  Predicting multiple real-world tasks in a single model often requires a
particularly diverse feature space. Multimodal (MM) models aim to extract the
synergistic predictive potential of multiple data types to create a shared
feature space with aligned semantic meaning across inputs of drastically
varying sizes (i.e. images, text, sound). Most current MM architectures fuse
these representations in parallel, which not only limits their interpretability
but also creates a dependency on modality availability. We present MultiModN, a
multimodal, modular network that fuses latent representations in a sequence of
any number, combination, or type of modality while providing granular real-time
predictive feedback on any number or combination of predictive tasks.
MultiModN's composable pipeline is interpretable-by-design, as well as innately
multi-task and robust to the fundamental issue of biased missingness. We
perform four experiments on several benchmark MM datasets across 10 real-world
tasks (predicting medical diagnoses, academic performance, and weather), and
show that MultiModN's sequential MM fusion does not compromise performance
compared with a baseline of parallel fusion. By simulating the challenging bias
of missing not-at-random (MNAR), this work shows that, contrary to MultiModN,
parallel fusion baselines erroneously learn MNAR and suffer catastrophic
failure when faced with different patterns of MNAR at inference. To the best of
our knowledge, this is the first inherently MNAR-resistant approach to MM
modeling. In conclusion, MultiModN provides granular insights, robustness, and
flexibility without compromising performance.
