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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.

Show MeSH
Stimulus configurations.(A) Overlapping lead (direct) and lag (simulated reflection) sounds. The temporal overlap defines periods of time during which both sounds were superposed, flanked by periods when the lead or lag sources were present alone. (B) Stimuli presented in the standard precedence effect, paradigm. The lead (gray) and lag (black) sounds were of equal length (30 ms) and onset-delay was 1.5, 3, 6, 12, or 24 ms. (C) Stimuli in which lag-alone segments were experimentally lengthened or shortened while maintaining a constant duration lead-alone segment (constant lead/lag delay). Lead and lag sounds were of unequal lengths. (D) Stimuli in which lead-alone segments were experimentally lengthened or shortened while maintaining a constant duration lag-alone segment (converse of C). When the lead-alone segment was 24 ms, the length of the lag-alone segment was shortened to 12 ms only in our physiological experiments (indicated by asterisks). (E) Single-source sounds among which paired-source stimuli were randomly interspersed in our behavioral experiments. Their durations were roved from 6–54 ms to invalidate duration as a possible cue. (F) Placement of sound sources in our physiological experiments. The plot represents the frontal hemisphere of the owl's auditory space [29]. Positive azimuths and elevations correspond to loci to the right and above an owl, respectively. A cell's SRF is shown in pseudo-color along with a scale bar indicating the average spike number over 4 repetitions. The source in the optimal location within the cell's SRF is referred to as the target. A second source placed at a location diametrically opposed across the owl's center of gaze from the target is referred to as the masker. In the experiments, the target or masker could lead, allowing us to examine a cell's response to simulated direct sounds and echoes.
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pone-0003598-g001: Stimulus configurations.(A) Overlapping lead (direct) and lag (simulated reflection) sounds. The temporal overlap defines periods of time during which both sounds were superposed, flanked by periods when the lead or lag sources were present alone. (B) Stimuli presented in the standard precedence effect, paradigm. The lead (gray) and lag (black) sounds were of equal length (30 ms) and onset-delay was 1.5, 3, 6, 12, or 24 ms. (C) Stimuli in which lag-alone segments were experimentally lengthened or shortened while maintaining a constant duration lead-alone segment (constant lead/lag delay). Lead and lag sounds were of unequal lengths. (D) Stimuli in which lead-alone segments were experimentally lengthened or shortened while maintaining a constant duration lag-alone segment (converse of C). When the lead-alone segment was 24 ms, the length of the lag-alone segment was shortened to 12 ms only in our physiological experiments (indicated by asterisks). (E) Single-source sounds among which paired-source stimuli were randomly interspersed in our behavioral experiments. Their durations were roved from 6–54 ms to invalidate duration as a possible cue. (F) Placement of sound sources in our physiological experiments. The plot represents the frontal hemisphere of the owl's auditory space [29]. Positive azimuths and elevations correspond to loci to the right and above an owl, respectively. A cell's SRF is shown in pseudo-color along with a scale bar indicating the average spike number over 4 repetitions. The source in the optimal location within the cell's SRF is referred to as the target. A second source placed at a location diametrically opposed across the owl's center of gaze from the target is referred to as the masker. In the experiments, the target or masker could lead, allowing us to examine a cell's response to simulated direct sounds and echoes.

Mentions: Although clicks afford advantages for experimentation, sounds in nature will often overlap temporally with reflections that arrive after short delays. As a result, there is a period of time when both leading and lagging sounds are present, the superposed segment, flanked by the lead-alone and lag-alone segments (Fig. 1A). What determines the echo-threshold in this case? On the one hand, it could be determined by a neural response, evoked during the superposed segment, at the onset of the lagging sound. In this case, echo-threshold is expected to correlate well with the length of the lead-alone segment. Alternatively, echo-threshold could correspond to a neural response during the lag-alone segment [17]. In this case, echo-threshold is expected to correlate well with the length of the lag-alone segment.


