  Advances in commercial wearable devices are increasingly facilitating the
collection and analysis of everyday physiological data. This paper discusses
the theoretical and practical aspects of using such ambulatory devices for the
detection of episodic changes in physiological signals as a marker for mental
state in outdoor environments. A pilot study was conducted to evaluate the
feasibility of utilizing commercial wearables in combination with location
tracking technologies. The study measured physiological signals for 15
participants, including heart rate, heart-rate variability, and skin
conductance. Participants' signals were recorded during an outdoor walk that
was tracked using a GPS logger. The walk was designed to pass through various
types of environments including green, blue, and urban spaces as well as a more
stressful road crossing. The data that was obtained was used to demonstrate how
biosensors information can be contextualized and enriched using location
information. Significant episodic changes in physiological signals under
real-world conditions were detectable in the stressful road crossing, but not
in the other types of environments. The article concludes that despite
challenges and limitations of current off-the-shelf wearables, the utilization
of these devices offers novel opportunities for evaluating episodic changes in
physiological signals as a marker for mental state during everyday activities
including in outdoor environments.
