\(\mu\)Cap is a bundled software package and comes with two additional separate applications: \(\mu\)Config and \(\mu\)Project. The governing principle of \(\mu\)Cap is based on repeatedly reading a specific pixel from the top left corner of the participants’ screen (for an example screen, see Fig. 1). Whenever this pixel changes color, \(\mu\)Cap will create a time stamp in a csv file.Footnote 2 By doing so, \(\mu\)Cap handles each participant separately, such that the progress of participants in different stages of the experiment will still be recorded precisely. This would matter, for example, if participants in a dictator game arrive at the donation decision screen at different points in time, for example, due to a preceding questionnaire. This procedure requires a minimum of additional programming effort by the experimenter. On the one hand, the tool \(\mu\)Config renders the creation of hand-written configuration files (i.e., files that define the association of colors and time stamps) unnecessary, as it offers experimenters a graphical interface to define colors \(\mu\)Cap will react to and to attach labels to events. On the other hand, additional programming in z-Tree is limited to adding a small box of 20 \(\times\) 20 pixels in the top left corner of the screen.Footnote 3
In a typical experiment, experimenters will use \(\mu\)Config when they program their experiment in z-Tree. A set of colors (using the RGB scheme) has to be defined in \(\mu\)Config and rectangles with the corresponding colors have to be placed in the top left corner of the z-tree screen. Virtually unlimited numbers of markers (i.e., color event combinations) can be defined to distinguish all parts of interest within the experiment. If the same part occurs more than once, markers can be re-used. Note that using the RGB scheme also enables users to only marginally vary the color of the rectangle (e.g., from 250, 250, 250 to 252, 250, 250) in a way such that \(\mu\)Cap recognizes the difference, but the participant does not. This might be especially valuable in a setting where the experimenter does not want the participant to know (or guess) what the instances of interest are.
After \(\mu\)Config has been set up correctly, \(\mu\)Cap will not only create video files of participants (including starting and stopping the recording at prespecified color changes)Footnote 4, but also correctly create the necessary time stamps. For \(\mu\)Cap to function properly, it simply needs to be executed on all clients (just like z-Leaf, the client program of z-Tree). After the start of the experiment, \(\mu\)Cap will be executed in the background, not visible to subjects.
As soon as video files and time stamps have been collected from the client computersFootnote 5, \(\mu\)Project will help to automatically create a new project in FaceReader™ (i.e., a file that will allow to batch process the analysis of facial expressions from the video material). Not only will this project automatically create the total number of subjects, but also load the video files and time stamps. Especially in projects with a large number of subjects, the automated processing of data using \(\mu\)Project can substantially reduce experimenters’ workload.
In a typical experiment, and to generate the desired output, an experimenter would typically follow these steps:Footnote 6 First, when programming the experiment, ensure that all screens in z-Tree include the small rectangular box with the desired RGB color code. Second, using \(\mu\)Config, generate the configuration csv file defining the markers for these color codes. Third, store the csv in the same folder as \(\mu\)Cap and make sure that all client computers can access this folder. Fourth, when running the experiment, make sure that all clients run \(\mu\)Cap and z-Leaf to generate the marker and video file for each subject. Fifth, collect all files and load them in \(\mu\)ProjectCreator, which in turn creates an frx file to be loaded in FaceReader™. Sixth, let FaceReader™ execute the frx file and save the resulting data file that indicates the strength of each emotion at every point in time. \(\mu\)Cap puts an additional column of data in the file that indicates the event markers.
\(\mu\)Cap can be used free of charge. We however kindly ask you to cite this paper in any academic publication or presentation when \(\mu\)Cap has been used (citeware). The most recent version of the package and documentation can be downloaded from http://mucap.david-schindler.de.