Final answer:
The speaker used participant observation to measure collective effervescence, which involves immersing oneself into a community and engaging in systematic observation of their cultural practices and rituals.
Step-by-step explanation:
In the context of measuring collective effervescence, the speaker mentioned in the question most likely used participant observation as the method to measure this phenomenon. This approach involves the researcher entering a cultural community and collecting information through observation of and participation in the culture. Therefore, options such as observing brain activity, analyzing social media posts, or conducting qualitative surveys are not directly indicated as the methods used. The reference provided points towards participant observation being a hallmark of cultural anthropology and a common method to develop a deep understanding of a culture and its practices.
Furthermore, the literature on cultural anthropology and sociology emphasizes the importance of qualitative research methods like participant observation for gaining a profound insight into human behavior, rituals, religious services, and the corresponding psychological impacts on individuals within a community.