Sound localization in a small passerine bird: discrimination of azimuth as a function of head orientation and sound frequency

Abstract

Sound localization is critical to communication when signalers are distributed widely in space and when reverberations that accumulate over distance might otherwise degrade temporal patterns in vocalizations. We readdress the accuracy with which a small passerine bird, the eastern towhee, Pipilo erythrophthalmus L., is able to resolve azimuth in the field. We then report results from two-alternative forced-choice (2AFC) experiments in which three of four subjects were able to discriminate an estimated speaker separation angle of approximately 7°. Subjects oriented laterally when discriminating azimuth in the 2AFC task and each subject preferred a different head orientation. Side biases occurred as a function of head orientation and, as a consequence, we conducted a second 2AFC experiment in which subjects were required to discriminate between two closely spaced lights. Subjects oriented similarly in this visual task, however, side biases did not occur as a function of head orientation. Despite side biases in the auditory task, performance generally declined when subjects were played tones with frequencies near ~3·kHz.

Multiplexed modulation of behavioral choice

“…In the absence of additional sensory input, each alternative behavior will occur at chance levels. This phenomenon has been observed in many versions of the twoalterative forced-choice task (Fechner, 1889) -in a variety of taxa such as birds (Klump et al, 1986;Nelson and Suthers, 2004), mice (Busse et al, 2011), monkeys (Britten et al, 1993) and humans (Green and Swets, 1966) -where, in absence of compelling input, the likelihood of each behavior hovers at chance. Under our model's assumption, leeches have sensors that are activated by shallow water, but have no sensors that are activated by deep water.…”

Spatial unmasking of birdsong in human listeners: Energetic and informational factors

“…While there is evidence that songbirds are capable of segregating mixtures of signals ͓see Hulse ͑2002͒ for a review͔, spatial factors have not yet been examined. Furthermore, some evidence suggests that spatial cues are not as salient for small birds as they are for humans ͑Park and Dooling, 1991; Dent and Dooling, 2004; however see Nelson and Suthers, 2004͒. It would be interesting to test zebra finches on the same stimuli used in this experiment, to address whether spatial unmasking enhances song identification in these birds.…”

Vocal tract filtering and sound radiation in a songbird

“…Towhees seem to discriminate and modulate sound frequencies above and below ~3.5·kHz differently (Nelson, 2002;Nelson, 2004;Nelson and Suthers, 2004). In addition: (1) sound frequencies above and below ~3.5·kHz often propagate differently over distance (e.g.…”