Foundations Of Cognitive Science

Index Projection Hypothesis

According to the index projection hypothesis (Pylyshyn, 2007), mental images are scaffolded by visual indices that are assigned to real world (i.e. to visually present) entities.  For instance, consider Pylyshyn’s application of the index projection hypothesis to the mental map paradigm used to study image scanning: “If, for example, you imagine the map used to study mental scanning superimposed over one of the walls in the room you are in, you can use the visual features of the wall to anchor various objects in the imagined map.  In this case, the increase in time it takes to access information from loci that are further apart is easily explained since the ‘images’, or, more neutrally, ‘thoughts’ of these objects are actually located further apart” (Pylyshyn, 2003b, p. 376).   In other words, the spatial properties revealed in mental scanning studies are not due to mental images per se, but instead arise from “the real spatial nature of the sensory world onto which they are ‘projected’” (Pylyshyn, 2003b, p. 374).


  1. Pylyshyn, Z. W. (2003). Seeing and Visualizing: It's Not What You Think. Cambridge, Mass.: MIT Press.
  2. Pylyshyn, Z. W. (2007). Things and Places: How The Mind Connects With The World. Cambridge, Mass.: MIT Press.

(Added March 2011)