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In this example there are six authors: Kosslyn, Koenig, Barrett, Cave, Tang, and Gabrieli (1996)
For the first and subsequent citations write the first author’s name followed by et al.
Narrative
This is how three or more authors would appear as part of a narrative:
Kosslyn et al. (1996)
Parentheses
And if you chose to use parentheses, this is how the citation would look:
(Kosslyn et al., 1996)
(American Psychological Association, 2010, p. 175)