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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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Potential explanation for localization dominance in the responses of neurons to single sounds.(A) PSTH showing the median neural responses that were evoked, in our sample of cells, by single-source targets (shown also in Fig. 2A). (B) Neural responses measured in time-windows of length and position that were the same as the lead-alone (onset; blue lines) or lag-alone segments (offset; red lines) under the standard paradigm. (C) Median responses evoked by lag-alone segments (orange line; shown also in Fig. 3A) and by single sounds during equivalent time-windows (red line; redrawn from panel A). The green line shows the proportion of lag-directed saccades for all subjects under the standard paradigm (shown also in Fig. 6A).
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pone-0003598-g007: Potential explanation for localization dominance in the responses of neurons to single sounds.(A) PSTH showing the median neural responses that were evoked, in our sample of cells, by single-source targets (shown also in Fig. 2A). (B) Neural responses measured in time-windows of length and position that were the same as the lead-alone (onset; blue lines) or lag-alone segments (offset; red lines) under the standard paradigm. (C) Median responses evoked by lag-alone segments (orange line; shown also in Fig. 3A) and by single sounds during equivalent time-windows (red line; redrawn from panel A). The green line shows the proportion of lag-directed saccades for all subjects under the standard paradigm (shown also in Fig. 6A).

Mentions: That localization dominance might be explained by the response dynamics of neurons to single sounds is shown in Figure 7. Figure 7A shows the PSTH that was derived from the responses of all neurons in our sample to a single sound source (shown also in Figure 2A). Figure 7B shows the cumulative response that was evoked during a variable time-window that encompassed either the onset or the offset of the single source (as indicated by lines below the PSTH of Fig. 7A). As expected, the cumulative response was far weaker for time-windows that encompassed the sound's offset (red lines). Figure 7C compares these responses, at the sound's offset (red line, redrawn from Fig. 7B), with those that were evoked during lag-alone segments of equivalent length (orange line; shown also in Fig. 3A). These responses are directly comparable because most of the response to the lagging sound was evoked during the lag-alone segment. Finally, the green line in Figure 7C shows the proportion of lag-directed saccades for all subjects in our standard paradigm (shown also in Fig. 6A). Taken together, these data suggest that the owl may rarely saccade to the source of the lagging sound, when the delay is short, because the lag-alone segment emerges from the superposed segment only shortly before it ends. As delay increases, the lag-alone segment begins to evoke a neural response, at the lead's offset, that closely resembles the steady-state portion of the neural response to a single-source. Viewed in this way, the weaker representation of the lag source need not be attributed to a lateral inhibition-like process [11], [38], although such a process is not excluded.


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

Nelson BS, Takahashi TT - PLoS ONE (2008)

Potential explanation for localization dominance in the responses of neurons to single sounds.(A) PSTH showing the median neural responses that were evoked, in our sample of cells, by single-source targets (shown also in Fig. 2A). (B) Neural responses measured in time-windows of length and position that were the same as the lead-alone (onset; blue lines) or lag-alone segments (offset; red lines) under the standard paradigm. (C) Median responses evoked by lag-alone segments (orange line; shown also in Fig. 3A) and by single sounds during equivalent time-windows (red line; redrawn from panel A). The green line shows the proportion of lag-directed saccades for all subjects under the standard paradigm (shown also in Fig. 6A).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2571984&req=5

pone-0003598-g007: Potential explanation for localization dominance in the responses of neurons to single sounds.(A) PSTH showing the median neural responses that were evoked, in our sample of cells, by single-source targets (shown also in Fig. 2A). (B) Neural responses measured in time-windows of length and position that were the same as the lead-alone (onset; blue lines) or lag-alone segments (offset; red lines) under the standard paradigm. (C) Median responses evoked by lag-alone segments (orange line; shown also in Fig. 3A) and by single sounds during equivalent time-windows (red line; redrawn from panel A). The green line shows the proportion of lag-directed saccades for all subjects under the standard paradigm (shown also in Fig. 6A).
Mentions: That localization dominance might be explained by the response dynamics of neurons to single sounds is shown in Figure 7. Figure 7A shows the PSTH that was derived from the responses of all neurons in our sample to a single sound source (shown also in Figure 2A). Figure 7B shows the cumulative response that was evoked during a variable time-window that encompassed either the onset or the offset of the single source (as indicated by lines below the PSTH of Fig. 7A). As expected, the cumulative response was far weaker for time-windows that encompassed the sound's offset (red lines). Figure 7C compares these responses, at the sound's offset (red line, redrawn from Fig. 7B), with those that were evoked during lag-alone segments of equivalent length (orange line; shown also in Fig. 3A). These responses are directly comparable because most of the response to the lagging sound was evoked during the lag-alone segment. Finally, the green line in Figure 7C shows the proportion of lag-directed saccades for all subjects in our standard paradigm (shown also in Fig. 6A). Taken together, these data suggest that the owl may rarely saccade to the source of the lagging sound, when the delay is short, because the lag-alone segment emerges from the superposed segment only shortly before it ends. As delay increases, the lag-alone segment begins to evoke a neural response, at the lead's offset, that closely resembles the steady-state portion of the neural response to a single-source. Viewed in this way, the weaker representation of the lag source need not be attributed to a lateral inhibition-like process [11], [38], although such a process is not excluded.

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