Towers of Hanoi and London: is the nonshared variance due to differences in task administration?

Although it has been assumed that the Tower of Hanoi and Tower of London are more or less interchangeable tasks dependent on executive function, a series of studies in our laboratory have indicated substantial nonshared variance between the performances on the two tasks. The purpose of the present study was to examine how much methods of administration, such as number of trials per problem, contribute to this nonshared variance. A new one-trial version of the Tower of Hanoi was developed to be identical to the Tower of London in four procedural characteristics. The one-trial version of the Tower of Hanoi was administered to 39 normal adults along with the traditional Tower of Hanoi and the Tower of London-Revised in two test sessions 5-7 weeks apart. The correlations between the two tasks were in the same range as found previously with the traditional task, indicating that administration differences do not account for the nonshared variance between the tasks. A reliability analysis of the one-trial tasks showed poor internal consistency. Also, the internal consistency of the 6-trial tower was artificially inflated by aspects of the administration and scoring procedures. Moreover, this task exhibited a ceiling effect on repeated testing. These results suggest that it would be of value to redesign the one-trial Tower of Hanoi systematically to increase its reliability and, potentially, its validity as a measure of executive functions.