A successful eye tracking study starts well before test day. One of the most important first steps is carrying out good recruitment. This means including all the participants needed to answer the research question or fulfill the study objectives. It also means excluding subjects that are likely to cause difficulty because of their inability to be eye tracked and/or deliver quality data.
Selecting the population sample and subject quotas establishes a profile of the people whose reactions to the test are of interest and for which generalization may be desired. For example, a commercial cereal package study might require 100 participants who are the primary grocery shoppers for a household, with 25% of these self-identifying as Hispanic and 50% between the ages of 28-44 years. This, then, is a description of the consumer profile whose engagement with a new box design we wish to understand.
Alternatively, a cognition and language researcher might specify a sample that is 50% male across 60 typically-developing 30-month-old children for a study about spatial referential language.
Excluding potentially problematic eye tracking subjects can increase the time and resource efficiency of a study without biasing the results. This is also done before data collection by adding screening or exclusionary criteria to the recruitment documents. Aside from any study-specific situations, the following are the most common potential exclusions on the basis of mechanical difficulty for video-based eye tracking:
Note: The impact of the above conditions varies on a spectrum and if your research involves a population that has one or more (i.e., older people, specific visual impairments such as central visual field deterioration) then special measures can be taken collect the necessary data. For example, over recruitment to meet subject quotas or providing a chin rest.
If the inclusion and exclusion criteria were satisfied during recruitment, then all subjects will be valid barring unusual situations such as a prosthetic eye. The next step involves ensuring that the final barriers to successful tracking are handled. The confirmatory contact prior to testing might include instructions such as:
When participants arrive onsite at the testing location, they will undergo your intake process including the signing of the informed consent document. Then, as they are positioned at the testing station, you will make a final assessment of their readiness for testing.