Hi Dave, I just wished to add my two bits regarding binaural listening and the rearward illusion you experience. Having investigated the effects of binaural electronic hearing protectors on localization, I do recall two sources of information (in addition to my own) where listeners experienced a rearward illusion of sound sources. The studies had to do with hearing protection devices (HPDs), but aspects of the studies apply to binaural listening in general. Of course, retaining head and pinna cues is what we desire with binaural recordings, but one man’s HRTF is another man’s, well...? In one of the (HPD) studies, pinna cues were absent because of occlusion, and this was believed to account for a rearward illusion. The references are
Russell G, Noble WG. Localization response certainty in normal and disrupted listening conditions: Towards a new theory of localization. J Aud Res 1976; 16: 143-50 Oldfield SR, Parker SP. Acuity of sound localization: A topography of auditory space: II, Pinna cues absent. Perception 1984; 13: 601-17 For Russell and Noble, it was believed that loss of canal resonance accounted for a rearward illusion (this was for listeners wearing earplugs). Under earphones, things are different. For example: In my study*, it was easy for subjects’ to discern left-from-right sound source location but discrimination between left rear and left front (or right rear and right front) was difficult. Front-back reversals accounted for the largest percentage of errors. Most errors made for the HPD conditions occurred at 120 degrees and 240 degrees (rear plane) and sounds coming from these locations were often judged as coming from 60 and 300 degrees (front plane), respectively. One listener, however, made localization errors opposite from other listeners. For this listener, regardless of condition, more ipsilateral errors were made to sounds coming from 0 degrees than for sounds coming from 180 degrees. Localization under HPDs for this listener was also unique: Stimuli presented at 60 and 300 degrees were often judged to originate from 120 and 240 degrees, respectively, which was opposite from the other listeners. Why a frontal or rearward proclivity for any particular listener is a good question. But it does appear that it is consistent for a given person. For me, binaural recordings almost always seem to be in the head (despite everyone’s best efforts), but sounds will appear to be outside of my head if they’re to the extreme left or right and include the requisite cues (beyond ILDs). Results from my HPD study suggested that binaural electronic HPDs retain the ILD cue needed for lateralization (I carefully matched the gain between earcups). However, pinna-head cues needed to make accurate front/back judgments are not retained. According to Oldfield and Parker, such errors would be anticipated despite stereo sound provided by the HPDs because the ITD of sound at the tympanic membrane does not uniquely specify a location in space, only the left/right component. Incidentally, manufacturers’ statements for their respective binaural electronic HPDs included ‘True ‘stereo’ for directional sound detection’ ‘Stereo sound so much like your own hearing that you retain your natural sense of sound direction’ ‘…provides you with 360 degrees awareness of sound direction with the clearest sound amplification available’ Hmmm... Check out the following and see what at least one study revealed. *Noise & Health, October-December 2007, Volume 9. I think it cost a bit to download; however, I won’t comment here on the cost of journal articles. If you’d like to see a PowerPoint regarding this study, you can download it from www.elcaudio.com/hearing/hpd_localization.pps [26.37 MB] I presented this study (and the PP) at a colloquium: Attendees included William (Bill) Yost and other noteworthy hearing scientists. Question: What if the same study was repeated only using an Ambisonic surround system? I wonder whether the same localization errors would occur. This, to some extent, might validate the usefulness of Ambisonics in hearing research. Another PP, for those interested in signal processing, otoacoustic emissions and hearing physiology (not too much psychoacoustics), can be downloaded from www.elcaudio.com/hearing/oae_study.pps [5.62 MB] (This study was kindly rejected by JASA, but it’s still in progress.) Kind regards, Eric C. -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20120113/c498bcad/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
