I like the term withheld click because it describes a moment when you could have clicked but didn't. We aren't talking about missed clicks here, but when one intentionally chooses not to click. In the talk she discussed guidelines for how to do this effectively and what to watch out for.
Various reasons people withhold a click include shaping successive approximations, extinction, differential reinforcement, inducing resurgence and others. Using it inappropriately or without developed skill can certainly lead to problems.
Withholding a click can lead to frustration if we don't, at the same time, set it up so that the animal makes a good guess as to what we're looking for in more behavior. It can also lead to an animal giving up because nothing seems to be working or they just can't get it right. More intense individuals may start throwing other behaviors at you in an attempt to get you to click something. For these reasons, we need to think carefully about how we are going to do this.
A key aspect to when you can withhold is the history of that behavior. If there is too little history, you have nothing to fall back on if the animal doesn’t understand. If you have spent a lot of time clicking for a behavior, then the animal thinks that behavior is good just as it is and also won’t understand if you stop clicking for it. Michele mentioned that handlers tend to fall into either side of this challenge: raising the criteria too fast, or staying at the same criteria too long. I know which I do and when!
She did say that if you use a well conceived training plan initially, and you want to change an established behavior, you can go back to an earlier stage and reestablish a history of clicks before withholding to ask for variety.
One thing I see people do fairly frequently is to build duration into a behavior, and then if the behavior falls apart for some reason (possibly due to poor information during the shaping process), they try withholding a click, but the animal simply thinks it’s about duration so they don’t offer any changes. This leads to frustration on the parts of both learner and trainer.
In addition to the animal being sufficiently prepared to benefit from withholding, the trainer must have a plan. She listed four pieces. The first is anticipation of what the change will be (you should have your training session and environment set up so that you are pretty sure that your learner will offer what you want, rather than something in the other direction). You must then be prepared to click that! If you don’t really know what your learner will offer, it’s hard to catch the right effort that first time. You must also be ready to to back to clicking previous criteria if things start to go awry or else your moment of silence will extend into more than a moment and the accompanying frustration or giving up. And finally, know yourself. Is your tendency to ask for too much too soon? Or is it to allow the animal to get stuck by not inviting variety?
Something else she mentioned which I feel requires time for a trainer to develop is how to assess the animal’s response to withheld click. She said there can be “thinking moments” and she looks for the animal to remain engaged mentally, even if physically still. So if you withhold a click and your animal then looks off into the distance or frantically starts trying things, those aren't thinking moments. Then when your animal does offer something and you click it, does he offer that new variety again and does he offer it quickly? If so, he probably made a conscious decision about what to do and understood the new click. If not, it may have been a random movement and the click not understood by the animal.