Computer signal detection by monitoring auditory evoked potentials

A digital computer, using a simple decision algorithm, attempted to determine when an acoustical signal had been presented to a cat by monitoring the amplitude of the evoked potentials (EP) at brainstem auditory nuclei. The signal-to-noise level at threshold and the shape and range of the decision model “psychometric functions” were similar to those obtained from humans in the same task. In addition, the detection performance obeys Weber’s law, the mean amplitude of the EP increases monotmonically with signal level, the variance of the amplitude is independent of both signal and noise level, and both the mean latency and the variance of the latency of the peaks decrease with increasing signal level. These findings suggest that the synchronization in firing of a population of single units plays a part in determining the amplitude of the EP. Interaural effects in detection performance were found at the inferior colliculus and, to a lesser extent, at the superior olive.     

Changes in middle latency auditory evoked potentials during meditation

In the present study of middle latency auditory evoked potentials during Brahmakumaris Raja Yoga meditation there was a decrease in the peak latency of the Na wave (a negative wave between 14 and 19 msec.) during meditation. Since the neural generator of this wave lies at the midbrain-thalamic level, from the results one can infer that the meditation reduces conduction time at this level.     

Long latency auditory evoked potentials

Experiment 1 elicited the P1, N1, P2, and N2 components of the long latency auditory evoked potential (AEP) using a 1000 Hz tone presented at 30, 50, or 70 dB SPL and 1-, 3-, or 5- second inter-stimulus intervals to assess the relative effects of the combination of these variables on component amplitude and latency. Four blocks of 16 tone presentations each were recorded from each subject to determine if changes in the AEP would occur because of short-term habituation. Both stimulus factors interacted significantly in a systematic fashion for the amplitude measures, with increases in latency also associated with increases in intensity and inter-stimulus interval. Only minor changes across the four trial blocks for either the amplitude or latency measures were observed over the various stimulus presentation conditions. Experiment 2 employed the same tone stimulus presented at 50 dB SPL and a 3-second inter-stimulus interval. Eight blocks of 64 trials were recorded from each subject on each day for four days to investigate long-term habituation effects. No substantial changes in any of the component amplitudes or latencies were obtained across the 32 trial blocks. It was concluded that intensity and inter-stimulus interval interact to determine AEP amplitude as well as latency values and that the constituent components do not change appreciably with repeated stimulus presentations, even after several days.     

Decision-related cortical potentials during an auditory signal detection task with cued observation intervals.

Cortical-evoked potentials were recorded from human subjects performing an auditory detection task with confidence rating responses. Unlike earlier studies that used similar procedures, the observation interval during which the auditory signal could occur was clearly marked by a visual cue light. By precisely defining the observation interval and, hence, syncrhonizing all perceptual decisions to the evoked potential averaging epoch, it was possible to demonstrate that high-confidence false alarms for accompanied by late-positive P3 components equivalent to those for equally confident hits. Moreover the hit and false alarm evoked potentials were found to covary similarily with variations in confidence rating and to have similar amplitude distributions over the scalp. In a second experiment wherein the signal intensity was increased to make signal presence and signal absence clearly discriminable and the a priori probability of signal presentation was varied from .5 to .9, it was demonstrated that correct rejections can be associated with a P3 component larger than that for hits. Thus it was possible to show, within the signal detection paradigm, how the two major factors of decision confidence and expectancy are reflected in the P3 component of the cortical-evoked potential.     

The impact of prestimulus EEG frequency on auditory evoked potentials during sleep onset.

Auditory evoked potentials were recorded during wakefulness, Stage 1, and Stage 2 non-REM sleep using a three-tone auditory oddball paradigm. Stage 1 sleep was divided into trials preceded by alpha and those preceded by theta. A negative wave peaking at about 100 ms, N1, displayed a significant decrease in amplitude with the onset of Stage 2 sleep. A later N2 peaked at about 250 ms in the waking state. This changed into a sleep-specific negative wave peaking at 300 ms (N300) at the alpha-theta transition within Stage 1. The P300 displayed a similar shift to become a P450 in Stage 2 sleep. N550 was specific to Stage 2, and was larger in response to rare, rather than frequent stimuli. There was no evidence of any enhancement to relevant rare stimuli compared with irrelevant rare stimuli.     

