Daniel S. Ruchkin

Guidelines for using human event-related potentials to study cognition: recording standards and publication criteria.

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.

Working memory retention systems: A state of activated long-term memory

High temporal resolution event-related brain potential and electroencephalographic coherence studies of the neural substrate of short-term storage in working memory indicate that the sustained coactivation of both prefrontal cortex and the posterior cortical systems that participate in the initial perception and comprehension of the retained information are involved in its storage. These studies further show that short-term storage mechanisms involve an increase in neural synchrony between prefrontal cortex and posterior cortex and the enhanced activation of long-term memory representations of material held in short-term memory. This activation begins during the encoding/comprehension phase and evidently is prolonged into the retention phase by attentional drive from prefrontal cortex control systems. A parsimonious interpretation of these findings is that the long-term memory systems associated with the posterior cortical processors provide the necessary representational basis for working memory, with the property of short-term memory decay being primarily due to the posterior system. In this view, there is no reason to posit specialized neural systems whose functions are limited to those of short-term storage buffers. Prefrontal cortex provides the attentional pointer system for maintaining activation in the appropriate posterior processing systems. Short-term memory capacity and phenomena such as displacement of information in short-term memory are determined by limitations on the number of pointers that can be sustained by the prefrontal control systems.

The Late Positive Complex

In summary, what we have tried to do in this paper is to present our view of the ways in which the ERP field has become more complex in recent years. It is not an overstatement to say that, in a certain sense, we know less now than we thought we knew five to ten years ago. New advances have brought with them new problems. But they also point, though not yet with complete clarity, to directions for new solutions. Possibly, as we make further progress toward the definition of various generators for different components, our problems may be simplified. But even this prediction cannot be made with certainty. It should be noted that we have tended in this chapter to emphasize the problems. There has also been a positive side to the recent developments. Because we are more aware of the overlap problem, we now work with methods that attempt to deal with it. We now know, for example, that P3b and SW can relate quite differently to behavioral variables. Decision time, which we had thought occurred at P3 latency, can now be assumed on the basis of recent findings to occur earlier, at the N2 component. The separation of the formerly unitary CNV into several components makes it more possible to develop unique functional roles for each of the components. A similar development has occurred with the separation of the poststimulus negativities into several components. Our constructs for various components are still on the fuzzy side, but the field has better tools at its disposal for making them more precise. Finally, the multiplicity of components, which appears overwhelming initially, provides us with more degrees of freedom in attempting to relate electrophysiological activity to behavior. A number of investigators have commented that the complexity of factors that enter into behavior could not be reflected in the relatively few ERP components we were dealing with. Now that more components are coming to be distinguished, the likelihood increases that we may be able to obtain ERP correlates of more of the dimensions involved in behavior.

Distinctions and similarities among working memory processes: an event-related potential study.

Working memory has been conceptualized as consisting of a number of components, such as an articulatory loop for rehearsing verbal material, a visuo-spatial sketch pad for maintaining visual images and a central executive that controls which information is made available for conscious processing. We recorded event-related brain potentials (ERPs) from normal human subjects while they maintained either visuo-spatial or phonological material in short-term memory for a 5-s interval. The results indicated that specialized brain systems for short-term storage of phonological and visuo-spatial information could be identified on the basis of marked differences between the topographies and morphologies of the ERP components elicited during these two types of short-term memory. The differences emerged during early encoding stages and continued through later retention stages.

Short-term memory storage and retention: an event-related brain potential study.

This experiment was concerned with event-related brain potential (ERP) activity related to short-term storage and retention of information in working memory. Our approach was to record the ERPs elicited by a stimulus that had to be memorized while varying the number of items (1, 3 or 6) in the task stimulus. In order to distinguish between ERP effects associated with perceptual complexity and retention of information, there was a second condition in which subjects were required to search the task stimulus for a match with a previously presented item. Thus, in the search condition subjects only had to remember one item (match or mismatch). ERP activity was recorded for 2450 msec after task stimulus offset. Two long-duration components varied as a function of task and memory load: a posterior positive wave and a frontal negative wave. Posterior positive wave amplitude was directly related to information load in the memory task but was negligible in the search task. Following the posterior positive wave was a frontal negative wave which occurred at the highest load level in the memory task but was totally absent in the search task. A P3b was elicited in both tasks. P3b was sensitive to information acquisition processes, but it did not distinguish between memory retention and visual search processes. While P3b amplitude did not vary with task or load, its latency increased with load in both tasks.

