Learn how to implement different experimental design components in Tobii Pro Lab
Once you are ready to implement your experiment, you will use the Design module in Tobii Pro Lab to set up your different experiment elements. In screen-based projects this is typically done by creating one or multiple timelines and adding different design elements to the timeline.
Before you continue, we are assuming that you have already defined the different details of your experimental design, such as:
If you sort out these details in advance, it will not only allow you to implement your experiment efficiently in Pro Lab but also account for the data analysis and export in your implementation.
The table below, shows you a list of common terms used in experimental design.
|Task||In its simplest form a task can be understood as “what subjects have to do in an experiment” (Philipp & Koch 2010), or it can be also defined as the way participants are asked to respond to stimuli in an experiment. An experiment can contain single or multiple tasks. Tasks are composed of different elements such as instructions, trials, and supporting elements.|
|Trials||In most experiments, a trial refers to a set of stimuli and supporting elements, that most often form self-repeating blocks of an experiment.|
|Stimulus||The stimulus represents your independent variable, and its possible variations. A stimulus is something the researcher presents to the study participants and simultaneously measures their response to it.|
|Response||A physical or physiological change that can be measured. Some examples are pressing a button, saying a word, moving the eyes, pupils dilating, heart rate increase, etc. The response is related to your dependent variable.|
|Supporting elements||Supporting elements are all other elements in the experiment that you present to the participant but do not measure their responses to, i.e., these elements are not necessary for computing your dependent variable, for example, cross marks used for centering the gaze of a participant before the start of the stimulus presentation, instructions, fillers, etc.|
Reference: Philipp, A. M., & Koch, I. (2010). The integration of task-set components into cognitive task representations. Psychologica Belgica, 50, 383–411.
In order to understand the relationship between these different terms and how experiments are implemented in Pro Lab’s Design module, let’s use a practical example.
Imagine that you want to run a study to evaluate the impact of two versions of the same ad on the viewing behavior of a group of consumers. In particular, you want to know if a specific ad item, which varies between the two versions, distracts the viewer from reading the text that contains the main message.
Since the two ads differ only in that item, they will appear quite similar to the participants. Consequently, to avoid any carry-over effects of exposing the same participant to both versions, you decide to use a between-subject design.
This research question can be operationalized by using a simple free viewing task, where you provide an instruction to the participants to simply look at the different ads and measure their visual behavior towards the two versions of the target ad.
To make your research question less obvious to the participants you decide to include several filler ads mixed with the target ads (stimuli). You also decide to use a fixation cross image before each ad (fillers and targets) to standardize the starting point of the viewing behavior of each participant. Each pair of fixation cross plus ad will constitute your trials. Finally, since you opted for a between-subject design you create 2 versions of the same task, each version containing the same filler ads but a different target ad.
This is how your planning might look...
Before we start the practical work of implementing it, let's summarize the design:
Until now we have been using common experimental design terms (Table 1) to decribe the experiment. The following steps will show you how to operationalize the terms in Pro Lab.
When you are finished, your experiment implementation should look something like this...
Let's summarize the implementation, now from Pro Lab's Design module perspective:
During the course of this example you have learned how to implement and operationalize an experiment in Pro Lab. The current example is fairly simple in it's implementation and did not cover all the available design elements (Table 2) or challenges but we hope it gives you an understanding of the approach you need to translate your own experiment into Pro Lab.
|Project||The Project is the main directory for your study. It contains all the stimuli, your task-trial implementation, recordings, event data, participant information, and your data selection definitions for analysis (times and areas of interest). There are different types of projects, depending on your study setup and type of eye tracker used to record eye movement data.|
|Timeline||Set up the task and its elements in "chronological" order. You may create different timelines within your project to help you manage your study design.|
|Element||It is an object you add to the timeline. This object will either work as a container for other elements or present and generate media. Each element posesses properties that you can change to customize the presentation of the content (according to the type of element).|
|Add "stimuli" (add images and video)||This element generates image and video stimuli, using a single media file. The suported media files are .bmp, .jpg or .png for images, and, .gif, .avi or .mp4 for video. Use external tools such as the Adobe Creative Suite, Elements, or other free tools such as Gimp and Inkscape to create the images and videos. Here, the word 'stimulus' does not have the same definition as Table 1, as these elements can be used to present supporting elements as well.|
|Add Group||This element works as a container for other elements and has its own timeline. It is used to add rules and actions to your presentation (e.g. to randomize and repeat the presentation of a group of images).|
|Add Web||This element will launch a URL in a Pro Lab Browser window. It automatically generates video recordings of the viewport, full page screenshots, web navigation TOIs and associated events. Using this element makes it easier to analyze and aggregate data of browsing behavior.|
|Add Screen recording||This element allows you to capture attention for any other type of stimuli shown onscreen (e.g.,non-supported browser webpages, non-supported video, other software). It generates video recordings of what is shown on the screen.|
|Add Instruction||This element enables you to include study introductions, directions, and/or task information as text on the screen. Using these embedded text instructions instead of verbal prompts helps ensure that the testing procedure is consistent across all participants. These elements won’t be automatically available in the analysis tools (metrics and visualizations).|
Pro Lab is a tool that allows you to creatively build and configure different types of eye tracking experiments. However, like other experiment building software, it has a certain logic and uses certain terms that require you to learn, before it can be used efficiently. This article explores the relationship between common research terms and the terminology used in Pro Lab and aims to help implement your design in Pro Lab.
For more terms and examples read also: