Browsing by Author "Knebel, Timothy F."

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    EEG theta power during Necker cube reversals
    Knebel, Timothy F. (Virginia Tech, 1993-06-05)
    The purpose of this thesis was to investigate a proposed neurophysiological model for Necker cube reversals by using electroencephalography. It is suggested that Necker cube reversals are mediated by sustained focused attention to the overall drawing with visual selective attention to vertices of the cube. The main hypotheses were that deliberate attention would increase Necker cube reversals over passive attention, there would be greater high theta power during the deliberate focusing of attention than during passive attentional processing, and there would be greater theta power in the right hemisphere. Thirty undergraduate psychology students had monopolar EEG recorded bilaterally from frontal and parietal electrode sites. The subjects viewed computer presentations of the Necker cube under two different experimental conditions: a passive condition in which they were not instructed to influence reversals, and an active condition in which subjects deliberately shifted their focus of attention.
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    Event-related potentials during auditory discrimination: attentional and intentional effects
    Knebel, Timothy F. (Virginia Tech, 1995-05-05)
    The purpose of this dissertation study was to assess the neurophysiological activity associated with selective attention, response selection, and response inhibition. The subjects were 27 right-handed college students, 14 men and 13 women, aged 18-21. They performed a go/no-go auditory discrimination task while EEG was recorded from 19 monopolar electrode sites and averaged for evoked potentials. Amplitudes and latencies were measured for four event-related potentials (N1, P2, N2, and P3) at three midline electrode sites (Fz, Cz, pz) and eight bilateral sites (Fp1, Fp2, F3, F4, C3, C4, P3, P4). Measures from the midline and bilateral sites were subjected to separate repeated measures ANOVAs for within subjects factors of condition (go and no-go), region (prefrontal, frontal, central, and parietal), and hemisphere (left and right). Grand averages and topographic isopotential maps were generated for each component and condition. Based on neurophysiological theories of attention and intention, and prior go/no-go studies, it was expected that the amplitudes of N1, P2, and P3 would be larger in the go condition. N2 was proposed to be associated with response inhibition and greater in the no-go condition. As N2 was proposed to be generated at the orbitofrontal region, it was expected that N2 would be larger over the prefrontal region, not shown in previous studies due to sparsity of electrode placement. It was expected that N1 would show a frontocentral distribution, but P2 and P3 would be concentrated centroparietally. It was hypothesized that N2 and P3 latencies would be longer in the no-go condition. The results supported the regional hypotheses, and were in the correct direction for the condition effects. Importantly, N2 demonstrated an extremely anterior prefrontal distribution. Nl showed a frontocentral distribution and was larger in the go condition for the bilateral sites. P2 had a centroparietal distribution. P3 was of higher amplitude at frontal and prefrontal sites during the no-go condition, but was higher at central and parietal sites overall. At the prefrontal region, P2 and P3 were higher over the right hemisphere, but N2 was greater over the left. P3 latency was longer in the no-go condition at all sites, and significantly longer at the prefrontal region than at the other regions.