I have discovered that there is small but budding group of cognitive scientists who study the psychological impact of indoor plants.
For example, here is a study on the effects of an indoor plant on creativity and mood from the Scandinavian Journal of Psychology.
Effects of an indoor plant on creative task performance and mood.
Shibata S, Suzuki N.
Scandinavian Journal of Psychology. 2004 Nov;45(5):373-81.
In this study, we investigated the effect of an indoor plant on task performance and on mood. Three room arrangements were used as independent variables: a room with (1) a plant, or (2) a magazine rack with magazines placed in front of the participants, or (3) a room with neither of these objects.
Undergraduate students (M= 35, F= 55) performed a task of associating up to 30 words with each of 20 specified words in a room with one of the three room arrangements. Task performance scores showed that female participants performed better in view of the plant in comparison to the magazine rack (p < 0.05).
Moreover, mood was better with the plant or the magazine rack in the room compared to the no object condition (p < 0.05). However, the difference in task performance was highly influenced by the evaluation about the plant or the magazine rack. It is suggested that the compatibility between task demand and the environment is an important factor in facilitating task performances.
Somehow, I feel my world view has not actually changed after reading that study.
But wait, there are also published research studies on:
Effects of the foliage plant on task performance and mood.
Effects of indoor plants on task performance and mood: a comparison between natural and imitated plants.
Influence of limitedly visible leafy indoor plants on the psychology, behavior, and health of students at a junior high school in Taiwan.
The association between indoor plants, stress, productivity and sick leave in office workers.
And someone even did their PhD on “Randomized clinical trials evaluating therapeutic influences of ornamental indoor plants in hospital rooms on health outcomes of patients recovering from surgery”.
Link to PubMed entry for Scandinavian Journal of Psychology study.