Automated ECG diagnostic P-wave analysis using wavelets.

P-wave characteristics in the human ECG are an important source of information in the diagnosis of atrial conduction pathology. However, diagnosis by visual inspection is a difficult task since the P-wave is relatively small and noise masking is often present. This paper introduces novel wavelet characteristics derived from the continuous wavelet transform (CWT) which are shown to be potentially effective discriminators in an automated diagnostic process. Characteristics of the 12-lead ECG P-wave were derived using CWT and statistical methods. A normal control group and an abnormal (atrial conduction pathology) group were compared. The wavelet characteristics captured frequency, magnitude and variance components of the P-wave. The best individual characteristics (i.e. ones that significantly discriminated the groups) were entered into a linear discriminant analysis (LDA) for four different models: two-lead ECG, three-lead ECG, a derived three-lead ECG and a factor analysis solution consisting of wavelet characteristic loadings on the factors. A comparison was also made between wavelet characteristics derived form individual P-waves verses wavelet characteristics derived from a signal-averaged P-wave for each participant. These wavelet models were also compared to standard cardiological measures of duration, terminal force and duration divided by the PR segment. Results for the individual P-wave approach generally outperformed the standard cardiological measures and the signal-averaged P-wave approach. The best wavelet model on the basis of both classification performance and simplicity was the two-lead model that uses leads II and V1. It was concluded that the wavelet approach of automating classification is worth pursuing with larger samples to validate and extend the present study.

Automated eye tracking system calibration using artificial neural networks.

The electro-oculogram (EOG) continues to be widely used to record eye movements especially in clinical settings. However, an efficient and accurate means of converting these recordings into eye position is lacking. An artificial neural network (ANN) that maps two-dimensional (2D) eye movement recordings into 2D eye positions can enhance the utility of such recordings. Multi-layer perceptrons (MLPs) with non-linear activation functions and trained with back propagation proved to be capable of calibrating simulated EOG data to a mean accuracy of 0.33 degrees . Linear perceptrons (LPs) were only nearly half as accurate. For five subjects, the mean accuracy provided by the MLPs was 1.09 degrees of visual angle ( degrees ) for EOG data, and 0.98 degrees for an infrared eye tracker. MLPs enabled calibration of 2D saccadic EOG to an accuracy not significantly different from that obtained with the infrared tracker. Using initial weights trained on another person reduced MLP training time, reaching convergence in as little as 20 iterations.

Low-probability event-detection and separation via statistical wavelet thresholding: an application to psychophysiological denoising.

OBJECTIVES: The aim of this paper is to introduce and test a general, wavelet-based method for the automatic removal of noise and artefact from psychophysiological data. METHODS: Statistical wavelet thresholding (SWT) performs blind source separation by transforming data to the wavelet domain, and subsequent filtering of wavelet coefficients based on a statistical framework. The observed wavelet coefficients are modelled using a Gaussian distribution, from which low-probability outliers are attenuated based on their z-scores. RESULTS: The technique was applied to both simulated and real event-related potentials (ERP) data. SWT applied to artificial data displayed increased signal-to-noise ratio (SNR) improvements as noise amplitude increased. ERP averages of filtered experimental data displayed a correlation of 0.93 with operator-filtered data, compared with a correlation of 0.56 for unfiltered data. The energy of operator-designated contaminated trials was attenuated by a factor of 7.46 relative to uncontaminated trials. SNR improvement was observed in simulated tests. CONCLUSIONS: Variations of SWT may be useful in situations where one wishes to separate uncommon/uncharacteristic structures from time series data sets. For artefact removal applications, SWT appears to be a valid alternative to expert operator screening.

Adaptive wavelet filtering for analysis of event-related potentials from the electro-encephalogram.

A challenging task in psychophysiology is the extraction of event-related potentials (ERPs) from the background electro-encephalogram. The task is made more difficult by the properties of ERPs, which typically consist of multiple features of variable latency, localised in time and frequency. A novel technique is described for analysis of ERPs, adaptive wavelet filtering (AWF), which is proposed as an alternative to trial averaging. Band-limited detail representations of each trial are obtained using wavelet analysis. The Woody adaptive filter is then used to align trials with respect to the evoked response. In a simulation study, the AWF extracts 39% of higher-frequency signal variance from background noise, compared with less than 1% for standard averaging and the Woody filter. The AWF is applied to a data-set of 448 ERPs, comprising right-finger button presses from eight subjects. Average split-half reliability of the AWF on scales up to 12 Hz was 0.51.

Identifying and reducing noise in psychophysiological recordings.

Psychophysiology continues to be a widely used methodology in the study of human behaviour, emotion and cognition. The new researcher is faced with a number of problems in the recording process since the desired physiological signal must be isolated from a variety of noise sources. Precautions and strategies that can be implemented in setting up the recording equipment and isolating the subject from interference are described. There are also a number of software techniques that can be applied to improve signal quality after the data have been acquired. An overview is provided of hardware and software methods used to maximise the signal quality.

Event-related potentials can reveal differences between two decision-making groups.

