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T W Picton

Publications and source records attributed to T W Picton.

At least 19 recordsLinked to original sources
PubMed1992

Perceptual closure and object identification: electrophysiological responses to incomplete pictures.

Event-related potentials were recorded during the naming of pictures of concrete objects. The pictures were presented at three levels of completeness: 10, 30, and 60%. The ERP waveforms were evaluated according to the level of picture completeness and the correctness of naming. A negative wave in the latency range of 250-550 ms was significantly more negative when the pictures were more incomplete, regardless of the correctness of response. This N400 wave is proposed as being related to hypotheses about the identity of the object. A late positive wave in the latency range of 550-650 ms followed the negativity, but only when the response was correct. This may reflect the subject's certainty about the perceptual analysis, a verification of the identity of the object. A slow parietal negativity lasting up to 2 sec was largest for the least complete picture. This therefore varied with the perceptual difficulty.

Adult↗
PubMed1992

The P300 wave of the human event-related potential.

The P300 wave is a positive deflection in the human event-related potential. It is most commonly elicited in an "oddball" paradigm when a subject detects an occasional "target" stimulus in a regular train of standard stimuli. The P300 wave only occurs if the subject is actively engaged in the task of detecting the targets. Its amplitude varies with the improbability of the targets. Its latency varies with the difficulty of discriminating the target stimulus from the standard stimuli. A typical peak latency when a young adult subject makes a simple discrimination is 300 ms. In patients with decreased cognitive ability, the P300 is smaller and later than in age-matched normal subjects. The intracerebral origin of the P300 wave is not known and its role in cognition not clearly understood. The P300 may have multiple intracerebral generators, with the hippocampus and various association areas of the neocortex all contributing to the scalp-recorded potential. The P300 wave may represent the transfer of information to consciousness, a process that involves many different regions of the brain.

Aging↗
PubMed1991

The timing of the processes underlying lateralization: psychophysical and evoked potential measures.

This article describes a technique to measure binaural integration time. A binaural noise with an interaural time difference of 0.8 msec was presented in three conditions: alone, with intervening noise that was identical between the two ears, or with uncorrelated intervening noise. Both behavioral responses and evoked potentials were recorded. When the stimulus was presented in a quiet background, it was accurately detected and lateralized with durations as short as 2 msec. The N1 peak of the evoked potential occurred at approximately 90 msec. When the stimulus occurred as a brief change in an ongoing correlated binaural noise, a duration of 10 msec was necessary before the sound could be accurately lateralized or an evoked potential elicited. The N1 peak occurred at approximately 120 msec. When the stimulus occurred as a change in an ongoing uncorrelated binaural noise, a duration of 60 msec was necessary for the subject to lateralize the stimulus and for an evoked potential to be elicited. The N1 peak occurred at about 130 msec. These results suggest that a period of approximately 60 msec is required to detect the correlation of an ongoing binaural noise and that a somewhat shorter period is necessary to track changes in a sound source that has already been lateralized. The simplicity of this technique makes it an attractive tool for assessing central auditory function.

Acoustic Stimulation↗
PubMed1991

Long-latency auditory evoked potentials during general anesthesia: N1 and P3 components.

The N1 and P3 auditory evoked potentials were recorded to evaluate their usefulness as measures of the level of consciousness in 14 ASA physical status I and II patients undergoing elective surgery. The anesthetic agents were thiopental, fentanyl, and isoflurane with or without nitrous oxide. Recordings were carried out before induction (preinduction) and during induction, surgical anesthesia, emergence, and recovery from anesthesia. The auditory response was evoked by 700-Hz tones that occurred occasionally and unpredictably in a train of 500-Hz tones delivered at 40 per second. The patients were asked to press a button whenever they detected a 700-Hz tone. Studies with normal subjects have repeatedly shown that detected tones (HITS) evoke N1 and P3 waves, whereas undetected tones (MISSES) evoke no recognizable waves. The responses evoked by HITS were compared with those evoked by MISSES. The amplitudes of N1 and P3 were significantly different from zero for HITS before induction and during induction and recovery but not during emergence. The amplitudes of N1 and P3 were not different from zero for MISSES during induction, surgery, and emergence. During recovery, the N1 and P3 for MISSES were small and the P3 for HITS was significantly larger than for MISSES. The results indicate that except during emergence, HITS were associated with clear N1 and P3 waves, whereas MISSES were not. The lack of either N1 or P3 for HITS during emergence perhaps occurred because the patients, although responsive, were not yet fully conscious. The N1 and P3 components of the auditory evoked potential may provide specific indicators for consciousness.

