RESNA 2006 Proceedings Selecting an Appropriate Scan Rate: The “.65 Rule”

Investigators have discovered that the ratio between a user’s reaction time and an appropriate scan rate for that user is approximately 0.65, which we refer to as “the.65 rule. ” As part of a larger effort to develop software that automatically adapts the configuration of switch access software, data was collected comparing subject performance with a scan rate chosen using the.65 rule and a scan rate chosen by the user. Analysis of the data indicates that for many people, the.65 rule produces a scan rate that is approximately the same as the average switch press time plus two standard deviations. BACKGROUND Row-column scanning is a technique used by individuals with significant physical impairments for entering text and other data into computers and augmentative communication devices. A common implementation of row-column scanning with one switch requires three switch hits to make one selection from a two-dimensional matrix of letters, numbers, symbols, words, or phrases, as illustrated in Figure 1. The first switch hit initiates a scan through the rows of the matrix. Each row of the matrix, beginning with the first, is highlighted in turn until the second switch hit is made to select a row. Each column of the row is then highlighted in turn until the target is highlighted, when the third switch hit is made t