| Summary: | 碩士 === 國立臺灣大學 === 心理學研究所 === 102 === The present study aims to explore how the competitions among task-relevant and task-irrelevant stimuli affect distractor processing using the recording of event-related potentials (ERP). In most of the previous studies, distractor processing was often evaluated indirectly by reaction times to target selection. Yet, reaction time simply reflects the consequence of all intermediated processes. Therefore, we used ERP experiments to underpin the different neural mechanisms underlying distractor processes in two experimental contexts. ERPs were monitored while participants performed a flanker task. In Experiment 1, stimulus competition was manipulated through varying whether the distractor can be perceptually grouped with the task-relevant target assuming that distractor grouped with the target is a strong competitor. Participants performed three experimental conditions: low-load, high-load, and dilution conditions. Target-nontarget feature similarity was low in the low-load condition and was high in the latter two conditions. More importantly, target and distractor shared the same color to reduce target processing load in the dilution condition. The results showed that that a highly salient distractor grouped with the target in color elicited strong activation in attention allocation under the dilution condition. As a result, the amplitude of distractor-elicited N2pc was greater under dilution than under the low-load and high-load conditions. Interestingly, the strong activation did not carry over downstream in processing to produce a strong competition against the target in response decision. Distractor compatibility did not modulate P300 amplitude in the dilution and high-load conditions but manifested in the low-load condition. These results suggest that the representation of distractor was diluted between the initial attention allocation and the response selection stages under the dilution condition. In Experiment 2, redundant target display was adopted to enhance target competition and the reaction time compatibility effect revealed that the location uncertainty played a role in enhancing distractor competition while the distractor distance did not. In Experiment 3A, redundant target display was also adopted to enhance target competition while distractor competition was manipulated by varying distractor size assuming that a large distractor is a strong competitor. The results showed that the high activation of redundant targets was able to suppress distractor activation during the stage of attention allocation as reflected by a distractor-elicited Pd. Distractor size did not modulate the distractor-elicited Pd but only the large distractor produced compatibility effect on P300. This finding suggests that a large distractor produced competition against the target in response decision even though it was suppressed at an early stage. Taken together, the results from two experiments support the contention that biased competition characterizes visual selection and relative stimulus activation strength influences biased competition at different stages of information processing.
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