Adult↗
PubMed1991

Human evoked potentials and the lateralization of a sound.

If an identical noise is presented to each ear with one ear receiving the noise slightly earlier than the other, the listener perceives the sound as originating from the side of the leading ear. If the interaural time-difference reverses, the subject perceives a shift in the lateralization of the sound to the other ear. This shift in lateralization evokes a late auditory potential with a negative wave at 135 ms and positive waves at 75 and 220 ms. This evoked potential specifically indexes central auditory processing since information about the timing of the auditory stimuli must be compared between the two ears. The response increases in amplitude with increasing interaural time-difference reaching maximum values between 0.3 and 1.5 ms. The response is evoked through acoustic frequencies below 2,000 Hz. In patients with multiple sclerosis the response is often abnormally delayed or small. The response may therefore be helpful in the clinical evaluation of patients with central auditory dysfunction.

Acoustic Stimulation↗
PubMed1991

The human auditory steady-state evoked potentials.

When auditory stimuli are presented at rates near 40/s, they evoke a steady-state middle latency response. This results from the super-position of the transient responses evoked by each of the rapidly presented stimuli. The steady-state evoked potentials are most appropriately analyzed using frequency-based techniques. The response is larger for stimuli of higher intensity and of lower tonal frequency. The amplitude of the response varies with the state of arousal of the subject. Sleep results in a decrease in the amplitude to between one third and one half of the amplitude during wakefulness. The response is even further attenuated by general anesthesia. This auditory steady-state evoked potential may therefore be helpful in monitoring the state of arousal of a patient undergoing anesthesia.

Adult↗
PubMed1991

Prognostic validity of brainstem electric response audiometry in infants of a neonatal intensive care unit.

This study compared the results of brainstem electric response audiometry (BERA) in infants of a neonatal intensive care unit to those obtained on the same children with pure-tone audiometry at 3 years of age. Six hundred children were initially tested in infancy, and complete follow-up information was obtained on 333. In 297 (89%) the BERA results accurately predicted the hearing status at the age of 3 years. Twenty-nine (9%) of the discrepancies were related to conductive hearing losses: 17 patients with a conductive hearing loss in the first few months of life had normal hearing at 3 years, and 12 patients normal in infancy had a conductive loss at 3 years. Two patients evaluated as a sensorineural hearing loss by BERA had normal hearing. These may have been due to a conductive loss. Six patients assessed as normal by BERA had significant hearing losses at the age of 3 years. Five of these had normal hearing at one frequency between 1,000 and 4,000 Hz. The sixth may have developed a sensorineural hearing loss after birth.

Audiometry, Evoked Response↗
PubMed1991

Effects of stimulus parameters on human evoked potentials to shifts in the lateralization of a noise.

Changing the interaural time difference (ITD) of a continuous binaural noise causes a shift in the perceived lateralization of the noise and evokes a late auditory evoked potential with negative peak at 130 ms and a positive peak at 220 ms. The response is mainly evoked by stimulus frequencies below 2,000 Hz and is mediated through the middle and apical regions of the cochlea. The threshold for perceiving the lateralization reversal and for eliciting a clear evoked potential is approximately 15 dB higher than the intensity required to perceive the onset of the noise. Increasing the ITD up to 1.0 ms increases the amplitude of the evoked potential and the perceived lateralization of the noise. Further increases in the ITD decrease the amplitude of the evoked potential and make the perception of the sound less 'compact'. Decreasing the intensity of the sound in one ear decreases the response to a change in ITD, but recognizable responses occur with interaural intensity differences up to 30 dB.

