In this paper, we have studied the optimum-apportionment modes of the presentation time of eight randomly-selected alphabet sounds that were sequentially presented through an auditory display to four young males by means of our time-continuous model of short-term memory. These modes are thought to allow for the easiest retention by the short-term memory. The average optimum-apportionment mode, as an average of individual scores of the optimum-apportionment mode, was also obtained. This mode has shown the same tendency as that in the case of six or seven alphabet sounds. That is, the presentation time of the alphabet sounds presented in the first part is long and the presentation time of the alphabet sounds presented in the latter part is short. Individual differences among the optimum-apporitionment mods appear in the middle part, from the third to seventh alphabet sounds. According to this, the modes can be roughly divided into two cases:in the first case, the presentation time of one alphabet sound presented in the middle part is longer than that of the previous alphabet sond and the following alphabet sound. In the other case, the presentation time of the alphabet sounds decreases monotonically with the serial position.