Considering not all students are interested in every topic of a subject or whole subjects, I like the idea of extrinsic motivation because as per the definition, it provides students with something positive to look forward to.
However, in the adult classroom, I think in terms of praise or materialistic rewards, it should be rare and given in public because of several reasons. One, when the adult student is finally rewarded with praise after many attempts, it holds more value because it was harder to achieve. Not to say, in a semester's worth of classes, the instructor should be so stingy with praise that it is given only in the last few weeks of class. Instead, rather than giving praise every class, it should be given every week or two weeks for an especially good point. It seems to me that by giving it all the time, it diminishes the value of the praise and students do not think they have to work too hard to receive it. Additionally, because these are adults and not children on the elementary and middle school level, constant praising won't seem juvenile.
Because the praise is so rare though, it could be beneficial to publicly praise the student in front of other students so the value of the commendation increases. Healthy competition can always work to promote a prosperous learning environment. Approving a student's work in terms of comments on research papers or projects is also crucial, but public praising can lift a student's academic spirit.
One last comment I'd like to make on this is that because the praise is rare, it is important for the instructor to still be supportive and kind in their disposition. An instructor who is too strict or severe in their teaching may not want to implement this because the extrinsic motivation will probably have more of a negative reaction.
