A method on a computing device for enhancing the memory and cognitive ability of a participant by requiring the participant to differentiate between rapidly presented aural stimuli. The method trains the time order judgment of the participant by iteratively presenting sequences of upward and downward formant frequency sweeps, in random order, separated by an inter-stimulus interval (ISI). The upward and downward formant frequency sweeps utilize frequencies common in formants, i.e., the characteristic frequency components common in human speech. Icons are associated with the upward and downward formant frequency sweeps to allow the participant to indicate an order in which the sweeps are presented (i.e., UP-UP, UP-DOWN, DOWN-UP, and DOWN-DOWN). Correct/incorrect selection of an order causes the ISI and/or the duration of the frequency sweeps to be adaptively shortened/lengthened. A maximum likelihood procedure may be used to dynamically modify the stimulus presentation, and/or, to assess the participant's performance in the exercise.