In September 1951 Adorno returned to the United States for a six-week visit, during which he attended the opening of the Hacker Psychiatry Foundation in Beverly Hills, met Leo Lowenthal and Herbert Marcuse in New York and saw his mother for the last time. After stopping in Paris, where he met Daniel-Henry Kahnweiler, Michel Leiris and René Leibowitz, Adorno delivered a lecture entitled "The Present State of Empirical Social Research in Germany" at a conference on opinion research. Here he emphasized the importance of data collection and statistical evaluation while asserting that such empirical methods have only an auxiliary function and must lead to the formation of theories which would "raise the harsh facts to the level of consciousness."