuse on non-intact skin. In addition, technicians should wear gloves during skin preparation and should abrade the skin no more than necessary, using only sterile, preferably non-sharp materials. The highest risk Is that associated with items that enter sterile tissue, such as subdermal electrodes and the needles and lancets sometimes used in skin preparation. Such Items must be sterile at the time of use and must be handled with extreme caution. [ABSTRACT FROM AUTHOR]

The effects of stimulus quality on the amplitude, peak latency, onset latency, and duration of the P300 component of the event-related brain potential were studied in patients with either left or a right anterior temporal lobectomy and in normal controls. Stimulus quality was reduced by adding "noise" letters to words which signaled either a left or a right hand button press. Consistent with an interpretation that stimulus quality affects the subject's degree of equivocation, P300 peak latency, reaction time, and errors were all inversely related to stimulus quality, whereas P300 amplitude was directly related to stimulus quality. There were no significant differences between normal controls and either patient group for any of the Event Related Potential parameters or reaction time. Right temporal lobectomy patients made, however, significantly more errors, particularly on the catch trials, which suggest that they did not process the stimuli as thoroughly and accurately as the subjects in the other two groups. The absence of significant group differences In either the lateral symmetry or overall P300 amplitude extends the evidence against the idea that anterior temporal lobe structures make any substantial contribution to the scalp P300 in a visual discrimination paradigm. Because of observed delays in the onset of P300 in the low-quality stimulus condition, procedures were developed to quantify both P300 onset latency and P300 duration. Reduced stimulus quality significantly increased P300 onset latency whereas P300 duration remained unaffected. indicating that stimulus categorization must occur prior to, and not during, P300. [ABSTRACT FROM AUTHOR]

Rösier and Heil (1991) were unable to replicate one of the results of our previous study of slow wave activity and mental arithmetic (Ruchkin, Johnson, Mahaffey, & Sutton, 1988). Thorough examination of the error rates indicates that the greater complexity of their response selection procedure caused crucial differences between how the task was performed in the two studies. Thus Rosler and Heil study emphasizes the need to avoid using a response that is so complex that it produces a superfluous task that obscures the results. [ABSTRACT FROM AUTHOR]

This experiment investigated how the P3a, P3b, and Slow Wave components of the event-related brain potential (ERP) respond to manipulations of the nature, timing, and extent of information delivery. There were two experiments in which the total amount of task information was distributed between pairs of successive stimuli (S[Sub1] and S[Sub2]) within each trial. The task was to predict the relation between S[Sub1] and S[Sub1]. In Experiment 1, the S[Sub1] could resolve no, partial, or all uncertainty with respect to the prediction outcome (correct or incorrect). Each S[Sub1] delivered three types of information: 1) outcome information-which resolved the subjects' uncertainty about the correctness of their prediction; 2) procedural information-which resolved uncertainty about how much outcome information would be delivered by S[Sub1]; and 3) memory information-the identity of S[Sub1], which had to be stored for subsequent comparison with S[Sub2]. In Experiment 2, the activity of these components was contrasted in two conditions in which the S[Sub1] delivered either memory information alone or both memory and procedural information. P3a and Slow Wave were sensitive only to outcome information. P3b was sensitive to all three types of information, and its scalp topography varied as a function of the type of information. The topographic variations indicate that P3b is not a unitary phenomenon but rather is a composite of activity arising from multiple intracranial sources of bioelectric activity. [ABSTRACT FROM AUTHOR]

The P300 component of the event-related brain potential (ERP) was studied in epileptic patients with unilateral resections of medial temporal lobe areas of the brain. The patients and controls were tested in an oddball paradigm in two conditions: counting and reaction time. Both auditory and visual stimuli were used to elicit ERP activity in different blocks. Despite the reported presence of locally-generated auditory and visual P300-1ike potentials in these areas, no evidence was found of any surgically-related hemispheric asymmetries in the scalp distribution of the P300 or Slow Wave for stimuli in either modality. Moreover, compared to normal controls, there were no significant reductions in overall P300 amplitude in the patients. The patients did show a double dissociation in their frontal ERP activity: the left temporal lobectomy patients showed apparent decreased frontal auditory P300 amplitudes but normal visual P300 amplitudes, whereas the right temporal lobectomy patients showed the opposite pattern. These results appeared to be due to the presence of a longduration slow wave rather than to alterations in P300 amplitude. These data do not support the presence of a significant contribution by u hippocampal/amygdala generator to the activity of the scalp-recorded P300 in the oddball paradigm. Topographic comparisons on normalized amplitudes revealed significantly different scalp distributions as a function of stimulus modality, event probability, and task for both the P300 and Slow Wave components. These data indicate that the amplitude variations associated with each experimental variable are due to the activity of a separate underlying neural source. The sources of task and probability effects on P300 and Slow Wave amplitude each appeared to be modality-independent generators. The nature of the third, modality-related generator is less clear. [ABSTRACT FROM AUTHOR]

The behavior of the early and late components of the event-related brain potential (ERP) elicited by auditory and visual stimuli was studied in 40 normal females between the ages of 7 and 20. The ERPs were collected using two different tasks (i.e., count and reaction time) in an oddball paradigm. Analysis of the early component (i.e., N1, P2, N2) latencies revealed small hut significant decreases with age in the visual modality hut no change in the auditory modality. Except for the visual N1, early component amplitudes did not change significantly over this age range. The results showed that auditory and visual P300 latencies, but not amplitude, changed at significantly different rates over this age range. P300 latencies in the auditory modality showed a relatively abrupt change around age 12, after which P300 latencies changed little and were essentially at their adult levels. The latencies of visual P300s showed a much smaller and more steady decrease with age. Thus visual P300 latencies were shorter than auditory P300s in young children but longer than auditory P300s in older children. Significantly different scalp distributions were found for auditory and visual P300s. Although all P300 activity was maximal over parietal scalp, visual P300s were significantly larger than auditory P300s over central and frontal scalp. The developmental differences, combined with the presence of significantly different scalp topographies for auditory and visual P300s, provide convergent evidence that P300 activity is not independent of the modality of the eliciting stimulus. [ABSTRACT FROM AUTHOR]

