I wrote this to try to clarify the space as people often talk about different things with HITL. Some mean active learning, others mean 'worker in the loop, researchers sometimes mean 'users in the loop'.<p>So, three main categories to HITL:<p>- HITL training -- e.g. active learning and interactive machine learning development<p>- workers in the loop -- the old school mechanical turk idea, but with a model only falling back to the worker when it's unsure<p>- users in the loop -- getting the user to steer the AI response, e.g. Smart Reply in gmail.<p>Although they're not applicable in all cases, we're starting to see far more companies adopt these approaches as it solves several problems with AI.<p>For example, Amazon Alexa (worked there) can't do standard user-in-the-loop. With voice interaction the user does not have patience to be read out a list of options. However, it does get weaker signals where the stops the current action ("alexa stop!"), and that informs the next action. Active learning is getting adopted there too, as with millions of live utterances coming through, reducing their annotation efforts can be a huge cost saving.