I read Rolf Jacobsen's 'Many Are Saying': The Function of Direct Discourse in the Hebrew Psalter.
What is Direct Discourse? Essentially, it's a quote. When the Psalmist puts words into her enemies mouth, such as "Aha, Aha" (a statement without substance) or "God does not hear", that's an example of Direct Discourse, designed to confront God with what the enemies are saying, or to contrast the words of God with the futile words of the enemies, or to express sentiments that appear to be irreverent by attributing them to an unrighteous person (which sets the stage for the Psalmist to wrestle with theological questions, such as why God allows evil), or to make the point that---if God does not deliver the Psalmist---there will be less praise of God, and more speech that mocks God. When the Psalmist quotes God, her aim may be to remind God or the congregation of God's promise (such as the unconditional Davidic covenant), or to promote righteousness among the community of Israel (as occurs in Psalm 50). When the Psalmist quotes herself, her aim may be to express where she was previously wrong---as when she says that she remarked at one point that she would never be moved, which encouraged her to rely less on God. (Yes, you read that correctly---Jacobson uses feminine pronouns for the Psalmist!)
That's what the book was about. Right now, I want to talk about Jacobsen's summary of certain positions on oracles in the Psalms, for it is a good description of Psalms scholarship. We'll start with J. Begrich, a scholar from the 1930's, who argued that, when there is a shift in mood in a Psalm from sad to happy, that is in response to an oracle of reassurance from a cultic functionary. Begrich tried to reconstruct those priestly oracles by drawing on Second Isaiah.
Then, there's Sigmund Mowinckel. Mowinckel agreed with Begrich's position, but Mowinckel's focus was more on liturgical context than the assurance of individuals. Mowinckel assigned certain Psalms to the Israelite New Years' festival---on which God assured the community. Mowinckel attributed the oracles to temple prophets, for they resemble prophetic style rather than "the typical apodictic style of the priestly writing" (Jacobsen's words on page 85). Although Mowinckel acknowledges that the wording of the oracles could have been prescribed by ritual, he also says that it could have been "left to the free and instantaneous inspiration of the prophet" (Mowinckel's words). My impression is that Mowinckel believes there was a part of the liturgy in which the temple prophet under inspiration assured the people, and---while the prophet could have followed a ritual oracle---he had some freedom in his expression.
Then there's H. Gunkel. Gunkel did not think that the prophetic elements in certain Psalms were due to a cult prophet, but rather to the influence of prophecy on the Psalms, as the Psalms imitated prophetic speech and referred to prophetic themes---such as God's restoration of Israel, God's defeat of Israel's enemies, and God's establishment of his kingdom. Gunkel dates this phenomenon to Israel's post-exilic period. Gunkel still locates these Psalms in the cult, but he holds that they are drawing from prophetic language and eschatology.
Jacobsen talks about other scholars, but their ideas appear to be variations of the views above. And some of them overlap with Jacobsen's position. In his discussion of Psalm 50, Jacobsen does not think that God's exhortation of his people in that Psalm to stop doing evil and to worship God in a heart-felt manner was the free expression of a temple prophet experiencing inspiration. Rather, Jacobsen argues that it was composed---as is evident in its appeal to the Decalogue. Jacobsen contends that God's speech in that Psalm was intended to remind the worshipers that they are interacting with God (who was in the temple), who cared about their behavior. For Jacobsen, Psalm 50 contains ritual speech that serves to remind the worshipers of God.