Sound Localization Experiments
USD Internet Psychology Laboratory
Background. The sound localization experiment is designed to provide some insight in to how the brain detects and processes sound location information. There are two major classes of information, or "cues", that the auditory system utilizes to localize sounds. These cues are referred to as interaural (i.e., between the ear) differences. First, sound localization is made possible by the interaural difference in the time-of-arrival (Delta T) of a sound wave. If a sound signal originates from a point 90 degrees to the right of straight-ahead, then the right ear will receive the signal several hundred microseconds before the left ear. The brain is capable of discriminating very small interaural differences in the time-of-arrival. The second cue involves the interaural difference in intensity (Delta I). The same signal as above will arrive at the right ear with a higher level of intensity than at the left ear.
To further complicate the matter, the relative efficiency of these cues differs across sound frequencies. For example, if a 500 Hz signal is presented at the same location as above, we are more likely to rely on Delta T as our primary localization cue. In contrast, we rely on the Delta I cue to localize sounds at high frequencies. All of these cues are directly related to properties of the human head, location and shape of the ear, and the sound waves themselves. For example, high frequency sounds possess a shorter wavelength than low frequency sounds. This high frequency sound wave has a tendency to be blocked by the head when a signal is located off center. Therefore, a sound shadow will be created and an interaural difference in intensity will be introduced as a result.
System Requirements. This experiment requires the use of stereo headphones and a Sound Blaster compatible sound card.
General Procedure. Both the Delta I, and Delta T studies will be conducted using a pair of headphones...