Table 1.

Features of the five displays and the details of their implementation.

			Type of Display
Features	Virtual speech	Virtual tone	HPI tone	HPI speech	Body pointing
Auditory source	Headphones	Headphones	Shoulder-mounted speaker	Shoulder-mounted speaker	Shoulder- mounted speaker
Compass location	Head	Head	Handheld pointer	Handheld pointer	Torso
Nonspeech acoustic signal	None	Tone (5 per second); swept tone (2.3 per second)	Tone (5 per second)	None	Tone (5 per second)
Acoustic off-course indicator	None	Yes; type of tone	Yes; tone if pointer is accurate; bearing if off by more than 90 degrees	Speech; straight left/right bearing if off by more than 90 degrees	Yes; tone if pointer is accurate; bearing if off by more than 90 degrees
Acoustic directional spatialization	Yes	Yes	None	None	None
Acoustic distance spatialization	Intensity	Intensity	Intensity	None	Intensity
Haptic pointer	None	None	Handheld	Handheld	Torso