People with absolute pitch process tones without producing a p300.

The P300 is a positive-going component of the event-related potential. In subjects with absolute, or "perfect," pitch, the P300 elicited by the less frequent of two auditory probes is small or absent. In these subjects, visual probes elicit a normal P300. These results support the view of P300 as a manifestation of the updating of working memory.

Optimizing the use of information: strategic control of activation of responses.

Recent studies indicate that subjects may respond to visual information during either an early parallel phase or a later focused phase and that the selection of the relevant phase is data driven. Using the noise-compatibility paradigm, we tested the hypothesis that this selection may also be strategic and context driven. At least part of the interference effect observed in this paradigm is due to response activation during the parallel-processing phase. We manipulated subjects' expectancies for compatible and incompatible noise in 4 experiments and effectively modulated the interference effect. The results suggest that expectancies about the relative utility of the information extracted during the parallel and focused phases determine which phase is used to activate responses.

Error-related scalp potentials elicited by hand and foot movements: evidence for an output-independent error-processing system in humans.

The error-related negativity (ERN) is a fronto-centrally distributed component of the event-related brain potential (ERP) that occurs when human subjects make errors in a variety of experimental tasks. In the present study, we recorded ERPs from 128 scalp electrodes while subjects performed a choice reaction time task using either their hands or feet. We applied the brain electric source analysis technique to compare ERNs elicited by hand and foot errors. The scalp distributions of these error potentials suggest that they share the same neural generator and, therefore, that the ERN process is output-independent. Together with other findings, the results are consistent with the hypothesis that the ERN is generated within the anterior cingulate cortex and is elicited by the activation of a generic error-processing system.

Dietary sodium and plasma volume levels with exercise.

Sodium is the major cation of the extracellular fluid and has a potent influence on fluid movement. Sodium has been likened to a sponge that draws fluids into the extracellular space, including the plasma volume, to equalize gradients in concentration. Conventional wisdom suggests limiting dietary intake of Na+ to decrease risk of hypertension. However, there are some extreme occupational or exercise-related conditions where sweat losses are great and Na+ losses may exceed normal dietary intake. This can occur acutely such as in an ultra-endurance event or chronically as in hard manual work in the hear. In such cases, additional Na+ in the form of a higher Na+ diet or adding Na+ to beverages used for fluid replacement may be warranted. A higher Na+ diet also appears to accelerate the cardiovascular and thermoregulatory adaptations that accompany heat acclimation or short term exercise training. Saline ingestion before exercise causes an expansion of plasma volume at rest and throughout the subsequent exercise bout. This expansion of plasma volume alters cardiovascular and thermoregulatory responses to exercise in ways that may lead to beneficial changes in endurance exercise performance. Plasma volume expansion also occurs with saline infusion during exercise, but exercise performance advantages have yet to be reported. The purpose of this article is to review the literature concerning dietary sodium and its influence on fluid balance, plasma volume and thermoregulation during exercise. It contains 2 major sections. First, we will discuss manipulations in daily Na+ intake initiated before or throughout an exercise regime. Second, we will examine studies where an acute Na+ load was administered immediately before or during an exercise trial. The dependent variables that we will discuss pertain to: (i) body water compartments, i.e. plasma volume; (ii) thermoregulatory variables, i.e. core temperature and sweat rate; (iii) cardiovascular variables, i.e. heart rate and stroke volume; and (iv) performance, i.e. time trial performance and time to exhaustion. Particular attention will be given to the route by which Na+ was administered, the environmental conditions, the level of acclimation of the participants and specifics relating to Na+ administration such as the osmolality of the Na(+)-containing beverage.

Strategies and mechanisms in nonselective and selective inhibitory motor control.

