Most models of human performance on the traveling salesperson problem involve clustering of nodes, but few empirical studies have examined effects of clustering in the stimulus array. A recent exception varied degree of clustering and concluded that the more clustered a stimulus array, the easier a TSP is to solve (Dry, Preiss, & Wagemans, 2012). However, a limitation to this conclusion arises because degree of clustering may have been partially confounded with cluster location. An experiment was conducted to test the effects of cluster location while holding degree of clustering constant. Stimuli with a cluster near a boundary were solved more quickly and accurately than stimuli with the same cluster located more centrally. The results support and extend the previous findings of MacGregor, Ormerod, & Chronicle (1999). They also qualify the results of Dry et al. (2012). To the extent that degree of clustering may have been confounded with the location of clusters in their stimuli, it is unclear to what extent each factor may have affected performance.
MacGregor, James N.
"Effects of Cluster Location on Human Performance on the Traveling Salesperson Problem,"
The Journal of Problem Solving:
2, Article 3.
Available at: http://docs.lib.purdue.edu/jps/vol5/iss2/3