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K C Squires

Publications and source records attributed to K C Squires.

11 recordsLinked to original sources
PubMed1979

Evoked potential correlates of human information processing.

The late positive component (P3) of the feedback evoked potential was investigated in two tasks: the detection of near-threshold auditory stimuli, and the estimation of 1 s time intervals. When the intensity or probability of the threshold stimuli was varied in the detection task, it became apparent that the feedback P3 was related to the 'contingent probability' of confirming or disconfirming feedback given a particular response. In the time-estimation task the relative probabiliti-s of confirming and disconfirming feedback were altered by changing the time-window wherein a response was judged correct. In these experiments it was found that the feedback P3 component was highly dependent upon the probability of the feedback, and relatively independent of its confirming or disconfirming meaning. With decreasing probability of the feedback stimuli, the P3 component became larger, later, and somewhat more frontal.

Auditory Perception↗
PubMed1978

Acute effects of alcohol on auditory brainstem potentials in humans.

Auditory brainstem potentials were recorded from human subjects before and after an intoxicating dose of alcohol. Following alcohol ingestion there were significant, progressive increases in the latencies of brainstem potential peaks III through VII. No changes in peak amplitudes were found. The results indicate that alcohol has a depressive effect on neural transmission within the primary auditory brainstem pathway.

Adult↗
PubMed1978

Auditory brain stem potentials in chronic alcohol intoxication and alcohol withdrawal.

Auditory brain stem evoked responses were in unrestrained rats during periods of acute and chronic alcohol intoxication, alcohol withdrawal, and recovery. Acute alcohol administration altered the auditory brain stem potentials by a prolongation of both peak latency and central conduction time, beginning with early peaks. Similar but lesser effects affecting only the latter peaks were observed during chronic alcohol intoxication. By contrast, alcohol withdrawal resulted in a decrease in the peak latencies of auditory brain stem potentials and a facilitation of central conduction time. Recovery of the auditory brain stem potentials to the normal form required at least three to four weeks. The present study provides the first quantitative data, to our knowledge, on manifestations of alcohol tolerance and withdrawal.

Acoustic Stimulation↗
PubMed1978

Age-related variations in evoked potentials to auditory stimuli in normal human subjects.

Auditory evoked potentials were recorded from 47 subjects ranging in age from 6 to 76 years in order to assess the effects of maturation and aging on the evoked (N1 and P2) and event-related (N2 and P3) components. Because of clear differences in the effects of age on the event-related components between children (less than 15 years of age) and adults the subjects were divided into two populations for analysis. For adults there was a systematic increase in the latency and decrease in amplitude of each component with age. Also the rate of the age-related increase in latency was proportional to the latency of the component. The scalp distributions of both the stimulus-evoked and event-related components were found to vary with age yielding a more nearly equipotential distribution for older subjects. For children the latencies of the event-related components decreased with age. The stimulus-evoked components had latencies which were not significantly different from those predicted from the adult data. In contrast to the adult data, age affected the scalp distributions of the stimulus-evoked components differently than the event-related components. These results suggest an aging process is relfected in the auditory evoked potential which is not the simple inverse of maturational processes.

Acoustic Stimulation↗
PubMed1978

Auditory brain stem potentials with alcohol.

Auditory brain stem potentials were recorded from unrestrained rats and from cats paralyzed with Flaxedil, before and after ingestion of intoxicating dosages of alcohol. The acute effect of alcohol was a cumulative increase in the central conduction times of successive brain stem potential peaks. Statistically significant latency changes were found for peaks attributed to neural structures as far peripherally as the medulla. This depressive influence of alcohol on sensory transmission was independent of variations in stimulus intensity and body temperature.

Acoustic Stimulation↗
PubMed1978

Long latency event-related components of the auditory evoked potential in dementia.

Long-latency auditory evoked potentials were recorded from two groups of patients, with and without dementia, and were compared with those from a population of normal subjects ranging in age from 15 to 76 years. A sequence of tones of two different frequencies (1000 Hz and 2000 Hz) was presented and each patient was asked to count the occurrences of the rare (P = 0.15) tones in the sequence. Evoked potential waveforms were averaged separately for the rare and frequent tone. Of the various evoked potential components elicited by the tones, the P3 component (latency 300-500 ms) was found to be the most sensitive to aging in normal subjects. It was also the only component which could be used to differentiate between the demented patients and the normal subjects or non-demented patients. The non-demented patients did not differ from normal in any waveform measure. The magnitude of the latency change of the P3 component in dementia relative to normal was sufficiently large that it may provide a practical and objective measure of dementia in a clinical setting.