Motor inhibition was studied in 3 versions of the stop-signal paradigm, with the stop signal requiring inhibition of any response (stop-all), a fixed alternative response (stop-change), or selective inhibition of only 1 of the responses (selective-stop). The lateralized readiness potential was used in Experiment 1 to distinguish between a selective, central, and a global peripheral inhibition mechanism. Inhibition was found to be effected by the central mechanism in the stop-change condition and by the peripheral mechanism in the other conditions. Manipulation of stimulus discriminability in Experiment 2 strongly affected the speed of selective motor inhibition, confirming that such inhibition was achieved by conditionally engaging the peripheral mechanism. These results support the idea that functionally distinct mechanisms and strategies are involved in inhibitory motor control in different situations.

Pre- and poststimulus activation of response channels: a psychophysiological analysis.

To examine mechanisms of response activation, we asked subjects to respond differentially to the central letter of one of four arrays--HHHHH, SSHSS, SSSSS, and HHSHH--and measured event-related brain potentials (ERPs) and electromyographic activity (EMG). For very fast responses, accuracy was at chance level for all arrays, suggesting that subjects were guessing. For intermediate latency responses, accuracy was above chance if the noise was compatible with the targets and below chance if it was incompatible, suggesting that these responses were based on partial stimulus analysis. For slow responses, accuracy was above chance for all arrays, suggesting that these responses were based on complete stimulus analysis. The occurrence and accuracy of fast responses could be predicted by examining motor potentials preceding the presentation of the array. Measures of the motor potentials in the period following the presentation of the array suggested that partial analysis of stimulus information could activate responses and that the level of response activation at the time of the EMG response was constant for trials with different response latencies. The data are discussed in terms of a response channel conception.

A psychophysiological investigation of the continuous flow model of human information processing.

Twelve subjects responded to target letters "H" or "S" by squeezing dynamometers with the left or right hand. Targets could be surrounded by compatible (e.g., HHHHH) or incompatible noise (SSHSS) letters. Measures of the P300 component of the event-related brain potential and of correct and incorrect electromyographic and squeeze activity were used to study stimulus evaluation and response-related processes. When incorrect squeeze activity was present, execution of the correct response was prolonged, indicating a process of response competition. This process occurred more often under incompatible noise conditions, which were also associated with a delayed P300. Thus, the noise/compatibility manipulation influenced both stimulus evaluation and response competition processes. In contrast, a warning tone that preceded array presentation on half the trials, increased response speed without influencing evaluation time. The data suggest that the latency and accuracy of overt behavioral responses are a function of (a) a response activation process controlled by an evaluation process that accumulates evidence gradually, (b) a response priming process that is independent of stimulus evaluation, and (c) a response competition process.

On the transmission of partial information: inferences from movement-related brain potentials.

Results are reported from a new paradigm that uses movement-related brain potentials to detect response preparation based on partial information. The paradigm uses a hybrid choice-reaction go/nogo procedure in which decisions about response hand and whether to respond are based on separate stimulus attributes. A lateral asymmetry in the movement-related brain potential was found on nogo trials without overt movement. The direction of this asymmetry depended primarily on the signaled response hand rather than on properties of the stimulus. When the asymmetry first appeared was influenced by the time required to select the signaled hand, and when it began to differ on go and nogo trials was influenced by the time to decide whether to respond. These findings indicate that both stimulus attributes were processed in parallel and that the asymmetry reflected preparation of the response hand that began before the go/nogo decision was completed.

Detecting early communication: using measures of movement-related potentials to illuminate human information processing.

In this paper we review evidence that suggests that the stimulus evaluation system can pass information to the response activation system before evaluation is completed ("early communication"). This evidence is derived from measures of the lateralized readiness potential, which have been related in previous research to the preparation for movement. Early communication is evident in conflict and congruence paradigms. In both paradigms, a single stimulus, or two different stimuli, deliver two aspects of information. In the conflict paradigm, the first aspect of information (derived from preliminary evaluation) primes the incorrect response, while the second primes the correct response. In the congruence paradigm, information derived from preliminary and complete evaluation is congruent. In both paradigms, lateralized readiness potential measures suggest that preliminary evaluation is able to prime the response system, although the overt motor response may not be released until evaluation is completed. This demonstration of early communication has both theoretical and practical implications. First, it does not support single-decision models of information processing. Second, it suggests that the lateralized readiness potential, a continuous, analog measure of the activity of the response system, can be used to make inferences about the nature of the evaluation process, and to localize the effects of various manipulations on the information processing system.