Acoustic Stimulation↗
PubMed1990

Human auditory steady-state response during general anesthesia.

The 40-Hz auditory steady-state evoked response (ASSR) is a sinusoidal electrical response of the brain to periodically presented auditory stimuli. It was recorded during anesthesia in 10 elective surgical patients to evaluate its usefulness as a measure of the level of consciousness. The anesthetic agents used were thiopental, fentanyl, and isoflurane with or without nitrous oxide. Recordings were carried out during the period before induction and during induction, surgical anesthesia, emergence, and recovery from anesthesia. The level of consciousness was measured with an auditory stimulus detection task. The electroencephalogram (EEG) was also recorded for comparison with the ASSR. The following indices were analyzed: total EEG power, relative power in the beta, alpha, theta, and delta frequency bands, and the median and spectral edge frequency. The amplitude of the ASSR was reduced significantly at the end of the induction period and decreased below noise levels during surgical anesthesia. It increased significantly during emergence and recovery. The amplitude during recovery remained significantly smaller than the preinduction values. The changes of the ASSR paralleled those of the level of consciousness. The EEG measurements were distorted by the presence of muscle artifacts that were prominent during emergence and recovery. The amplitude of the ASSR appears to provide a more reliable indicator of the level of consciousness than the EEG.

Adult↗
PubMed1990

Human evoked potentials to shifts in the lateralization of a noise.

A continuous noise was generated by running a sequence of random numbers through a digital-analog converter and connecting the output through an amplifier and filter to an earphone. Two channels were programmed to generate identical noise stimuli with one channel delayed relative to the other. When these stimuli were presented through earphones, the subject lateralized the noise to the side receiving the leading stimulus. Changes in the relative timing of the two stimuli caused the noise to shift its lateralization. Since these shifts occurred without any detectable change in the ongoing monaural noise, any potentials they evoked were specifically related to binaural interaction. The response recorded from the vertex contained a positive-negative-positive complex with peak latencies of 75, 136 and 220 ms. This response was similar to that evoked by the onset of a monaural stimulus although it was slightly smaller and significantly later. Despite several attempts, we were unable to record any definite earlier evoked potentials.

Adolescent↗
PubMed1990

Thresholds for short-latency auditory-evoked potentials to tones in notched noise in normal-hearing and hearing-impaired subjects.

The thresholds for the short-latency auditory evoked potentials (SLAEPs) to short-duration tones presented in notched-noise masking were evaluated in 20 normal-hearing and 20 hearing-impaired subjects. The differences (dB) between these thresholds (dB nHL) and the pure-tone behavioral thresholds (dB HL) across all 40 subjects were 11.6, 6.1, 6.3 and 0.8 dB for 500, 1,000, 2,000 and 4,000 Hz, respectively. These differences were significantly smaller for the hearing-impaired subjects than for the normal-hearing subjects. Ninety-eight percent of the SLAEP threshold estimations were within 30 dB of the subjects' pure-tone behavioral thresholds and 91% were within 20 dB.

Adolescent↗
PubMed1989

Brainstem auditory evoked response in the ferret (Mustela putorius).

