Monaural perception under dichotic conditions

Abstract

Most people have two ears, but we can hear with only one ear. The ability to use two ears can substantially improve performance in many circumstances. There are times, however, when the addition of a second ear results in poorer performance (i.e., contra-aural interference). Contra-aural interference is of interest because it is not explained by current auditory models, it has theoretical ramifications, and its understanding could lead to improvements in the quality of life of the hearing-impaired. More generally, the techniques and results can be applied to fields in which information is combined across an array of sensors (e.g., vision with two eyes and radar arrays). This thesis includes both psychophysical measurements and black-box modeling of level discrimination. Level discrimination was chosen to study contra-aural interference since it has traditionally been considered a monaural task (dependent on only a single ear) even though the loudness of a sound depends on both ears (i.e., binaural). This thesis demonstrates that the ability to discriminate small changes in the level of a low-frequency target stimulus presented at one ear can be adversely affected by a distractor stimulus presented simultaneously and contra-aurally to the target.

(cont.) The thesis focuses on conditions in which the target and distractor perceptually fuse; the dominant perception of the stimulus is a compact auditory image with a salient loudness and position and a secondary image referred to as the "time-image". Contra-aural interference was greatest when the introduction of the distractor decreased the reliability of both the perceived loudness and position of the dominant-image. Although the tasks used in this thesis are artificial, their simplicity allows for detailed computational modeling. The results are consistent with a model based on non-optimal integration of the information carried by the dominant-image and the time-image. The modeling separates the effects of internal coding noise and decision noise (criterion jitter). The techniques used to separate the internal coding noise from the criterion jitter can be applied to a broad range of psychology experiments.