PubMed · 7445024
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C Ellenberger. 1980. Introduction to visually evoked potentials.. https://pubmed.ncbi.nlm.nih.gov/7445024/
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This report describes the development and evaluation of mathematical models for predicting human performance from discrete wavelet transforms (DWT) of event-related potentials (ERP) elicited by task-relevant stimuli. The DWT was compared to principal components analysis (PCA) for representation of ERPs in linear regression and neural network models developed to predict a composite measure of human signal detection performance. Linear regression models based on coefficients of the decimated DWT predicted signal detection performance with half as many free parameters as comparable models based on PCA scores. In addition, the DWT-based models were more resistant to model degradation due to over-fitting than PCA-based models. Feed-forward neural networks were trained using the backpropagation algorithm to predict signal detection performance based on raw ERPs, PCA scores, or high-power coefficients of the DWT. Neural networks based on high-power DWT coefficients trained with fewer iterations, generalized to new data better, and were more resistant to overfitting than networks based on raw ERPs. Networks based on PCA scores did not generalize to new data as well as either the DWT network or the raw ERP network. The results show that wavelet expansions represent the ERP efficiently and extract behaviorally important features for use in linear regression or neural network models of human performance. The efficiency of the DWT is discussed in terms of its decorrelation and energy compaction properties. In addition, the DWT models provided evidence that a pattern of low-frequency activity (1 to 3.5 Hz) occurring at specific times and scalp locations is a reliable correlate of human signal detection performance.
Electric current-induced phase alternations have been imaged by fast magnetic resonance image (MRI) technology. We measured the magnetic resonance phase images induced by pulsed current stimulation from a phantom and detected its sensitivity. The pulsed current-induced phase image demonstrated the feasibility to detect phase changes of the proton magnetic resonance signal that could mimic neuronal firing. At the present experimental setting, a magnetic field strength change of 1.7 +/- 0.3 nT can be detected. We also calculated the averaged value of the magnetic flux density BT parallel to B0 produced by electric current I inside the voxel as a function of the wire position. The results of the calculation were consistent with our observation that for the same experimental setting the current-induced phase change could vary with location of the wire inside the voxel. We discuss our findings in terms of possible direct MRI detection of neuronal activity.
In olfaction, it is not possible to determine which nostril is being stimulated, i.e., lateralize, when a pure olfactory substance, e.g., phenylethyl alcohol or vanillin, is administered into one nostril, and, simultaneously, an odorless, solvent blank into the contralateral nostril. We subjected volunteers to extensive training, with feedback on each trial, in an attempt to determine whether it was possible, in these well-trained subjects, to overcome this apparent impossibility. We failed to obtain any evidence to support the notion that a pure olfactory stimulus could be lateralized when the odorant and blank were presented simultaneously. The task, however, became simple when the odorant and the blank entered each nostril sequentially. We investigated, using a two-channel olfactometer, temporal parameters that enabled such discrimination. We controlled the duration of odorant and blank air puffs, as well as their mutual timing, to determine the threshold stimulus onset-disparity, i.e., the interval between stimulus onset and blank onset, that resulted in an inability to lateralize. Latencies shorter than the threshold interval would be perceived as simultaneous stimulation. We determined that the onset interval was between 200 and 400 ms, depending on the duration of the stimuli (a shorter interval was noted for stimuli of 150-ms duration relative to 300- and 450-ms stimuli). This was also true when two odorants were applied, rather than an odorant and a blank, and the subject was instructed to focus on the sequence of odorant delivery and side of stimulation. The temporal onset threshold was the same for lateralization and for order of stimulation. Whether the olfactory system per se mediates this discrimination or whether inputs from olfaction and chemesthesis, via trigeminal free nerve endings stimulated by air-stream onset, combine to allow this discrimination has yet to be determined.