It really depends on circumstances and audience. However contrary to some statements in the previous answer, in international conferences is normal to refer to scientists by
surname, via their group, like in "research done in the group of xxx"; xxx is surname, but you can add name or title.
Shall I give you examples?
Me, speaking to a relatively small and "friendly" audience about my supervisor : "as name told us, recently a new..."
Me, speaking in a big session: "as professor yyy told us....."
If that professor did not tell us anything, because physically absent, but I really have to use his/her work in a technical way, of course I will say "surname showed that equation x has a solution...... " (although it is much better to show a useful reference without mentioning it, but I think this is another issue).
Referring to someone that is not a professor, is less common to ear of doctor, but possible. I would say "as name told us" or "as *name surname * told us..." in the two distinct audiences as above.
Imagine a student... If he and the supervisor are known, it is easy to say "my supervisor....".
A lot of registers are possible, those above are just indication.
If two bigs refer to each other, they will call each other by names. It can happen they are sharing the stage.
It is also related to the age difference between speaker - audience - spoken name , which again is subjective and cultural.
So be flexible.
But I would say that calling someone Professor is almost the norm.
To give a ground to my answer, I have attended hundreds of conferences and meetings worldwide.
Ps: I never noticed it in real conferences, but often the impression is that US Americans think that their way is the standard, but it is not. The fact that international conferences are hold in English has nothing, or little to be precise, to do with the manners within the conference, and even less with the cultural background of the participants.
Coincise: you can easily imagine a summer school, a session of a conference, or even a conference, all having English as official language but no American participants. I think this render the idea of what we are discussing about.