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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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Peri-stimulus time histograms (PSTHs) showing neural responses evoked by a subset of stimuli.Each bar shows the median neural response (>50 repetitions/cell; 1-ms bins). Thin lines show the first and third quartiles (Q1, Q3). Each cell's response was normalized to the maximum number of spikes evoked, within a single bin (usually the first or second bin after 0-ms), by 30 ms noise-bursts presented from the center of each cell's SRF [11]. (A) Responses evoked by a single 30 ms target. (B) Responses evoked by a single 30 ms masker. (C) Responses evoked by two, simultaneous, uncorrelated, noise-bursts presented from both the masker and target loci. (D) Responses evoked when the target led by 3, 12 or 24 ms. (E) Responses evoked when the target lagged.
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pone-0003598-g002: Peri-stimulus time histograms (PSTHs) showing neural responses evoked by a subset of stimuli.Each bar shows the median neural response (>50 repetitions/cell; 1-ms bins). Thin lines show the first and third quartiles (Q1, Q3). Each cell's response was normalized to the maximum number of spikes evoked, within a single bin (usually the first or second bin after 0-ms), by 30 ms noise-bursts presented from the center of each cell's SRF [11]. (A) Responses evoked by a single 30 ms target. (B) Responses evoked by a single 30 ms masker. (C) Responses evoked by two, simultaneous, uncorrelated, noise-bursts presented from both the masker and target loci. (D) Responses evoked when the target led by 3, 12 or 24 ms. (E) Responses evoked when the target lagged.

Mentions: Histograms compiled from the responses of all neurons in our sample to representative targets and maskers are shown in Figure 2. The responses of a single representative neuron are shown in the Supplemental Materials (Figure S1). The height of each filled bar in Figure 2 shows the median normalized firing-rate within each 1-ms bin. Targets evoked strong responses (Fig. 2A), while maskers, presented alone, evoked weak responses (Fig. 2B; see also Fig. 1F). Because spontaneous firing-rates were low in all of our cells (spikes/ms/cell: median = 0.00028, first quartile = 0, third quartile = 0.0017), we cannot say whether or not the masker, by itself, had an inhibitory influence. Figure 2C depicts the neurons' responses to two, simultaneous, uncorrelated, noise-bursts presented from both the masker and target loci. Responses to these stimuli were weak due to the superposition of the two sources' waveforms, which, in turn, decorrelates the signals binaurally [30]–[33]. The second row of PSTHs (Fig. 2D) shows the median responses of sampled neurons to lead/lag pairs when targets led by 3, 12, or 24 ms. Overall spike counts increased with delay, but most of this increase was due to an increase in the length of time, from the start of the stimulus, during which only the leading target was present (the lead-alone segment or the onset-delay). The responses decreased as soon as the lagging masker was activated. The bottom row of PSTHs (Fig. 2E) shows the median responses when targets lagged. Responses increased as soon as the masker, which led, was deactivated and continued for a period of time that was determined by the length of the lag-alone segment (Fig. 2E).


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

Nelson BS, Takahashi TT - PLoS ONE (2008)

Peri-stimulus time histograms (PSTHs) showing neural responses evoked by a subset of stimuli.Each bar shows the median neural response (>50 repetitions/cell; 1-ms bins). Thin lines show the first and third quartiles (Q1, Q3). Each cell's response was normalized to the maximum number of spikes evoked, within a single bin (usually the first or second bin after 0-ms), by 30 ms noise-bursts presented from the center of each cell's SRF [11]. (A) Responses evoked by a single 30 ms target. (B) Responses evoked by a single 30 ms masker. (C) Responses evoked by two, simultaneous, uncorrelated, noise-bursts presented from both the masker and target loci. (D) Responses evoked when the target led by 3, 12 or 24 ms. (E) Responses evoked when the target lagged.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2571984&req=5

pone-0003598-g002: Peri-stimulus time histograms (PSTHs) showing neural responses evoked by a subset of stimuli.Each bar shows the median neural response (>50 repetitions/cell; 1-ms bins). Thin lines show the first and third quartiles (Q1, Q3). Each cell's response was normalized to the maximum number of spikes evoked, within a single bin (usually the first or second bin after 0-ms), by 30 ms noise-bursts presented from the center of each cell's SRF [11]. (A) Responses evoked by a single 30 ms target. (B) Responses evoked by a single 30 ms masker. (C) Responses evoked by two, simultaneous, uncorrelated, noise-bursts presented from both the masker and target loci. (D) Responses evoked when the target led by 3, 12 or 24 ms. (E) Responses evoked when the target lagged.
Mentions: Histograms compiled from the responses of all neurons in our sample to representative targets and maskers are shown in Figure 2. The responses of a single representative neuron are shown in the Supplemental Materials (Figure S1). The height of each filled bar in Figure 2 shows the median normalized firing-rate within each 1-ms bin. Targets evoked strong responses (Fig. 2A), while maskers, presented alone, evoked weak responses (Fig. 2B; see also Fig. 1F). Because spontaneous firing-rates were low in all of our cells (spikes/ms/cell: median = 0.00028, first quartile = 0, third quartile = 0.0017), we cannot say whether or not the masker, by itself, had an inhibitory influence. Figure 2C depicts the neurons' responses to two, simultaneous, uncorrelated, noise-bursts presented from both the masker and target loci. Responses to these stimuli were weak due to the superposition of the two sources' waveforms, which, in turn, decorrelates the signals binaurally [30]–[33]. The second row of PSTHs (Fig. 2D) shows the median responses of sampled neurons to lead/lag pairs when targets led by 3, 12, or 24 ms. Overall spike counts increased with delay, but most of this increase was due to an increase in the length of time, from the start of the stimulus, during which only the leading target was present (the lead-alone segment or the onset-delay). The responses decreased as soon as the lagging masker was activated. The bottom row of PSTHs (Fig. 2E) shows the median responses when targets lagged. Responses increased as soon as the masker, which led, was deactivated and continued for a period of time that was determined by the length of the lag-alone segment (Fig. 2E).

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