Machine Assisted Analysis of Vowel Length Contrasts in Wolof

Growing digital archives and improving algorithms for automatic analysis of text and speech create new research opportunities for fundamental research in phonetics. Such empirical approaches allow statistical evaluation of a much larger set of hypothesis about phonetic variation and its conditioning factors (among them geographical / dialectal variants). This paper illustrates this vision and proposes to challenge automatic methods for the analysis of a not easily observable phenomenon: vowel length contrast. We focus on Wolof, an under-resourced language from Sub-Saharan Africa. In particular, we propose multiple features to make a fine evaluation of the degree of length contrast under different factors such as: read vs semi spontaneous speech ; standard vs dialectal Wolof. Our measures made fully automatically on more than 20k vowel tokens show that our proposed features can highlight different degrees of contrast for each vowel considered. We notably show that contrast is weaker in semi-spontaneous speech and in a non standard semi-spontaneous dialect.Comment: Accepted to Interspeech 201

Strategies for Representing Tone in African Writing Systems

Tone languages provide some interesting challenges for the designers of new orthographies. One approach is to omit tone marks, just as stress is not marked in English (zero marking). Another approach is to do phonemic tone analysis and then make heavy use of diacritic symbols to distinguish the `tonemes' (exhaustive marking). While orthographies based on either system have been successful, this may be thanks to our ability to manage inadequate orthographies rather than to any intrinsic advantage which is afforded by one or the other approach. In many cases, practical experience with both kinds of orthography in sub-Saharan Africa has shown that people have not been able to attain the level of reading and writing fluency that we know to be possible for the orthographies of non-tonal languages. In some cases this can be attributed to a sociolinguistic setting which does not favour vernacular literacy. In other cases, the orthography itself might be to blame. If the orthography of a tone language is difficult to user or to learn, then a good part of the reason, I believe, is that the designer either has not paid enough attention to the function of tone in the language, or has not ensured that the information encoded in the orthography is accessible to the ordinary (non-linguist) user of the language. If the writing of tone is not going to continue to be a stumbling block to literacy efforts, then a fresh approach to tone orthography is required, one which assigns high priority to these two factors. This article describes the problems with orthographies that use too few or too many tone marks, and critically evaluates a wide range of creative intermediate solutions. I review the contributions made by phonology and reading theory, and provide some broad methodological principles to guide someone who is seeking to represent tone in a writing system. The tone orthographies of several languages from sub-Saharan Africa are presented throughout the article, with particular emphasis on some tone languages of Cameroon

Speed perturbation and vowel duration modeling for ASR in Hausa and Wolof languages

International audienceAutomatic Speech Recognition (ASR) for (under-resourced) Sub-Saharan African languages faces several challenges: small amount of transcribed speech, written language normalization issues, few text resources available for language modeling, as well as specific features (tones, morphology, etc.) that need to be taken into account seriously to optimize ASR performance. This paper tries to address some of the above challenges through the development of ASR systems for two Sub-Saharan African languages: Hausa and Wolof. First, we investigate data augmentation technique (through speed perturbation) to overcome the lack of resources. Secondly, the main contribution is our attempt to model vowel length contrast existing in both languages. For reproducible experiments, the ASR systems developed for Hausa and Wolof are made available to the research community on github. To our knowledge, the Wolof ASR system presented in this paper is the first large vocabulary continuous speech recognition system ever developed for this language

A Tutorial on Acoustic Phonetic Feature Extraction for Automatic Speech Recognition (ASR) and Text-to-Speech (TTS) Applications in African Languages

At present, Siri, Dragon Dictate, Google Voice, and Alexa-like functionalities are not available in any indigenous African language. Yet, a 2015 Pew Research found that between 2002 to 2014, mobile phone usage increased tenfold in Africa, from 8% to 83%.[1] The Acoustic Phonetic Approach (APA) discussed in this paper lays the foundation that will make Automatic Speech Recognition (ASR) and Text-to-Speech (TTS) applications possible in African languages. The paper is written as a tutorial so that others can use the information therein to help digitalize many of the continent’s indigenous languages. [1] http://www.pewglobal.org/2015/04/15/cell-phones-in-africa-communication-lifeline/. Retrieved on November 10, 2017

Speech Technologies for African Languages: Example of a Multilingual Calculator for Education

International audienceThis paper presents our achievements after 18 months of the ALFFA project dealing with African languages technologies. We focus on a multilingual calculator (Android app) that will be demonstrated during the Show and Tell session

Intrinsic vowel F0, the size of vowel inventories and second language acquisition

The phenomenon of intrinsic vowel F0 (IF0), in which high vowels exhibit higher F0 than low vowels, has been widely attested in languages of the world. Most often, IF0 is regarded as an automatic, physiologically determined phenomenon, whereas some claim that IF0 is a controlled feature, introduced to enhance vowel contrasts. This paper presents new evidence on this issue by means of a cross-linguistic investigation of the influence of vowel inventory size on IF0 and a study of IF0 in second language (L2) acquisition. IF0 was measured in three language varieties: Arabic (a language with 3 vowels), Dutch (a 12-vowel system), and Dutch spoken by native Arabic-speaking learners. IF0 was significantly larger in Dutch than Arabic, but did not differ significantly between Arabic and Dutch produced by L2 learners. No spectral differences between the corresponding vowels of the three language varieties were found. While confirming the universality of IF0, these results also suggest that the size of IF0 may be language-specific, depending on the need to enhance vowel contrasts. Thus, these results agree well with a mixed physiological-enhancement account, which assumes that IF0 is physiologically determined, but also at least in part the effect of an interacting, controlled mechanism

Skilled reading in isiZulu: what can we learn from it?

Research on reading in African languages is particularly pertinent in South Africa now, inview of the poor reading performance in many South African schools. This paper is basedon a study of competent adult readers of isiZulu that analysed what its orthography (the wayit is written) requires of readers. As an agglutinative language with a conjoined writingsystem, isiZulu carries meaning not only in separate words, but also in morphemes thatcluster together, forming long complex words. Eye tracking data shows that competentreaders of isiZulu move their eyes across text in saccades (shifts of the point of focus) thatare short in comparison with the saccades of efficient reading of English. It also shows thatreaders of isiZulu fixate on points of text for longer periods than do readers of English.The study links eye movement data to information gained from a stimulated recall process,to discover strategies consciously used by competent readers of isiZulu. Some of thesestrategies, such as visualisation, are common to efficient readers of all languages, whileothers might be peculiar to agglutinating and/or tonal languages. These strategies informsuggestions for the development of effective reading skills in isiZulu.The key argument of the paper is that the orthography of isiZulu has features that requireattention by teachers of reading if their learners are to benefit from the advantages thatreading in their first language should bring

Speech Communication

Contains reports on two research projects.U. S. Air Force Cambridge Research Laboratories, Office of Aerospace Research, under Contract F19628-69-C-0044National Institutes of Health (Grant 2 RO1 NB-04332-06