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J L Kenemans

Publications and source records attributed to J L Kenemans.

At least 19 recordsLinked to original sources
PubMed1998

Caffeine and visuo-spatial attention.

The effects of two doses of caffeine (1.5 and 3 mg/kg) on various aspects of visual selective attention were investigated in 24 healthy human subjects. Specific task conditions were compared to provide measures of selectivity for a location in the visual field, of distractibility, of selectivity among response alternatives, and of strategic influences. In two out of three tasks, caffeine speeded responses significantly. However, these effects did not differ across conditions within-task, so there was no indication that they were to due to (a) specific effect(s) on one or more of the attentional sub-functions. The results suggest that the beneficial effects of caffeine in low-load conditions cannot be attributed to reduced distractibility or increased suppression of task-irrelevant response tendencies.

Adult↗
PubMed1998

Localization of spatial attention processes with the aid of a probe technique.

A sudden visual onset is thought to 'attract attention to its location' within less than 100 ms. We attempted to measure the effect of this attentional process on the event-related potential (ERP) to a probe presented about 140 ms after the onset, and to delineate the spatiotemporal characteristics of such an effect, if any. ERPs were recorded from 30 channels from 6 subjects while they performed a target detection task. Both targets and probes could be located in each of the 4 quadrants (eccentricities 6.1 degrees and 7 degrees, respectively). For a given single target, the subsequent probe was either presented near the location of the target ('valid target') or at the diagonal opposite ('invalid target'). Appropriate 'neutral' conditions (probes preceded by no target, or by simultaneous targets in all quadrants) were applied, and ERPs to probes were corrected for the contribution of the ERPs to targets. The earliest effect of (in)validity was found at about 120 ms after probe onset for lower field probes. This effect consisted of enhanced posterior positivity for valid relative to neutral relative to invalid conditions. This positivity was superposed on a contralateral, extrastriate negative ongoing wave peaking at about 150 ms ('N150'). Source localization suggested that the (in)validity effects originate from deep medial parietal areas. The source corresponding to the N150 activity was not influenced by (in)validity. An earlier deflection to the probe at 80 ms ('NP80') depended on location, but not on (in)validity, and seemed to be of striate origin. Results are discussed in terms of a model postulating an attention-independent 'input module' from which activation is fed to a 'location module' embodying the actual attention mechanism.

Adult↗
PubMed1997

Feature processing and attention in the human visual system: an overview.

A recent development in the cognitive modelling of visual selective attention is the incorporation of design principles derived from the neuroanatomy and neurophysiology of the primate visual system. In this paper, we describe these recent 'neurocognitive' models in more detail, point out the underlying neurobiological principles, and show that in all cases attention is implemented as an energetical resource which can be directed to representations and pathways in the system. In the second part of the paper, we specify the predictions derived from this 'energy hypothesis', and evaluate available data pertaining to this issue. We present new analyses of electrophysiological data in order to directly test the hypothesis that attention modulates feature-specific representations. It will be shown that in the case of sustained spatial attention, the data are in agreement with this hypothesis, whereas in the case of nonspatial attention, there is no evidence of a modulation of feature-specific pathways by attention.

Attention↗
PubMed1997

The effects of sleep loss on task performance and the electroencephalogram in young and elderly subjects.

The effects of 28-h sleep loss on performance, reaction time (RT) distribution functions, and spectral composition of the EEG were evaluated in three choice-RT tasks for young (N = 12, aged 18-24 years) and old (N = 12, aged 62-73 years) subjects. Manipulations of stimulus degradation, stimulus-response compatibility, and interstimulus interval variability were to affect encoding, response selection, and motor adjustment stages, respectively. In order to discriminate between independent variables that were presumed to be computational or energetical in nature, effects on EEG spectra and RT-distributions were studied. Spectra of the EEG indicated higher cortical arousal levels for the elderly than for the young. The most dramatic effect of sleep loss on performance was a marked increase in the number of omitted responses. This effect was smaller for the elderly than for the young. The results suggest that the detrimental effects of sleep loss are smaller in the elderly, which is consistent with an inverted-U relationship between arousal and performance. The age effects on the processing stages were mainly limited to response selection.

Adolescent↗
PubMed1996

Effects of task variables on measures of the mean onset latency of LRP depend on the scoring method.

