Physiological responses are an integral part of our emotions and experiences, and we all exhibit physically detectable signs of our emotional and experiential state. For example, at your thesis or dissertation defense, you will most likely feel anxious and nervous; these feelings are accompanied by an increase in your heart rate, respiration rate, and galvanic skin response (sweat gland activity). Despite the existence of these physiological markers, a majority of graduate program curricula focus on learning to measure behaviors, emotions, and cognitions rather than on measuring bodily changes. Although these more traditional psychological measures are informative, the study of psychophysiology adds an additional piece of information by allowing one to measure the relationship between psychological and physiological response. By measuring these physiological changes, you gain valuable, objective insight into an individual’s internal state that may have otherwise gone unnoticed and unreported.
Psychophysiology measures have become more and more popular in research studies. According to a survey conducted by the authors, in the January through April 2009 issues of Psychological Science, approximately 27 percent of the empirical articles included some type of psychophysiological measure, compared to 13 percent of the journal’s studies published between January and April 2004. Furthermore, physiological measurements can be incorporated into many psychological domains. For example, Richman, Bennett, Pek, Siegler, and Williams (2007) measured cardiovascular reactivity (i.e., blood pressure and heart rate) in white and black adults who were administered an anger recall task. They found that participants who had higher cardiovascular reactivity and slower recovery tended to score higher on measures of past discrimination, low cynicism, and high optimism. Thus, Richman and colleagues’ findings suggest that cardiovascular reactivity may differ based on past experiences (e.g., discrimination) and personality traits (i.e., cynicism and optimism).
Although the idea of integrating psychophysiology into your research design may seem appealing, it can be quite daunting for the novice. Yet, with some basic knowledge, it is quite doable. Table 1 gives information on some common psychophysiology measures, the output indices normally associated with the measure, why you might use the measure, and what equipment or materials are available.
Research Design “Must Knows”
Take a history. Beyond determining the most appropriate participants for your research question of interest (e.g., which gender, what age), you must also consider possible confounding variables. For example, the consumption of caffeine prior to a heart rate assessment might artificially inflate one’s heart rate and thereby confound your data. Therefore, it is important to identify and address variables that may lead to physiological differences between people that are unrelated to your research question. As such, be sure to take a thorough history for each participant.
Clarify your collection methods. Other important details to consider while designing your study involve the time of data collection, event markers, and epoch periods. Some psychophysiological measures, such as cortisol levels, vary greatly throughout the day; therefore, it is important to obtain samples at the same time across days (Gunnar & White, 2001). During the session, it is also vital to obtain event markers, which will allow you to identify precisely when an event occurred during the data collection. Some equipment includes a way to event mark; however, it also can be just as easy to use a stopwatch to note the time a stimulus was presented. Lastly, researchers who collect psychophysiological data must use epoch periods, or recording periods, that are long enough to capture the event of interest. Although this may vary among measures, a minimum of 60 seconds is typically recommended for cardiovascular recording (Berntson et al., 1997).
Pay attention to your units. Once you have collected your data and you begin data analysis, it is important to be aware of the units of the measure you are analyzing. For example, cardiac data can be analyzed as beats per minute or as heart periods (i.e., time between heart beats), which are inversely related. Moreover, it is important to understand the direction of a measure; a decrease in a measure can actually mean an increase in physiological arousal. For example, in the measurement of pulse transit time, the time it takes the blood pulse to go from the heart to one’s finger, a decrease in time (i.e., pulse gets to finger faster) indicates increased arousal. At first it may seem counterintuitive, but it makes sense: The faster the heart is pumping, the quicker the blood pulse will get to your finger, and the less time it takes. Yet in other measures (e.g., heart rate), an increase in the metric indicates an increase in arousal. Always be aware that an increase in an output index does not necessarily reflect an increase in arousal.
How to Learn More
The authors both agree that they learned the most by doing rather than reading, though we highly recommend the Handbook of Psychophysiology (Cacioppo, Tassinary, & Berntson, 2007). With this basic information in mind, start talking to others, and get experience in various labs that collect psychophysiological data. Before long, you will develop the skills to run your own psychophysiology experiments.
Berntson, G.G., Bigger, T., Dwain, E.L., Grossman, P., Kaufmann, P.G., Malik, M., et al. (1997). Heart rate variability: Origins, methods, and interpretive caveats. Psychophysiology, 34, 623-648.
Cacioppo, J.T., Tassinary, L.G., & Berntson, G.G. (Eds.). (2007). Handbook of psychophysiology. New York: Cambridge University Press.
De Meersman, R.E., & Stein, P.K. (2007). Vagal modulation and aging. Biological Psychology, 74, 165-173.
Fowles, D.C., Edelberg, R., & Lykken, D.T. (1981). Publication recommendations for electrodermal measurements. Psychophysiology, 18, 232-239.
Gunnar, M.R., & White, B.P. (2001). Salivary cortisol measures in infant and child assessment. In L.T. Singer & P.S. Zeskind (Eds.), Biobehavioral assessment of the infant (pp. 167-189). New York: Guilford Press.
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Richman Smart, L., Bennett, G.G., Pek, J., Siegler, I., & Williams, R.B. (2007). Discrimination, dispositions, and cardiovascular responses to stress. Health Psychology, 26, 675-683.
Shapiro, D., Jamner, L.D., Lane, J.D., Light, K.C., Myrtek, M., Sawada, Y., et al. (1996). Blood pressure publication guidelines. Psychophysiology, 33, 1-12.