Human Visual Attentiveness and Response to Biophilic Interior Design: An Eye-Tracking Study

Interior environments shape human attention during cognitively demanding tasks, yet spatial design variables are rarely evaluated using objective behavioural metrics. Biophilic design, the integration of natural elements into built environments, has been associated with restorative and psychological benefits, but prior work largely relies on self-report measures and binary comparisons be-tween the presence and absence of nature. Whether increasing the intensity of biophilic elements produces continuous cognitive benefit or introduces measurable performance thresholds remains empirically underexamined. We present a novel experimental study investigating the effects of graded plant saturation on attentional behaviour using eye-tracking analytics. Fifteen participants completed a standardized reading task across four systematically varied levels of plant density positioned within their peripheral field of view. This repeated measures design enabled direct comparison of attentional performance within individuals un-der controlled environmental conditions. Fixation duration, saccadic frequency, gaze dispersion, and reading speed were analysed as indicators of attentional stability and cognitive load. Post-experiment interviews were conducted to examine whether subjective affective perceptions aligned with measured behavioural patterns. Results indicate a non-linear cognitive–affective response to biophilic saturation. Moderate levels of plant integration were associated with improved fixation stability and reading efficiency, accompanied by self-reported increases in perceived comfort and focus. However, higher-density conditions yielded a performance plateau and, in some cases, increased gaze dispersion consistent with distraction effects. Alignment between behavioural metrics and subjective reports was observed for many participants, although variability emerged among individuals reporting certain physiological or neurocognitive conditions, suggesting moderated sensitivity to saturation levels. By operationalizing biophilic intensity as a graded environmental variable and triangulating computational eye-tracking data with subjective perception, this work advances a behavioural evaluation framework for interior spatial design in Human-Computer Interaction (HCI) contexts. The findings challenge linear “more-is-better” assumptions and support evidence-based calibration of biophilic interventions in cognitively demanding in-door environments.