Regarding the Commentary on the Vimuttimagga, the author, Duncan, has no idea what she is talking about. The ‘after-image’ she refers to is from Western psychology. This after-image is a brief (it quickly fades after removal of the stimulus) retinal image caused by bleaching of the receptors (retinal fatigue) at the back of the eye due to prolonged stimulus. An example is when one briefly looks at the sun and then turns one’s gaze away, the image of the sun briefly remains, and in this case, is quickly replaced by a ‘negative after image’, which also quickly fades.
In respect to the development of the Jhanas, which according to the Visudddhimagga is a system of concentration meditation/absorptions, three images/signs are outlined; the physical/preliminary image (parikamma-nimitta), the visualised image (uggaha-nimitta), which is what is known in psychology as an ‘eidetic image’ and which arises from the physical image, and the so called purified image (patipbhaga-nimitta) which arises from the visualised image. The term after-image is sometimes applied to either the uggaha-nimitta or patipbhaga-nimitta, but usually refers to the patipbhaga-nimitta. Other terms/translations are also sometimes used.
Essentially, whereas the after-image is a mere retinal image (not a meditation experience, as such), i.e. it is peripheral to the CNS, the uggaha-nimitta and the patipbhaga-nimitta are central, i.e. they arise in the brain/mind.