The effect of click intensity, repetition rate and binaural interaction on the brainstem auditory evoked response (BAER) was examined in sixteen pigmented adult male ferrets. Potentials were recorded from platinum needle electrodes inserted over the vertex and left and right mastoids. Square waves, 100 microseconds in duration, were transduced by earphones enclosed in an assembly designed to fit securely over the ferret's external ear. The BAER in the ferret consists of four prominent vertex-positive peaks (P1-P4) and a fifth peak of smaller amplitude and more variable latency. The mean latencies of P1-P4 at 104 dB peak SPL were 0.96, 1.83, 2.75 and 3.62 ms. Reducing intensity over a 70 dB range resulted in a reduction in amplitude and a corresponding increase in latency ranging between 0.57 and 0.67 ms. Also, increasing click repetition rate resulted in a reduction in amplitude and an increase in latency. With intensity fixed at 104 dB peak SPL comparison of latencies at 10 and 50/s showed a mean increase of 20, 50, 60 and 80 microseconds for P1-P4, respectively. The effect of binaural interaction on the BAER was examined using the procedure of Dobie and Berlin (1979); the response evoked by binaural stimulation was subtracted from the summed left and right monaural responses to obtain a binaural interaction component. Binaural interaction in the ferret gave rise to a distinct vertex-negative wave with a latency similar to P4. An increase in click intensity over a 70 dB range resulted in a monotonic increase in amplitude and a decrease in latency of the binaural interaction component.

Acoustic Stimulation↗
PubMed1989

Traumatic brain injury, aging and reaction time.

The effects of traumatic brain injury (TBI) and aging were compared on tests of simple and complex reaction time (RT). Simple RT was not significantly affected by aging or TBI. TBI patients, however, tended to be slower on Simple RT tasks, and had a larger standard deviation. Individuals over age 60 and patients of any age with TBI demonstrated slower RT with choice RT tests. In addition, both groups (those over 60 and TBI patients) were less able than other groups to inhibit the processing of redundant information. For the TBI patients, this occurred primarily on reassessment. These results suggest that the deficit in both aging and TBI is not only a generalized neuronal slowing but a more specific impairment in attentional control processes, exhibited as a deficit in focused attention.

Adolescent↗
PubMed1988

Electrophysiological manifestations of typicality judgment.

Ten male subjects participated in an event-related potential study of typicality judgment of words that were of either high or low frequency of usage. The amplitude of a negative wave with an average peak latency of 490 msec (N400) correlated with the goodness-of-fit of a word to a particular category independent of frequency, with poor examples of the category evoking a significantly more negative waveform. The relative insensitivity of the N400 to word frequency suggests that the N400 reflects some postlexical evaluation rather than lexical access.

Adult↗
PubMed1988

Auditory evoked potentials in the assessment of hearing.

The auditory evoked potentials are the best available technique for identifying infants with a hearing impairment before the age of 6 months. They are also very important in the evaluation of patients with suspected retrocochlear hearing loss. New developments may soon allow the determination of hearing thresholds at different frequencies and a more accurate assessment of patients with central auditory dysfunction.

Audiometry, Pure-Tone↗
PubMed1987

Human auditory steady-state evoked potentials during selective attention.

The human auditory steady-state evoked potentials were examined during several different tasks requiring attention. Both Fourier analysis and signal averaging were used to measure the responses at stimulus rates between 37 and 41/sec. There was no effect of attention on the amplitude and phase of the steady-state evoked potentials when subjects either counted successive increments in stimulus intensity or read a book. In a dichotic listening task, there were clear changes in the late transient evoked potentials with selective attention but no changes in the steady-state responses. Furthermore, the steady-state potentials recorded during reading were not different from those obtained while the subjects were selectively attending to the auditory stimuli in one ear. There is therefore no evidence that the auditory steady-state responses are affected by attention.

Adult↗
PubMed1987

Reliability estimates for steady-state evoked potentials.

The steady-state evoked potentials are most efficiently recorded using Fourier analysis. The reliability of this evoked potential is best estimated using either Hotelling's T2 or phase coherence. Using these techniques, the response to 500 Hz tones presented at a rate of 40/sec can be reliably recognized on average down to intensities of below 15 dB SL in an awake subject. Sleep significantly decreases the amplitude of the response and significantly raises the threshold for recognizing the response by 11 dB.

Adult↗