Previous research has shown that a complex decision is dependent on an underlying utility metric that is used by decision making processes to accumulate preference for one alternative. This study postulated that a state of indecision may arise if this underlying metric is poorly organized. The underlying metric was examined with a paired comparison task while measuring event-related potentials (ERP) for subjects classified as 'career decided' and 'career undecided'. Stimuli for comparison were presented either sequentially or simultaneously. The simultaneous condition produced results consistent with the hypothesis that undecided subjects have a poorly organized value metric as revealed in both the behavioral data and the P3 component. A relationship between P3 amplitude and word distance on the underlying metric was found only for the decided group. This was interpreted in terms of the previously documented relationship between P3 and the constructs of decision confidence and task difficulty.

Imagery in human classical conditioning.

Many clinical strategies use patients' imagery to explore and treat phobic and posttrauma reactions, however little attention has been paid to the underlying assumption that imagery of relevant stimuli may help maintain conditioned behavior. In this article, the authors examine the premise that mental images can potentiate and substitute for physical stimuli in human classical conditioning. The authors review empirical evidence to detail the role of images of conditioned stimuli (CS) and unconditioned stimuli (US) during pre-exposure to stimuli, the actual pairing of the CS and US, and extinction when the CS is presented alone. The evidence suggests that mental imagery can facilitate or diminish the outcome of classical conditioning in humans and, more tentatively, that mental images can substitute for actual US and CS in autonomic conditioning. They argue that researchers should explore the role of mental imagery in conditioning through the use of advances in the measurement of imagery. Finally, they analyze anxiety and trauma reactions as examples of how applied areas can be used to explore and benefit from developments in this area.

Gender differences during processing of the Stroop task.

An assertion was made that "There are no sex differences in Stroop interference" (MacLeod, 1991, p. 203) in spite of some evidence to the contrary (e.g., Sarmany, 1977). To resolve the discrepancy, this study examined the nature of gender differences in the context of other variables. 6 men and 8 women were tested, using response speed and errors made as dependent measures. Independent variables were gender, perceptual input (Stroop) task, congruency of stimuli, manual response output, and trial block. Contrary to MacLeod, men were consistently slower than women over trial blocks by some 46 msec., although their error rates did not differ significantly. Response output interacted with gender, with Stroop task, and with trial block. Congruent stimuli were processed faster than incongruent ones. Differences may be ascribed to greater verbal and fine motor abilities of women and greater spatial ability of men.

Do neuroleptics impair learning in schizophrenic patients?

Dopamine (DA) has been shown to be involved in reward-related (incentive) learning but not stimulus-stimulus (s-s) associative learning. Schizophrenic individuals receive neuroleptics (DA receptor blockers) for therapy and therefore may have impaired incentive learning. To test this hypothesis, in experiment 1, schizophrenic outpatients receiving haloperidol or flupenthixol and matched controls were tested on tasks involving incentive or s-s learning. Patients were also given the Brief Psychiatric Rating Scale (BPRS). Results showed the patients to be significantly impaired in every task. However, only impairments of s-s learning were correlated with psychiatric state. Thus, deficits on the tasks involving incentive learning were interpreted as resulting from neuroleptic drugs rather than psychiatric state. Experiment 2 tested 26 schizophrenic inpatients receiving a variety of neuroleptics (converted to chloropromazine equivalency (CPZEQ)) on the same tasks. A blood sample was collected from the patients and from age-matched controls and prolactin levels were found to be significantly higher in the patients. Multiple regression analysis was used on patient data to determine whether prolactin level or CPZEQ were related to performance. It was found that incentive learning but not s-s associative learning was significantly predicted by one of these two indexes of neuroleptic drug dose. The results of these experiments provide some support for the hypothesis that neuroleptics might impair incentive but not s-s associative learning in schizophrenics. The observation that neuroleptics affect human incentive learning might lead to more efficient use of behavior modification programs in the treatment of schizophrenia.

A Pavlovian procedure for improving sexual performance of noncopulating male rats.

Previous research has shown that Pavlovian conditioning, based on unconsummated arousal, can increase copulatory rate in laboratory rats. This investigation tested whether a similar procedure could improve the performance of males that initially fail to copulate successfully. Male rats that did not reach ejaculation with a receptive female on a pretest were randomly assigned to one of two groups: CS-US paired or CS-US unpaired. The CS consisted of a period of placement in a running wheel which allowed measurement of incidental activity. The US was (arousing) exposure to a female separated from the male by a wire mesh screen. The CS immediately preceded the US for the paired group but the two were unpaired for the control group. Following conditioning, CS and No-CS tests were given, with both copulation and activity measures taken. Subjects in the paired group were significantly more likely to achieve ejaculation on the CS test than those in the control group, and they were also more active during the test. In contrast, differences on the No-CS test were not significant, consistent with expectations from a Pavlovian explanation. These data show the efficacy of Pavlovian procedures in improving sexual performance, with a possible application to increase arousal to selected cues for human subjects, e.g., some individuals with erectile dysfunction.

Pavlovian conditioning of sexual arousal: first- and second-order effects.

Despite the likely importance of Pavlovian conditioning in sexual behavior, previous evidence of reliable or sizeable effects is very sparse. This report includes four experiments in the conditioning of sexual arousal in the males of a mammalian species, namely, the rat. In each case the unconditioned response (UR) was unconsummated arousal after exposure to a female. There was evidence of a substantial conditioned effect, as shown by decreases in the time to complete copulation during postconditioning conditioned stimulus (CS) tests. It is also possible to establish a second-order conditioned response (CR), which retains its strength even after extinction of the first-order response. These results confirm the power of Pavlovian contingencies in sexual responding and provide implications for conditioning theory and applied work.