Smartphone Sensing of Greenspace Exposure and Affect in People with and without Schizophrenia (Preprint)

BACKGROUND Exposure to natural vegetation (i.e., “greenspace”) is related to beneficial outcomes, including higher positive and lower negative affect, in those with and without mental health concerns. Only recently have researchers started to examine dynamic associations between greenspace exposure and affect within individuals over time. Smartphone-based Ecological Momentary Assessment (EMA) and passive sensors (e.g., GPS, microphone) allow for frequent sampling of data that may reveal potential moment-to-moment mechanisms through which greenspace exposure impacts mental health. OBJECTIVE In the current study we examined associations between greenspace exposure and affect (both self-reported and inferred through speech) in people with and without schizophrenia spectrum disorders (SSD) at the daily level using smartphones. METHODS Twenty people with SSD and 14 healthy controls reported on their current affect three times per day over seven days using smartphone-based EMA. Affect expressed through speech was labeled from ambient audio data collected via the phone’s microphone. Greenspace exposure, defined as the normalized difference vegetation index (NDVI), was quantified based on continuous geo-location data collected from the phone’s GPS. RESULTS Greater greenspace exposure showed small to moderate associations with lower EMA-reported negative affect across groups. In controls, greenspace exposure on a given day was associated with significantly lower EMA-reported anxiety on that day (b = -0.40, p < 0.05, 95% CI [-0.76, -0.04]), but significantly higher use of negative affect words (b = 0.66, p < 0.05, 95% CI [0.29, 1.04]). There were no significant associations between greenspace exposure and affect at the daily level among participants with SSD. CONCLUSIONS Findings speak to the utility of passive and active smartphone assessments for identifying potential mechanisms through which greenspace exposure influences mental health. We identified preliminary evidence that greenspace exposure could be associated with improved mental health by reducing experiences of negative affect.