Towards explaining the positive effect of vegetation on the perception of environmental noise

Audio-visual interactions play a significant role when humans perceive the environment. In this review paper, it is analysed how visible vegetation can be used to mitigate negative environmental noise perception with a focus on noise annoyance. Existing research has been analysed in view of three potentially explaining mechanisms namely source (in)visibility, the mere presence of visible green, and vegetation as a source of natural sounds. The source concealing potential vegetation has cannot fully explain reported findings. The restorative properties of visible vegetation seems the dominant mechanism. Visible natural features of good quality lead to sustained attention restoration and stress relief, counteracting negative outcomes of endured environmental noise exposure. There is strong evidence that noise annoyance experienced at home largely decreases when outdoor nature is present in the window pane. Additional support regarding the importance of such micro-restorative experiences is found by research at the working place, in hospital environments and at schools. Non-directly visible neighbourhood green shows to be positive as well, but with a smaller impact on noise perception. Natural sounds and especially bird songs are relaxing on theirselves, and support the restorative action of nature by suggesting nearby and vital nature. Based on rough quantitative estimates, the equivalent level reduction of (high quality) visible green from home could reach 10 dBA. This equivalent level reduction comes on top of the physical sound pressure level reduction one might obtain behind vegetation belts. At higher exposure levels, the improved noise perception one can get from vegetation is larger than at lower levels. The bulk of literature is concerned with road traffic noise, although scarce research suggests the applicability is much broader. Personal characteristics are expected to play a role in the interaction between noise perception and vegetation too.