spacer gif spacer gif spacer gif spacer gif spacer gif
QUICK SEARCH:   [advanced]


spacer gif
     Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents    

First published online September 5, 2008
Journal of Experimental Biology 211, 2976-2988 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.020057
This Article
Right arrow Summary Freely available
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Supplementary Material
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Hausmann, L.
Right arrow Articles by Wagner, H.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Hausmann, L.
Right arrow Articles by Wagner, H.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?

In-flight corrections in free-flying barn owls (Tyto alba) during sound localization tasks

Laura Hausmann*, Dennis T. T. Plachta, Martin Singheiser, Sandra Brill and Hermann Wagner

Institute of Biology II, RWTH Aachen, Kopernikusstraße 16, 52074 Aachen, Germany


Figure 1
View larger version (9K):
[in this window]
[in a new window]

  		Fig. 1. Schematic of the experimental setup. The room of 4.2x3.2x3.2 m (lengthxwidthxheight) was covered with planar and pyramidal foam. Speaker devices contained target loudspeakers LS 1 to LS 4. The two-dimensional horizontal distance to the speaker row was 2.35 to 3.35 m, whereas the linear distance from the perch (owl position) to the speakers was 2.97 to 3.87 m (cf. Table 1). Background speakers (BS) provided masker noise. C1 to C4 are infrared cameras. Cameras C3 and C4 were mounted on the ceiling. Camera C1 was mounted at a height of 25 cm on the wall opposite the perch; camera C2 was placed at a height of 95 cm on the side wall. Tracker, DynaSight head tracking device. Landing positions of the owls as deviation (in cm) from the center of the target LS were plotted in a polar coordinate system as positive and negative x- and y-coordinates, respectively (see inset).

 

Figure 2
View larger version (72K):
[in this window]
[in a new window]

  		Fig. 2. Typical flight path. (A–H) The head turn movement during a flight is shown in an example with the stimulus sequence LS 3-2, with a 700 ms stimulus delay. (I) The same flight as in A–H shown from above. The individual images of the flight path recorded by camera C1 (Fig. 1, 25 Hz sampling rate) are overlaid. (J) As in I, images of a flight sequence are overlaid. The initial stimulus was emitted by LS 3, the in-flight stimulus by LS 1 with a 900 ms delay. The reflections of the head tracker are visible as a white, dotted line. The body and wings appear as low-contrast shades (small arrows). The positions of the speakers LS 1 to LS 4 are marked with circles. The turning angle, {alpha}, in degrees was calculated by extending the lines formed by the head tracker reflections before and after the correction turn, which appears as a sharp discontinuity in the trace of tracker reflections (white arrow). Although the trajectory could be curved, only the first prominent discontinuity corresponded to the saccadic head turn visible in the frontal view (C1) and was used for determination of the turning angle. The remaining (or error) angle β to the target is given as the angular difference between the actual flight trajectory and the extended line to the center of the target speaker. Note that the room is not lit, but the images were recorded with infrared cameras.

 

Figure 3
View larger version (19K):
[in this window]
[in a new window]

  		Fig. 3. Correction turns and hits. (A) The percentage of trials in which the owl performed a correction turn towards the in-flight target loudspeaker is plotted against the in-flight stimulus delay. Significant differences between the owls are indicated and marked with asterisks depending on the significance level (*P≤0.05, **P≤0.01, ***P≤0.001). The difference between owl W and owl H was highly significant for any in-flight stimulus delay smaller than 1100 ms, but is not shown for clarity. Dotted lines indicate a significant decrease of correction turns (%) with respect to the baseline (0–700 ms). Note the decrease of the performance with increasing in-flight stimulus delay for long delays. (B) For each owl, the percentage of hits within a 20 cm radius of the in-flight target speaker is plotted. The percentage refers to the overall number of trials where the in-flight target speaker differed from the initial target speaker (owl W, 472 trials; owl Q, 475 trials; owl H, 505 trials). Significant differences are marked with asterisks (Fisher's exact test). (C) In trials in which the distance to the speaker devices was less than 3.35 m (either 2.85 m or 2.35 m), the owls failed to perform correction turns at lower in-flight stimulus delays.

