Window shading and materiality for psychophysiological stress in hospital waiting areas: a Spatial Frequency perspective through amplitude spectrum slopes in Virtual Reality

Indoor Environmental Quality (IEQ) can influence psychophysiological stress in hospital waiting areas; however, specific visual features warrant further investigation. We introduce amplitude spectrum slope (− α ) as an image-based metric that characterizes Spatial Frequency in scene images and participants’ recorded views. We conducted a VR experiment where 47 healthy young adults viewed conditions combining open/closed blinds and biophilic/artificial materiality. Outcomes included STAI-S, EEG-derived FAA, HRV-derived RMSSD, and preference ratings. Open blinds and biophilic materiality showed smaller STAI-S changes (b = −0.301, −0.444) and larger RMSSD changes (b = 2.877, 2.665 ms). In separate mixed models adjusted for age, gender, and STAI-T, each 0.1 decrease in personal α towards 1 (range: 1–2) was associated with lower STAI-S (−0.361), and higher RMSSD (+2.296 ms) and FAA (+0.092). Our findings support open blinds and biophilic materiality in fostering reduced stress in healthcare environments, while α provided a spectral measure for visual IEQ assessment.