How fixation durations are related to the functional visual field and attentional guidance

点击翻译按钮获取中文摘要

Every day we search for items in our environment, but the accuracy and the speed of the search process become critical when medical doctors search for nodules on radiographs or when airport security screeners search for dangerous items in the carry-on baggage. A “guided search” occurs if we know the visual features of the search target (e.g., in search for a blue car at the parking spot). Then the visual system is set to prioritize items with that features such that not every item has to be attended serially during search (e.g., when red and green cars are not inspected as possible target candidates). A constraining component for guidance in visual search processes is the retinal inhomogeneity of the eyes: If we search for a key on an empty desktop, we can often find it immediately, even at the corner of our eye. However, if the desktop is messy and full of distracting items, we usually must perform multiple gaze fixations at different locations to find the key. That is, as a general rule, visual processing becomes less reliable, the further away an item is from the central fixation, and the more items are in the visual field. The visual area within which a target can reliably be detected around the center of fixation is called the functional visual field (FVF) and it shrinks if a difficult target is searched for. Two important components that affect search difficulty are the similarity between distractors and the target, as well as the heterogeneity of the distractors. The proposed project begins with the closer investigation of how gaze fixation durations are affected by the two of these components. The resulting findings will be the basis for an innovative method that is going to be established in the project in order to measure the size of the FVF when participants perform standard visual search tasks on a screen. While current state-of-the-art methods simulate gaze contingent spotlights which obscure the peripheral visual input during search, the method of the project yields an alternative to measure the FVFs size without such a manipulation that may affect search behaviour. Importantly, the new method reveals which fixations are spatially guided during the search course and can be applied in search for simple, artificial stimuli, and potentially also in search through complex scenes or radiographs where it is difficult to define the number of distractors. However, further examination is necessary by the application on experiments where participants search for targets of different visual feature dimensions and by comparisons with other methods to estimate the FVF’s size, which is the purpose of the proposed project.