 

Figure 4
View larger version (28K):
[in this window]
[in a new window]

  		Fig. 4. Head turn latencies. (A) Histogram of the pooled head turn latencies [number of trials (N) with the particular head turn latency]. Bin size was 40 ms. Head turn latencies were cumulated between about 150 and 250 ms, with a median of 180 ms. (B) Head turn latencies in ms (mean ± s.d.) were pooled for trials with a distance of 50 cm and 100 cm between the initial and the in-flight target speaker, respectively. (C) Head turn latencies (ms; mean ± s.d.) of the owls significantly (black regression line, slope –0.1493±0.02935; goodness of fit, r2=0.8661; P≤0.0307) decreased with increasing stimulus delay (ms). (D) Head turn latencies of all trials are plotted against the landing precision in cm for trials with a distance of 50 cm (circles, grey regression line, y=127.3+1.976x) and 100 cm (triangles, black regression line, y=155.6+1.096x) between the initial and the in-flight speaker. The linear regression was highly significant (P≤0.001).

 

Figure 5
View larger version (6K):
[in this window]
[in a new window]

  		Fig. 5. Processing of in-flight stimuli and correction turns. If the initial stimulus was emitted by LS 1 and the in-flight stimulus by LS 2, the angle {alpha} of the correction turn required to hit the target is smaller for a short in-flight stimulus delay (A) than for a longer delay (B). T is the take-off of the owl for target strike. The black horizontal arrow marks the moment where the in-flight stimulus is given, C refers to the beginning of the correction turn. The neuronal and motor processing time is assumed to be constant for any stimulus delay.

 

Figure 6
View larger version (8K):
[in this window]
[in a new window]

  		Fig. 6. Turning angles. (A) The mean turning angles in degrees are plotted against the stimulus delay. The linear regression (solid line, slope 0.03691±0.00941) shows that the turning angle increases with the stimulus delay. Both parameters are significantly correlated. The number (N) of analyzed trials is given below each data point. Angles were not significantly different between stimulus delays or owls. (B) Turning angles were significantly (P≤0.05) smaller for speaker sequences with a distance of 50 cm than of 100 cm between the initial and the in-flight target. The number of trials (N) is given above each column.

 

Figure 7
View larger version (37K):
[in this window]
[in a new window]

  		Fig. 7. Representative polar scatter plot of landing positions (owl Q). (A) The center of the plots corresponds to the target speaker position. The landing positions of trials with a correction turn (triangles) or without a correction turn (black dots) are plotted clockwise from 0 to 359 deg. in a circular diagram. The central gray circle indicates the `hit' area of a 20 cm radius around the centre of the target speaker. The maximum landing distance was 128 cm (see gray line and number). Gray and black dots outside the circle indicate the landings in a particular quadrant. (B-E) The landing positions of the three owls were analyzed for trials without (B,D) or with a correction turn (C,E) for the distribution of their angles [{theta} (degrees); B,C] and distances [{rho} (cm); D,E]. The positions were divided into bins of 30 deg. ({theta}) or 10 cm ({rho}) and plotted into histograms. In trials without correction turn the distribution of angles is double-peaked between 75 and 135 deg. and between 195 and 255 deg. (B). The distances exhibit one peak at distances between 35 and 115 cm (D). In trials with a correction turn, the distribution of angles is less bifurcated than in trials without a correction turn (C). Distances are distributed around values between 5 and 35 cm (E).

 

Figure 8
View larger version (6K):
[in this window]
[in a new window]

  		Fig. 8. Landing precision. The distance to the target loudspeaker was pooled for all stimulus delays. Trials with a correction turn (left two rows) and without a correction turn (right two rows) were analyzed separately. The first and third rows from the left present trials with adjacent target speakers (50 cm distance), the second and fourth rows from the left those with a 100 cm distance. Significant differences between stimulus delays are marked with asterisks (***P≤0.001). The number of trials (N) included in the analysis is given below the x-axis.

 

Figure 9
View larger version (13K):
[in this window]
[in a new window]

  		Fig. 9. Error angles. (A) The remaining angle β (in degrees) between the actual turning angle and the extended line between the owl's flight path and the center of the in-flight target speaker was measured, as shown in Fig. 2J. The error angle did not depend on the in-flight stimulus delay. Plotted is the mean ± s.d. Due to technical limitations, only in-flight stimulus delays larger than 700 ms were considered for the analysis, as far as the owl's turn was visible from above on the video recording. The number of trials, N, is given at the base of each column. (B) For pooled data from all owls and delays, the error angles are significantly larger (t-test, P≤0.0003) for the 100 cm distance between speakers than for the 50 cm distance.

 

Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati   Add to Twitter Twitter    What's this?



© The Company of Biologists Ltd 2008