Using a Smartphone to Measure Heart Rate Changes during Relived Happiness and Anger
The use of smartphones is continuously increasing. Applications allow recent generations of mobile devices to be used for a wide range of tasks that require computational power. Not surprisingly, people are enthu- siastically exploring the possibilities that smartphones provide for scientific research. For example, custom made smartphone applications allow cognitive scientists to collect data from more diverse populations than are typically used in laboratory experiments. Technological advances continue to increase the possible applications of mobile devices. Using a smartphone camera, it is now possible to accurately measure a person’s heart rate (HR) using photoplethysmography (PPG). This optical technique measures HR by monitoring the subtle changes in skin color as the capillaries in the tissue expand and contract with each heartbeat. Although smartphone applications that measure HR are primarily developed for health-related purposes, HR is also an important physiological indicator of the emotional state of an individual. For example, HR increases during anger, anxiety, fear, and happiness, whereas HR decreases during sadness, anticipatory pleasure, and suspense-related emo- tions. Smartphone applications that rely on PPG to measure an individual’s HR provide several advantages over more traditional HR measurement equip- ment. First, they are easy to use, and provide reliable measurements as long as experimenters follow simple instructions. Second, the use of mobile devices allows HR to be measured easily outside of a lab environment. Finally, the increasing availability of smartphones makes them a cost-effective way to measure HR for researchers with limited financial means. The goal of the current study is to demonstrate how smartphones, and more specifically PPG applications that use the digital camera of a smartphone, can be used to measure differences in HR as a function of relived emotional experiences. Although PPG techniques to measure HR have been available for nearly 80 years , it has primarily been used in clinical settings to monitor patients. The goal of this paper is to highlight the possibilities PPG offers for emotion researchers. First, an experiment where HR mea- surements were collected with a smartphone while partici- pants relived anger or happiness emotions is presented. Finally, recent technological advances that open up the possibility to measure a person’s HR using a video camera placed at a distance of several meters will be discussed. Following recent recommendations to incorporate repli- cation studies in academic teaching students of a first-year introduction to psychology course were asked to perform a partial replication of a classic study by Ekman et al. In their study, Ekman et al. measured the autonomic nervous system activity of participants for six emotions elicited by a relived emotions task and a directed facial action task. In the replication attempt, students only used the relived emotions task, where participants were asked to relive a past emotional experience, and participants’ HR was collected for only two emotions, namely anger and happiness. HR was measured using a free smartphone application, and students used their own smartphones. If first-year students can replicate results from the scientific literature with their smartphones, this would provide a strong demonstration of the usefulness and reliability of mobile devices to measure differences in HR caused by emotional experiences.