How information density modulates viewport switching costs: evidence from a dual-task behavioural study

Viewport transitions are common in complex information systems, yet their associated cognitive costs remain underexplored. This study investigates how visual information density modulate attentional reorientation demands during viewport transitions. Using a dual-task paradigm involving visual enumeration and auditory discrimination, temporal patterns of auditory perceptual sensitivity, response bias and auditory response time were analysed as indirect indicators of residual attentional capacity under visual load. Results indicated that current viewport density played a central role in shaping viewport switching costs. Transitions to low-density viewports were associated with more efficient attentional reorientation, whereas transitions to high-density viewports imposed greater early reorientation demands. In contrast, inter-viewport density difference did not show statistically robust effect, although descriptive patterns suggested a possible advantage for stable low-density transitions. These findings provide an initial, pattern-based account of how information density influences viewport switching cost and offer preliminary design implications for visual information density management in multi-viewport interfaces.