The aim of this study (2011) was to find out if plants have an effect on attention capacity of students. Attention restoration theory (ART) states that being in contact with vegetation or views of natural elements might contribute to attention restoration. Exposure to plants could restore attention during short or long breaks from work, and therefore leave directed attention to rest more effectively.

The study was performed in controlled laboratory settings, where 34 participants were randomly assigned to an office with either indoor plants or the same setting without plants. Attention capacity was assessed three times: immediately after entering the laboratory (T1), after performing a demanding cognitive task (T2), and after a five-minute break (T3). Attention capacity was measured using a reading span test (RST) which provides a realistic measure of attention capacity, where participants were presented with sentences and had to memorize the last words. Participants also did a proofreading test and answered a questionnaire.

The study showed, that

• Performance of the plant group improved from T1 to T2 (p = 0.01)
• Performance of the non-plant group did not improve from T1 to T2
• There were no improvements in either group between T2 to T3

The findings of this study were contrary to the hypotheses that a main effect of fatigue from T1 to T2 should have occurred – the proofreading task may not have been demanding enough to cause attention fatigue. Researchers think that improvement due to practice was not cancelled out by fatiguing effect in plant condition, supporting ART theory. The possible restorative effects of looking out the window did not seem to outrange the restorative effects of the indoor plants.

Attention capacity did not improve from T2 to T3 for either the plant or the no-plant group. Several reasons were suggested why attention restoration failed in the present study: first, the proofreading task was not challenging enough, so it could have been that a break could not improve performance as the students were already performing at their best. Second, the plant environment might not have been fascinating enough, or a longer than 5 min break would have been needed.

An alternative model to ART could also explain why performance was better for the plant group during work: the difference found in performance between the two groups may have been caused by a buffering or stress-reducing effect of the indoor plants.

Researchers conclude, that the present study confirms that natural elements can affect cognitive performance in an office work environment, even though the mechanisms behind it could not fully be answered by this research assessment. The results can be understood in the context of ART, as well as an environment-arousal model of cognitive performance. More research is recommended to examine what and how the work environment affects cognitive processes.