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Biomedical subjects

A W Gaillard

Publications and source records attributed to A W Gaillard.

At least 37 records · Page 2Linked to original sources
PubMed1981

Attention effects on auditory EPs as a function of inter-stimulus interval.

The present study focuses on the effect of the duration of the inter-stimulus interval (ISI) on the 'processing negativity', the endogeneous negative brain potential elicited by attended stimuli in various selective-attention paradigms. Three constant ISIs are used, 250 msec. 800 msec, and 2000 msec, in a selective dichotic-listening situation in which the subject's task is to detect occasional slight pitch changes in the input to a designated ear. Frontal (Fz), vertex (Cz), and parietal (Pz) evoked potentials (EP) are recorded. The processing negativity is observed in each condition, even in that involving the 2 sec ISI, which is in contrast with the commonly held view that this attention effect is only obtained with very short ISIs. The processing negativity was observed to have two components: (1) an early, central component of small amplitude which appears to be independent of the ISI: (2) a later, frontal component of large amplitude and long duration which is certainly elicited with long ISIs such as the 800 msec and 2000 msec ISIs used here, but also appears to be present even in the short-ISI condition overlapping the central component. This suggests that it is the frontal component which is sensitive to the ISI.

Acoustic Stimulation↗
PubMed1981

EP components, visual processing stages, and the effect of a barbiturate.

In a 2 x 2 x 2 factorial experiment, ten subjects carried out a visual choice reaction task. In addition to RT measurement, evoked potentials (EPs) were recorded from the central (Cz) and occipital (Oz) derivations. Independent variables were drug treatment (barbiturate versus placebo), visual stimulus intensity and visual stimulus degradation. The reaction time data showed that visual intensity and degradation had additive effects, which indicates that these variables affect independent stages, i.e. stimulus preprocessing and stimulus encoding. The effect of barbiturate on RT was additive with intensity but appeared to interact with degradation. This suggests a selective effect of that drug on the encoding state. EP components also showed selective effects of intensity, degradation and drug treatment. It was suggested that these components may be related to stages in the reaction process.

Adult↗
PubMed1981

Mismatch negativity in a phonetic discrimination task.

The hypothesis was tested that in a discrimination task the number of phonetic features available determines the latencies and amplitudes of the components of the evoked potentials. Six conditions varying in the number and type of discriminatory cues were compared. The condition containing a three phonetic feature discrimination produced shorter latency evoked potentials as compared with the conditions containing one or two such features or an acoustic difference only. The N2 component, the so-called mismatch negativity, was particularly sensitive to the number of phonetic features.

Discrimination Learning↗
PubMed1980

Some baseline effects on the CNV.

A method is described to investigate how the contingent negative variation (CNV), developing in the S1-S2 interval of a reaction task, is influenced by slow potential shifts (SPSs) occurring before S1. Enhanced CNV amplitudes were found when the SPSs before S1 were positive, whereas with negative SPSs attenuated amplitudes were obtained.

Cerebral Cortex↗
PubMed1979

Some effects of an ACTH 4-9 analog (Org 2766) on human performance.

The effects (on human beings) of the ACTH analog Org 2766 were investigated for a range of performance tests: complicated serial reaction task, running memory span, verbal learning and non-verbal mental ability tests (closure flexibility and non-verbal abstraction). Subjective ratings on feelings were taken and heart rate was measured. Only the 30-min reaction task produced significant drug effects. In this task performance tends to deteriorate as a function of time on task. During the test period there is a gradual increase in the number of lapses in performance due to moments of inattention. This deterioration is counteracted by the ACTH 4-9 analog, a result also found in previous study using ACTH 4-10 (Org OI63). Thus ACTH fragments which are devoid of endocrine effects seem to have a beneficial effect on goal-directed motivation oriented on the requirements of the task.

Adrenocorticotropic Hormone↗
PubMed1979

The terminal CNV and stimulus discriminability in motor and sensory tasks.

Slow EEG potentials were recorded during the foreperiod of a signal detection task which involved different levels of discrimination difficulty. The subject was required to react to S2 as quickly as possible or to delay his response by 1 s. It was found that the contingent negative variation (CNV) was attenuated when no speeded response was required and that larger amplitudes preceded the easy rather than the difficult discrimination. In addition, no differences were found between correct and incorrect detections. On these grounds it is concluded that the CNV is not positively correlated with perceptual sensitivity.

Cerebral Cortex↗
PubMed1977

Drug effects on EEG frequency spectra as a function of interstimulus interval.

The frequency spectra of EEG background activity preceding the stimulus in a serial simple RT task were investigated as a function of interstimulus interval (ISI). The percentage of power in the alpha and theta bands increased with longer ISIs while the delta activity decreased. Additionally, the effects of an amphetamine and a barbiturate were investigated. The increase in alpha activity with longer ISI conditions were larger after barbiturate than after placebo, while it remained constant after amphetamine treatment. Contrary to expectation, no systemic changes in alpha activity were found during the 3-h session for any of the treatments. It is suggested that the background EEG during the foreperiod of an RT task mainly reflects phasic arousal. The characteristics of the background EEG in the present experimental situation may be quite different from that recorded under "relaxed" no-task conditions.

Adult↗