It is often said that the most difficult thing to grasp in historical study is personality and personal motivation. Of course, that has not stopped historians, and particularly historians who write biography or "Big Man" history- that is, history focused around large personalities who are said to be responsible for historical change. Only in the last few generations have the problems of this type of history really been explored.

To provide one example of the problem of big man history and trying to read motivations: Alexander the Great. The sources that we have for Alexander the Great are all from centuries after his life. They are based on earlier sources that no longer survive, however, including some that were contemporary to Alexander's life or immediately afterwards. So nearly all we know of Alexander, aside from occasional contemporary inscriptions or numismatic evidence (coinage), is filtered through three to four centuries of distance and source transmission. And the various sources that we do have contradict each other in many ways, particularly when it comes to Alexander's motives.

So, Plutarch's Life of Alexander, chapter 38 ( http://penelope.uchicago.edu/Thayer/E/Roman/Texts/Plutarch/Lives/Alexander*/5.html ), records that the burning of the palace of the Persian king at Perseopolis was caused by a drunken party in which a courtesan named Thais decided it would be fun to burn down the palace. Plutarch then notes that his sources disagree on whether it was done like this, or whether the deed was pre-meditated. This is what another historian of Alexander, Appian declares in book 3.18.11ff: he says that Alexander burned the palace as retribution for the burning of Athens in the Persian Wars (unfortunately, I can't find an online translation to link to). So we have two versions of Alexander's motivations; we know that Plutarch and Arrian both had access to contemporary sources.

And there's the problem for modern scholars. Those who have a pre-concieved notion of what Alexander's character was will choose to privilege one of the two stories, and will find all sorts of convoluted reasons to do so. For Tarn, who believed Alexander was a noble conqueror attempting to unify mankind, of course the Plutarch version is correct, and he focuses on Plutarch's statement that Alexander was repentant afterwards and claims that Plutarch is relying on more reliable sources here. For Badian, who views Alexander as a cynical Machiavellian ruler, of course Arrian is correct, and he can find all sorts of reasons to justify why Arrian is following more reliable sources. But the honest answer is that we simply have no idea which is correct- but that will not stop historians and biographers of Alexander the Great from speculating on his motives and offering pseudo-objective reasons for why their interpretation is correct.

I hope that example gives you an idea about the problems historians have with great man history and describing the thoughts of historical figures. Most historians these days are much more willing to recognize the problems of doing it, but it's pretty impossible to avoid it all together. Now, of course, the Alexander problem is particularly bad, and often historians (especially modern historians) have a lot more access to contemporary evidence or the writings of historical figures themselves. But even so, determining the thoughts of historical figures will nearly always be a guessing game and will vary depending on your preconceived ideas about that person.

It;s called psychohistory and I think it can be productive if the data is good. In particular, I think it's valid if we have an individual's own words or writings. It's probably fair to draw some conclusions about Hitler's psychology from reading Mein Kampf, for example and practically every New Testament scholar tries to analyze Paul.

In many cases, though, the data is too incomplete or unreliable to have confidence in any conclusions.

Coming from an anthropological perspective, it is generally split among different camps on whether ideas can actually be known and examined. Combinations of processual archaeology and cognitive anthropology can offer insight into the major ideas, customs, and practices of groups of people, but when it comes to individual thought it is dangerous to assume knowledge. What may seem an obvious conclusion to the researcher or historian may be entirely different from the individual in questions thought. Modern and cultural biases inherently color our perspective on the past. It may be possible to ascertain motivations and explanations for actions, but even with first-hand sources it is impossible to know with 100% accuracy what someone's true feelings were.

Many biographers and researchers attempt to understand the minds of their subject individual, although some of the cues you are looking for were not able to be seen until recently historically speaking with the advent of film. You can't exactly pick up much in the way of subtle cues from written records or archaeological context.

While I don't know of any specific examples, I may be able to point you in the right direction for your question. Analyzing the physical/verbal cues of U.S. presidents has been a focus of research, especially for presidential races (ex.Nixon/Kennedy debates). I believe there has been a research of this sort on major figures of WWII and the Cold War as well.

You may also find appropriate information among specialized research of major figures in positions of power, in particular European rulers, Egyptian dynasties, United States government, and religious leaders such as Catholic Popes/Cardinals.