Ceiling reflections are as detectable as lateral ones despite weak binaural cues

Evidence

Figure 6.6 shows data from Olive and Toole (1989) in which it is seen that the thresholds for the side wall and the ceiling reflections are almost identical. This is counterintuitive, because one would expect a lateral reflection to be much more strongly identified by the binaural discrimination mechanism because of the large signal differences at the two ears. For sounds differing only in elevation, we have only the spectral cues provided by the external ears and the torso (HRTFs). — Toole, Floyd E, Sound reproduction- the acoustics and…, 625

All this said, it still seems remarkable that a vertically displaced reflection, with no apparent binaural (between the ears) differences, can be detected as well as a reflection arriving from the side, generating large binaural differences. Not only are the auditory effects at threshold different—timbre vs. spaciousness—the perceptual mechanisms required for their detection are also different. — Toole, Floyd E, Sound reproduction- the acoustics and…, 628

Categorization

• QUESTION: Interesting open puzzle: what monaural spectral mechanism allows vertical reflections to be as detectable as lateral ones that produce strong binaural cues?
• DEEPTHINKING: Points to a fundamental asymmetry in the auditory system — two distinct detection pathways (spectral vs. binaural) converge at the same threshold — worth sitting with.
• corroborated: 3 independent passages support this claim — Toole, Floyd E, Sound reproduction- the acoustics and…, 625; Toole, Floyd E, Sound reproduction- the acoustics and…, 628
• XREF: connects to: Basic binaural cues cannot fully explain front-back and elevation judgments; Interaural level differences of 1-2 dB produce just-audible lateral displacement — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1714; Shoebox-shaped concert halls naturally produce abundant lateral reflections — David Howard, Jamie Angus, coustics and Psychoacoustics, 1969 (+1 more)

Broader Connections

• Basic binaural cues cannot fully explain front-back and elevation judgments #corroborates (0.82)
• Interaural level differences of 1-2 dB produce just-audible lateral displacement #corroborates (0.75) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1714