| dc.description.abstract | Animals are capable of learning occurrences that may happen in the environment, and the knowledge of their learning is reflected in their following behavior. According to the prior information, animals can adjust their attention allocations to specific events. For example, performance in searching task and antisaccade cost can be affected by probability events. However, how expectation modulates participants’ behavior and their underlying neural mechanisms are still unclear. Expectation can be measured as the probability for an action and the magnitude of the reward. The present study will manipulate probability and reward size separately. In the first part of this study, three tDCS experiments were utilized to establish the causal links between brain regions and location probability effect. The contribution of reward effect is examined in the behavior experiment in the second part.
In experiment 1 and 2, offline anodal (excitatory) tDCS was applied with the active electrode placed over the rFEF or SEF. In experiment 3, offline cathodal (inhibitory) tDCS was applied over rFEF. Directly after tDCS stimulation, participants were asked to complete a pro- or anti- saccade task which manipulated location probability. The results in experiment 1 and 2 indicated that saccade latencies for prosaccades were significantly shorter when anodal tDCS was applied to the rFEF but not SEF. Additionally, when applying anodal tDCS in FEF produced a larger effect for low probability locations than high probability locations led a major interaction between tDCS condition and location probability. In experiment 3, cathodal tDCS led faster saccade latencies in antisaccades. The results demonstrate that reduction on saccade latencies induced by both anodal and cathodal tDCS over the rFEF, which confirms the role of rFEF in saccade initiation. The findings also dissociate the critical roles of the rFEF and SEF in the effect of location probability and confirm the importance of rFEF in processing location probability information. The current tDCS experiments suggest that the FEF plays a critical role in modulating the location probability effects and the saccade latencies.
In the second part of the study, we investigated other factor that is essential to expectation. In experiment 4 and 5, reward size was manipulated in the prosaccade task and antisaccade task. The separation of two saccade types could exam the effect of reward when the spatial attention and motor preparation is compatible or not. The results confirm the reward effect in a visual selection task. Moreover, we provided the potential stages that top-down control might influence in saccade latencies.
In summary, the results show that two top-down factors are related to expectation, probability and reward, can account for attentional allocation of saccadic preparation. The prior expectation is not only an important factor for motor preparation, but also critical for the flexibility of visual attention. | en_US |