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Biomedical subjects

M G Coles

Publications and source records attributed to M G Coles.

At least 19 recordsLinked to original sources
PubMed1999

Error-related processing during a period of extended wakefulness.

The nature of error detection as manifested by the error-related negativity was examined in both a Sternberg memory search task and a visual search task. Both tasks were performed in conditions with consistent or varied stimulus-response mapping and loads of three or six letters. After subjects were trained extensively in all conditions, they performed the tasks throughout the night without sleeping. The data suggest that the effectiveness of error detection decreases over time because of a decrease in the quality of perceptual processing. Error detection also suffers when performance requires more search-related resources. In both cases, the representation of the correct response is compromised. These results indicate that error detection depends on the same perceptual and cognitive processes that are required for correct performance.

Adult↗
PubMed1998

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.

Adolescent↗
PubMed1997

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.

Adult↗
PubMed1997

The dimensionality of the flanker compatibility effect: a psychophysiological analysis.

The psychophysiological approach was used to evaluate the effects of feature similarity and "intrinsic response mapping" on the flanker compatibility effect. Symbol (e.g., < > < and </<) and letter arrays (e.g., HCH and SCS) were used. Results showed that delays in stimulus evaluation and both peripheral and central response competition contributed to the compatibility effect, with the contribution of these processes depending on feature similarity and the intrinsic response mapping of the stimuli. For letter stimuli, the difference in the size of the compatibility effect for similar and dissimilar arrays could be accounted for in terms of stimulus evaluation. For symbol arrays, differences in size of the compatibility effect could be accounted for by response competition. Thus, symbol and letter arrays do not appear to be processed differently; what is different is the degree to which stimulus and response-related processes are affected by incompatibility.

Adult↗
PubMed1997

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.

Body Temperature Regulation↗
PubMed1996

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.

Adolescent↗
PubMed1996

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.

Adult↗
PubMed1996

Event-related brain potentials and error-related processing: an analysis of incorrect responses to go and no-go stimuli.

Recent research has suggested that there is a component of the event-related brain potential, the error-related negativity (ERN), that is associated with error detection and remedial actions such as error inhibition, immediate error correction, or error compensation. The present experiment used a go/no-go task to define more precisely the functional significance of this component. In this task, an ERN was observed for incorrect responses on go trials (errors of choice) and for responses on no-go trials (errors of action). Because errors of action cannot be corrected immediately by executing another response, these results indicate that the process manifested by the ERN is not dependent on immediate error correction. Other aspects of the data converge in suggesting that the ERN process is more closely related to error detection and that the connections between detection and remedial actions may depend on the task situation.

Adult↗
PubMed1995

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.

Arousal↗
PubMed1995

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.

Adolescent↗
PubMed1992

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.

Decision Making↗
PubMed1992

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.

Adult↗
PubMed1990

Event-related brain potentials as indices of information extraction and response priming.

Measures of overt response and of the event-related brain potential (ERP) were used to investigate the processing of a priming stimulus varying in its information content. Subjects were shown sequences of 2 letters that served as a priming and an imperative stimulus. In 3 randomly interspersed conditions the imperative stimulus had a 0.80, 0.50, or 0.20 probability of physically matching the priming letter. The different probability conditions were signaled by the position of a dot flanking the priming letter. Reaction time and accuracy data indicated that the subjects primed their responses as a function of the information conveyed by the priming stimulus. The amplitude and latency of the P300 to the priming stimulus were sensitive to the amount of information conveyed by the priming stimulus and the duration of the processing required. The readiness potential in the foreperiod was lateralized as a function of the priming stimulus. Furthermore, the larger the amplitude of the P300 to the priming stimulus, the larger the lateralization of the readiness potential, indicating that information extraction, indexed by the P300, was related to response priming, indexed by the readiness potential. The results indicate that ERP measures make manifest covert aspects of the priming process occurring in the foreperiod.

Adolescent↗