Experiments 1–3 show that CQ's negative afterimages at the affected region of the visual field were no different in strength
(Experiments 1–2) and duration (Experiment 3) from those at his unaffected region. In the experiments below, we assessed CQ's positive
afterimages parametrically. To be able to distinguish positive from
negative afterimages, we chose to use a green adapting stimulus, so
it would be easy for him to label his perceived afterimage. A nulling
procedure as we used to assess his negative afterimage could not be
used, because CQ stated that his positive afterimages were displaced