A clicker trainer asked me: can a punisher also be a reinforcer? For example, Shutzhund working dogs take stick hits and come back fighting for more. It seems that they do not see it as punishment. Some world class trainers describe these dogs as adrenalin addicts.
The short answer is, don’t equate an aversive stimulus with a punishment. A punishment, technically, is anything that shortens or stops a behavior. In these cases, you or I might do less of whatever we did that triggered an adversary to strike at us; a fighter might do more. An aversive stimulus is not necessarily punishing; it depends on the recipient. Rain is punishing to cats, who might respond by going inside; reinforcing to ducks, who might respond by going outside, and a matter of indifference to cows; who stay where they are.
We need to separate the 'thing' --the cookie or the stick or the click or the newspaper headline or whatever--from its outcome. What defines its function is not what it looks like to common sense, but how it changes the behavior. If that stick doesn't slow the dog down then no matter how scary it looks to us, it's not functioning as a punisher. If the dog won't take the treat, no matter how delicious it looks to us, then in that situation it is not a reinforcer.
Technically, a treat has no specific definition; it’s just anything we’ve chosen that we think our learner might like. One man’s treat is often another man’s poison. It’s the reinforcer that we define as anything the animal will work for. Only the animal can truly tell what that particular item might be.
It’s one of the often misunderstood subtleties of Skinner’s thinking. His vocabulary deals with processes and the resulting postcedents—outcomes—rather than with one type or another of specific items or events.