Pictures of green spaces make you happier.

Reynolds points to work by van den Berg et al. showing that viewing pictures of green versus built urban areas enhances parasympathetic nervous system activity that is calming and restorative. This results are consonant with those obtained by a Stanford study on the effects of a brief nature experience on rumination, and also with discussions of "blue mind" (cf. calming effect of blue water) versus "red mind."

This laboratory study explored buffering and recovery effects of viewing urban green and built spaces on autonomic nervous system activity. Forty-six students viewed photos of green and built spaces immediately following, and preceding acute stress induction. Simultaneously recorded electrocardiogram and impedance cardiogram signal was used to derive respiratory sinus arrhythmia (RSA) and pre-ejection period (PEP), indicators of respectively parasympathetic and sympathetic activity. The findings provide support for greater recovery after viewing green scenes, as marked by a stronger increase in RSA as a marker of parasympathetic activity. There were no indications for greater recovery after viewing green scenes in PEP as a marker of sympathetic activity, and there were also no indications of greater buffering effects of green space in neither RSA nor PEP. Overall, our findings are consistent with a predominant role of the parasympathetic nervous system in restorative effects of viewing green space.