CAMBRIDGE -- Addressing a symposium last night on women in science, Harvard University's president, Lawrence H. Summers, could hardly have sounded more transformed from the man who discussed the same issue in January.
Summers's comments last night about the effects of subtle, unconscious bias against women and the impact of encouragement or discouragement on young minds were virtually diametrically opposite from those he made at a National Bureau of Economic Research conference three months ago.
''This has been, as you can imagine, a period of substantial and intense immersion and education for me on the topics I have just been discussing," he said at the end of his half-hour remarks to about 40 students and professors. ''I hope I have learned."
In his Jan. 14 talk, Summers said his ''best guess" was that ''issues of intrinsic aptitude" play a significant role in explaining the shortage of women at the top of science careers and that discrimination and socialization were probably ''lesser factors" explaining the dearth of women in science and engineering.
The comments angered many Harvard professors, especially because the number of tenured job offers made to women in the Faculty of Arts and Sciences had declined significantly during Summers's presidency of nearly four years.
His January speech also led to an outpouring of unrelated complaints about his leadership that culminated last month in a vote of ''no confidence" by the Faculty of Arts and Sciences.
Summers has repeatedly apologized, and in February he acknowledged to the faculty that his remarks were made beyond his knowledge of the relevant fields. But last night's welcoming address to a three-day conference organized by Harvard undergraduates gave the most detailed picture to date of his evolved thinking.
''It was fantastic," computer science professor Margo I. Seltzer said of Summers's talk last night. ''I'm astonished at how far he has come in a short period of time."
In contrast to his January comments, he spoke last night at length about research on ''implicit bias." He described studies showing that orchestras hired more women when auditions were conducted behind a screen and said research shows that academic papers submitted to peer-reviewed journals met different fates depending on whether a man or woman's name was attached.
Summers recommended that people visit the website of psychology professor Mahzarin Banaji, who offers tests measuring bias.
''If a lawyer who defends himself has a fool for a client, any of us who thinks we can judge whether we are biased or not is probably making a serious mistake," Summers said.
He also pointed out that half of Harvard students start college with plans to major in science, but only one-quarter actually do. The attrition rate, he said, is slightly greater for female students.
Summers added that professors need to be aware of the great influence that positive or negative signals can have on their students. He said he had been drawn to economics but also was dissuaded from some other fields ''by experiences where I lagged slightly and where I was made to feel inadequate."
He described an occasion when he gave the wrong answer to a physics question and ''the person who saw my answer looked on with a certain stunned belief that I could be so stupid."
On another personal note, Summers stressed the importance of helping both men and women balance work and family and said he blocks off time to spend with his children. Whenever interruptions arise, he said, even the opportunity to meet with a donor, ''the answer is no."
Following the controversy he created, Summers set up two task forces that are due within a few weeks to recommend ways the university can improve hiring and retention of women.
''I suppose I've done my part over the last several months to increase interest in these topics," he said, eliciting laughs. ''I wish interest in these topics had been increased in a somewhat different fashion . . . but we have the opportunity to do some things at Harvard that are truly important."
Some in the audience said they are not ready to judge whether Harvard, and Summers, will do important things for women.
''It was interesting to hear him talk about these issues again," said Mariangela Lisanti, a senior and director of the conference.
But she added: ''The real test will be how quickly and effectively these ideas are put in place, and whether they can effect real change."
Bombardieri can be reached at firstname.lastname@example.org.