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M N Verbaten

Publications and source records attributed to M N Verbaten.

67 records · Page 4Linked to original sources
PubMed1986

Habituation of early and late visual ERP components and the orienting reaction: the effect of stimulus information.

Single trial event-related potentials at Fz, Cz, Pz and Oz were measured concurrently with pupil reactions and skin conductance reactions in a habituation paradigm. One group of subjects (n = 16) was given 36 simple visual stimuli and a second group (n = 16) 36 complex visual stimuli of equal duration, brightness and dimensions. No task-relevance was given to the stimuli. Under these circumstances we found rapid habituation (within 6 trials) of the vertex N1. Because we used long, variable interstimulus intervals, the N1 decrease could not be explained by refractory effects. Habituation rates of N1 and the concurrently measured SCR did not differ. Although the P3 showed significant habituation over the 12 trials (except at Oz), it habituated slower than the N1 and the SCR. The complex stimulus condition elicited larger P3b waves. No effect of stimulus complexity was found on the N1 and the SCR. The relevance of these results for the OR is discussed.

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↗
PubMed1984

Eye-movements in a two-dimensional plane: a method for calibration and analysis using the vertical and horizontal EOG.

A method for calibration, orthogonalization and standardization of eye movements is described. The method is based on linear transformation of the horizontal and vertical EOG. With this method it is possible to measure the locus of eye fixation on a TV screen and its associated fixation time. Because of the used time constant (TC) of 36 sec, subjects must look at the centre of the TV screen or at random places on the screen during the interstimulus intervals (ISIs). For the EOG registration pre-amplifiers with a long TC were used to cut off slow changes in polarization caused by the electrode-electrolyte combination. In the calibration procedure only four orthogonal stimulus points were used. In an experiment to evaluate this method, subjects had to fixate letters on a TV screen in 12 different pre-determined positions. The distance between the measured locus of fixation and the coordinates of the stimulus was measured. The mean horizontal errors ranged from 1.4-2.2 degrees of arc and the mean vertical errors from 2.4-3.8 degrees of arc across subjects. It was concluded that accuracy was within acceptable limits, despite the fact that eye movement behaviour during the ISI was free. It was shown that the method is insensitive to non-orthogonality of the vertical and horizontal EOG. Calibration and transformation can be done by any real time computer system. The method is suitable for measuring, e.g. the visual orienting reaction (VOR), and it can also be applied in event related potential (ERP) studies where ocular fixation is used.

Adult↗
PubMed1981

The influence of information on habituation of the "Wiener" filtered visual even related potential and the skin conductance reaction.

In this study the influence of the information value of visual stimuli on habituation in event related potentials (ERPs) at Fz, Cz and Oz locations and the skin conductance reaction (SCR) was investigated. An improved 'Wiener' filter was used to reduce the number of stimulus presentations. This enabled us to study P300 and SCR decrement in the same period of time. SCRs and Wiener filtered ERPs were determined over six stimulus presentations. Half of the 26 subjects received for 36 times a stimulus with a high information value in terms of complexity and the other half of the subjects 36 stimuli with a low information value. The results of this study show that decrement of the P300 amplitude occurs in about the same period of time as the SCR magnitude decrement. P300 habituation was manifested only in the fronto-central leads, the occipital P300 did not show habituation. A second difference in the topography of the P300 was that the effect of stimulus information was only found in the fronto-central leads and not in the occipital lead. As earlier studies, we did not find an effect of information on SCR habituation. The results show that the fronto-central P300 showed two important characteristics of the orienting response (OR). They are that habituation occurs in about the same period of time as in which a classical OR index as the SCR habituates and P300 amplitudes are larger when the information value of the stimuli is higher.

Adult↗
PubMed1981

A statistical Wiener filter using complex analysis of variance.

The Wiener filter is a digital filter in the frequency domain which enables the detection of signals in noise on the basis of a relatively small number (N) of signals-in-noise series. However, the variance associated with the Wiener filter increases sharply with low N or low signal-to-noise ratio, sometimes resulting in large negative transfer coefficients (H(w)'s). This causes an unacceptable distortion of the extracted signal. The classical solution for this problem is rather arbitrary; clipping all H(w)'s less than zero. It can be shown that this approach has limited practical value and does not lead to optimal filtering of the signal. The solution presented in this paper is based on the fact that the large negative H(w)'s in the case of a small N are caused by using an estimate for the noise-power which deviates from the actual noise-power. This makes the use of a statistical procedure feasible. By using complex analysis of variance it is possible to test which part of the spectrum is due to the signal and which part of the spectrum is due to the noise. H(w)'s not reaching a preset significance criterion are set to zero. The statistical Wiener filter acts as an adaptive multi-band-pass filter with band-passes determined by (a posteriori) detected signal components. It is demonstrated that this procedure leads to better suppression of the noise in signal-in-noise series.

Analysis of Variance↗
PubMed1980

The influence of task relevance and stimulus information on habituation of the visual and the skin conductance orienting reaction.

