Most research into sport skill performance divides the world into two groups, novices and experts. Most sports have their own measures of where the dividing line is between these groups. Expertise would imply performance results not just experience. So, a golfer who has been hacking away for 20 years but still can't break 100 would still be put in the "novice" category. Sport scientists design experiments that compare performance between the groups given some variables, and then hypothesize on the reason for the observed differences. Beilock, et al have looked at golf putting from several different angles over the years. Their research builds on itself, so let's review in reverse chronological order.
Back in 2001, they began by comparing the two competing theories of choking, distraction theory vs. explicit monitoring theory, and designed a putting experiment to find the better explanation. Distraction theory explains choking by assuming that the task of putting requires your direct attention and that high pressure situations will cause you to perform dual tasks - focus on your putting but also think about the pressure. This theory assumes there is no automaticity in skill learning and that we have to focus our attention on the skill every time. Explicit monitoring theory claims that over time, as we practice a skill to the point of becoming an "expert", we proceduralize the task so that it becomes "automatic". Then, during a high pressure situation, our brain becomes so concerned about performance that it takes us out of automatic mode and tries to focus on each step of the task. The research supported the explicit monitoring theory as it was shown that the golf putting task was affected by distractions and pressure for the experts but not the novice putters.
So, how do we block out the pressure, so that our automaticity can kick in? Another 2001 study by Beilock looked at mental imagery during putting. Using the same explicit monitoring theory, should we try to think positive thoughts, like "this ball is going in the hole" or "I have made this putt many times"? Also, what happens if a stray negative thought, "don't miss this one!" enters our brain? Should we try to suppress it and replace it with happy self-talk? She set up four groups, one receiving positive comments, one receiving negative comments, one receiving negative comments followed by positive comments and one receiving none as a control group. As expected, the happy people did improve their putting over the course of the trials, while the negative imagery hurt performance. But, the negative replaced with positive thought group did not show any more improvement over the control group. So, when faced with a high pressure, stressful situation ripe with the possibilities of choking, try to repeat positive thoughts, but don't worry too much if the occasional doubt creeps in.
Our strategy towards putting should also vary depending on our current skill level. While learning the intricacies of putting, novices should use different methods than experts, according to a 2004 study by Beilock, et al. Novice golfers need to pay attention to the step by step components of their swing, and they perform better when they do focus on the declarative knowledge required. Expert golfers, however, have practiced their swing or putt so often that it has become "second nature" to the point that if they are told to focus on the individual components of their swing, they perform poorly. The experiment asked both novices and expert golfers to first focus on their actual putting stroke by saying the word "straight" when hitting the ball and to notice the alignment of the putter face with the ball. Next, they were asked to putt while also listening for a certain tone played in the background. When they heard the tone they were to call it out while putting. The first scenario, known as "skill-focused", caused the novices to putt more accurately but the experts to struggle. The second scenario, called "dual-task", distracted the novices enough to affect their putts, while the experts were not bothered and their putting accuracy was better. Beilock showed that novices need the task focus to succeed while they are learning to putt, while experts have internalized the putting stroke so that even when asked to do two things, the putting stroke can be put on "auto-pilot".
Finally, in 2008, Beilock's team added one more twist to this debate. Does a stress factor even affect a golfer's performance in their mind before they putt? This time, golfers, divided into the usual novice and expert groups, were asked to first imagine or "image execute" themselves making a putt followed by an actual putt. The stress factor was to perform one trial under a normal, "take all the time you need" time scenario and then another under a speeded or time-limited scenario. The novices performed better under the non-hurried scenario in imagining the putt first followed by the actual putt. The experts, however, actually did better in the hurried scenario and worse in the relaxed setting. Again, the automaticity factor explains the differences between the groups.
The bottom line throughout all of these studies is that if you're learning to play golf, which includes putting, you should focus on your swing/stroke but beware of the distractions which will take away your concentration. That seems pretty logical, but for those that normally putt very well, if you feel stress to sink that birdie putt, don't try to focus in on the mechanics of your stroke. Trust the years of experience that has taught your brain the combination of sensorimotor skills of putting.
Just remember the Chevy Chase/Ty Webb philosophy; "I'm going to give you a little advice. There's a force in the universe that makes things happen. And all you have to do is get in touch with it, stop thinking, let things happen, and be the ball.... Nah-na-na-na, Ma-na-na-na...."
Sian L. Beilock, Thomas H. Carr (2001). On the fragility of skilled performance: What governs choking under pressure? Journal of Experimental Psychology: General, 130 (4), 701-725 DOI: 10.1037//0096-3418.104.22.1681
Sian L. Beilock; James A. Afremow; Amy L. Rabe; Thomas H. Carr (2001). "Don't Miss!" The Debilitating Effects of Suppressive Imagery on Golf Putting Performance Journal of Sport and Exercise Psychology, 23 (3)
Beilock S.L.; Bertenthal B.I.; McCoy A.M.; Carr T.H. (2004). Haste does not always make waste: Expertise, direction of attention, and speed versus accuracy in performing sensorimotor skills Psychonomic Bulletin & Review, 11 (2), 373-379
Sian Beilock, Sara Gonso (2008). Putting in the mind versus putting on the green: Expertise, performance time, and the linking of imagery and action The Quarterly Journal of Experimental Psychology, 61 (6), 920-932 DOI: 10.1080/17470210701625626