Many drum communication systems around the world transmit information by emulating tonal and rhythmic patterns of spoken languages in sequences of drumbeats. Their rhythmic characteristics, in particular, have not been systematically studied so far, although understanding them represents a rare occasion for providing an original insight into the basic units of speech rhythm as selected by natural speech practices directly based on beats. Here, we analyse a corpus of Bora drum communication from the northwest Amazon, which is nowadays endangered with extinction. We show that four rhythmic units are encoded in the length of pauses between beats. We argue that these units correspond to vowel-to-vowel intervals with different numbers of consonants and vowel lengths. By contrast, aligning beats with syllables, mora or only vowel length yields inconsistent results. Moreover, we also show that Bora drummed messages conventionally select rhythmically distinct markers to further distinguish words. The two phonological tones represented in drummed speech encode only few lexical contrasts. Rhythm thus appears to crucially contribute to the intelligibility of drummed Bora. Our study provides novel evidence for the role of rhythmic structures composed of vowel-to-vowel intervals in the complex puzzle concerning the redundancy and distinctiveness of acoustic features embedded in speech.

In the real world, human speech recognition nearly always involves listening in background noise. The impact of such noise on speech signals and on intelligibility performance increases with the separation of the listener from the speaker. The present behavioral experiment provides an overview of the effects of such acoustic disturbances on speech perception in conditions approaching ecologically valid contexts. We analysed the intelligibility loss in spoken word lists with increasing listener-to-speaker distance in a typical low-level natural background noise. The noise was combined with the simple spherical amplitude attenuation due to distance, basically changing the signal-to-noise ratio (SNR). Therefore, our study draws attention to some of the most basic environmental constraints that have pervaded spoken communication throughout human history. We evaluated the ability of native French participants to recognize French monosyllabic words (spoken at 65.3 dB(A), reference at 1 meter) at distances between 11 to 33 meters, which corresponded to the SNRs most revealing of the progressive effect of the selected natural noise (−8.8 dB to −18.4 dB). Our results showed that in such conditions, identity of vowels is mostly preserved, with the striking peculiarity of the absence of confusion in vowels. The results also confirmed the functional role of consonants during lexical identification. The extensive analysis of recognition scores, confusion patterns and associated acoustic cues revealed that sonorant, sibilant and burst properties were the most important parameters influencing phoneme recognition. . Altogether these analyses allowed us to extract a resistance scale from consonant recognition scores. We also identified specific perceptual consonant confusion groups depending of the place in the words (onset vs. coda). Finally our data suggested that listeners may access some acoustic cues of the CV transition, opening interesting perspectives for future studies.

Whistled speech in a non-tonal language consists of the natural emulation of vocalic and consonantal qualities in a simple modulated whistled signal. This special speech register represents a natural telecommunication system that enables high levels of sentence intelligibility by trained speakers and is not directly intelligible to naïve listeners. Yet, it is easily learned by speakers of the language that is being whistled, as attested by the current efforts of the revitalization of whistled Spanish in the Canary Islands. To better understand the relation between whistled and spoken speech perception, we look herein at how Spanish, French, and Standard Chinese native speakers, knowing nothing about whistled speech, categorized four Spanish whistled vowels. The results show that the listeners categorized differently depending on their native language. The Standard Chinese speakers demonstrated the worst performance on this task but were still able to associate a tonal whistle to vowel categories. Spanish speakers were the most accurate, and both Spanish and French participants were able to categorize the four vowels, although not as accurately as an expert whistler. These results attest that whistled speech can be used as a natural laboratory to test the perceptual processes of language.

The present study compares the perceptual categorization of four CV syllables /ta, da, ka, ga/ in two different speech registers-modal speech and whistled speech-of Tashlhiyt Berber used in the Moroccan High Atlas. Whistled speech in a non-tonal language such as Tashlhiyt is a special speech register used for long distance dialogues that consists of the natural production of vocalic and consonantal qualities in a simple modulated whistled signal. The technique of whistling imposes various restrictions on speech articulation, which result in a simplification of the phonetics of spoken speech into a 'whistled formant'. Here, we describe this simplification for Tashlhiyt syllables /ta, da, ka, ga/ and use them as stimuli in a behavioral experiment. We analyze and compare the perceptual categorization obtained from native Tashlhiyt listeners (trained since childhood in whistled speech) for both speech registers on these 4 syllable types. Results show that whistled stimuli were fairly well identified (~42%) above chance (25%), though less well than spoken ones (~84%). The detailed analysis of confusions between CVs enabled us to understand better how whistled consonants are perceived, highlighting the phonological contrasts that are best perceived and retained from spoken to whistled speech in this language.

This study presents a method developed for lightning forecasting in eastern Amazonia, based on the estimates of the hourly evolution of the convective available potential energy (CAPE). The CAPE is a computed index of the air stability situation over a given area of the Earth. This parameter is determined from vertical profiles of temperature and humidity of the atmosphere, obtained through radiosondes. The CAPE values may also be estimated during the period between soundings, by using the meteorological variables observed continuously at surface weather stations. Two data mining techniques were used for the forecasts: k-Nearest Neighbor and Decision Tree. For the calculation of the CAPE and its estimated hourly evolution, we used radio soundings data made available by a site of the University of Wyoming, in addition to surface temperature data provided by the METAR code, both collected at the Belém-Brazil airport, during 2009. The CAPE index levels, indicative of strong convection in the area were compared to data of actual lightning activity, provided by the STARNET detection system, in a circular area of 100 km radius, centered at that airport. The angular coefficient of the adjusted line equation to the hourly evolution values of the CAPE and the average value of the CAPE were the predicting attributes, while the number of lightning flashes detected by the STARNET was the classification attribute. The results indicated that it is possible to predict the lightning class of occurrences with an accuracy of the 70%, in this research area.