  Previously, a machine speech chain, which is based on sequence-to-sequence
deep learning, was proposed to mimic speech perception and production behavior.
Such chains separately processed listening and speaking by automatic speech
recognition (ASR) and text-to-speech synthesis (TTS) and simultaneously enabled
them to teach each other in semi-supervised learning when they received
unpaired data. Unfortunately, this speech chain study is limited to speech and
textual modalities. In fact, natural communication is actually multimodal and
involves both auditory and visual sensory systems. Although the said speech
chain reduces the requirement of having a full amount of paired data, in this
case we still need a large amount of unpaired data. In this research, we take a
further step and construct a multimodal chain and design a closely knit chain
architecture that combines ASR, TTS, image captioning, and image production
models into a single framework. The framework allows the training of each
component without requiring a large number of parallel multimodal data. Our
experimental results also show that an ASR can be further trained without
speech and text data and cross-modal data augmentation remains possible through
our proposed chain, which improves the ASR performance.
