Time-Dependent Modulation of Saliency-Driven Visual Attention in Free Viewing.
PURPOSE This study investigated similarities in gaze behaviour across observers and examined whether salient visual features guided visual attention during free viewing, to clarify bottom-up and top-down influences on visual attention in complex, natural scenes. METHODS Forty-five healthy adults (Median age (IQR):38(24)y) viewed ten static real-world scenes (with/without social elements) for 15seconds each while their gaze was simultaneously recorded using a remote eye-tracking system. Fixation heatmaps were generated, and gaze parameters were computed. Using a bootstrapping approach, random subsets of gaze data were compared to assess gaze similarity. Heatmap similarities were analysed during the first 7.5s (tearly), last 7.5s (tlate), and total 15s viewing period using Jensen-Shannon Divergence (JSD), where JSD=0 indicated identical maps, and JSD=1 indicated no similarity. A saliency map of each scene was obtained using Itti & Koch's computational model, and the proportion of fixations overlapping salient regions was calculated to quantify saliency's influence during free viewing. RESULTS Across the total viewing period, 52-84% of fixations overlapped with model-predicted salient regions, with higher proportions observed in less crowded scenes and lower proportions in scenes containing socially meaningful elements. Temporal comparison showed a higher proportion of saliency-directed fixations during the tearly phase [median (IQR): 72% (23%)], accompanied by greater inter-group gaze similarity [median (IQR) JSD: 0.15 (0.02)], indicating more shared, saliency-driven viewing during the first 7.5s. CONCLUSIONS The data suggest that free viewing is initially consistent and saliency-driven but becomes progressively individualised over time as top-down influences increase, with this temporal shift modulated by scene characteristics. Free-viewing can hold clinical value in assessing the dynamic interaction between bottom-up saliency and top-down cognitive context in individuals with visual or cognitive impairments.