Slow wave and P300 in signal detection

Abstract CNV, P300 and slow wave amplitude correlates of auditory detection accuracy were studied for both hits and correct rejections. Baseline-to-peak measures gave no indication of the downturn of P300 at very high detection accuracies reported by Hillyard et al. (1971). Principal Components-Varimax Analyses (PCVA) of the event-related potentials (ERPs) were performed. The PCVA basis wave forms for P300 and slow wave showed that baseline-to-peak measures of P300 represent a composite of the two. The weighting coefficients for P300 and slow wave showed an opposite pattern in relationship to accuracy: P300 weighting coefficients increased monotonically with increased accuracy, whereas slow wave weighting coefficients decreased monotonically with increased accuracy. For both P300 and slow wave, findings were similar for both hits and correct rejections. These and earlier findings (Roth et al., 1978; Ruchkin et al. 1980) suggest that overlap between P300 and slow wave should be examined in future P300 experiments. No differences were found in relation to experimental conditions for the CNV in the baseline-to-peak measures or in the PCVA measures. The PCVA showed that there was significant CNV activity in the post-stimulus epoch and therefore the CNV represents another source of overlap with P300 and slow wave when peak-to-baseline measures are used. P300 and slow wave PCVA components have little activity in the pre-stimulus epoch indicating that they are determined by post-stimulus events. The increase of slow wave amplitude with decreasing accuracy is interpreted as reflecting the need for further processing when intensity is so low as to make a decision difficult. This ‘further processing’ interpretation is consistent with other studies in which slow wave has been shown to vary with task demands

Cognition and Event‐Related Potentials II. The Orienting Reflex and P300

This panel was expected to review the literature pertaining to the effects of novelty and surprise on E R P components, particularly the P300, and the literature on the orienting reflex (OR). This paper records the correspondence between members of the panel before the conference. I t consists of an edited version of the material that was circulated to the conference participants before the meeting. No major reconciliation of views resulted from the conference discussion, nor could one be expected, given the rather different perspectives adopted by the panelists. The issues presented raise questions that need to be considered by psychophysiologists. This paper, therefore,

Multiple visuospatial working memory buffers: Evidence from spatiotemporal patterns of brain activity

Numerous studies have shown that the visual system involves different cortical pathways in the perception of object (ventral visual pathway) and spatial (dorsal visual pathway) information. The present study was concerned with whether human visuospatial working memory divides along similar lines. We used event-related brain potentials (ERPs) recorded from scalp of normal humans to show the existence of different buffering systems for the retention of object and spatial visual information. Subjects were presented with object or spatial stimuli to be retained for a 3.6-sec interval. The ERPs isolated brain activity associated with retention from earlier storage and later retrieval processes. The ERP scalp topographies indicated that the underlying patterns of brain activation were different during retention of object and spatial information.

A Review of Event‐Related Potential Components Discovered in the Context of Studying P3a

In a seminal paper published in 1965, Sutton, Braren, Zubin and John first reported the P3 component recorded from the scalp of human subjects. The method used was to have subjects guess prior to each trial whether a randomly presented tone or flash of light would occur, and to have the subject discover whether the guess was correct or not when the stimulus for that trial was delivered. In another condition, the same stimulus was presented on all trials and the subject so informed. The result was that P3, a positive going wave with a peak latency of about 300 msec, was elicited when the subject was uncertain as to which stimulus would occur. Since the stimuli provided the subject with information concerning the correctness of the guess, Sutton et al. suggested that P3 was associated with information delivery. In a second study, Sutton, Tueting, Zubin and John (1967) presented one or two clicks, separated by 580 msec, on a random trial-by-trial basis. In addition, the clicks of a given trial were randomly loud or soft. In one condition, the subject guessed prior to each trial whether one or two clicks would be delivered. In another condition, the subject guessed whether the clicks would be loud or soft. Thus, in the first condition, the point in time when the subject learned the correctness of the guess was when the second click was, or was not, presented. It was found that the P3 was elicited by the second click and its absence. When guessing loudness, however, the subject learned the correctness of the guess when the first click was presented (the second click, if present, always had the same intensity as the first). In this condition, the presence or absence of the second click was not associated with P3. Hence, P3 was elicited by a stimulus (or the absence of a stimulus) that delivered relevant information.

Emitted P potentials and temporal unvertainty

Abstract Characteristics of emitted P 300 potentials, which may be elicited by the non-occurrence of a stimulus at a particular point in time, were investigated. An experiment was conducted in which the subject made a prediction prior to each trial whether or not the stimulus would occur. The time of occurrence or non-occurrence of the stimulus, either 700 msec or 1500 msec after a warning stimulus, was varied from block to block. Prior to each prediction block, data were obtained on the subjects time estimation for that interval. Using Woodys procedure, latency corrected averages were computed. As previously found, for all subjects the amplitudes of the latency compensated average emitted P 300 s were lower than the latency compensated average evoked P 300 s. In general, the decrement from evoked to emitted P 300 was greater for the 1500 msec interval than for the 700 msec interval. The greater decrement in evoked to emitted P 300 amplitude at 1500 msec is attributed to the increased temporal uncertainty associated with the apprehension of stimulus non-occurrence at the longer interval, as evidenced by the greater variability of the time estimates at 1500 msec. A trial-by-trial analysis of the latencies of the emitted and evoked P 300 s supported previous findings of greater latency variability for emitted P 300 s than for evoked P 300 s. Variability of both emitted P 300 latencies and time estimates was greater for the 1500 msec interval than for the 700 msec interval. In general subjects whose time judgment variability increased most for the longer interval were also the subjects whose emitted P 300 latency variability increased most.