The study of auditory illusions has been important in elucidating the rules of auditory grouping in humans, which adhere to principles first described by Gestalt psychologists to explain the formation of visual objects. For example, the human auditory system perceptually restores short, deleted segments of speech and other sounds (e.g., tones) when the resulting silent gaps are filled by a potential masking noise. This “temporal induction” of missing sounds accounts for phenomena such as “phonemic restoration” of speech and the so-called “continuity illusion”. Results from studies of such illusions suggest that the Gestalt principle of “continuity” allows humans to perceive complete auditory objects in the face of incomplete or degraded acoustic information in the presence of noise. Although similar findings have been reported in two nonhuman primates and one songbird, the general relevance of such illusory percepts in acoustic communication across a wide range of taxa remains unknown. The present study tested the hypothesis that female treefrogs experience the illusory perceptual restoration of discrete pulses in the male sexual advertisement signal when they are deleted and replaced by a potential masking noise. While added noise restored some attractiveness to degraded signals, there was no evidence that the frogs experienced the illusion of perceiving actual pulses that were missing. Instead, the added noise appeared to function as an acoustic ornament that made some signals more attractive than others as a result of an inherent sensory bias for greater sensory stimulation. Whether such sensory biases themselves adhere to Gestalt principles of auditory grouping remains to be demonstrated.
Abstract: