During an interview, a patient's attention is repeatedly pulled away by every small sound or movement in the room, and he takes far longer than expected to stop reacting each time a background noise recurs. What is this?

This is distractibility: a disturbance of active attention in which the person is diverted by almost any new stimulus, and takes longer than usual to habituate to a recurring stimulus, exactly as described. It is not thought blocking, since distractibility differs from thought blocking, in which the flow of thought stops abruptly rather than being pulled toward an external stimulus. It is not perplexity, which is a bewildered inability to make sense of experience, whereas distractibility concerns the inability to sustain attention on one thing. And it is not flight of ideas, which involves a rapid succession of internally generated, associatively linked ideas rather than attention being pulled toward external stimuli.