Temporal dynamics of fixation duration, saccade amplitude, and viewing trajectory.

The prospective goal of our study is a quantitative estimation of the contribution of various factors and mechanisms during image viewing. In this paper, experimental data about temporal dynamics of eye movement parameters and viewing trajectory are considered. Three images were presented to each subject (n = 12) under two experimental conditions: "free viewing of initial images" and "search for modified regions in previously presented images". Averaged fixation duration and saccade amplitude, as well as type of viewing trajectory were determined in each consequent period of trials having 30 fixation points. Viewing trajectories were classified into three types: (1) scanning, (2) grouped, and (3) mixed. In spite of individual variations (subject and image), several common peculiarities of temporal dynamics of image viewing were revealed. Specifically: (i) fixation duration in the first and last trial periods were less than during the second one; (ii) saccade amplitude had opposite dynamics; (iii) the scanning trajectories dominated in the first and last periods as compared with the second one; (iv) the mixed and grouped trajectories are more pronounced in the second period; (v) independent of their temporal consequence, the periods with maximal fixation duration differed from those with minimal duration by saccade amplitude and dominating viewing trajectories.