This review article (2009) summarizes the results of ~50 empirical studies on how the absence of nature in our surroundings can have negative effects on our health and well-being. This idea is based on the biophilia hypothesis: the presence of plants has been a signal for food, water and shelter – the means to survival – for our ancestors. As our modern environment is far from what our brains have adapted into, this mismatch is likely to have negative effects on us.

The visual aspect of nature has been studied in outdoor and indoor environments, and it appears to be useful for stress relieving, mental restoration, and improved mood. These effects can be either conscious, in the sense that we simply find nature visually appealing; or unconscious – the absence of plants and other natural elements may indicate an unsafe environment and cause our brains to induce stressful reactions. The unconscious effects might explain why other visually pleasing objects, such as designer lamps or abstract paintings, do not have similar effects as plants have.

The researchers conclude, that:

• Even individuals who do not express appreciation for plants and nature could still experience negative effects from their absence
• Although the visual effect of nature seems to be an important factor, it is difficult to exclude from other effects such as the quality of indoor air