An interactive test of serial behavior: age and practice alter executive function.

We describe an interactive, computer-based test inspired by the Trail Making Test (TMT). In this new test, young (mean age = 20.4 years) and older participants (mean age = 74.9 years) used natural, pointing responses to order series of numbers, letters, or intermixed letters and numbers. This interactive test, which avoids several deficiencies of TMT, assesses participants' baseline speed for detecting and responding to individual items, captures the time for each response, and segregates erroneous responses from correct ones. The inter-response times with intermixed letters and numbers showed that participants did not always switch between the two different ordering tasks, but instead often recall letter-number pairs as single units. An additive factors analysis decomposed test times into functional components, including executive function, which took longer in older participants. With modest practice, both young and older participants sped up their ordering of intermixed numbers and letters, probably reflecting increased automaticity and reduced dependence upon executive function.