## 3 Methodology
### Experimental Protocol  
The experimental protocol can be seen in Figure 2. Trial counterbalancing was used to avoid participants' improving task performance influencing the outcomes of the study. Specifically, this meant randomising the order of the illumination conditions for each participant. This was done to help address concerns regarding the assumption underlying the use of the instructional film: that participants perform the task consistently between trials. By randomising the order of the illumination conditions, the influence of any hypothetical improvements in task performance with each subsequent trial is reduced. Note, that the term _trial_ is used here to refer to each attempt at the instructional film. A familiarisation task was also included in the protocol to reduce variation in task performance with each subsequent trial. Specifically, subjects were shown the video clips associated with each facial action included in the instructional film, via the Qualtrics form, and prompted to replicate each one until they felt they could reproduce it to the best of their ability. Participants were allowed as much time as they needed, which was typically around 15 min (exact data was not recorded). To ensure participants did not rush through this familiarisation task, they were asked to assess the difficulty of replicating each individual facial action. This data could then also be used to help evaluate the efficacy of the instructional film approach. To aid the practice of producing the facial actions, participants were given a mirror for the duration of the familiarisation task. After practising each movement, the participants were also given the chance to familiarise themselves with the speed and style of the instructional video through the viewing of a short preview. After this preview, they were asked to assess the pacing of the activity. As part of the protocol participants were also asked to sit quietly and wait for three minutes before each trial. This length of time was chosen based on the following criteria:  
* To allow participants to approach a baseline heart rate, hence providing a similar cardiovascular signal between trials allowing for a fair comparison of system performance. * To reduce the intensity of the experiment session, allowing participants to relax and not become overwhelmed to the point they cannot maintain a consistent level of task performance. * To not reduce the intensity of the experiment session to the point where participants are bored, which may also affect their task performance. * To provide enough time for the investigator to prepare for the next trial. Figure 1: Plot of mean pixel values for the red, green, and blue channels in the instructional film. Note the bright screen at the start of the instructional film, followed by the short dark section, and then the series of facial action stimuli that the participants are tasked with reproducing. The video data captured in this study could not be anonymised, as participants' faces had to be clearly visible in the recordings. Hence, based on legal requirements, the decision was made to only keep this footage for the necessary period for processing--evaluated as 60 days by the researchers involved [60]. After this point in time, the data extracted from the footage could subsequently be maintained with no way of associating the identity of the participant with their data. This was achieved by destroying all communications between participants and investigators, such as replies to recruitment emails. Moreover, the randomly generated participant codes from Qualtrics were used to label the data pertaining to each subject. To ensure that the data were secure, password protection was used on the folders in which the data were stored. Participants were all employees of Bang & Olufsen in Struer, Denmark. There was no financial reward for being a part of the study. To be eligible, participants had to be over the age of 18 and have no known heart problems.