MTurk allows you to pay participants bonuses once you approve their work. This is particularly important if you want to add incentives to your experiments in a meaningful way.
The easiest way to pay a worker is through the menus. Go to Manage and look for the batch you just launched and select Results. You will see a screen like the one below.
As you can see, the last variable shown (Q2Age) captures the code that you gave to the participants in your survey. This code will act as your key for identifying workers and decisions. Once you found the code of the particular worker you want to reward, select the associated Worker ID. This will take you to the following screen:
Select Bonus Worker and specify the amount you wish to pay (at least $0.01). You might also want to send the worker a message detailing the reason for the bonus. Once you are done, press Pay Bonus Now.
Now, you might guess that this process would be quite tedious whenever you want to pay more than a handful of workers. Indeed, in situations where you have to pay bulk bonuses, there is a semi-automatic mechanism way to do it that nevertheless requires a slightly more sophisticated technique (discussed in the next section).