Evaluation of the effects of spatial separation and timbral differences on the identifiability of features of concurrent auditory streams

When using non-speech as an information delivery medium, information patterns are mapped onto auditory variables. The efficiency of delivering information to listeners depends on the usage of auditory variables. A discriminable auditory display can reduce the ambiguity of listeners’ perceptual representation of auditory inputs. However, there is lacking an understanding of the way in which listeners decode information embedded in sound through identifying auditory variations. This thesis aims to develop an understanding of the influence of auditory variables on the identifiability of the features of auditory display. The auditory display in this thesis relates to auditory graph where series of quantitative values were mapped onto pitches and presented over time. This thesis explores the effects of spatial separation and timbre on the identifiability of the features of simultaneously presented auditory graphs. Features that listeners were required to identify included an increased periodic modulation in pitch that occurred in only one stream of two displayed auditory streams or a difference in the overall shape of the pitch contour of two displayed auditory streams. Both of these tasks required divided attention between stimuli forming two auditory streams, which were presented via headphones in order either to appear at two separate spatial locations, or to be co-located at a single location. Also, the displayed stimuli could differ in timbre, allowing for an evaluation of the relative influences of timbral difference and spatial separation on the identifiability of the target features. One hypothesis tested here was that when simultaneously presented auditory graphs were composed of the same timbre, their pitch contours would be more easily identified when displayed at spatially separated locations. A second hypothesis tested here was that the enhancement of identification performance due to spatial separation of simultaneously presented auditory graphs would be greatest for auditory streams that differ least in timbre, and that discrimination performance given streams with more distinct timbre would be less influenced by spatial separation of the streams. In a subsequent divided attention study using only spatially separated auditory streams, the perceptual salience of timbral differences in an identification task was investigated using timbral attribute ratings. Finally, in a data sonification case study employing multiple auditory streams exhibiting spatial and timbral differences, a qualitative approach was taken that aimed to deepen understanding of the way people listen and think in such contexts. Overall, the applied method demonstrated the influence of spatial separation and timbral differences on the feature identification for simultaneously presented auditory streams. Although there is potential for further refinement of the methods applied here, this work provided an examination and elucidation of the relative salience of two prominent factors involved in determining the effectiveness of concurrent auditory displays and delineated some of their limitations in supporting two different identification tasks. The responses, collected using an open questionnaire administered after participation in some of the experiments, highlighted the intricate relationships that exist in the allocation of attention between perceptually segregated concurrent streams, and in the auditory display processing activities and listening strategies of human subjects engaged in divided attention tasks.