Greetings All, Many thanks for the insightful responses to my recent post (Catching the same fly twice). I was pleased to read that most folks on the mailing list are a lot more qualified to discuss Ecological Psychology than I was (and thanks to E. Deleflie for the kind and insightful note).
Dr. Peter Lennox brought up a point that I had considered adding to my post. The point has to do with what spatial perception is/does. I very much agree that discerning or sensing a CHANGE in distance is more important than static, directional localization. This, too, can be intertwined with Gibson’s (and others) papers on point-of-impact, although Ecological Psychology deals more with vision that hearing. I will, however, unabashedly reveal that I received a D on high-school physics project because I wrote that the Doppler shift was mostly bogus when it comes to discerning motion (towards or away from the observer) because the Doppler shift yields a CONSTANT pitch shift until the point where it passes the observer. Years later, a paper was published by Michael McBeath (pronounced McBeth, as he told me) et al that proved that my earlier and ‘naive’ notion was correct. McBeath wrote: ‘Despite this fact of physics [re Doppler shift], most people tend to hear a pitch rise as the train approaches and a pitch fall as the train departs... We tested this phenomenon in the laboratory by presenting listeners with simulated Doppler shifted tones and asking them to track with a joystick the changes in pitch that they heard... Since the physical measurement of frequency and the perceptual experience of frequency (i.e. pitch) were going in opposite directions, we called this phenomenon the Doppler illusion. The pattern of pitch change that is heard (rising then falling) resembles the pattern of LOUDNESS change that occurs. We argue then that the Doppler illusion is due to the change in loudness that occurs as the train approaches. More generally, dynamic changes in loudness can influence perceived pitch in a previously undocumented way.’ [Source = http://www.acoustics.org/press/133rd/4pppa3.html] A lot of my research questions aren’t what the normal-hearing listener perceives, but what the hearing-impaired listener perceives. Sadly, we can't put ourselves in these shoes, even with simulations. It is for this reason that I wish to create a PHYSICAL replica of the acoustic environment, not merely an illusion that is 'real' to normal-hearing persons. Dr. Cynthia Comptom-Conley (Gallaudet University) did her dissertation on an 8-speaker surround system that was (originally) intended to be useful for audiologists. She demonstrated that hearing aid users made the same number and TYPE of mistakes in the surround environment as they did in similar, real-world environments. This, then, ‘proved’ that the surround system accurately replicated the real world. I know the system’s designer, and had recommended incorporating additional stimuli to extend the usefulness of the system. The designer frowned on Ambisonics, stating that recordings made with a Soundfield mic sounded muddy (Egad!! Did I mention he had hearing loss and wore hearing aids?). The sole recording for the research-oriented surround system was made with 8 Sennheiser gradient mics, each equally spaced in a horizontal array. Photos of this recording system show a KEMAR centered in the mics, but I learned that the photo was all for show (KEMAR really was being used as a dummy--to impress other dummies??). The system is novel and useful because it fits in a standard audiometric test booth, but I believe an Ambisonics system would be a lot more flexible (not to mention it's easier to make field recordings with a Soundfield mic). Saying that HA users make the same mistakes in an artificial environment doesn’t really 'prove' that this environment provides the same sensation to hearing impaired people as a natural environment would, but the results certainly lend credence to the system, at least to the extent that one can demonstrate that directional mics are beneficial to hearing aid users. So, akin to gamers who are fooled by illusions, or normal hearing people who make mistakes when presented with distorted stimuli (to simulate hearing loss), my quest for the elusive Holy Grail of audio reality is to build a system that provides the same PHYSICAL pressures, wavefront curvatures and directions, phase angles, blah blah that existed at the recording site. Hopefully, too, the ‘sweet spot’ would be large enough to permit normal head movement--the use of a bite brace just isn’t natural (the aforementioned system has a radius of 2 feet, so head movements are frowned upon). From what I've read, acoustic holography, wave field reconstruction, or high-order Ambisonics are my best bets towards achieving this lofty goal. If the system is REAL enough (again, referring to physical replication, not perceptual illusion), then iterations of the recording made through the system should yield recordings with identical, physically measurable attributes. By the way, thanks Dave for sharing insight and experience regarding your recording of a recording. I have access to a fairly large, semi-anechoic room (all walls, floor and ceiling well treated) that could be useful for such an experiment. I'll keep you posted. As always, I greatly appreciate everyone’s help and insight! Best always, Eric -------------- next part -------------- An HTML attachment was scrubbed... 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