This study investigated the hypothesis that task-relevant stimuli induce orienting reactions (ORs) that are stronger and more resistant to habituation when their information content is high than when it is low. Task-relevance was given to the stimuli by rewarding the subjects for correct recognition at the end of the experiment. The dependent variables in this study were the visual orienting reaction (VOR), the skin conductance reaction (SCR), their habituation scores and the number of spontaneous fluctuations in skin conductance (SFs). 28 subjects received two blocks of 14 trials. Half the subjects received the higher information condition first and then the lower information condition, while the other half received the reversed order. The VOR habituated quickly and was not significantly influenced by information value. SCR amplitudes were larger and SCR-habituation slower to stimuli containing more information. The results were interpreted as supporting the hypothesis that the SCR is associated with a secondary phase of the orienting process.

Adult↗
PubMed1979

The influence of visual information on habituation of the electrodermal and the visual orienting reaction.

In this study the influence of the information value of visual stimuli on habituation of the visual orienting reaction (VOR) and the skin conductance reaction (SCR) was investigated. 28 subjects received two blocks of 14 trials. Half the subjects received the higher information condition first and then the lower information, the other half received the conditions in the reversed order. Subjects fixated the stimuli with the higher information value longer than the stimuli with the lower information value during the 14 trials and habituated slower. This effect of information was absent in the second block and VOR habituation was also faster in this block. There was no difference in SCR amplitudes nor in SCR habituation scores between the two information conditions, neither in block 1 nor in block 2. The results of this study are discussed in relation with a two-stage model of the OR.

Adult↗
PubMedDate not supplied

Single trial ERP estimation in the frequency domain using orthogonal polynomial trend analysis (OPTA): estimation of individual habituation.

A new Event Related Potential (ERP) model is described in which ERPs are estimated as single cortical responses. This model is based on an Orthogonal Polynomial Trend Analysis of Variance (OPTA) in the frequency domain. The orthogonal polynomials are limited to the fifth order in this study. The means and trend-coefficients which are used to estimate the ERPs are tested for significance with the F-statistics. Coefficients not reaching a preset significance criterion are set to zero. Subsequently significant means and trend-coefficients multiplied with the polynomials are inversely transformed to the time domain for each trial. The method is demonstrated with artificial signal-in-noise EEG (electroencephalogram) series in which the signal component (the ERP) decreases in a relatively short time span. The estimated signals approximate closely the input signals and a signal-to-noise improvement on single trial level is reached of about a factor 10. Comparison with the statistical 'Wiener' filtering method shows that the OPTA detects weaker signals. Single trial ERPs estimated with the OPTA from EEGs collected in a habituation paradigm suggest that the averaged evoked potential model may be inadequate in detecting ERP change over a few trials. It is shown that the frontal P3b wave habituated in 7-9 trials, a habituation speed which is comparable to the habituation rate of the visual orienting reaction and the electrodermal orienting reaction.

Analysis of Variance↗
PubMedDate not supplied

Stimulus information and habituation of the visual event related potential and the skin conductance reaction under task-relevance conditions.

The influence of information value of visual stimuli on habituation of event related potentials (ERPs) at Fz, Cz, Pz and Oz and of the skin conductance reaction (SRC) was investigated under task-relevance condition. An improved Wiener filter was used to reduce the number of stimulus presentations to estimate an ERP. Twenty-six subjects received two times a block of 36 stimulus presentations. Half of the subjects received a stimulus with a high information value in terms of complexity and then a stimulus with a low information value. The other half of the subjects received the reversed order. Wiener filtered ERPs and SCRs were determined over ensembles of six stimulus presentations. The habituation of the P300 component was restricted to the fronto-central leads, and was delayed when compared to the results of a former study (Woestenburg, Verbaten and Slangen, 1981b) where non-signal stimuli were used. Also information effects were noticed on these fronto-central leads, but not on the SCR. This reaction habituated as in the former non-signal study. The P300 at the parieto-occipital leads showed larger amplitudes than the fronto-central P300 and these components did not habituate. At the Oz lead early waves habituated and late waves increased during ensemble 1 to 6.

Adult↗
PubMedDate not supplied

The removal of the eye-movement artifact from the EEG by regression analysis in the frequency domain.

A new method to remove the eye-movement artifact from the electro-encephalogram (EEG) is described. It is based on complex regression analysis. Transfer of eye-movement activity to EEG can have frequency dependent amplitude and phase characteristics. The proposed method is suitable for handling such transfer because the regression formula is used in the frequency domain. The method is demonstrated with artificial signal-in-noise EOG (electro-oculogram) and EEG series. In the EEG noise an event related potential (ERP) is buried as a constant signal and in the EOG noise a changing EOG response (saccadic eye-movement) is simulated before adding the whole series to the EEG series. Also decreasing levels of transfer from EOG on EEG leads are simulated as the EOG artifact diminishes from the frontal to the occipital area. Because of the possible frequency dependent phase characteristics also a 24 msec time-shift of the EOG is simulated. The complex regression coefficient (P(jw)) of the EOG and EEG series is first calculated and then 'common' regression is removed from the EEG. To do this the estimated P(jw) is tested for significance with the F-statistic and significant EOG activity is subtracted in the frequency domain from the EEG on a single trial base. Then each EEG record is inversely transformed to the time domain. It was found that the complex P(jw)s as used in the subtraction formula, corrects very accurately the influence of the EOG artifact on EEG activity. Finally an application of the method in a real life situation is reported.

Electroencephalography↗