The accuracy of absolute localization judgments for speech stimuli

Communication signals are likely to be one of the primary forms of acoustic stimulation within three-dimensional auditory displays, yet the ability to localize these signals has received relatively little study. We investigated the ability to localize single-word speech targets, spoken by one male and one female talker, as compared to the ability to localize click targets. On each trial, the targets could arise from any one of 239 speaker locations that surrounded the subject in azimuth and ranged from -45 degrees to +90 degrees in elevation. The results showed that localization accuracy relative to the median plane (the Left/Right dimension) was good for both the speech and nonspeech targets. However, with speech targets, there were more front/back reversals (inaccurate judgments relative to the frontal plane, the Front/Back dimension) and typically less accurate elevation judgments (inaccurate judgments relative to the horizontal plane, the Up/Down dimension) than were found with click targets. These results have important implications for applications of spatial hearing technology and suggest that need for caution when designing three-dimensional auditory displays in order to assure that spatial information is conveyed appropriately.