Attention and cardiac activity: heart rate responses during a variable foreperiod, disjunctive reaction time task.

A variable foreperiod disjunctive reaction time task was used to evaluate the effects of stimulus discriminability on cardiac activity. In two sessions, 20 male undergraduates received easy or difficult auditory discrimination trials in blocked and random series. In the random session only, when the warning stimulus provided information about the difficulty of the subsequent discrimination, difficult trials were associated with greater foreperiod deceleration. Cardiac accelerations also tended to be greater in the foreperiods of difficult trials. There was an effect of both warning and imperative stimuli on the heart rate of the cycle in which the stimuli occurred which depended on the difficulty of the trial. The results are discussed in terms of the psychological significance of the different heart rate responses.

Why is there an ERN/Ne on correct trials? Response representations, stimulus-related components, and the theory of error-processing.

The ERN or Ne is a component of the event-related brain potential that occurs when human subjects make errors in reaction time tasks. It is observed in response-locked averages, time-locked to the execution of the incorrect response. Recent research has reported that this component is present on correct response trials, thereby challenging the idea that the component is specifically related to error-processing. In this paper, we argue that the ERN or Ne observed on correct trials can be attributed to one or both of two factors: either there is error-processing on correct trials, and/or the response-locked averages used to derive the ERN/Ne are contaminated by negative components evoked by the stimulus. For this reason, there is no reason to abandon theories that relate the ERN/Ne to error-processing.

Event-related potentials in a passive and active auditory condition: effects of diazepam and buspirone on slow wave positivity.

The effects of single, oral doses of diazepam (10 mg), buspirone (10 mg) and placebo on auditory event-related potentials were assessed in healthy volunteers. Subjects received two series of auditory stimuli: a series of identical stimuli presented in a neutral, passive condition and a series of identical standard tones (P = 0.8), but now intermixed with target tones (P = 0.2), in an active, oddball condition. The analysis focused on the average value of the potential in two different phases, from 250 till 574 ms post-stimulus (including P300) and from 576 till 900 ms post-stimulus (including late slow wave positivity). Event-related potentials for the standards of the oddball task were compared with the potentials of the same stimuli presented in the neutral condition. In addition, the classical comparison between the target and the standard in the oddball task was made. The first comparison was designed to isolate any effect of a change in the level of vigilance and attention due to involvement in the oddball task. This effect was evident as an increase in positivity that was smaller in the diazepam condition. The second comparison was designed to isolate the distinctive processing associated with task-relevant stimuli. This revealed that the P300 was reduced in the 250-574 ms window in the diazepam group. Both results suggest that cognitive processing of relevant stimuli is reduced by diazepam. Presumably, this is associated with the sedative effects of this drug. Consistent with this interpretation, subjects under the influence of diazepam made more omissions in the detection of targets in the oddball condition and had longer reaction times. In contrast to diazepam, the anxiolytic buspirone did not appear to have measurable effects on cognition.

Dissociation between behavioral and psychophysiological measures of response preparation.

Two measures of response preparation were compared: lateralized readiness potentials (LRPs) and reaction times (RTs) to probe stimuli. Subjects responded with the left and right hands to target S's and T's of one size, withholding responses to nontarget S's and T's of a different size. The size discrimination was more difficult than the S vs. T discrimination, so the name of a nontarget letter was expected to prime the response hand to which it was assigned. This priming had no effect on LRPs but did influence RTs to separate probe stimuli, suggesting that LRPs and probe-RTs are sensitive to different aspects of response preparation.

Where did you go wrong? Errors, partial errors, and the nature of human information processing.

