Acoustic Landmarks Research Articles

Effects of food abundance and wind on the use of tree lines by an insectivorous bat, Pipistrellus pipistrellus

We tested the hypotheses that the distance bats fly from tree lines depend on food abundance and protection from wind. We monitored the activity of pipistrelle bats (Pipistrellus pipistrellus) and measured insect abundance and wind speed and direction at fixed distances up to 50 m from tree lines. We compared bat behaviour in different situations: with and without wind and with low and high insect abundances in adjacent open areas. In all situations, pipistrelle bats' activity decreased with increasing distance from the tree line. Within nights, we found no effect of wind speed on bat activity (sound recorded per 5 min) on the leeward side of the tree lines. Between nights, however, bats concentrated their activities closer to the tree lines at high wind speeds or angles of incidence of wind from 45° to 90°. A significant relationship between bat and insect abundances was found only when the tree line was bordered by insect-rich grassland. Since wind and insect abundance only partly explained the distances bats flew from tree lines, two alternative explanations, namely predator avoidance and the use of tree lines as acoustic landmarks, are discussed. Pipistrelle bats using a double row of trees as a commuting route at dusk flew mainly between the tree lines, regardless of insect abundance or wind speed. It is argued that predator avoidance explains this behaviour, being a constraint on movements of bats at relatively high light levels. At high wind speeds and angles of incidence greater than 45°, the proportion of pipistrelle bats commuting on the leeward side of the tree lines increased.

Acoustic perception of landscape elements by the pond bat (Myotis dasycneme)

AbstractWe tested the hypothesis that echolocating bats use landscape elements as acoustic landmarks. We predicted that bats should be able to perceive distant landscape elements using echolocation and hence change their echolocation behaviour in relation to these elements. Echolocation parameters of commuting pond bats Myotis dasycneme (Boie, 1825) were related to the bats' distance from banks of different sized canals. Pulse durations emitted while bats flew over canals of 13, 19, and 25 m wide increased successively. Interpulse intervals were equally long at 13, 19, and 25 m wide canals, but significantly longer at a 30 m wide canal. The mean interpulse interval used by bats flying along the midline of the 30 m wide canal was just sufficiently long to prevent overlap of an echo from the canal bank and a new outgoing pulse. The results indicate that pond bats perceive the canal banks by gradually adapting their pulse emissions to the distance to the banks. This suggests a role for the banks as acoustic landmarks.

Entropy rate based speech segmentation

The sequence of estimates of the speech signal’s entropy rate is investigated as a potential basis for speech segmentation. Raising and falling edges of that entropy rate curve and its maxima and minima are considered as candidates for segment boundaries. These prominent points are compared to the phonetic segment boundaries and to acoustic landmarks [S. A. Liu, J. Acoust. Soc. Am. 100, 3417–3430 (1996)]. The comparison is made using the ‘‘Kiel corpus of read speech’’ which is a phonetically manually labeled corpus of German utterances. The evaluation considers the entropy rate labels against the background of the phone segments. In particular the position and the count of the entropy rate labels within each phone are appraised. The average results are reported both as totals and broken down into phone classes and phones. The frame duration of the entropy rate estimation controls the smoothness of the curve and hence the label count per phone. A similar evaluation relates the entropy rate labels to the acoustic landmarks.

A method of acoustic landmark extraction for mobile robot navigation

Describes a method to extract multiple acoustic landmarks for the indoor navigation of a mobile robot. The environment is modeled by specular vertical walls. An ultrasonic sensor mounted on the mobile robot scans around the surrounding walls and detects multiple echo pulses. On the horizontal plane at the height of the ultrasonic sensor from the floor, the two-dimensional environment is described by the distance as a function of angle in the scan. Due to the specularity of the walls, the distance function has a manageable number of retroreflective parts that can be used as landmarks. By virtue of the constancy of the relative positions between the ultrasonic sensor and the walls in scanning, the echo pulses reflected from a certain reflection points (RP) have the same time-of-flight in the ultrasonic scan data. The authors determine the position of an RP from the collection of the echo pulses that have the same time-of-flight. The direction to an RP is estimated from the orientation of the ultrasonic sensor at which the maximum magnitude is obtained for the group of echo pulses that correspond to the RP. The mean time-of-flight of the group of echo pulses provides the distance to the RP. Some experimental results are provided to show the validity and the performance of the proposed method.

