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Discrimination of mixed-directional whistles by a bottlenose dolphin (Tursiops truncatus)
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10.1121/1.4816404
/content/asa/journal/jasa/134/3/10.1121/1.4816404
http://aip.metastore.ingenta.com/content/asa/journal/jasa/134/3/10.1121/1.4816404

Figures

Image of FIG. 1.
FIG. 1.

Harmonic structure of a single bottlenose dolphin whistle measured at (A) 0°, (B) 45°, (C) 90°, (D) 135°, and (E) 180° relative to the on-axis position of the dolphin. The whistle displays a characteristic mixed-directional property in which higher harmonics are more directional than lower frequency harmonics (from ).

Image of FIG. 2.
FIG. 2.

(Color online) Spectrogram of a recorded whistle (A) that was used as a model for the synthetic analog (B). The synthetic whistle was projected and recorded under the same conditions used in the experiments.

Image of FIG. 3.
FIG. 3.

(Color online) Spectrogram of (A) a catch trial and (B) a change trial of the alternating sound task. (A) During a catch trial a single “background” whistle sound repeated for the duration of the trial (e.g., X, X, X, X, X, X, X, X). The dolphin was trained to remain silent if no change occurred. (B) During a change trial the background whistle sound changed to an alternating sequence with a “target” sound (e.g., X, X, X, X, Y, X, Y, X). If the dolphin correctly whistled in response to the change, acoustic feedback (buzzer) was activated that served as a “bridge” to fish reinforcement. The dolphin typically produced a “victory squeal” in response to the buzzer ( ). Response latency (RL) was calculated as the time between the onset of the target stimulus (Y) and the onset of the dolphin's whistle response. Increased response latency has been shown to be positively correlated with task difficulty ( ).

Image of FIG. 4.
FIG. 4.

Proportion response for each angular difference. (A) Shown is a plot from the fixed level condition in experiment I, while (B) also shown is a plot from the roving level condition in experiment II. The angular difference of 0° is for identical stimuli and can be considered a false alarm rate. Also 45° to 180° can be considered proportion correct.

Image of FIG. 5.
FIG. 5.

(Color online) Box plots of response latency for each angular difference. (A) Shown is a plot from the fixed level condition in experiment I, while (B) also shown is a plot from the roving level condition in experiment II. The central line on each box represents the median, while the edges represent 25% and 75% quartiles. Whiskers represent the data range, while pluses represent outliers. Outliers were defined as any data value greater than q+1.5(q − q), where q and q where the 75th and 25th percentiles, respectively. (A) Response latency in the fixed level condition for 90°–180° had similar median values between 300 and 400 ms. Discrimination between whistles with an angular difference of 45° was elevated with a median of 700 ms. (B) Response latency in the rove condition for 90°–180° had similar median values between 310 and 340 ms. Discrimination between whistles with an angular difference of 45° was elevated with a median of 392 ms and a broader distribution.

Image of FIG. 6.
FIG. 6.

Example stimuli and model output. (A and B) Stimuli are from 0° and 135°, respectively. (C and D) Their corresponding model outputs after m-weighting, gammatone filtering, half-wave rectification, low-pass filtering, and amplitude compression. A primary feature of the constant- model outputs are that lower frequencies are represented by more channels. Higher frequency harmonics display less frequency resolution, which may explain why the dolphin had a difficult time discriminating between 0° and 45°.

Image of FIG. 7.
FIG. 7.

Simulation results. (A) Performance in the fixed level condition for the dolphin (open circle), the level model (closed circle), the harmonic model (plus), and the profile model (square). All models were capable of producing dolphin-like performance. (B) Performance in the rove condition. The profile model produced dolphin-like performance, while the level and harmonic models produced performance that departed from the dolphin's performance. (C) False alarms rates for each whistle type in the fixed level condition. The abscissa represents the whistle type from Table I . No false alarms were committed by the dolphin or any of the models. (D). False alarms for the rove condition. The level model produced a large amount of false alarms, which indicate that the model was responding to the level changes produced by the roving level.

Tables

Generic image for table
TABLE I.

Pressure spectral density levels of each harmonic relative to the level of the fundamental frequency (dB re: 1 μPa/Hz). Each harmonic (f0, h2, h3…h10) is displayed with its peak frequency (Hz) below it. Spectral density levels of each harmonic relative to the level of the fundamental frequency are shown for each simulated whistle from five different azimuth positions (0° to 180°). Cells with “nd” represent harmonics that were “not-detectable” from . No harmonics were included in “nd” cells.

Generic image for table
TABLE II.

Proportion correct for each azimuth combination. Gray cells represent angular differences of 45° (discriminations in which the whistles were most similar).

Generic image for table
TABLE III.

Response latency for each azimuth combination. Gray cells represent angular differences of 45° (discriminations in which the whistles were most similar).

Generic image for table
TABLE IV.

Proportion correct for each azimuth combination in the rove condition. Gray cells represent angular differences of 45° (discriminations in which the whistles were most similar).

Generic image for table
TABLE V.

Response latency for each azimuth combination in the rove condition. Gray cells represent angular differences of 45° (discriminations in which the whistles were most similar).

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/content/asa/journal/jasa/134/3/10.1121/1.4816404
2013-09-01
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Discrimination of mixed-directional whistles by a bottlenose dolphin (Tursiops truncatus)
http://aip.metastore.ingenta.com/content/asa/journal/jasa/134/3/10.1121/1.4816404
10.1121/1.4816404
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