Biomedical subjects

J L Kenemans

Publications and source records attributed to J L Kenemans.

43 records · Page 3Linked to original sources

PubMed1992

Time effects on event-related brain potentials and vigilance performance.

A review of the literature showed that in vigilance or oddball tasks, changes over time in event-related potentials (ERPs) and performance measures often seem to be unrelated, but a number of studies had some shortcomings. In the present study a visual vigilance experiment was carried out, in which single-trial ERPs and performance data of 40 males were obtained. A relationship between time trends in behavioral and ERP measures was found: an early P3 amplitude and response latency (RT) showed an inversely varying relation over time. Analysis of covariance showed that the two linear trends tap the same aspect of processing: both trends became insignificant when adjusted for common variance. A negative correlation between mean values of P3 amplitude and RT rather than for change scores has been observed in previous studies, but has been ignored in the literature. However, correlations with RT have also been reported for other ERP deflections. Although there were several correlations between mean scores, most time-induced changes in ERP parameters appeared to be unrelated to worsening performance, for which several explanations are advanced. The ERP results do not support the hypothesis that a decrement in performance is caused by increasing difficulty discriminating targets from nontargets. A gradual decline in effort or resources allocated to the task might be an alternative explanation of performance deterioration. However, an effort-hypothesis cannot easily be tested. Effort is often invoked post hoc, and has previously been associated with many ERP components. The relationship between ERPs and the signal detection measures "sensitivity" d' and "response bias" beta is discussed.

Adolescent↗

PubMed1992

Visual stimulus change and the orienting reaction: event-related potential evidence for a two-stage process.

In a previous study it was found that infrequent deviant visual stimuli, in a series of standards, elicited event-related potentials (ERPs) with enhanced P2-N2s and P3 amplitudes, suggesting that these parameters reflect processes related to the orienting reaction (OR). In the present study a similar oddball series was presented against the background of a second class of stimuli. With respect to the latter stimuli, subjects had to perform either a very involved (hard) or an easy task. EEG was recorded to oddball (probe) stimuli from Oz, Pz, Cz, and Fz. Analysis of average ERPs revealed that, in the easy condition, deviant probes elicited both enhanced P2-N2s and enhanced P3s, relative to the standards. In contrast, in the hard condition P2-N2, but not P3, was enhanced by stimulus change. In addition, overall P3 amplitude to probes was smaller in the hard condition (sequence-independent load effect). Analysis of single-trial ERPs (SERPs) with orthogonal polynomial trend analysis largely replicated these effects. In addition, SERP analysis also revealed a sequence-independent load effect on P2, as well as a decreasing P3 to deviant stimuli in the Easy condition, which was observed at Cz and Fz, but not at Pz or Oz. The results are interpreted as suggesting that P2-N2 and P3 reflect different stages of the OR, one of automatic and one of capacity-limited processing.

Adult↗

PubMed1991

Removal of the ocular artifact from the EEG: a comparison of time and frequency domain methods with simulated and real data.

Frequency-dependent transfer from EOG to EEG may be insufficiently accounted for by simple time domain regression methods (Gasser, Sroka, & Möcks, 1986; Woestenburg, Verbaten, & Slangen, 1983). In contrast, a multiple-lag time domain regression analysis, using lagged regression of EEG on EOG, must theoretically account for both frequency dependence and independence. Two data sets were constructed, in which the transfer from EOG to EEG was either frequency-independent (constant gain) or frequency-dependent. Subsequently, three different correction methods were applied: 1) a simple regression analysis in the time domain; 2) a multiple-lag regression analysis in the time domain; and 3) a regression analysis in the frequency domain. The major results were that, for data set 1, the three methods constructed the original EEG equally well. With data set 2, reconstruction of the original EEG was achieved reasonably well with the frequency domain method and the time domain multiple-lag method, but not with simple time domain regression. These three correction procedures were also applied to real data, consisting of concomitantly recorded EEG and high-variance EOG series. No appreciable differences in outcome of the three methods were observed, and estimated transfer parameters suggested that these data were marked by weak frequency dependence only, which can be accounted for by simple time domain regression (and also by the other two methods).

Blinking↗

PubMed1989

"Initial-" and "change-orienting reactions": an analysis based on visual single-trial event-related potentials.