Brainstem auditory evoked potentials in receptive developmental language disorder

It has been hypothesized that receptive developmental language disorder (RDLD) may be explained by an auditory processing deficit. The neuroanatomical locus of this deficit is unknown. Brainstem auditory evoked potentials (BAEPs) reflect the functioning of the auditory nerve and auditory brainstem pathways to high-frequency acoustical stimulation in humans and reflect the first stages of auditory processing. These were studied in 12 subjects with RDLD (four females and eight males, ages 12 to 19) and twelve control subjects (three females and nine males, ages 14 to 24). Click intensity and rate of stimulation were varied. The BAEPs for the RDLD group were comparable to the control group as well as to hospital norms across intensity levels and stimulation rates. The evidence obtained suggests that a disorder in the neurophysiological systems underlying the BAEPs and reflecting initial stages of auditory processing is not essential for RDLD.     

Meditation alters representations of peripersonal space: Evidence from auditory evoked potentials

Meditation commonly gives rise to the feeling that the self and the surrounding world are no longer separate, as if the boundary between them has dissolved. We propose this may occur due to alterations in representations of peripersonal space (PPS), the reachable space surrounding the body which is integral to a sense of where one’s bodily “self” is located in space. Thirty-one participants completed an auditory oddball paradigm before and after a guided meditation, during which we measured their P3 evoked potential, a marker of attentional salience. Pre-meditation, participants exhibited an enhanced attentional response to stimuli presented within PPS, relative to beyond PPS. Post-meditation, this PPS attentional enhancement was negated, with no distinction between responses to stimuli within versus beyond PPS. The results suggest that meditation leads to a constriction of PPS boundaries, even in novice meditators, elucidating one potential cause of the perceptual changes associated with meditation.     

Hemispheric asymmetry of auditory evoked potentials to comparisons within and across phonetic categories

In 10 right-handed Ss, auditory evoked responses (AERs) were recorded from left and right temporal and parietal scalp regions during simple discrimination responses to binaurally presented pairs of synthetic speech sounds ranging perceptually from /ba/ to /da/. A late positive component (P3) in the AER was found to reflect the categorical or phonetic analysis of the stop consonants, with only left scalp sites averaging significantly different responses between acoustic and phonetic comparisons. The result is interpreted as evidence of hemispheric differences in the processing of speech in respect of the level of processing accessed by the particular information processing task.     

Critical-band effects in two-channel auditory signal detection

Two-channel auditory signal detection was investigated with 50-msec sinusoidal signals masked by binaurally uncorrelated noise. In the two-channel tasks, the signals in each earphone channel were presented with an independent probability during the single observation interval and the observers were required to detect the inputs in a single earphone (selective-attention condition) or in both earphones (divided-attention condition). When the signals in each earphone were within the same critical band (the assumed singled processing unit in frequency domain), there was a decrement in detection performance in both the selective- and divided-attention (i.e. dichotic) conditions compared with the monaural condition. However, when signals were separated in frequency by several critical bands, a decrement in dichotic performance, as compared with monaural performance, occurred only in the divided-attention condition. These findings are discussed in terms of their implications regarding models of multichannel signal processing and the definition of input channels in terms of earphones.     

Auditory evoked potentials during selective listening to dichotic speech messages

The sensitivity of the scalp-recorded, auditory evoked potential to selective attention was examined while subjects monitored one of two dichotically presented speech passages for content. Evoked potentials were elicited to irrelevant probe stimuli (vowel sounds) embedded in both the right- and the leftear’s message. The amplitude of the evoked potential was larger to probe stimuli embedded in the attended message than to probe stimuli in the unattended message. Recall performance was unaffected by the presence of the probes. The results are interpreted as supporting the hypothesis that this evoked potential sensitivity reflects an initial “input selection” stage of attention.     

Personality and augmenting/reducing in visual and auditory evoked potentials

Previous studies have indicated a relationship between evoked potential augmenting/reducing and extraversion or sensation seeking. However, the proposed mechanism of protective inhibition can account for this fact only if the relationship generalizes across different modalities and response definitions. The present study was designed to test this, using six intensities of visual and six intensities of auditory stimuli along with the EPI and SSS questionnaires.For the visual stimuli, the slope of the P90-N120 amplitude at the vertex correlated significantly with both the extraversion and the disinhibition scales in the way that augmenting/reducing theory predicts.However, over the primary visual area, no component showed the same personality relationship as the vertex wave, and one early component showed the opposite. This result suggests that personality differences in VEPs may reflect different ways of allocating processing resources between primary and association areas, rather than a generalized tendency to inhibit strong stimuli.In the auditory modality, personality differences were not apparent in the amplitude slopes, possibly due to the confluence from primary and association areas in AEPs in the vertex lead.There was a general tendency for latencies to correlate positively with extraversion and disinhibition, in congruence with Eysenck's theory on the biological basis of extraversion.     

