A precedence effect resolves phantom sound source illusions in the parasitoid fly Ormia ochracea

Abstract

Localizing individual sound sources under reverberant environmental conditions can be a challenge when the original source and its acoustic reflections arrive at the ears simultaneously from different paths that convey ambiguous directional information. The acoustic parasitoid fly Ormia ochracea (Diptera: Tachinidae) relies on a pair of ears exquisitely sensitive to sound direction to localize the 5-kHz tone pulsatile calling song of their host crickets. In nature, flies are expected to encounter a complex sound field with multiple sources and their reflections from acoustic clutter potentially masking temporal information relevant to source recognition and localization. In field experiments, O. ochracea were lured onto a test arena and subjected to small random acoustic asymmetries between 2 simultaneous sources. Most flies successfully localize a single source but some localize a 'phantom' source that is a summed effect of both source locations. Such misdirected phonotaxis can be elicited reliably in laboratory experiments that present symmetric acoustic stimulation. By varying onset delay between 2 sources, we test whether hyperacute directional hearing in O. ochracea can function to exploit small time differences to determine source location. Selective localization depends on both the relative timing and location of competing sources. Flies preferred phonotaxis to a forward source. With small onset disparities within a 10-ms temporal window of attention, flies selectively localize the leading source while the lagging source has minimal influence on orientation. These results demonstrate the precedence effect as a mechanism to overcome phantom source illusions that arise from acoustic reflections or competing sources.cocktail party problem ͉ sound localization ͉ temporal window of attention

Behavior and modeling of two-dimensional precedence effect in head-unrestrained cats

“…In previous PE studies, speaker pairs were usually placed symmetrically in the frontal hemifield and rarely located off-center, i.e., both in the left or the right hemifield of the subject (Lee et al 2009). Figure 11A shows the final gaze positions (open symbols) for single (left column) and paired (other columns) sound sources located to the left of the cat (Ϫ120°,0) and (Ϫ60°,0) using the 5-Hz pulse train.…”

“…None of those studies tested diagonal conditions in which two paired sound sources differ in both horizontal and vertical locations. In addition, very few studies have tested sound pairs both located in the lateral hemifield (flies: Lee et al 2009). …”

Using Virtual Acoustic Space to Investigate Sound Localisation

“…Coding ambiguities lead to the formation of phantom sources. Many animals perceive phantom sound sources (Lee et al 2009;Mazer, 1998;Saberi et al, 1998Saberi et al, , 1999Tollin et al 2003). The main parameter for azimuthal localisation in the frontal hemisphere is the ITD.…”

Comparative Aspects of Hearing in Vertebrates and Insects with Antennal Ears

“…Forward and backward masking, illusory percepts of nonexistent tones (such as the Zwicker illusion [6]), perceptual merging of separate auditory streams, the precedence effect suppressing the perception of echoes that has been demonstrated in insects and vertebrates [7,8] (and which some blind people can unsuppress), auditory hallucinations, and a frustrating inability to distinguish between distinct phonemes of a foreign language -all of these phenomena indicate that evolution has not shaped the auditory system as an objective detector of acoustical reality. Instead, the auditory system, like any biological system, has evolved to help animals to find food, escape predators, and mate.…”