The lateralized readiness potential (LRP) can be used to index the start of response activation. The onset of the average LRP can be computed as the latency at which the component starts to deviate significantly from zero or as the latency at which a certain proportion of its maximum amplitude is attained. The properties of both measures as estimates of the mean onset latency of the LRP were examined. Experiment 1 was a simulation study in which the mean onset latencies were known. Results indicated different types of bias for the two measures and greater reliability for a proportional measure. In Experiment 2, the sensitivity to bias, consistency, and linearity of both measures were evaluated in a set of empirical data. By all three criteria, a proportional onset measure was superior. It is recommended that the choice of the measure should depend on the hypothesis to be tested, so that conclusions are based on the more conservative test.

Adult↗
PubMed1996

Perceptual factors affecting age-related differences in focused attention: performance and psychophysiological analyses.

In this study, the impact of two perceptual factors, feature similarity and spacing, on age-related differences in performance and psychophysiological measures were investigated within a focused attention paradigm. Young and old subjects performed an Eriksen letter identification task, in which centrally presented targets were flanked by response-compatible or response-incompatible letters. In feature similarity conditions, targets and flankers had a low or high amount of feature overlap. In spacing conditions, flankers were presented at four different lateral positions from the target. In the condition with high feature overlap and shortest target-flanker distance, old subjects showed greater interference by incompatible flankers than young subjects. Feature similarity was of little influence on age-related differences. However, spacing turned out to be of critical importance. Age-related interference effects disappeared when the target-flanker distance increased. This appears to be due to a decrease in response competition.

Adult↗
PubMed1995

The temporal selectivity of additive factor effects on the reaction process revealed in ERP component latencies.

An experiment was conducted to relate individual components of the event-related brain potential to specific stages of information processing in a two-choice reaction time (RT) task in a group of undergraduate students. Specifically, the latency of the P300 component and the lateralized readiness potential (LRP) were studied as a function of variations in stimulus degradation and response complexity. It was hypothesized that degrading the stimulus would delay the P300 and LRP to the same extent as RT, and that increasing response complexity would affect RT but not P300 latency. The extant literature did not permit any hypothesis regarding the effect of response complexity on LRP latency. The two task variables were found to have additive effects on RT. As predicted, variations in stimulus degradation influenced the latencies of both components, whereas alterations in response complexity had no effect on P300 latency. A significant new finding was that the onset latency of the LRP remained unchanged across levels of response complexity. The overall pattern of results supports the notion of temporal selectivity of stage manipulations that is derived from discrete stage models of human information processing. Furthermore, these results refine the functional interpretation of the LRP by indicating that within the conceptual framework of a stage model the processes this component indexes succeed the start of response choice but preceded the start of motor programming.

Adult↗
PubMed1995

Caffeine and selective visual processing.

This work addressed five issues: a) Does caffeine modulate electroencephalogram (EEG) background activity in a manner consistent with the idea of cortical "arousal"? b) Is performance in a simple speeded task improved under caffeine? c) Is visual processing more selective under caffeine? d) Does caffeine affect sensory discrimination? and e) Does it affect motor processes? We presented 16 subjects with a visual selection task under conditions of either caffeine or placebo. Background EEG data, gathered before administration of the task, revealed that caffeine resulted in lower slow-alpha power, relative to placebo, which is consistent with the idea of increased cortical "arousal." During the selection task, subjects had to respond manually to a given target conjunction of spatial frequency and orientation. Other conjunctions shared spatial frequency, orientation, or neither with the target. The four conjunctions were presented in a random sequence, with SOAs ranging between 750 and 950 ms. Event-related potentials (ERPs) to the conjunctions were recorded at standard scalp locations Fz, Cz, Pz, and Oz. Under caffeine, subjects made faster responses to target conjunctions (382.9 vs. 404.5 ms) and more hits, whereas the false-alarm rate was equal across conditions. Caffeine did not affect the selection potentials normally obtained in this task by subtracting, from ERPs to nontargets with the target spatial frequency, those to nontargets with the other frequency. However, an early differential positivity (50-160 ms) was found specifically under caffeine, indicative of increased selectivity. Difference ERPs as a function of physical parameters were not affected by caffeine, indicating no effect on sensory discrimination. Onsets of response-related lateralizations above the motor cortex were not affected by caffeine, suggesting that the shorter reaction times under caffeine were due to faster central or peripheral motor processes.

Adult↗
PubMed1995

Auditory event-related potentials to deviant stimuli during drowsiness and stage 2 sleep.