Learning-disordered children's evoked potentials during sustained attention

Evoked potentials and performance of 19 learning-disordered (LD) and 19 normally achieving children were studied in two versions of the Continuous Performance Test (CPT). In both CPT procedures, LD children made more errors of omission and commission than did normal children. Evoked potential differences between groups were especially prominent in the more difficult BX version of the CPT. LD children displayed significantly smaller late positive components (LPC) of the evoked potential to critical stimuli in the task. There were no LPC differences between diagnostic groups for noncritical stimulus categories. The results suggest a deficit in behavioral and cortical indices of sustained attention among LD children.This research is based on a doctoral dissertation in psychology submitted by the first author (Dainer, 1980) and supervised by the second author. The research was partly supported by NIMH Grant MH 32103 and New York State Health Research Council Contract 1396 to the second author. We are grateful to the Strong Memorial Hospital Learning Disorders Clinic; B.O.C.E.S. School #1, Fairport, New York; Rochester Learning Disabilities Association; and Winifred Stebbins for referring learning-disordered children, and to the Rochester Central YMCA for referring normally achieving children. The University of Rochester College of Arts and Science provided partial support for computer funds. For their assistance, we are grateful to Lance Bauer, John Chapman, Michael Davidson, Dale McAdam, James Metz, and Lawrence Ota.     

Visual signal detection measured by event-related potentials

We compared the performance of 10 well-functioning university students who had experienced a mild head injury (MHI) an average of 6.4 years previously and 12 controls on a series of standard psychometric tests of attention, memory, and thinking and on a series of auditory oddball vigilance tasks to which we also took event-related potentials (ERPs). The MHI and Control groups performed equivalently on all the psychometric tasks and on self-report questionnaires of everyday memory and attention difficulties. The MHI group performed more slowly and with lower accuracy on only the most difficult of the oddball tasks, yet they showed substantially and significantly reduced P300 amplitudes and subsequent attentuation on all the oddball tasks, both easy and difficult. There were no alterations of N1, P2, and N2 components. These data suggest that despite excellent behavioral recovery, subtle information processing deficits involving attention nevertheless may persist long after the original injury and may not be apparent on a variety of standard psychometric measures.     

Deferred decision in human signal detection: A preliminary experiment

In the detection task characterized by deferred decision, the observer is allowed to determine how many observations he will make before deciding whether or not a signal is present, and he is called upon to balance the goals of maximizing accuracy and conserving time. The human observer appears capable of using the optimal process of cumulating sensory information over successive observations, but certain common training procedures lead him to use a less efficient process. Though he displays a consistent decision bias, his performance is also in good agreement with the optimal model of the process of terminating a sequence of observations.     

Central auditory processing. VI. Detecting ear dominance by evoked potentials

An electrophysiological method is described for measuring the direction and strength of a subject's ear dominance for pitch using the P3 component of event-related potentials. Results of these experiments reveal that the P3 can be used effectively for these measures in man.     

Cortical potentials evoked by confirming and disconfirming feedback following an auditory discrimination

Vertex potentials elicited by visual feedback (signals following an auditory intensity discrimination have been studied with eight Ss. Feedback signals which confirmed the prior sensory decision elicited small P3s, while disconfirming, feedback elicited P3s that were larger. On the average, the latency of P3 was also found to increase with increasing disparity between the judgment and. the feedback information. These effects were part bf an overall dichotomy in waveshape following confirming vs disconforming feedback. These findings are incorporated in a general model of the role of P3 in perceptual decision making.     

The diagnostic significance of auditory evoked brain stem potentials in multiple sclerosis

30 patients suffering from multiple sclerosis were examined by BERA among other audiological tests. In 47% we stated significant pathological BERA-latencies, in 53% pathological interpeak-intervals. The most patients have symptoms of brainstem, but 3 cases spinal symptoms. There are no constant correlations to subjective hearing threshold measurements. According to literature BERA, especially the measurement of interpeak-intervals, increases diagnostic security of the diagnosis multiple sclerosis.