| Summary: | 碩士 === 國立陽明大學 === 神經科學研究所 === 100 === Human beings’ information processing system is limited and often deals with an overwhelming amount of stimuli that are competing for one’s attention at the same time. Our cognitive processes are highly affected by the emotional stimuli in the visual environment. The aim of this thesis is to investigate 1) how the irrelevant emotional distractors affect the saccadic behaviors 2) whether different level of attentional disengagement interact with emotional distractors 3) whether the emotional effects reflect a specific neural mechanism or merely biased selective attention. Three behavioral experiments and two tDCS (transcranial direct current stimulation) experiments were conducted.
We used a fixation gap paradigm to manipulate the amount of attentional disengagement and to elucidate how it affects the influence of emotional faces in saccadic behaviors. The experiment contained two conditions: a gap condition (the fixation offset preceding target onset) and an overlap condition (the fixation remain present throughout the entire trials). In Experiment 1, participants were asked to make a saccade to a neutral face and ignore the distractor: a fearful face or a scrambled face. Our results showed that a fearful face distractor generally increased saccade latency and error rates in both conditions. Intriguingly, saccade curvatures were more away from the fearful face than the scrambled face only in the overlap condition. In order to eliminate the possible low-level effect (face v.s. non-face) causing emotional distractors effect, in the Experiment 2, the distractor was an inverted fearful face or a scrambled face. The results showed that no significant difference in both conditions. In Experiment 3, we manipulated the distractors valence (fearful face or happy face) to address whether positive affective stimuli also influence saccadic behaviors. The data showed that in happy face condition was more distraction than in fearful face condition. The results from the behavioral data suggest that irrelevant emotional distractors could indeed modulate both the temporal and the spatial programming of the saccade.
Two tDCS experiments were utilized to establish the causal links between brain regions and these cognitive functions. In Experiment 4 and 5 tDCS was placed over the superior temporal sulcus and the frontal eye field to investigate the functional roles of these areas in the facial expression processing and eye movements processing. To summarize, our results showed dissociation that rSTS is involved in facial expression processing while rFEF only plays a critical role in saccadic behaviors but not in emotional processing. The rSTS plays a critical role for processing emotional facial expression even when it is not relevant in the task. The results imply that emotional modulations might boost the processing of particular stimuli.
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