Spiritualism and the Occult
There is not a great deal of documentation to be found regarding this particular topic, but there are hints that experiments in occult practices such as seances were of interest to Mahler, Lipiner, and Kralik at least.
Lipiner was probably influenced in this regard by his studies in philosophy with Gustav Theodor Fechner, one of the founders of experimental psychology who also had interests in the metaphysical direction -- as evidenced the his book title Über das Seelenleben der Pflanzen (Of the Spiritual Life of Plants). [See his entry in the catalog of the Bryn Mawr Serendip online exhibition Mind and Body: Rene Descartes to William James.]
Kralik noted in his memoirs that "[Lipiner] and an even more mystically inclined friend led me into the seances of a spiritualist where we observed some writing mediums." He said that "We also read the chief works of this movement, but did not find ourselves inclined to pursue these questionable attempts further."
However, Mahler appears to have maintained at least some degree of interest in the topic. In her memoirs, Alma Mahler relates an occasion while they were living in New York where they attended a seance and provides this description of her explorations (this is in 1911)...
Despite Alma Mahler's disclaimer, it is clear from the history of the Circle that the occult was not merely "new" to Mahler in 1911.