Phonological Structure and Phonetic Form

1. Introduction Patricia Keating Part I. Intonation: 2. Articulatory evidence for differentiating stress categories Mary E. Beckman and Jan Edwards 3. 'Stress shift' as early placement of pitch accents Stefanie Shattuck-Hufnagel 4. Constraints on the gradient variability of pitch range, or, pitch level 4 lives! D. Robert Ladd 5. 'Gesture' in prosody Bruce Hayes 6. What is the smallest prosodic domain? Vincent J. van Heuven 7. The segment as smallest prosodic element: a curious hypothesis Allard Jongman Part II. Syllables: 8. Articulatory phonetic clues to syllable affiliation Alice Turk 9. The phonology and phonetics of extrasyllabicity in French Annie Rialland 10. Phonetic correlates of syllable affiliation Francis Nolan 11. Syllable structure and word structure Janet Pierrehumbert Part III. Feature Theory: 12. The phonetics and phonology of Semitic pharyngeals John J. McCarthy 13. Possible articulatory bases for the class of guttural consonants Louis Goldstein 14. Phonetic evidence for hierarchies of futures Kenneth N. Stevens 15. Do acoustic landmarks constrain the coordination of articulatory events? Louis Goldstein Part IV. Phonetic Output: 16. Phonetic evidence for sound change in Quebec French Malcah Yaeger-Dror 17. Polysyllabic words in the York Talk synthesis system John Coleman 18. Phonetic arbitrariness and the input problem Keith Johnson 19. Lip aperture and consonant releases Catherine P. Browman 20. Change and stability in the contrasts conveyed by consonant releases John Kingston Indexes.

Inferring articulatory movements from acoustic properties at fricative-vowel boundaries

Formant transitions provide context-dependent acoustic cues that can be interpreted in terms of the articulatory kinematics involved in moving from a consonant to a vowel. Formant frequencies were measured at identified acoustic landmarks for eight English fricatives preceding front, back, and back-rounded vowels. Formant onset times designated the point when the energy increased most rapidly and evidence of the first formant was first observed. Comparing the two-dimensional representation of F2×F3 onset frequencies along the voicing dimension showed the voiceless fricatives to be more dependent on vowel context. The onset frequencies for voiced fricatives reflect a more extreme supraglottal posture, while the voiceless fricative measures can be considered to be at a point closer to the vowel because voicing begins at a later time relative to the oral release gesture. Formant structure in the noise before the release, to the extent that it is visible in the consonantal interval prior to voicing onset, can provide additional place information for voiceless fricatives. Formant onset data are compared with measurements reported from investigations of place categorization of stop consonants. [Work supported by NIH.]

A mapping between trainable generalized properties and the acoustic correlates of distinctive features

It has been suggested that the acoustic correlates of distinctive features may be most reliably measured relative to important acoustic events, or landmarks [K. N. Stevens et al., Proc. Int. Conf. Spoken Language Process. 1, 499–502 (1992)]. Theoretical and empirical literature in the field of phonetics describes many of the acoustic correlates of distinctive features, but these acoustic correlates are often described in terms of formant frequencies and amplitudes, aspiration noise, and other attributes which are difficult for a speech recognizer to measure reliably. This paper reports on a preliminary attempt to compile a table of acoustic correlates of distinctive features, and to map these correlates to reliable acoustic measurements in the vicinity of an acoustic landmark. The acoustic measurements are simple energy and spectral change measurements, defined in terms of frequency and timing parameters which may be optimized for maximum feature discrimination using the technique described by Phillips and Zue [Proc. Int. Conf. Spoken Language Process. 1, 795–798 (1992)]. The table is indexed by distinctive feature, and if an acoustic correlate is likely to be salient only in a given phonological context, the context is given as a list of neighboring and simultaneous distinctive features. [Work supported by NSF.]

Acoustic segmentation and phonetic classification in the SUMMIT system

This paper describes recent work on acoustic segmentation and phonetic classification as part of an effort in speech understanding system development. The signal representation is based on an auditory model that incorporates known properties of the human auditory system, including critical‐band filtering, saturation, adaptation, forward masking, and synchrony detection. Acoustic landmarks are determined using a measure of local similarity. These landmarks are embedded in a multilevel structure in which information ranging from coarse to fine is represented in an organized fashion. An analysis of the acoustic structure, using 500 utterances from 100 different talkers, shows that it captures over 96% of the acoustic‐phonetic events of interest with an insertion rate of less than 5%. Phonetic classification is achieved by defining a set of generic property detectors based on the knowledge of acoustic phonetics. The settings of the parameters are obtained by a search procedure, using a large body of training ...

Sounds audible to migrating birds

We have measured sound levels from frog choruses in eastern New York State at altitudes of up to several hundred metres. Rana pipiens choruses from small ponds often could be recorded by a radio microphone up to 500 m, and on an especially favourable night with light winds they were clearly audible even at 965 m at about 20 dB SPL in the 1·5 to 2·5 2·5 kHz frequency band. Sound travels upward much farther and more predictably than along the surface. Many natural sounds, including those from frogs, insects, whitecaps, and perhaps wind-blown vegetation, arise from large areas and therefore act as extended sources. The intensities of such sounds decrease with altitude more slowly than expected from the inverse square law. Natural sound fields provide migrating birds with a potential source of information about the kind of land or water below them, and their progress over acoustic landmarks could inform them about wind velocity. Because atmospheric absorption increases with frequency, several hundred metres of air act as a low-pass filter, so that altitude could be estimated from the relative reduction of higher frequencies in a familiar sound.