Student or Learner
What "material" does it mean? Any text material about diving or any kind of content learned?
ex)Imagine that you're a diver in the group that learned while underwater. In this setting, the world has a different look and feel than it does above water: The sound of your breathing is quite prominent; so is the temperature. As a result, you might end up thinking about your breathing during learning, and this will likely create memory connections between these thoughts of breathing and the materials you are learning...
I think it refers to the teaching material of the diving course, but the diving course analogy applies to wider learning contexts.