Human performance is seldom perfect, and even when an overt response is correct it may be accompanied by partial-error activity that does not achieve the level of a complete incorrect response. Partial errors can be detected in measures of the lateralized readiness potential, of the electromyogram, and of response force. Correct responses accompanied by partial errors tend to have slower reaction times than "clean" correct responses (because of response competition), and condition differences in reaction time can, on some occasions, be explained in terms of differences in the incidence of partial errors. In two-choice reaction time tasks, partial errors are more frequent when the imperative stimulus contains information that favors both responses, than when it contains information that favors only one response. The non-random nature of partial errors supports the inference that partial information about the stimulus is used to guide responses. A similar inference is supported by the observation that, in hybrid choice Go/No-go tasks, the kinds of partial errors that follow a No-go stimulus represent activation of the response that would have been correct had the stimulus been a Go stimulus. Finally, we note that the human processing system is capable of monitoring its own behavior and of initiating remedial actions if necessary. The activity of an error-detection system, as revealed by measures of the error-related negativity, is related to the degree to which responses are slowed after errors.

Resource reciprocity: an event-related brain potentials analysis.

The amplitude of the P300 component of the Event-Related Potential (ERP) has proven useful in identifying the resource requirements of complex perceptual-motor tasks. In dual-task conditions, increases in primary task difficulty result in decreases in the amplitude of P300s elicited by secondary tasks. Furthermore, P300s elicited by discrete primary task events increase in amplitude with increases in the difficulty of the primary task. The reciprocity in P300 amplitudes has been used to infer the processing tradeoffs that occur during dual-task performance. The present study was designed to investigate further the P300 amplitude reciprocity effect under conditions in which primary and secondary task ERPs could be concurrently recorded within the same experimental situation. Forty subjects participated in the study. Measures of P300 amplitude and performance were obtained within the context of a pursuit step tracking task (the primary task) performed alone and with a concurrent auditory discrimination task (the secondary task). Primary task difficulty was manipulated by varying both the number of dimensions to be tracked (from one to two), and the control dynamics of the system (velocity or acceleration). ERPs were obtained from both secondary task tones and primary task step changes. Average root-mean-square (RMS) error estimates were also obtained for each tracking condition. Increased primary task difficulty, reflected in increased RMS error scores, was associated with decreased secondary task P300 amplitudes and increased primary task P300 amplitudes. The increases in primary task P300 amplitudes were complementary to the decrements obtained for the secondary task, supporting the hypothesis of reciprocity between primary and secondary task P300 amplitudes across different manipulations of primary task difficulty.

Magnitude versus parity in numerical judgements: event-related brain potentials implicate response conflict as the source of interference.

When subjects make 'odd/even' and 'low/high' decisions about digits, information about the digit's magnitude can interfere with the decision about the digit's parity. The present experiment used a psychophysiological approach to examine whether this interference arises at the level of response processing. Subjects performed a choice-reaction time task involving low/high and odd/even judgements about the digits 2 through 9. The data point to a response locus for the interference effect with the size of the effect being dependent on the ease with which magnitude information can be used to prime the appropriate response. This, in turn, is influenced by the 'naturalness' of the mapping between magnitude and response hand as well as by the distance of a digit to the low/high cut-point.

When complexity helps: an electrophysiological analysis of multiple feature benefits in object perception.

Fournier, L. R., Eriksen, C. W. and Bowd, C. (1998. Multiple feature discrimination faster than single feature discrimination within the same object? Perception & Psychophysics 60, 1384-1405) found that judging the presence of multiple features within an object is faster than judging the presence of the least discriminable of these features alone (multiple feature benefits, MFBs). When an 'absent' response is required, responses are slower when some of the relevant (target) features are present (multiple feature costs, MFCs). The present study utilized psychophysiological measures (of the event-related brain potential and the electromyogram) to determine the contributions of response priming and stimulus evaluation processes (P300 latency) to these effects. P300 latency and reaction time (RT) both showed evidence of MFBs and MFCs. These findings suggest that MFBs and MFCs can be attributed to processing that occurs prior to response selection. No dissociations between P300 latency and RT measures were found for 'present' responses across the single and multiple feature judgements. However, for 'absent' responses, partial dissociations were found between these measures, and partial errors and longer response execution intervals were observed more often when an object contained some target features. These findings suggest that response priming contributes to MFCs, but may not contribute to MFBs.