Matching acoustical and visual context yields convincing binaural externalization

Evidence

In the 1970s Sennheiser had a simple mass-market binaural microphone product, positioning small microphone capsules just outside the ears, but not in them. The encoded HRTFs had large errors. The headphones in use were of questionable performance, so the HRTFs were further degraded. Recordings made in one venue and played back in a different one were entertaining but not convincing. In-head localization was the norm. However, out of interest, I sat in my stereo seat wearing the binaural microphone and made a recording of my stereo system playing. I then put on headphones, sat in the same stereo seat and played the binaural recording. It was uncanny. The beginning of the tape presented the household background noises as they were before putting the headphones on. It was as though nothing had changed. When the music began it was convincingly externalized—remarkable. The acoustical and visual contexts matched. Rotating the head destroyed the effect. — Toole, Floyd E, Sound reproduction- the acoustics and…, 296

A few years later I visited a researcher with common interests: Prof. Jens Blauert in Bochum, Germany. He and his students had just done some experiments in which successful image externalization was reported, attributed to improved matching of personalized HRTFs, but noting that several listeners shared the experience with the same HRTFs. He demonstrated it for me, and, to his dismay, it did not work for either of us. His conclusion was that the setup had been relocated to a corner of a lab; it was not in the original record/reproduction location. The acoustical and visual contexts did not match, and his adaptation had faded. — Toole, Floyd E, Sound reproduction- the acoustics and…, 297

Categorization

• XREF: Connects to the earlier chapter and reader’s interest in how physical stimuli produce perceptual responses; the acoustic-visual context matching mechanism underpins why binaural reproduction usually fails. — connects to: Head-tracking binaural convolution yields convincing externalized spatial audio; Visual-vestibular room matching is required for binaural externalization to persist; Even crude binaural devices produce externalization after brief adaptation (+6 more)
• QUESTION: How exactly does the visual context (sitting in the same stereo seat) gate the neural adaptation to binaural cues? Worth chasing the mechanism.
• corroborated: 3 independent passages support this claim — Toole, Floyd E, Sound reproduction- the acoustics and…, 296; Toole, Floyd E, Sound reproduction- the acoustics and…, 297

Broader Connections

• Dynamic head tracking restores externalized sound localization in binaural reproduction. #expands (0.82)
• Static binaural images sound inside the head until head movement is tracked #contradicts (0.80)
• Even crude binaural devices produce externalization after brief adaptation #corroborates (0.78)
• Binaural recordings capture natural direction cues only when ears match the listener #qualifies (0.72)