04.12.2018

New article accepted in "Journal of Vision"

Title: "Disentangling bottom-up vs. top-down and low-level vs. high-level influences on eye movements over time" by Heiko H. Schütt, Lars O. M. Rothkegel, Hans A. Trukenbrod, Ralf Engbert and Felix A. Wichmann

Abstract:

Bottom-up and top-down, as well as low-level and high-level factors influence where we fixate when viewing natural scenes. However,
the importance of each of these factors and how they interact remains a matter of debate. Here, we disentangle these factors by
analysing their influence over time. For this purpose we develop a saliency model which is based on the internal representation of
a recent early spatial vision model to measure the low-level bottom-up factor. To measure the influence of high-level bottom-up
features, we use a recent DNN-based saliency model. To account for top-down influences, we evaluate the models on two large
datasets with different tasks: first, a memorisation task and, second, a search task. Our results lend support to a separation of
 visual scene exploration into three phases: The first saccade, an initial guided exploration characterised by a gradual broadening
 of the fixation density, and an steady state which is reached after roughly 10 fixations. Saccade target selection during the initial
 exploration and in the steady state are related to similar areas of interest, which are better predicted when including high-level
 features. In the search dataset, fixation locations are determined predominantly by top-down processes. In contrast, the first
 fixation follows a different fixation density and contains a strong central fixation bias. Nonetheless, first fixations are guided
 strongly by image properties and as early as 200ms after image onset, fixations are better predicted by high-level information.
 We conclude that any low-level bottom-up factors are mainly limited to the generation of the first saccade. All saccades are
 better explained when high-level features are considered, and later this high-level bottom-up control can be overruled by top-down
 influences.