1887
banner image
No data available.
Please log in to see this content.
You have no subscription access to this content.
No metrics data to plot.
The attempt to load metrics for this article has failed.
The attempt to plot a graph for these metrics has failed.
Effects of filtering of harmonics from biosonar echoes on delay acuity by big brown bats (Eptesicus fuscus)
Rent:
Rent this article for
USD
10.1121/1.3459823
/content/asa/journal/jasa/128/2/10.1121/1.3459823
http://aip.metastore.ingenta.com/content/asa/journal/jasa/128/2/10.1121/1.3459823

Figures

Image of FIG. 1.
FIG. 1.

Diagram of 2-choice electronic-echo delay discrimination set-up with bat on Y-shaped platform: Bat’s broadcast sounds are picked up by microphones (m), delayed and filtered electronically, and returned as echoes of virtual targets from loudspeakers (s). Delay of is fixed at , which simulates a target range of 54.5 cm. Delay of S− is fixed later, at , which simulates a target range of 68.3 cm. The difference between S− and corresponds to the index point described in Fig. 2. For the present experiments, and S− undergo various filtering conditions to assess effects on performance at index point. Idealized percent-error performance curve illustrates relation between peak in error curve when S− matches delay of and the still-elevated performance occurring at .

Image of FIG. 2.
FIG. 2.

Experiment 1. Effects of removing harmonics on delay acuity: (a) Spectrograms for stimuli used as echoes of a representative bat broadcast containing FM1 and FM2. Highpass filtering restricts the echo band to 20–90, 28–90, 32–90, or 66–90 kHz, which removes progressively larger segments from the low-frequency end of FM1. Lowpass filtering to 20–44 kHz completely removes FM2, leaving FM1 mostly intact. Filters have roll-off of 115 dB/octave to sharply cut out the unwanted part of the echo spectrum. Both and S− are filtered as indicated and then delivered with the index delay difference of (Fig. 3). (b) Bar-graph showing performance on delay-discrimination tasks (percent errors) for four bats (150 trials/bat), with mean performance ±1 SD (circles). Removal of FM1 in small stages causes progressive, significant loss of delay acuity (more errors) for difference between and S− , culminating in chance performance for echoes containing only FM2. Performance recovers but still is not completely normal when echoes contain only FM1.

Image of FIG. 3.
FIG. 3.

Experiment 2. Relative salience of harmonics: (a) Spectrograms for representative stimuli containing only FM1 or only FM2 for and S−. Full-band, normal echoes are shown at left. At right, contains only FM2 while S− contains FM1 and FM2 (full band). (b) Bar graph showing performance on delay-discrimination tasks (percent errors) for four bats with mean performance ±1 SD. As already shown in Fig. 2, performance on delay difference is good if echoes contain only FM1 but chance if echoes contain only FM2. When offered a choice between S− containing FM1 and FM2 versus containing FM2 alone, bats prefer S− even though it is delivered later than .

Image of FIG. 4.
FIG. 4.

Experiment 3. Effects of harmonic-split filtering on delay acuity: (a) Spectrograms for representative stimuli testing the effect of introducing the harmonic-split filters on the index delay discrimination task. Full-band, normal echoes with no harmonic split for and S− are shown at left (note slight overlap of harmonics at 50–55 kHz). Next, to split the harmonics into two parallel electronic channels, echoes for both and S− are filtered at 20–44 kHz to remove FM2 and 66–90 kHz to remove FM1. The isolated harmonics are delayed and amplified differently, then recombined (added) to create split-harmonic echoes that now have a narrow spectral gap eliminating frequencies around 55 kHz where FM1 and FM2 overlap. echoes have either the harmonic split alone (FM1 and FM2 both at ) or the harmonic split plus offset of FM2 relative to FM1 (FM1 at , FM2 at ). S− echoes have the harmonic split alone (FM1 and FM2 at ). (b) Bar graph showing performance on delay-discrimination tasks (percent errors) for four bats (150 trials/bat, with mean performance ±1 SD shown by circles). Introduction of harmonic-split filters with no other change causes small, significant decrease in acuity (more errors) compared to full-band echoes . Addition of offset to FM2 relative to FM1 causes large decline in acuity beyond what occurs for split-harmonic condition with no delay difference .

Image of FIG. 5.
FIG. 5.

Experiment 4. Amplitude-latency trading and compensatory time shift: (a) Spectrograms for representative stimuli used to assess the loss in delay acuity if FM2 is decreased by 3 dB relative to FM1, and for testing the role of amplitude-latency trading by advancing FM2 in time by a compensatory . (Amplitude-latency trading ratio for bats is .) The two spectrograms at left show full-band, normal echoes with no harmonic split for and with harmonic split for (from Fig. 4). Next two spectrograms show FM2 decreased in strength by 3 dB relative to FM1, or decreased by 3 dB and moved earlier in time by . All S− are full-band echoes with no harmonic split (at right). (b) Bar graph showing performance on delay-discrimination tasks (percent errors) for four bats (150 trials/bat, with mean performance ±1 SD shown by circles). Introduction of harmonic-split filters with no other change causes small, significant decrease in acuity (more errors) compared to full-band echoes . Decreasing FM2 by 3 dB causes further, large decline in performance , but advancing FM2 in time by compensates for amplitude-latency trading and restores performance . Results show no evidence for perceptual effect from 3 dB loss of FM2 except for the associated latency shift.

Tables

Generic image for table
TABLE I.

Electronic filter settings and attenuation of stimuli for four experiments.

Loading

Article metrics loading...

/content/asa/journal/jasa/128/2/10.1121/1.3459823
2010-08-09
2014-04-19
Loading

Full text loading...

This is a required field
Please enter a valid email address
752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Effects of filtering of harmonics from biosonar echoes on delay acuity by big brown bats (Eptesicus fuscus)
http://aip.metastore.ingenta.com/content/asa/journal/jasa/128/2/10.1121/1.3459823
10.1121/1.3459823
SEARCH_EXPAND_ITEM