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Biomedical subjects

W C McCallum

Publications and source records attributed to W C McCallum.

At least 19 recordsLinked to original sources
PubMed1989

Slow potential changes related to the velocity of target movement in a tracking task.

During an 18 sec smooth pursuit tracking task slow waves in the EEG were found to be correlated with the absolute velocity of the target. They were maximum at the vertex. These are thought to be concerned with the prediction of the future position of a target in some cerebral feed-forward system in which both input information and output motor action are integral parts and illustrate sensorimotor integration in man.

Adult↗
PubMed1989

Late components of auditory event-related potentials to eight equiprobable stimuli in a target detection task.

Fourteen normal subjects undertook a target detection task in which eight different but equiprobable stimuli were presented in an unpredictable sequence (four tone frequencies to either the left or the right ear). One tone/ear combination was designated as a target, to be responded to with a rapid button press. Event-related potentials were recorded from an array of six scalp electrodes. In Condition 1 no responses were required; in Condition 2 a response was required to the highest tone in one designated ear; in Condition 3 a response was required to the second highest tone in the ear opposite to the Condition 2 target. Event-related potentials to the no-task condition (1) included a P3-type late positive component. P3 increased in amplitude to target tones in Conditions 2 and 3, but showed equally large amplitude increases and some decrease in latency to nontarget tones in those conditions. However, a frontal Slow Wave component was elicited more specifically by target stimuli. An attended ear effect was evident in a processing negativity that extended for some hundreds of milliseconds prefrontally, but tended to be comprised of two separate negativities over fronto-central locations.

Adult↗
PubMed1988

Brain slow potential and ERP changes associated with operator load in a visual tracking task.

Brain electrophysiological changes occurring during the course of a visual tracking task were recorded from 24 normal subjects under varying conditions of workload. Recordings were made with directly coupled amplifiers from 4 scalp midline locations and of vertical and horizontal EOG. The task was to track with a joystick a moving letter on a video monitor screen. Various decisions and button pressing responses were required from the subject during the course of each tracking trial, the total duration of a trial being 28 sec. Trial difficulty was varied by requiring identification of 'targets' or 'non-targets' based on a pre-learned 1-, 3- or 6-letter set of possible targets, by varying speed and distance travelled by the letter and by the introduction of movement perturbation. Sustained negative slow potential (SP) shifts were associated with the introduction and course of each trial. These had 2 phases: an early phase related to memorization and rehearsal and a later stage associated with the tracking itself. Increasing tracking difficulty resulted in an increased negative DC shift during the tracking stage. Increased memory set size caused a reduction in the negative shift during the preparatory, memorization phase. The experimental manipulations of difficulty also resulted in a number of changes in the amplitude and/or latency of ERP components associated with the various points of decision or response.

Adult↗
PubMed1986

Brain indicators of altered attention and information processing in schizophrenic patients.

Late components of brain event-related potentials reflect aspects of selective attention, stimulus evaluation, and possibly memory update mechanisms. Several of these components were measured during an auditory target detection task, performed by 20 schizophrenic and 20 normal subjects. Both the amplitude of those components and a more general late amplitude measure were significantly reduced in schizophrenics, for both target and non-target stimuli. One general late amplitude measure, from the scalp vertex, could alone correctly classify 85% of patients and 95% of controls. The source of these differences may lie in a protracted positive potential shift.

Acoustic Stimulation↗
PubMed1984

The effects of physical and semantic incongruities on auditory event-related potentials.

Twenty subjects listened to a series of simple sentences, spoken by a male voice, in which the last word was on occasions either made semantically incongruous or was unexpectedly spoken by a female voice. Averages of ERPs to the last words revealed that a consistent late negative component (N456) was associated with semantic incongruity and a late positive component (P416) with physical (voice) incongruity. The results were consistent with those in the visual modality by Kutas and Hillyard (1980a,b) and are interpreted in terms of the facilitatory and inhibitory effects of contextual priming on the processing of the words concerned. In a subsidiary experiment 6 subjects were required to repeat the last words of the same set of sentences as rapidly as possible. Verbal response latency increased by 62 msec to physically incongruous words and by 185 msec to semantically incongruous words.

Auditory Perception↗
PubMed1980

Brain slow potential changes elicited by missing stimuli and by externally paced voluntary responses.

Brain evoked potential changes were recorded from the scalp of 22 normal subjects and from the cortex of two patients in conditions where expected auditory stimuli were missing. It was found that such stimulus omissions could be used to initiate slow potential shifts (CNVs) in a warned foreperiod response task. Further slow potential shifts with durations of over 3 sec were recorded preceding self-initiated, but externally paced, responses made to one of a train of clicks. The experiments confirmed the cortical origins of the missing stimulus potentials, and illustrated the dependence of the CNV on endogenous factors rather than the physical properties of external stimuli. Contrary to most previous reports the negative component of the missing stimulus potential was in this study virtually identical in latency and amplitude to the N1 component of the click evoked potential. The slow potential shifts observed in the self-initiated condition contained elements of both the CNV and Bereitschaftspotential and appeared to reflect the steadily increasing cortical involvement during preparatory foreperiods.

Auditory Perception↗
PubMed1977

Cortical potentials associated with the detection of visual events.

A positive-going potential, which reaches a maximum at the vertex and midline parietal scalp electrodes, occurs in the human being when an infrequent, significant event occurs in a continuously observed visual display. It is not time locked to eye movements or operant response and appears to be generated when the observer recognizes an event that he has been instructed to detect.

Cerebral Cortex↗