Dr. laguardia is a cognitive neuroscientist who is interested in the effect of brain concussions on the ability to recognize faces. he conducts a quasi-experimental study in which he examines football players before and after the regular season, using the benton facial recognition test (a published, widely used measure of one's ability to recognize faces) to compare those who received concussions to those who did not. he finds that players who had concussions during the regular season performed worse on the benton facial recognition test than did players who did not experience concussions. in interrogating the construct validity of dr. laguardia's study, what can be concluded about his independent variable?