The Collaborative International Dictionary of English v.0.48:

Aftersensation \Aft"er*sen*sa`tion\, n. (Psychol.)
   A sensation or sense impression following the removal of a
   stimulus producing a primary sensation, and reproducing the
   primary sensation in positive, negative, or complementary
   form. The aftersensation may be continuous with the primary
   sensation or follow it after an interval.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

aftersensation
    n 1: an image (usually a negative image) that persists after
         stimulation has ceased [syn: afterimage,
         aftersensation]