Subject: Re: auditory localization From: "Henry, Paula (Cont,ARL/HRED)" <PHenry(at)ARL.ARMY.MIL> Date: Fri, 7 May 2004 10:22:03 -0400Elyana: Great question, and one that I have given considerable thought. I don't know that there is any easy answer as to the "correct" number. However, any time you allow participants to visually observe the total number of possible sources, then the number of possible responses, and the corresponding probability of being correct on any given trial is restricted. Depending on the precision that you are looking for in the measure, you would want to either include more sources or more potential response locations. This could be done by either increasing the number of sources, or by placing inactive loudspeakers between your present loudspeakers. The use of inactive or "dummy" loudspeakers would increase the number of total possible responses without increasing the number of source locations. For instance, if you used only 4 loudspeakers as sources and response possibilities, the chance of a participant getting any single presentation correct would be 1/4 or 25%. If you increase the number of response locations (to say, 10 -- 2 additional loudspeakers between each pair of sources) without increasing the number of actual sources, you've essentially tricked the participant into thinking that there are more than 4 possible choices. I'm not 100% sure (my mind is not comprehending the implications on probability for this), but the chances of a correct response could reasonably be expected to decrease. Eventhough the number of sources is the same, the number of possible responses has increased. One side note is that the use of additional loudspeakers to "stretch" a listener's response range will work to a greater or lesser extent depending on the signal characteristics, the distance between listener and loudspeakers, and other related variables. For instance, if the listener-to-loudspeaker distance is on the order of 1 m, the horizontal separation between loudspeakers for a given azimuth is much smaller than if the listener-to-loudspeaker distance is 4 m. So, the addition of dummy loudspeakers in the smaller distance may be more successful than in the larger distance. Our visual input is very strong and can override our auditory input as evidenced by phenomena such as the ventriloquist effect. For this reason, the participant has to believe that the sounds can come from any of the loudspeakers, so things such as wires need to be "connected" for all loudspeakers, including those that serve as "dummies". Good luck! Paula P. Henry, Ph.D., CCC-A Research Audiologist Visual and Auditory Processes Branch Human Research and Engineering Directorate Army Research Laboratory Aberdeen Proving Ground, MD 410-278-5848 -----Original Message----- From: AUDITORY Research in Auditory Perception [mailto:AUDITORY(at)LISTS.MCGILL.CA] On Behalf Of Elyana Makowski Sent: Friday, May 07, 2004 9:30 AM To: AUDITORY(at)LISTS.MCGILL.CA Subject: auditory localization Hi, I am a PhD student and my research project is on the use of localization cues (ILD and ITD) in the horizontal plane. My set up consists of 11 speakers arranged at 18 degree intervals from -90 to +90 degrees in the azimuthal plane. Currently, I have tested normally hearing subjects, and will soon be testing hearing aid users and cochlear implant users. Recently, an issue has been brought up as to the number of speakers that I am using, with the suggestion being made that better results could be measured if I used more speakers. My question is does anyone know how many speakers are necessary to accurately measure the average localization error? How many speakers are enough? Thank you, Elyana _________________________________________________________________ It's fast, it's easy and it's free. Get MSN Messenger today! http://www.msn.co.uk/messenger