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Independence of echo-threshold and echo-delay in the barn owl.

Nelson BS, Takahashi TT - PLoS ONE (2008)

Bottom Line: Under this paradigm, there were two possible stimulus segments that could potentially signal the location of the echo.By lengthening the echo's duration, independently of its delay, spikes and saccades were evoked by the source of the echo even at delays that normally evoked saccades to only the direct source.An echo's location thus appears to be signaled by the neural response evoked after the offset of the direct sound.

View Article: PubMed Central - PubMed

Affiliation: Institute of Neuroscience, University of Oregon, Eugene, Oregon, USA. bsnelson@uoregon.edu

ABSTRACT
Despite their prevalence in nature, echoes are not perceived as events separate from the sounds arriving directly from an active source, until the echo's delay is long. We measured the head-saccades of barn owls and the responses of neurons in their auditory space-maps while presenting a long duration noise-burst and a simulated echo. Under this paradigm, there were two possible stimulus segments that could potentially signal the location of the echo. One was at the onset of the echo; the other, after the offset of the direct (leading) sound, when only the echo was present. By lengthening the echo's duration, independently of its delay, spikes and saccades were evoked by the source of the echo even at delays that normally evoked saccades to only the direct source. An echo's location thus appears to be signaled by the neural response evoked after the offset of the direct sound.

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Behavioral paradigm.(A) Placement of 10 loudspeakers and a central fixation LED, in polar coordinates. In trials with a lead/lag pair, one of the pair of speakers was assigned a radius of 10°, 15°, 20°, 25°, or 30° and a random polar angle. The second member of the pair had an identical radius, but was 180° opposite the first speaker. Corresponding Cartesian coordinates (azimuth and elevation) are also shown. The stimulus paradigms used in the behavioral trials were identical to those shown in Fig. 1 for physiology. (B) Example of a head saccade. The saccade shown here was made with an unusually large error (30°) relative to that of the closest source, in this case, the lagging source. Despite this error, the angle of the saccade was far greater when compared with that of the leading source (150°), thereby allowing us to determine whether the saccade was lead- or lag-directed. The color scale indicates saccade velocity.
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pone-0003598-g005: Behavioral paradigm.(A) Placement of 10 loudspeakers and a central fixation LED, in polar coordinates. In trials with a lead/lag pair, one of the pair of speakers was assigned a radius of 10°, 15°, 20°, 25°, or 30° and a random polar angle. The second member of the pair had an identical radius, but was 180° opposite the first speaker. Corresponding Cartesian coordinates (azimuth and elevation) are also shown. The stimulus paradigms used in the behavioral trials were identical to those shown in Fig. 1 for physiology. (B) Example of a head saccade. The saccade shown here was made with an unusually large error (30°) relative to that of the closest source, in this case, the lagging source. Despite this error, the angle of the saccade was far greater when compared with that of the leading source (150°), thereby allowing us to determine whether the saccade was lead- or lag-directed. The color scale indicates saccade velocity.

Mentions: Our conclusions are based on observations in three owls, C, S, and T (N = 33–66 trials/condition/subject). The stimuli were the same as those in the physiology component (Figs. 1A–D), except that they were presented in the free field (Fig. 5A). Saccades to single sources had latencies and errors similar to those reported by Spitzer and Takahashi [28]. We also confirmed that latencies to paired sources were significantly longer than those to single sources and that saccade errors to lead and single sources were comparable for all lag-alone segments. Saccade errors and latencies are summarized in Supplemental Materials Figure S2. Unlike in this previous study, saccades to lag sources were comparable in error to those of leading and single sources for lag-alone segments of 12 and 24 ms. Errors in trials with shorter lag-alone segments (<3 ms) were larger, but because there were few lag-directed turns (due to localization dominance), this observation must be viewed with caution. This result was, nevertheless, consistent with another study quantifying spatial discrimination in the owl under simulated echoic conditions [33].