This study is concerned with slowly varying, long-duration brain event-related potential (ERP) components, referred to as Slow Wave activity. Slow Wave activity can be observed in the epoch following P3b, suggesting that it reflects further processing invoked by increased task demands, beyond the processing that underlies P3b. The present experiment was designed to distinguish Slow Wave activity related to specific types of task demands which arise during difficult perceptual (pattern recognition) and conceptual (arithmetic) mental operations. Three late ERP components that respond differentially in amplitude to manipulation of perceptual and conceptual difficulty were identified: 1) A P3b, with a topography focused about P[sub z], evidently related to the subjective categorization of easy and difficult conceptual operations, that increased when the subjective low-probability operation was performed; 2) A longer latency, centro-parietal positive Slow Wave that increased directly with perceptual difficulty but was not affected by conceptual difficulty; 3) A very long latency negative Slow Wave, broadly distributed over centro- posterior scalp, that increased directly with conceptual difficulty while its onset was delayed when perceptual difficulty increased. [ABSTRACT FROM AUTHOR]

A model of P300 amplitude is proposed that reduces the many hypothetical constructs invoked to explain variations in P300 amplitude to three dimensions: 1) Subjective Probability, 2) Stimulus Meaning, and 3) Information Transmission. Evidence is presented to support the assertion that variables on the subjective probability and stimulus meaning dimensions have independent and additive contributions to overall P300 amplitude. The amplitude contributions of both of these dimensions, however, are modulated by a multiplicative relation with the proportion of transmitted stimulus information. Within each dimension, the fundamental experimental variables and their interrelations are specified. An example is presented to show how, by using an additive factors method, the respective amplitude effects of the probability and stimulus meaning dimensions can be separated. Supporting data are presented to show that the proposed model provides a reasonable and testable framework in which to conceptualize P300 results. [ABSTRACT FROM AUTHOR]

Event related brain potentials (ERPs) were recorded from subjects who were instructed to count one of three, equally probable tones presented in a random sequence. In another condition, the subjects had to count one of two stimuli, one of which was presented with a probability of.33. The data support the view that the pattern of variation of P300 amplitude with the sequential structure of the series depends on the category to which events are assigned, rather than on the individual stimuli eliciting the P300. Furthermore, the data support the idea that the amplitude of P300 elicited by task-relevant stimuli is determined by the subjective probability associated with the eliciting event. [ABSTRACT FROM AUTHOR]

Some event-related brain potential (ERP) studies of working memory have used delayed match-to-sample designs in which a stimulus (S1) is held in memory for comparison with a subsequent stimulus (S2). During the SI-S2 interval, ERP slow negativities varied with both the type and amount of material held in working memory. One interpretation is that these slow waves index working memory operations. An alternative explanation is that they only reflect general preparatory processing for the response to S2. To decide between these explanations, we used two visual processing tasks that required similar preparation for S2. In one task, visual memory rehearsal operations were required. During the S1-S2 interval, there were clear differences between the amplitudes, topographies, and the effect of information load on the slow waves in the two tasks, thus ruling out preparation only as an explanation. [ABSTRACT FROM AUTHOR]

Event-related potentials (ERPs) recorded from the human scalp can provide important information about how the human brain normally processes information and about how this processing may go awry in neurological or psychiatric disorders. Scientists using or studying ERPs must strive to overcome the many technical problems that can occur in the recording and analysis of these potentials. The methods and the results of these ERP studies must be published in a way that allows other scientists to understand exactly what was done so that they can, if necessary, replicate the experiments. The data must then be analyzed and presented in a way that allows different studies to be compared readily. This paper presents guidelines for recording ERPs and criteria for publishing the results.

A. R. Haig, E. Gordon, and S. Hook (1997) disputed G. McCarthy and C. C. Wood's (1985) contention that scaling should be used when assessing the statistical significance of between condition (or group) differences in the shapes of event-related potential (ERP) scalp topographies. Haig et al. based their contention upon the lack of empirical realism in McCarthy and Wood's model of within-group ERP noise, claiming that McCarthy and Wood's results could not be generalized to realistic ERP data. We argue, on both empirical and theoretical grounds, that Haig et al. do not make a compelling case against generalization of McCarthy and Wood's results. Moreover, Haig et al.'s conclusion is based upon a misconception of how scaling should be used. We conclude that when a quantitative measure of differences between topographic shapes is needed, scaling is not an option--it is a requirement.

The triarchic model of P300 amplitude (Johnson, 1986, 1988a) postulated that the overall amplitude of the P300 recorded at any given electrode site represented the summation of activity from different neural generators, each related to the processing of a different type of information. However, neither of these original accounts provided an explicit description of the methods required to establish experimentally the presence of multiple neural sources. This paper reviews the triarchic amplitude model, the subsequently obtained data that support the postulated presence of multiple generators underlying the P300, and the methods used to demonstrate the presence of these multiple sources. These methods are straightforward because it is only necessary to show that the portions of P300 amplitude associated with different experimental variables have different scalp distributions. The implications of the multiple-generator basis of P300 on such factors as component definition, neural source analyses, and the cognitive processes underlying its activity are discussed.