Twelve subjects were tested using a 3-tone auditory oddball paradigm consisting of a standard 1000 Hz tone (P = 80%) and two deviants, namely, a 1200 Hz tone and a 2000 Hz tone (both P = 10%). Testing took place in 3 conditions: (1) attend, in which the subject had to count one of the deviant tones; (2) ignore, in which the subject read a book; and (3) sleep, in which the subject was encouraged to go to sleep during presentation of the tones. In the awake conditions stimulus deviance elicited mismatch negativity (MMN) and P3. During drowsiness, no separate mismatch negativity (MMN) could be detected, but the 2000 Hz tone evoked a broad fronto-central early negative deflection, suggesting an overlap of N1 and MMN. In the same condition, P210, N330 and P430 appeared, all being sensitive to magnitude of deviance. During stage 2, the P210, N330 and P430 amplitudes increased, most notably to the large deviant. These data indicate that differential processing of auditory inputs is maintained during drowsiness and stage 2 sleep, but do not support the notion that MMN or P3 activity comparable to the waking state occurs to oddball stimuli during this stage. It is hypothesised that during light sleep, scanning of the environment is performed by a different system than in the awake state and that during drowsiness a gradual switch between these two systems takes place.

Acoustic Stimulation↗
PubMed1995

Selective processing of two-dimensional visual stimuli in young and old subjects: electrophysiological analysis.

In this study, we compared selection of conjunctions of spatial frequency and orientation in young and old subjects, using performance and event-related brain potential (ERP) measures. Responses to target conjunctions were slightly but significantly slower in older subjects; lateralized readiness potential (LRP) onsets did not differ between groups. Older subjects made more false-positive responses to stimuli sharing only spatial frequency with the target. Difference waves associated with selection of separate dimensions included frontal positivity and occipital and central negativity and were 20-50 ms slower in older subjects. Later parts of these difference waves had smaller amplitudes in older subjects. Sensory discrimination, assessed through the effects of physical stimulus parameters on ERPs, was not clearly affected by age. Data are interpreted in terms of a relationship in older subjects between longer latencies of difference waves but equal LRP onsets and a higher false-alarm rate.

Adult↗
PubMed1994

A comparison of different methods for estimating single-trial P300 latencies.

Inferences from comparative analyses of reaction time and P300 latency are stronger when the various aspects of the distribution across trials are treated in the same way for both variables. To this end, a number of studies have resorted to estimation of P300 latency at the single-trial level. This report presents a comparative evaluation of two common methods for such single-trial analysis, i.e., peak-picking and template-matching. Both methods were applied to a representative set of real data, comprising different task conditions and two age groups. Relevant scoring parameters were varied: low-pass filter settings (down to 0.94 Hz) for peak-picking, template duration (250-970 msec) and use of covariance vs. correlation for template-matching, and use of a noise-range criterion for both methods. It is concluded that peak-picking with a 3.4 Hz filter, and template-matching using covariance and template duration between 600 and 800 msec, are best in terms of sensitivity and reliability, with peak-picking surpassing template-matching. Also, the marked increase in the number of rejected trials when the noise-range criterion was applied resulted in unwanted modulation of behavioral effects of task conditions and age groups.

Adult↗
PubMed1992

Effects of bromazepam on single-trial event-related potentials in a visual vigilance task.

Thirty females performed a visual vigilance task under the influence of bromazepam (6 and 12 mg) in a placebo-controlled, double blind, experiment. Measures employed were percentage of hits, percentage of false alarms, response latency (RT), A' (sensitivity), B" (cautiousness), and RI (responsivity), as well as signal- and non-signal event-related potentials (ERPs). Bromazepam did not aggravate the normally occurring decrement in performance in vigilance tasks, but had an effect on overall level of performance: accuracy was reduced under the influence of the drug, but speed improved. A Drug x Period interaction for cautiousness (B") indicated increasingly less cautiousness with bromazepam, which probably contributed to faster motor responses (and more errors) than in the placebo group. The ERP data suggest that the effects of bromazepam are already manifest in the early stages of information processing (attention-detection) as mirrored by a drug effect on N1 amplitude. Deterioration at this early stage may affect later processing stages (P2-N2 amplitudes). As a result, subjects under the influence of the drug probably accumulate less signal evidence for their final evaluation.

Adult↗
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↗