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

Nelson BS, Takahashi TT - PLoS ONE (2008)

Stimulus configurations.(A) Overlapping lead (direct) and lag (simulated reflection) sounds. The temporal overlap defines periods of time during which both sounds were superposed, flanked by periods when the lead or lag sources were present alone. (B) Stimuli presented in the standard precedence effect, paradigm. The lead (gray) and lag (black) sounds were of equal length (30 ms) and onset-delay was 1.5, 3, 6, 12, or 24 ms. (C) Stimuli in which lag-alone segments were experimentally lengthened or shortened while maintaining a constant duration lead-alone segment (constant lead/lag delay). Lead and lag sounds were of unequal lengths. (D) Stimuli in which lead-alone segments were experimentally lengthened or shortened while maintaining a constant duration lag-alone segment (converse of C). When the lead-alone segment was 24 ms, the length of the lag-alone segment was shortened to 12 ms only in our physiological experiments (indicated by asterisks). (E) Single-source sounds among which paired-source stimuli were randomly interspersed in our behavioral experiments. Their durations were roved from 6–54 ms to invalidate duration as a possible cue. (F) Placement of sound sources in our physiological experiments. The plot represents the frontal hemisphere of the owl's auditory space [29]. Positive azimuths and elevations correspond to loci to the right and above an owl, respectively. A cell's SRF is shown in pseudo-color along with a scale bar indicating the average spike number over 4 repetitions. The source in the optimal location within the cell's SRF is referred to as the target. A second source placed at a location diametrically opposed across the owl's center of gaze from the target is referred to as the masker. In the experiments, the target or masker could lead, allowing us to examine a cell's response to simulated direct sounds and echoes.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2571984&req=5

pone-0003598-g001: Stimulus configurations.(A) Overlapping lead (direct) and lag (simulated reflection) sounds. The temporal overlap defines periods of time during which both sounds were superposed, flanked by periods when the lead or lag sources were present alone. (B) Stimuli presented in the standard precedence effect, paradigm. The lead (gray) and lag (black) sounds were of equal length (30 ms) and onset-delay was 1.5, 3, 6, 12, or 24 ms. (C) Stimuli in which lag-alone segments were experimentally lengthened or shortened while maintaining a constant duration lead-alone segment (constant lead/lag delay). Lead and lag sounds were of unequal lengths. (D) Stimuli in which lead-alone segments were experimentally lengthened or shortened while maintaining a constant duration lag-alone segment (converse of C). When the lead-alone segment was 24 ms, the length of the lag-alone segment was shortened to 12 ms only in our physiological experiments (indicated by asterisks). (E) Single-source sounds among which paired-source stimuli were randomly interspersed in our behavioral experiments. Their durations were roved from 6–54 ms to invalidate duration as a possible cue. (F) Placement of sound sources in our physiological experiments. The plot represents the frontal hemisphere of the owl's auditory space [29]. Positive azimuths and elevations correspond to loci to the right and above an owl, respectively. A cell's SRF is shown in pseudo-color along with a scale bar indicating the average spike number over 4 repetitions. The source in the optimal location within the cell's SRF is referred to as the target. A second source placed at a location diametrically opposed across the owl's center of gaze from the target is referred to as the masker. In the experiments, the target or masker could lead, allowing us to examine a cell's response to simulated direct sounds and echoes.
Mentions: Although clicks afford advantages for experimentation, sounds in nature will often overlap temporally with reflections that arrive after short delays. As a result, there is a period of time when both leading and lagging sounds are present, the superposed segment, flanked by the lead-alone and lag-alone segments (Fig. 1A). What determines the echo-threshold in this case? On the one hand, it could be determined by a neural response, evoked during the superposed segment, at the onset of the lagging sound. In this case, echo-threshold is expected to correlate well with the length of the lead-alone segment. Alternatively, echo-threshold could correspond to a neural response during the lag-alone segment [17]. In this case, echo-threshold is expected to correlate well with the length of the lag-alone segment.

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