Scanpaths of Complex Image Viewing: Insights From Experimental and Modeling Studies.

From the first works of Buswell, Yarbus, and Noton and Stark, the scan path for viewing complex images has been considered as a possible key to objective estimation of cognitive processes and their dynamics. However, evidences both pro and con were revealed in the modern research. In this article, the results supporting the Yarbus-Stark concept are presented. In psychophysical tests, two types of images (three paintings from Yarbus` works and four textures) were used with two instructions, namely, "free viewing" and "search for modified image regions." The focus of the analysis of experimental results and modeling has been given to local elements of the scan path. It was shown that each parameter used (square of viewing area, S; distance between center of mass of viewing area and image center, R; parameter Xi, based on duration of the current fixation and angle between preceding and following saccades), reflects the specificity of both visual task and image properties. Additionally, the return gaze fixations which have a set of specific properties and mainly address to the areas of interest on image were revealed. Evidently these facts can be formalized in an advanced mathematical model as additional instrument to study the mechanisms of complex image viewing.

Distractor effect at initial stages of recognition depends on visual image properties.

In the present study, we describe a new method for estimation of distractor effect at image viewing. Dynamics of gaze fixation duration was compared at presentation of distractor during recognition of two types of target stimuli: fading-in contour images and black static cross. Circular blue distractor was applied to a target stimulus at some fixation points during initial stages of image recognition. All stimuli were presented in the center of computer screen inside the foveal part of the vision field. Subjects received the following instructions: to fixate their gaze on target image, recognize target stimulus as quick as possible and press the keyboard button to stop a trial. Our experiments have shown that (i) the median of the distractor effect (increase of fixation duration) was significantly less in trials with fading-in contour images, than in trials with cross image presentation (415 and 610 ms, p < 0.05); (ii) fixation duration without distractors had no significant difference between fading-in image trials (390 ± 10 ms) and cross image trials (438 ± 22 ms); (iii) mean recognition time for fading-in images was significantly more than for cross image (13.9 ± 4.3 s, and 2.47 ± 0.84 s). Possible prospective to use the presented method are discussed.

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.