Subjects were 111 older adult drivers (age 65 to 89 years; mean age 72.3) and 80 middle-aged drivers (age 40 to 64 years; mean age 57.2). These drivers were recruited from the general community surrounding Iowa City, Iowa, by means of announcements in local newspapers or public service announcements, visits to local churches, senior centers and living facilities, and from visitors to the medical complex who were not seeking medical care, such as family members or friends of patients. All participants held a valid state driver’s license and were still driving, had no neurological diagnosis or complaints, and no personal or family report of abnormal cognitive decline. Specific exclusion criteria included personal or family report of abnormal cognitive decline, documented neurological disease, brain lesions due to cerebrovascular or neoplastic disease, alcoholism, stroke, depression or other psychiatric conditions, vestibular disease, and motion sickness. This study was approved by the Institutional Review Board at the University of Iowa, and informed consent was obtained in accord with institutional and federal guidelines for human subjects’ safety and confidentiality.