Isomorphic problems are to cognition what optical illusions are to perception. By drawing attention to anomalies such as problems which are
identical in form but vary widely in difficulty
they highlight cognitive processes normally hid-
den a m o n g the minutiae of our theories. Results
are reported from an experiment in which sub-
jects solved a three disk Tower of Hanoi problem
and its Monster Globe change isomorph using
direct manipulation tableaus or paper and pencil.
Subjects using direct manipulation were found to
solve the Monster Globe problem in half the time
taken by paper and pencil subjects. A n explana-
tion revolving around attunement to environmen-
tal constraints is advanced to account for this
difference.