Acoustic Stimulation↗
PubMed1977

On the influence of task relevance and stimulus probability on event-related-potential components.

Fifteen subjects were presented with series of tones. Any one tone was either loud or soft, and in any one series the probability of one tone intensity was either 0.9 or 0.1. Subjects were instructed to count the frequent tones or to count the rare tones. The stimuli were also presented while the subjects were solving a word-puzzle. Event-related potentials (ERPs) were recorded from 9 scalp locations (F3, C3, P3, FZ, CZ, PZ, F4, C4, P4) referred to linked mastoids. ERP components were measured with a Principal Components analysis and the relations between these measures and the independent variables were evaluated with the ANOVA procedure. This paradigm allowed an evaluation of the effect of stimulus probability, stimulus relevance, and task relevance on the waveform of the ERPs. We conclude that the P350 component is enhanced whenever the eliciting stimulus is both rare and in some sense relevant to the subject's task and the degree of enhancement is greatest when the rare--relevant tone is loud. A "slow wave" component which follows P350 is related to the same variables but has a scalp distribution quite different from that of P350. The slow wave shows a progressive shift in polarity from negative to positive from the frontal to the parietal sites, while the P350 is of nearly equal amplitude (and positive) at the central and parietal sites and has a smaller (positive) and amplitude at FZ. A third prominent component, negative in polarity, peaking at about 210 msec, is most pronounced following rare stimuli, whether or not they were task relevant. The amplitude of N210 tended to be largest at the frontal electrode. This study then demonstrates that when suitable measurement techniques are used, multiple endogenous ERP components can be observed, each related to distinct aspects of cognitive behavior.

Acoustic Stimulation↗
PubMed1977

Bisensory stimulation: inferring decision-related processes from P300 component.

Three experiments were conducted to evaluate the P300 component of the human evoked response as an index of bisensory information processing. On different blocks of trials, subjects were presented with auditory stimuli alone, visual stimuli alone, or with audiovisual compounds. In each series there were two possible stimuli, one of which was presented less frequently than the other; the subjects' task was to count the infrequent stimuli. In the first two experiments the information in the two modalities was redundant, whereas in the third the modalities provided nonredundant information. With redundant information, the P300 latency indicated bisensory facilitation when the unimodal P300 latencies were similar; when the unimodal latencies were dissimilar, the bisensory P300 occurred at the latency of the earlier unimodal P300. Reaction times paralleled P300 latency. When the information in the two modalities was nonredundant, both P300 amplitude and reaction-time data indicated interference between the two modalities, regardless of which modality was task relevant. P300 latency and reaction time did not covary in this situation. These data suggest that P300 latency and amplitude do reflect bisensory interactions and that the P300 promises to be a valuable tool for assessing brain processes during complex decision making.

Acoustic Stimulation↗
PubMed1976

Beyond averaging: the use of discriminant functions to recognize event related potentials elicited by single auditory stimuli.

A test of the stepwise discriminant analysis (SWDA) procedure for assessing single-trial event related potentials (ERPs) is presented. Discriminant functions (DFs) were built from a data base composed of single-trial ERPs from sixteen subjects who were presented trains of loud and soft tones. Loud tones occurred randomly on 10% of the trials. Subjects either counted the rare--loud stimuli or solved a hidden-word puzzle. Various DFs at three electrode sites (Fz, Cz and Pz) were obtained to assess the feasibility of performing pairwise discriminations between the various combinations of events which are defined by this procedure. For the pair of events which yielded the most striking differences between their average ERP waveforms it was possible to classify correctly, an average of 84% of the events using information from one electrode site, and 89% of the events if information from multiple electrode sites was used. A "subject-independent" DF was developed from these data and applied to data obtained from seven new subjects. This subject-independent function proved to be sufficiently generalized to classify correctly 81% of the trials. The nature of classification errors by this procedure is discussed.

Auditory Cortex↗
PubMed1975

Two varieties of long-latency positive waves evoked by unpredictable auditory stimuli in man.

Two distinct late-positive components of the scalp-recorded auditory evoked potential were identified which differed in their latency, scalp topography and psychological correlates. The earlier component, called "P3a" (latency about 240 msec), was elicited by infrequent, unpredictable shifts of either intensity or frequency in a train of tone pips whether the subject was ignoring (reading a book) or attending to the tones (counting). The later component, called "P3a" (mean latency about 350 msec), occurred only when the subject was actively attending to the tones; it was evoked by the infrequent, unpredictable stimulus shifts, regardless of whether the subject was counting that stimulus or the more frequently occurring stimulus. Both of these distinct psychophysiological entities have previously been refered to as the "P3" or "P300" in the literature.

Adult↗