It depends. When she is giving me head, while I can always get off on the sensations alone, my imagination often adds that extra push that makes the orgasm feel more intense. In fact it is during a BJ that I can most concentrate on scenarios of past and future due to not having to do anything but lie there usually with closed eyes and sometimes in the dark.
While having regular sex I can mostly rely on the visual and her reactions to get me there but every now and then I have difficulty finishing due to starting without realizing how tired I really was. In those cases, I do use my thoughts to finally come, usually using the memories of past swinging encounters.