Information from Impact Sounds: Normal and Impaired Hearing Brent Kirkwood Ph.D. Project October 2003 - October 2006

Project Description In their everyday lives, people gather an abundance of information from the sounds present in the environments in which they act. With the exception of speech, these sounds have generally not been considered by psychoacousticians as providing information to listeners, but as producing sensations such as loudness, pitch, and timbre. It is first argued that this oversight must be addressed in order to provide an efficient and accurate means of understanding the real-world functionality of the human auditory system. Impact sounds were then chosen for this project as a common everyday sound for experimental investigation. In the first experiment, the influence of stimulus presentation method was investigated. Using only acoustic cues, normal-hearing subjects estimated the lengths of wooden rods dropped onto a linoleum floor. Their length estimation accuracy was compared for three presentation methods: 1) live presentation, 2) headphone playback of binaurally recorded stimuli, and 3) headphone playback of monophonically recorded stimuli. Subjects made larger errors when listening to monophonically recorded stimuli than when performing the task live. Binaural recordings were not found to produce results that were worse than live presentation. The results indicate that spatial cues may be an important aspect in auditory length perception, and that the selection of an inappropriate presentation method can deprive listeners of information normally available to them in the real world. The second experiment was an investigation of whether hearing-impaired listeners are as capable as normal-hearing listeners in hearing three ecologically relevant properties of impact sounds resulting from dropped rods: 1) the materials of the rods, 2) the lengths of the rods, and 3) the heights from which the rods are dropped. The results of listening tests are presented in which two subject groups, normal hearing and hearing impaired, have been tested with and without hearing aids. Hearing-impaired subjects without their hearing aids were found to perform worse, as a group, at judging the three parameters. Equipped with hearing aids, they remained worse than the unaided normal-hearing subjects at judging only material. The results are therefore informative about the abilities of normal-hearing and hearing-impaired listeners, and about the influence of the hearing aids. Finally, an experiment in auditory scene analysis was conducted in an attempt to help bridge the gap between classical psychoacoustics and an information-based approach to auditory perception. Unfortunately, the results were inconclusive and therefore not promising for bridging this gap. However, the outcome of this experiment emphasizes the need to use an ecological approach for studying the human auditory system. Publications Kirkwood, B. C. (2008) Impact Sound Perception by Hearing Aid Users. Poster Presented at the 2008 Meeting of the American Auditory Society (AAS). Kirkwood, B. C. (2007) Information from Impact Sounds: Normal and Impaired Hearing. Ph.D. Thesis. Technical University of Denmark. Kirkwood, B. C. (2007) Impact Sound Perception by Hearing Aid Wearers. Poster Presented at the 2007 International Symposium on Auditory and Audiological Research (ISAAR). Kirkwood, B. C. (2005) The Influence of Presentation Method on Auditory Length Perception. In Heft, H. and Marsh, K. L., editors, Studies in Perception and Action VIII, Lawrence Erlbaum Associates, pp. 145-148. (OCR scan of original version © Lawrence Erlbaum Associates - used with permission) Kirkwood, B. C. (2005) As good as the real thing? Performance differences for live versus recorded stimuli in an everyday listening task. In Rasmussen, A. N., Poulsen, T., Andersen, T., and Larsen, C. B., editors, Hearing Aid Fitting: Proceedings of the 21st Danavox Symposium 2005, pp. 519-529. Kirkwood, B. C. (2005) Maintaining Realism in Auditory Length-Perception Experiments. Proceeding of the Aalborg University Ph.D. Course Writing and Reviewing Scientific Papers. Kirkwood, B. C. (2005) The Influence of Presentation Method on Auditory Length Perception. Poster Presented at the International Conference on Perception and Action XIII, Monterey, CA. Kirkwood, B. C. (2005) As Good as the Real Thing? Performance Differences for Live versus Recorded Stimuli in an Everyday Listening Task. Poster Presented at the 21st Danavox Symposium, Kolding, Denmark.