fig2

Figure 2. Classification of DRL approaches for HRI. Consistent with the 3+1 reading developed in the main text, categories 3.1-3.3 answer where human information enters and are drawn as siblings, whereas category 3.4 is not a fourth sibling but a certification layer (dashed band) that any of the other three can carry. Corresponds to Table 2. DRL: Deep reinforcement learning; HRI: human-robot interaction.