Inhibitory Motor Control in the Stop-signal Task
| Autor: | Hsin-Ru Li, 李芯如 |
|---|---|
| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 In a stop-signal task, the subjects are given a primary task to perform with and, on occasion, a stop-signal is presented to stop the action initiated. A race model was proposed to estimate the time necessary for processing the stop-signal (i.e. the SSRT) and to account for the processes. For over 20 years, behavioral data in the stop-signal task have been modeled successfully in terms of a race between two independent processes that respond to the stop-signal and the Go-target. In Experiment 1, we compared the SSRTs of simple and choice task, and found that the SSRTs of the tasks do differ from each other. In Experiment 2, we investigated whether the response bias could influence the stop processes when occurrence probability of stop-signal varies. We manipulated stop-signal occurence to be 20%, 50%, and 80%, and found that the SSRT decreased when stop-signal occurence increased. Our interpretation is that there might be a top-down influence to the processing of stop-signal. To confirm this, we reduced difference between various probability levels (20%, 40%, and 60%) in the experiment 3. Concurrently, we recorded ERP for more closely inspecting its evolution in temporal aspect. The RT data reversed our previous results. For ERP analysis, by subtracting ERP trace of the Go-only trials from those with stop-signal, the successful-stopping trials (SSTs) elicited a fronto-central positive effect whereas unsuccessful-stopping trials (USSTs) evoked a centro-parietal positive effect. The positive effect peaked later in the USSTs than in the SSTs. More specific, we found an N2-like component occurring only in the USST difference waveform, which behaved more actively in the 60% condition. For avoiding the subjects’ strategy, the probability of stop-signal occurrence is usually less than 50%. In Experiment 4, we modified probability levels to 20%, 30%, and 40%, and used a tracking method to adjust the time of stop-signal occurrences. The behavioral results are line up with previous studies using stop-signal paradigm－the SSRTs are not significant in different probability levels. And the ERP results are replicated the previous experiment. It confirmed that the probability could modify the N2 effect in USST. On the other side, we explored whether the motivation of subject could influence the inhibition processes. In Experiment 5, we used a typical stop-signal paradigm and the tracking method in both condition－neutral and motivational. In the behavioral data, there is no difference from each other. The ERP results show the obvious N2 effect in USST that reflected the stronger processing of monitoring. Together these fndings indicate that the successful-stop P3 reflect functionally distinct aspects of response control, while stop N2 reflect the monitoring processing. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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