An experiment was conducted to test the hypothesis that exercise affects memory in the elderly. participants aged 60 and older who responded to an ad in the local newspaper were recruited for the study. all the participants were presented with the same study list. then half of the participants were asked to walk on a treadmill for 20 min, while the other half of the participants were asked to complete sudoku puzzles for 20 min. then all the participants were given a recognition test for the items in the study list. the treadmill exercise group scored significantly lower on the recognition test than the sudoku puzzle group. the most likely population for this study is