"... some LDS apostles, including Orson Pratt and Heber J. Grant, felt inadequate because they had not had such encounters.
"In the twentieth century, charismatic apostleship changed in several ways. First, the 'charge' at ordination no longer obligated apostles to seek visions. Second, the Presidency and apostles began down-playing the importance of these experiences. Third, apostles began speaking of a non-visionary 'special witness of Christ' by the Holy Ghost in terms which allowed listeners to conclude that the apostles referred to an actual appearance of deity. Fourth, apostles were reluctant to discuss their visionary experiences publicly. Fifth, evidence indicates that a decreasing number of apostles experienced visions before or after ordination.
"The change in the apostolic 'charge' apparently began with the appointment of Reed Smoot as an apostle in 1900. General church authorities had long regarded him as 'reliable in business, but [he] has little or no faith.' President Lorenzo Snow blessed him to receive 'the light of the Holy Ghost' so that he could bear testimony of Jesus Christ and Joseph Smith. That was an extraordinary departure from the apostolic charge as given since 1835.
"...Twentieth-century apostles began applying this 'as if' approach to their spoken testimonies. Usually this involved wording their 'special witness' of Christ in a way that encouraged listeners to assume the leader has had a more dramatic encounter with the divine than actually claimed."
The full discussion ranges from pages 1 through 6 and would require too much typing to do it here. But the above, taken only from pages 1-2, gives you some more particulars than my brief reference before. The whole discussion is documented with references from the Church's archives where the writer reviewed the transcripts of the actual ordinations, etc. They are all set out in the footnotes, which are omitted from the quote I have excerpted above.