Effect of Cane Length on Drop-Off Detection Performance

Although individuals who are blind have used a stick or a cane for their independent travel since the early years of human history, designs for modern long canes did not appear until World War II, when the systematic long cane techniques were developed by Hoover (1962). Ergonomic factors, such as the length of the cane, may affect how well a cane user can detect the presence of obstacles and changes in surface elevation, including drop-offs. Reliable drop-off detection with a long cane, an essential component of surface preview (Blasch, La Grow, & De l'Aune, 1996), is critical for the safety of travelers who are blind who use canes, since missing drop-offs or other changes in elevation in the walking surface may cause them to fall or accidentally stumble into the collision path of approaching vehicles. Kim, Wall Emerson, and Curtis (2009) found that cane users were able to detect drop-offs more reliably when they used the constant contact technique than when they used the two-point touch technique. The characteristics of cane users may also influence the users' performance in detecting drop-offs. In Kim, Wall Emerson, and Curtis's (2010a) study, younger users were able to detect drop-offs more reliably than were older cane users. Cane users who lost their vision early in life also detected drop-offs more reliably than did those who lost their vision later (Kim et al., 2010a). In addition, those who had regularly used a cane for at least two years performed better than did those who were less experienced (Kim, Wall Emerson, & Curtis, 2010c). Detecting drop-offs may also be influenced by ergonomic factors, such as the type of cane tip (Kim, Wall Emerson, & Curtis, 2010b) and length of the cane (Rodgers & Wall Emerson, 2005). How the length of a cane may affect the detection of drop-offs is of particular interest because there appear to be different opinions on this matter among cane users. According to the traditional method (called the "sternum method"), a proper cane length is defined as the vertical distance from the ground to 2 inches above the xiphoid process (La Grow & Weessies, 1994). In a study conducted with 10 adult cane users who were visually impaired (that is, those who were blind or had low vision), Rodgers and Wall Emerson (2005) reported that the use of a standard-length cane, measured by the sternum method, allowed the users to detect drop-offs significantly better than with the canes that were either 5%-15% shorter or 10%-20% longer than the standard length. However, some cane travelers have advocated for a cane that is substantially longer than the standard length. For example, Willoughby and Monthei (1998) suggested that although a cane user' s stride, walking speed, and reflexes should be considered, a cane that reaches only to the sternum is not long enough to ensure safety for an average cane user. In addition, Kish (2009) suggested, on the basis of personal anecdotal experience, that children up to age 6 should use canes that are as long as their height and that adult travelers need to use canes that are about chin high. Given this controversy, we investigated whether the length of the cane affects the detection of drop-offs. We also examined whether there is an interaction between the length of a cane and the depth of a drop-off. METHOD A repeated-measures design with block randomization was used for the study. We recruited 15 sighted students (13 female and 2 male) aged 22 to 55 (median age = 34) from the orientation and mobility (O&M) program at Western Michigan University who were familiar with both the two-point touch and constant contact techniques. These students had received 1 month to 4 months (median = 1.4 months) of cane training. A 32-foot-long walkway with six carpeted plywood platforms (8 feet long, 4 feet wide, and 8 inches high) was used for the study. We placed two plywood boards (2 feet long and 4 feet wide) on top of braced rectangular frames (2 feet long, 4 feet wide, and 2 inches high) against the lengthwise end of the walkway to change the depth of the drop-off from trial to trial. …