Real-Time Visual Stimulus Selection through Attentional and Decisional Processes

Our senses continuously receive a staggering amount of information from our environment. To operate efficiently in a natural environment, our brain needs to select in real-time a subset of the information impinging on our senses. Two processes play a crucial role in real-time stimulus selection and filtering: attentional and decisional processes. The broad goal of our study was to investigate how attentional and decisional processes select visual inputs for processing. The study was divided into three parts: The first and second parts studied visual attention. The last part examined decisional processes. In the first part, we investigated the allocation of exogenous attention when perceptual groups were formed or dissolved. By varying the relative timing between the cue onset and the formation, or dissolution of perceptual groups, we sought to understand the relationship between processes organizing inputs into meaningful units (perceptual grouping) and the processes selecting from these units (attention). The time-course of attentional benefits of grouping was remarkably similar in the case of group formation and dissolution, operating within a half-second time frame. The results revealed the dynamics of how attention and grouping work in synergy during the transient period when groups form or dissolve. Attentional processes can be divided into two types: a fast reflexive process, called exogenous attention, and a slower, voluntary process, called endogenous attention. In the second part, we investigated whether endogenous and exogenous attention, operate independently or interact. The experiment demonstrated that there is an interaction between the endogenous and exogenous systems when the task was discrimination. The evidence for interaction was weak when subject’s task was detection. The interaction between the two orientation types depends on the validity of both types of orientations. When endogenous cue was valid, exogenous cue’s strength was weakened. The endogenous cue was significantly dominant than the exogenous cue. The detection tasks required significantly less time compared to discrimination tasks. In the last part, we examined information sampling by decisional processes. We tested the Small Sample Advantage (SSA) theory through predictions and found that for the low environmental contingency values, subjects preferred small sample sizes. For the remaining values, the prediction results were not conclusive. Under SSA, probability density function analysis indicates that the percentage correct can never exceed 50%. However, we carried out simulations to test whether the specific realization corresponding to our experiment could yield performance higher than 50% under SSA. Simulation results showed that indeed this was the case and produced an estimate of internal decision level used by the subjects.