**3.1 Identification of emitting sound in straight-line sequences**

## *3.1.1 Factors considered in experiments*

First, this study assesses individuals' capacity to identify a spatial sequence of sound stimuli and examines the factors that influence individuals' identification performance. Therefore, two experiments were conducted for ten healthy male students (20–21 years old) of Hannan University with no abnormal hearing diagnosed during their annual medical examination. They participated in this experiment without remuneration. Experimenter and all participants provided informed consent before these experiments.

The identification procedure of sound sequence requires the participants to continuously recognize sound localization for sequentially emitting sound through the loudspeakers. The sound localization is a listener's ability to identify the location of a detected sound in direction and distance. Various factors that cause changes in the pressure and sound wave frequency affect individuals' sound localization performance. Therefore, it is expedient to consider the influence of emission speed (emission-time interval) and the distance between loudspeakers to assess the subjects' identification performance. Furthermore, considering the preceding effect, the position of the subject relative to the loudspeaker should be considered a factor affecting the identification of the sound stimulus. Thus, the stimulus type, emissiontime interval, distance between loudspeakers, and subject's position were considered as experimental factors in the first experiment.

Previous studies on emergency-alert sounds reported that stimuli containing a wide range of frequencies are more likely to be recognized than those with a single frequency [12]. Furthermore, swept-sound stimuli from low to high frequencies can be recognized more easily during evacuation guidance procedures. Therefore, in this experiment, the phrase "Here is an emergency exit," spoken by a female voice in Japanese because the human voice is an acoustic stimulus with many frequencies superimposed on it. It also was used in previous studies on evacuation guidance procedures using the preceding effect [4, 5].

As a result of the above considerations, the two types of acoustic stimulus were set to experimental factor, the female voice and a sound that linearly changed from 500 to 1000 Hz in 1 s (swept-sound). The distance between the loudspeakers was set to two levels, 3 and 5 m, while the emission-time intervals were set to 1 and 0.5 s. The longer the time interval, the faster the sound moved. The subjects were instructed to stand in one of two fixed places—just below a loudspeaker in the center of the grid or between loudspeakers.
