Ultrasound tongue imaging (UTI) provides a convenient way to visualize the vocal tract during speech production. UTI is increasingly being used for speech therapy, making it important to develop automatic methods to assist various time-consuming manual tasks currently performed by speech therapists. A key challenge is to generalize the automatic processing of ultrasound tongue images to previously unseen speakers. In this work, we investigate the classification of phonetic segments (tongue shapes) from raw ultrasound recordings under several training scenarios: speaker-dependent, multi-speaker, speaker-independent, and speaker-adapted. We observe that models underperform when applied to data from speakers not seen at training time. However, when provided with minimal additional speaker information, such as the mean ultrasound frame, the models generalize better to unseen speakers.
Earlier work concerned with speech recognition from ultrasound data has mostly been focused on speaker-dependent systems @cite_25 @cite_0 @cite_7 @cite_14 . An exception is the work of @cite_12 , which investigates the classification of tongue gestures from ultrasound data using convolutional neural networks. Some results are presented for a speaker-independent system, although the investigation is limited to two speakers generalizing to a third. @cite_2 present a method for automatic tongue contour extraction from ultrasound data. The system is evaluated in a speaker-independent way by training on data from eight speakers and evaluating on a single held out speaker. In both of these studies, a large drop in accuracy was observed when using speaker-independent systems in comparison to speaker-dependent systems. Our investigation differs from previous work in that we focus on child speech while using a larger number of speakers (58 children). Additionally, we use cross-validation to evaluate the performance of speaker-independent systems across all speakers, rather than using a small held out subset.
@cite_14 @cite_7 @cite_0 @cite_2 @cite_25 @cite_12
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This paper describes a machine learning approach for extracting automatically the tongue contour in ultrasound images. This method is developed in the context of visual articulatory biofeedback for speech therapy. The goal is to provide a speaker with an intuitive visualization of his her tongue movement, in real-time, and with minimum human intervention. Contrary to most widely used techniques based on active contours, the proposed method aims at exploiting the information of all image pixels to infer the tongue contour. For that purpose, a compact representation of each image is extracted using a PCA-based decomposition technique (named EigenTongue). Artificial neural networks are then used to convert the extracted visual features into control parameters of a PCA-based tongue contour model. The proposed method is evaluated on 9 speakers, using data recorded with the ultrasound probe hold manually (as in the targeted application). Speaker-dependent experiments demonstrated the effectiveness of the proposed method (with an average error of 1.3 mm when training from 80 manually annotated images), even when the tongue contour is poorly imaged. The performance was significantly lower in speaker-independent experiments (i.e. when estimating contours on an unknown speaker), likely due to anatomical differences across speakers. Speaker verification systems traditionally extract and model cepstral features or filter bank energies from the speech signal. In this paper, inspired by the success of neural network-based approaches to model directly raw speech signal for applications such as speech recognition, emotion recognition and anti-spoofing, we propose a speaker verification approach where speaker discriminative information is directly learned from the speech signal by: (a) first training a CNN-based speaker identification system that takes as input raw speech signal and learns to classify on speakers (unknown to the speaker verification system); and then (b) building a speaker detector for each speaker in the speaker verification system by replacing the output layer of the speaker identification system by two outputs (genuine, impostor), and adapting the system in a discriminative manner with enrollment speech of the speaker and impostor speech data. Our investigations on the Voxforge database shows that this approach can yield systems competitive to state-of-the-art systems. An analysis of the filters in the first convolution layer shows that the filters give emphasis to information in low frequency regions (below 1000 Hz) and implicitly learn to model fundamental frequency information in the speech signal for speaker discrimination. This paper presents a method for automatically animating the articulatory tongue model of a reference speaker from ultrasound images of the tongue of another speaker. This work is developed in the context of speech therapy based on visual biofeedback, where a speaker is provided with visual information about his her own articulation. In our approach, the feedback is delivered via an articulatory talking head, which displays the tongue during speech production using augmented reality (e.g. transparent skin). The user’s tongue movements are captured using ultrasound imaging and parameterized using the PCA-based EigenTongue technique. Extracted features are then converted into control parameters of the articulatory tongue model using Gaussian Mixture Regression. This procedure was evaluated by decoding the converted tongue movements at the phonetic level using an HMM-based decoder trained on the reference speaker's articulatory data. Decoding errors were then manually reassessed in order to take into account possible phonetic idiosyncrasies (i.e. speaker phoneme specific articulatory strategies). With a system trained on a limited set of 88 VCV sequences, the recognition accuracy at the phonetic level was found to be approximately 70 . Index Terms: articulatory tongue model, articulatory talking head, ultrasound imaging, GMM, speech therapy This article addresses the problem of continuous speech recognition from visual information only, without exploiting any audio signal. Our approach combines a video camera and an ultrasound imaging system for monitoring simultaneously the speaker's lips and the movement of the tongue. We investigate the use of convolutional neural networks (CNN) to extract visual features directly from the raw ultrasound and video images. We propose different architectures among which a multimodal CNN processing jointly the two visual modalities. Combined with an HMM-GMM decoder, the CNN-based approach outperforms our previous baseline based on Principal Component Analysis. Importantly, the recognition accuracy is only 4 lower than the one obtained when decoding the audio signal, which makes it a good candidate for a practical visual speech recognition system.