Section: New Results

Test of the psychological validity of AI algorithms.

In this section, we focus on the utilisation of machine learning algorithms of speech and language processing to derive testable quantitative predictions in humans (adults or infants).

• Two PhDs were defended this year. In [14], Adriana Guavara Rukoz presented a computational model of the perception of non-native speech contrasts based on standard ASR pipelines is presented. An adaptation of the model is proposed to account for forced-choice classification psycholinguistic experiments and directly reproduced classical results. The general finding is that, suprisingly, the acoustic model part of a phone recognizer is sufficient to account for experimental data, even those apparently related to phonotactic properties of the native language. The 'language model' part does not improve the correlation with adult data (if anything, it degrades it). Yet the match between model and human is not perfect, and is was hypothetized that improvement in the acoustic model could help. In [13], Julia Maria Carbajal presented a study of the effect of multilingual exposure on language acquisition. She used a computational model of language separation based on i-vectors to reproduce some of the known effects of phonological distance on language discrimination in infants.

• In [16], we investigate whether infant-directed speech (IDS) facilitates lexical learning when compared to adult-directed speech (ADS). To study this, we compare the distinctiveness of the lexicon at two levels, acoustic and phonological, using a large database of spontaneous speech in Japanese. At the acoustic level we show that, as has been documented before for phonemes, the realizations of words are more variable and less discriminable in IDS. At the phonological level, we find that despite a slight increase in the number of phonological neighbors, the IDS lexicon contains more distinctive words (such as onomatopeias). Combining the acoustic and phonological metrics together in a global discrimination score, the two effects cancel each other out and the IDS lexicon winds up being as discriminable as its ADS counterpart. We discuss the implication of these findings for the view of IDS as hyperspeech, i.e., a register whose purpose is to facilitate language acquisition.

• Existing theories of cross-linguistic phonetic category perception agree that listeners perceive foreign sounds by mapping them onto their native phonetic categories. Yet, none of the available theories specify a way to compute this mapping. As a result, they cannot provide systematic quantitative predictions and remain mainly descriptive. Here [17], Automatic Speech Recognition (ASR) systems are used to provide a fully specified mapping between foreign and native sounds. This is shown to provide a quantitative model that can account for several empirically attested effects in human cross-linguistic phonetic category perception.

• Spectacular progress in the information processing sciences (machine learning, wearable sensors) promises to revolutionize the study of cognitive development. In [15], we analyse the conditions under which 'reverse engineering' language development, i.e., building an effective system that mimics infant's achievements, can contribute to our scientific understanding of early language development. We argue that, on the computational side, it is important to move from toy problems to the full complexity of the learning situation, and take as input as faithful reconstructions of the sensory signals available to infants as possible. On the data side, accessible but privacy-preserving repositories of home data have to be setup. On the psycholinguistic side, specific tests have to be constructed to benchmark humans and machines at different linguistic levels. We discuss the feasibility of this approach and present an overview of current results.