The original concept of a checklist in a multi crew aircraft required one person to challenge and the second person responded. This policy ensured as far as possible, that no item was missed. After all, two people were involved.
This proven concept was thrown out of the cockpit window with the introduction of fly-by-wire modern jet transports. Aircraft manufacturers have gone away from the original concept and designed checklists based upon so called "Area of Responsibility". At the request of the captain (or PF) a first officer might read a checklist by first calling aloud (challenge) the checklist item; then reply to his own challenge without any input (reply) by the captain.
What often happens is the captain hears the first challenge and then the self response by his F/O but without any verbal confirmation from the captain. This often leads to complacency, where, instead of being actively involved with the checklist, the non-responder simply scratches his balls and impatiently waits for the other guy finish challenging and responding to himself. In some Boeing types for example, the majority of checklist items are read by the PM as a challenge and response to himself. There seems little point in calling the policy "Challenge and Response" when done by the checklist reader challenging himself and responding to himself that he has done the job.
The original concept of one pilot challenging while the other pilot confirmed (after checking the switch position etc), was once hailed as a major improvement in flight safety. The change from a seemingly fool-proof flight safety concept to what is now basically a one man band concept is called progress? . ?