The present study was concerned with brain potentials elicited by, respectively, the first of a series of stimuli ("initial-orienting reaction", I-OR), and infrequent deviants ("change-orienting reaction", C-OR). Single-trial event-related potentials (ERPs) to visual stimuli were estimated from recordings at Oz, Pz, Cz and Fz. The design included both a habituation series as well as a series of occasional deviant trials against a background of standards. This was done with both task-relevant and neutral stimuli, and in two interstimulus interval (ISI) conditions: 2.45 s and 8.45 s. In the latter ISI condition, skin conductance responses (SCRs) were recorded as well. Decrease (Habituation) in the habituation series was found for a non-specific N1, a posteriorly distributed P3, and the SCR, but not for P2-N2. Deviant stimuli produced an enhancement of the central P2-N2, the P3, the N1 (on the first few deviant trials only, in both ISI conditions), and the SCR (with task-relevant stimuli only). Elongation of ISI delayed both short-term and long-term decrease of P3, but had no effect on enhancement of P2-N2 due to stimulus deviance. It was concluded that, with respect to ERP parameters, the I-OR is marked by the N1, whereas the C-OR coincides with the P2-N2.

Adult↗

PubMed1988

Effects of task relevance on habituation of visual single-trial ERPs and the skin conductance orienting response.

Single-trial event-related potentials were recorded at Oz, Pz, Cz, and Fz, concurrently with skin conductance reactions and fixation behavior in a habituation paradigm. A total of 48 subjects received 16 identical visual stimuli; 24 of them were instructed to pay attention, whereas the other half were given a neutral instruction. Two early negative components (N1 and N2), as well as a late positive component (P3) were identified. N1 and skin conductance reaction (SCR) showed fast decrement over trials, whereas N2 and P3 habituated slowly. Habituation of N1 and SCR was delayed by task instructions; N2 was hardly seen at all in the neutral condition. The task effects on N1 and N2 were observed only at Oz. It is concluded that the processing of relevant stimuli differs structurally from the processing of neutral stimuli; this difference may be observed even at a latency of 100 ms. The N1 appears to be related to the SCR, whereas this does not hold for P3; the N2 is related to selection negativities reported by other authors.

Adult↗

PubMed1986

The effects of uncertainty and task-relevance on habituation and recovery of the electrodermal and visual orienting reaction.

Habituation and recovery of the skin conductance reaction (SCR) and visual orienting reaction (VOR) were investigated. Half the subjects (total N = 48) were instructed to memorize a complex visual stimulus (TR), while the other half received a non task-relevant instruction (NTR). All subjects were exposed to two series of 16 identical stimuli. At trial 17 the location of the stimulus changed. Half the subjects in both groups received a priori information about the stimuli, the other half did not. Task-relevance led to slower SCR habituation and longer VORs. In the TR condition the VOR latency time rapidly decreased, indicating the development of a set. In terms of SCR frequency, but not in terms of SCR magnitude OR recovery was stronger in the task-relevant condition. However, all subjects oriented visually to the stimulus change. No habituation of the VOR was found using a drift-free technique for measuring eye-movements. It is concluded that the SCR and the VOR latency data supply evidence for a structural difference between task-relevant and task-irrelevant ORs.

Adult↗

PubMedDate not supplied

Event-related potentials to conjunctions of spatial frequency and orientation as a function of stimulus parameters and response requirements.

ERPs were recorded from subjects who were required to push a button in response to a given conjunction of spatial frequency and orientation (target), and to ignore conjunctions sharing with the target only frequency (frequency-relevant), only orientation (orientation-relevant), or neither (irrelevant). Differences between ERPs to irrelevant and frequency-relevant stimuli were identified as frontal selection positivity (Fz, 150-200 msec post-stimulus), selection negativity (Oz, just after 200 msec), and vertex N2b (200-250 msec). For relevant orientations, the selection negativity and the N2b were also found, but the frontal selection positivity was elicited only when the spatial frequency was relevant as well. Neither of these 3 waves was sensitive to spatial frequency or orientation per se. Other waves (N80, N180) did show such sensitivity, but this was independent of stimulus relevance. Hence, direct evidence for the neural-specificity theory, stating that task-related selective ERP responses reflect differential enhancement of activity in stimulus-specific pathways, was not obtained. It is further concluded that ERPs associated with selection of frequency and orientation are highly comparable to those associated with other visual dimensions (e.g., color), and that selection of multiple visual dimensions may be hierarchical at one level of processing and independent at another.

Adult↗