At the same time, the mental health of guitarist Syd Barrett was deteriorating; he was often unresponsive and would not play, leading to the cancellation of several performances and their first US tour. In December 1967, reaching a crisis point with Barrett, Pink Floyd added guitarist David Gilmour as the fifth member. According to Jenner, the group planned that Gilmour would "cover for [Barrett's] eccentricities". When this proved unworkable, "Syd was just going to write. Just to try to keep him involved."