title: Rhesus monkeys (Macaca mulatta) hear rising frequency sounds as looming.
abstract: 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.
authors.affiliation: Neuroscience Institute, Department of Psychology, Green Hall, Princeton University, Princeton, NJ 08540, USA. aslfg@princeton.edu
authors.forename: Asif A
authors.initials: AA
authors.lastname: Ghazanfar
authors.forename: Joost X
authors.initials: JX
authors.lastname: Maier
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001288:Attention; D001307:Auditory Perception; D053483:Eye Movement Measurements; D005133:Eye Movements; D019416:Head Movements; D008253:Macaca mulatta; D008297:Male; D010775:Photic Stimulation; D011571:Psychoacoustics; D013016:Sound; D013997:Time Factors