Eye movements are principally driven by two factors: bottom up salience and top-down perceived interest that is based on our semantic interpretation of the scene. The two effects interact strongly while free viewing natural scenes. However, the exact extent to which each of these factors control overt eye movements, and also their variations over time, though an important aspect, is not well understood. By performing a trellis based optimization on existing state-of-the-art Saccadic Models, using the ground truth data obtained from a carefully controlled eye-tracking experiment, we are able to quantify the extent to which top-down and bottom-up factors interact during the course of free viewing natural images. In line with the claims of earlier qualitative studies, we are able to measure that, gaze, though initially bottom-up driven, is soon countermanded by top-down perceived interest, in the time range of 200 ms–2 secs. At a much later duration however, the bottom-up effects reappear again, albeit to an extent lesser than that of initial levels. It is therefore extremely paramount, to give enough importance to the top-down effects of attention in addition to bottom-up visual salience, during the analysis of overt eye-movement data.
['Yashas Rai', 'Patrick Le Callet', 'Gene Cheung']
Quantifying the relation between perceived interest and visual salience during free viewing using trellis based optimization