“…Notable examples are the clockwork RNN (Koutnik et al, 2014), gated feedback RNN (Chung et al, 2015), hierarchical multi-scale RNN (Chung et al, 2016), fast-slow RNN (Mujika et al, 2017), and higher order RNNs (HORNNs) (Soltani and Jiang, 2016). These modern RNN architectures have found various applications in motion classification (Neverova et al, 2016;Yan et al, 2018), speech synthesis (Wu and King, 2016;Achanta and Gangashetty, 2017;Zhang and Woodland, 2018), recognition (Chan et al, 2016), and other related areas (Liu et al, 2015;Krause et al, 2017;Kurata et al, 2017). These applications of hierarchical RNN architectures further confirm the relevance of hierarchically organized sequence generators for capturing complex dynamics in our everyday environments.…”