Independence of echo-threshold and echo-delay in the barn owl.

Nelson BS, Takahashi TT - PLoS ONE (2008)

Behavioral paradigm.(A) Placement of 10 loudspeakers and a central fixation LED, in polar coordinates. In trials with a lead/lag pair, one of the pair of speakers was assigned a radius of 10°, 15°, 20°, 25°, or 30° and a random polar angle. The second member of the pair had an identical radius, but was 180° opposite the first speaker. Corresponding Cartesian coordinates (azimuth and elevation) are also shown. The stimulus paradigms used in the behavioral trials were identical to those shown in Fig. 1 for physiology. (B) Example of a head saccade. The saccade shown here was made with an unusually large error (30°) relative to that of the closest source, in this case, the lagging source. Despite this error, the angle of the saccade was far greater when compared with that of the leading source (150°), thereby allowing us to determine whether the saccade was lead- or lag-directed. The color scale indicates saccade velocity.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2571984&req=5

pone-0003598-g005: Behavioral paradigm.(A) Placement of 10 loudspeakers and a central fixation LED, in polar coordinates. In trials with a lead/lag pair, one of the pair of speakers was assigned a radius of 10°, 15°, 20°, 25°, or 30° and a random polar angle. The second member of the pair had an identical radius, but was 180° opposite the first speaker. Corresponding Cartesian coordinates (azimuth and elevation) are also shown. The stimulus paradigms used in the behavioral trials were identical to those shown in Fig. 1 for physiology. (B) Example of a head saccade. The saccade shown here was made with an unusually large error (30°) relative to that of the closest source, in this case, the lagging source. Despite this error, the angle of the saccade was far greater when compared with that of the leading source (150°), thereby allowing us to determine whether the saccade was lead- or lag-directed. The color scale indicates saccade velocity.
Mentions: Our conclusions are based on observations in three owls, C, S, and T (N = 33–66 trials/condition/subject). The stimuli were the same as those in the physiology component (Figs. 1A–D), except that they were presented in the free field (Fig. 5A). Saccades to single sources had latencies and errors similar to those reported by Spitzer and Takahashi [28]. We also confirmed that latencies to paired sources were significantly longer than those to single sources and that saccade errors to lead and single sources were comparable for all lag-alone segments. Saccade errors and latencies are summarized in Supplemental Materials Figure S2. Unlike in this previous study, saccades to lag sources were comparable in error to those of leading and single sources for lag-alone segments of 12 and 24 ms. Errors in trials with shorter lag-alone segments (<3 ms) were larger, but because there were few lag-directed turns (due to localization dominance), this observation must be viewed with caution. This result was, nevertheless, consistent with another study quantifying spatial discrimination in the owl under simulated echoic conditions [33].

Bottom Line: Under this paradigm, there were two possible stimulus segments that could potentially signal the location of the echo.By lengthening the echo's duration, independently of its delay, spikes and saccades were evoked by the source of the echo even at delays that normally evoked saccades to only the direct source.An echo's location thus appears to be signaled by the neural response evoked after the offset of the direct sound.

View Article: PubMed Central - PubMed

Affiliation: Institute of Neuroscience, University of Oregon, Eugene, Oregon, USA. bsnelson@uoregon.edu

ABSTRACT
Despite their prevalence in nature, echoes are not perceived as events separate from the sounds arriving directly from an active source, until the echo's delay is long. We measured the head-saccades of barn owls and the responses of neurons in their auditory space-maps while presenting a long duration noise-burst and a simulated echo. Under this paradigm, there were two possible stimulus segments that could potentially signal the location of the echo. One was at the onset of the echo; the other, after the offset of the direct (leading) sound, when only the echo was present. By lengthening the echo's duration, independently of its delay, spikes and saccades were evoked by the source of the echo even at delays that normally evoked saccades to only the direct source. An echo's location thus appears to be signaled by the neural response evoked after the offset of the direct sound.

Show MeSH