Spatial unmasking of birdsong in zebra finches (Taeniopygia guttata) and budgerigars (Melopsittacus undulatus)

Abstract

Budgerigars and zebra finches were tested, using operant conditioning techniques, on their ability to identify a zebra finch song in the presence of a background masker emitted from either the same or a different location as the signal. Identification thresholds were obtained for three masker types differing in their spectrotemporal characteristics (noise, modulated noise, and a song chorus). Both bird species exhibited similar amounts of spatial unmasking across the three masker types. The amount of unmasking was greater when the masker was played continuously compared to when the target and masker were presented simultaneously. These results suggest that spatial factors are important for birds in the identification of natural signals in noisy environments.

Figure 1

Sonograms of (A) one of the target zebra finch songs, (B) a chorus masker, (C) a modulated noise masker, and (D) a song-shaped noise masker.

Figure 2

Mean psychometric functions for budgerigars (left column) and zebra finches (right column) for targets embedded in three noises (top row), modulated noises (middle row), and choruses (bottom row). d′ values are shown as a function of TMR for the co-located (black circles) and separated (white circles) speaker conditions. Error bars represent between-subject standard deviations. The birds were tested at slightly different TMRs, resulting in offset psychometric functions.

Figure 3

Individual d′ thresholds for the zebra finches (top row) and budgerigars (bottom row) for the noise (left panels), modulated noise (center panels), and chorus (right panels). Thresholds are shown as black circles for the co-located conditions and as white circles for the separated conditions. Zebra finches were run on an additional 180° speaker separation condition. Those thresholds are shown as white squares.

Figure 4

Mean psychometric functions for budgerigars (left column) and zebra finches (right column) for targets embedded in continuous noise (top row), continuous modulated noise (middle row), and a continuous chorus (bottom row). d′ values are shown as a function of TMR for the co-located (black circles) and separated (white circles) speaker conditions. Error bars represent between-subject standard deviations. The birds were tested at slightly different TMRs, resulting in offset psychometric functions.

Figure 5

Individual d′ thresholds for the four zebra finches (top row) and three budgerigars (bottom row) for the continuous noise (left panels), continuous modulated noise (center panels), and a continuous chorus (right panels). Thresholds are shown as black circles for the co-located conditions and as white circles for the separated conditions.

Figure 6

Mean thresholds for zebra finches (top panels) and budgerigars (bottom panels) with the co-located (left panels) and separated (right panels) speaker conditions. Thresholds for the brief masker are in black and thresholds for the continuous masker are in white. Error bars represent between-subject standard deviations.

Figure 7

Mean spatial unmasking for zebra finches (top panel) and budgerigars (bottom panel) for the three masker types. Unmasking for the brief masker is shown in black and for the continuous masker is shown in white. Error bars represent between-subject standard deviations.