Rising sound intensity provides an important cue for the detection of looming objects. Studies with humans indirectly suggest that rising pitch can also signal a looming object. This link between rising intensity and rising frequency is puzzling because no physical rise in frequency occurs when a sound source approaches. Putative explanations include (a) the idea that the loudness of sound depends on its frequency, (b) the frequent co-occurrence of rising intensity with rising frequency in vocalizations generates an association between the 2 features, and (c) auditory neurons process amplitude- and frequency-modulated sounds similarly. If these hypotheses are valid, then rhesus monkeys (Macaca mulatta)-which share some homologies in the vocal production apparatus and auditory system-should also associate rising frequency with rising intensity, and thus should perceive rising frequency as a looming sound source. A head-turning assay and a preferential-looking paradigm revealed that monkeys show an attentional bias toward rising versus falling frequency sounds and link the former to visual looming signals. This suggests that monkeys hear a rising frequency sound as a looming sound source even though, in the real world, no such link exists.
All Science Journal Classification (ASJC) codes
- Behavioral Neuroscience
- audiovisual looming
- doppler effect