Percent correct mixes how well two states can be told apart with how willing you are to say “yes.” Signal detection separates those quantities.
Studio move: keep d′ fixed and slide criterion. Accuracy changes. Sensitivity does not. That is the whole argument against “percent correct” as a grade for a mind, a diagnosis, or a work of art that is easy to over-call.
Half the trials show a low-contrast T. Press J for yes, F for no. Your hit and false-alarm rates become your own d′.
Waiting.