We need to consider both how well people can manipulate
symbols mentally and what happens as a result. The clearest evidence
for people’s ability to manipulate symbols in their mind’s
eye comes from Kosslyn’s (1985) studies of mental imagery.
Kosslyn’s basic research paradigm was to have his subjects create
a mental image and then to instruct them directly to change
it in some way, usually by zooming in and out on it. Evidence
for the success of his subjects at doing this was found in their
ability to answer questions about properties of the imaged objects
that could only be inspected as a result of such manipulation.