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When formulating an approach to a research study, planning experiments, and choosing the right technology for the job, size matters. Research studies with human subjects generally fall into three scale-related categories: individual, small-group, and large-group studies. When we discuss “size” in this context, we are talking about the number of subjects sampled together at one time and in one location.

Single-participant studies sample data from subjects separately while dyadic research gathers input from two subjects at the same time and place. It may be necessary, however, to take readings from three, four, or dozens of study subject simultaneously. In such cases, researchers often want to measure how the participants react to identical stimuli or the same external conditions such as those found in a classroom, courtroom, or theater setting. Researchers may also seek to measure how subjects react or interact with other members of the study group such as during business exchanges, in a meeting room environment, or in game sessions or other competitive settings.

These large-group studies present critical challenges that may not normally occur in single-participant studies. First, the stimuli to which the participants respond must be presented in a uniform and synchronous manner. Whether the stimuli are visual or auditory, thermal or olfactory, electrical or haptic, all study subjects must be able to respond to the same stimulus.

A recent study in behavioral economics measured psychophysiological reactions to various stimuli in the form of market and trading games in which multiple interactions took place between a set of “players.” Timing was critical to accurately measure the participants’ physiological responses to trades, losses, and gains. Both the presentation of stimuli and the recording of the participants’ reactions had to be precisely synchronized.

Methods for recording subjects’ response may include biopotential data such as ECG/EKG, EEG, EMG; transducer signals that can include electrodermal activity (EDA), respiration, and temperature; eye tracking; video recording; subjective response; or fNIRS, to name just a few examples. In the above study, participants were equipped with a photodiode that recorded responses during a decision-making experiment. Signals from the photodiodes were transmitted to a 16-channel BIOPAC MP150 Data Acquisition System (since replaced by the MP160 Data Acquisition System), allowing the simultaneous, synchronous recording of timing data from up to 16 subjects.

Child StudiesSynchronizing data is just one consideration when conducting multi-participant studies. Other logistical challenges arise when participants must interact with their surroundings. Another large-group study compared physical and psychological activity among seven-year-old elementary school children as they learned geometry through movement-based teaching methods. This presented several challenges, including the age of the subjects and the need for freedom of movement. Such problems are common to large-group studies that require multiple participants to move unimpeded by recording apparatuses. Typically, a researcher will choose between either a minimally invasive tethered device that can be wired to a data acquisition unit (e.g., BIOPAC ECG100D Smart Amplifier) or a wireless device (e.g., BIOPAC BN-ECG2 Wireless ECG Amplifier) that permits additional freedom of movement. In this study, the researchers used wearable devices to record the children’s energy expenditure, intensity of movements, EDA, body heat flux, and skin temperature.

While large-group studies present an array of unique challenges to gathering data, these challenges can be overcome through careful planning and by choosing the right tools for the job. BIOPAC offers a wide range of scalable technologies, software, and accessories for conducting research with individual subjects, pairs, or large groups that can be adapted to an array of scenarios and research settings.

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