An Overview of GPS Systems and Adaptations: Implications for the Older User with Vision Impairment

GPS consist of a series of 24 satellites that circle the earth in a variety of planes and transmit radio signals (El-Rabbany, 2002; Garmin, 2000). These components in space interact with earth-based control centres that monitor the satellites and signals being sent. A GPS receiver interprets the radio signals and, by incorporating Geographic Information System (GIS) data, can provide spatial information about such environmental aspects as roads, railways, mountains, rivers and other landmarks commonly found on print maps. The satellites can also pinpoint the carrier of the GPS-GIS device, commonly referred to as a GPS unit (Ponchillia, Rak, Freeland, & LaGrow, 2007; Ponchillia et al., 2007). In summary, a GPS unit has two main functions. First, the GPS unit provides the user with locational information by determining the user’s position via the GPS technology and relates it to map information via the GIS technology. Second, it allows the user to mark specific latitude-longitude positions with electronic markers that can be used to locate landmarks (Ponchillia et al., 2007). Using the information provided by a GPS unit, the user can plan routes, check to see whether or not they are on route while travelling, receive updates on the time it will take to arrive at the destination and know when the destination is reached (Ponchillia, Rak, et al., 2007).

Wayfinding or navigation techniques used by people with vision impairment are subject to such limitations as lack of accessible environmental information, difficulties with route planning and the unreliability of locational information solicited from the public. Wayfinding skills can also be compromised if the person has trouble understanding spatial concepts, using mental maps and soliciting aid (Ponchillia, Rak, et al., 2007). In addition to traditional mobility aids such as long canes and guide dogs, adapted GPS devices benefit people with vision impairment because they provide additional environmental information.

For example, an adapted GPS system, called the Personal Guidance System by its creators, was first developed in 1991 (Golledge, Loomis, Klatzky, Flury, & Yang, 1991). The system provided people with vision impairment information about nearby points of interest, guided them along routes to destinations and located their position in their environment (Loomis, Marston, Golledge, & Klatzky, 2005).

An evolution of adapted GPS systems has since occurred with the first commercial device becoming available in 2000 (Ponchillia et al., 2007). Today there are a number of devices on the market offering a variety of display interfaces, functions and applications such as the BrailleNote GPS, Trekker GPS, Trekker Breeze and Wayfinder Access.

HumanWare, a technology company specialising in accessibility, with a team of researchers called the Sendero Group, developed the BrailleNote GPS (BGPS) in 1994 as a wayfinding solution for people with vision impairment. BrailleNote is an accessible personal digital assistant (PDA) that provides braille output (HumanWare Group, 2007; Ponchillia, Rak, et al., 2007). BrailleNote provides a number of functions, for example, a word processor, web browser, voice recorder and daily planner. When combined with the BGPS satellite navigation add on, it can calculate the location of the user, and then plot a route to the specified destination. The BGPS has five major functions that include:

The Trekker GPS device is developed by HumanWare. This system uses GPS and digital maps as a wayfinding solution. Whereas BGPS relies on a braille output, Trekker is aimed at users who prefer to be more discrete by using an audible output. Spoken directions can be accessed, routes recorded and audible information provided about landmarks the user travels past. Trekker is smaller than the BGPS and more affordable and combined with all its features, makes it a popular choice for people who are already familiar with computers and screen readers (HumanWare Group, 2007). For those users who might not be familiar with more complex technologies, the Trekker Breeze offers a smaller, simplified device with similar features. Trekker Breeze has an audible output like Trekker but has fewer buttons and can be operated by one hand, perhaps making it more suitable for the older person.

Wayfinder Access (WFA) is an accessible GPS software developed by Wayfinder Systems AB, designed to be used on a mobile phone handset. When used in conjunction with a screen reader such, it provides an audible navigation tool for users with a compatible mobile phone. Like BGPS, WFA provides the user with information about their surroundings, for example, nearest crossroads, places of interest and stored favourites. It also gives the ability to calculate routes and provide directional information in terms of cardinal and clockface directions (TalkNav, 2008).

The GPS devices discussed are loaded with digital maps available from the manufacturer and rely on GIS spatial information to provide a navigation tool.

The discussion so far has focused on the implications of GPS devices for people with vision impairment. Though what are the implications for older people who are vision impaired? Although personal preferences and individual differences must be considered, several generalisations about the older population in reference to different display interfaces and devices are possible.

Textual information is provided to GPS users who are vision impaired through synthesised speech, a refreshable braille display or a combination of both (Loomis et al., 2005). This type of display is sufficient in many navigational tasks and could include such instructions such as “turn left and go straight for four blocks”. However, this information might not be satisfactory when travelling in large, open areas or when searching for specific landmarks. In these situations, textual information may be substituted or supplemented with a display that provides spatial information as well as directions and distances relative to the user. An additional display can be achieved through the use of virtual sound, a haptic/auditory interface, vibrotactile stimulators or a Haptic Pointer Interface (Loomis et al., 2005; Marston et al., 2007).

Virtual sounds are those sounds that are perceived as coming from spatial locations (Marston et al., 2007), that is, they appear to be coming from a particular direction and distance in space. Virtual sound is achieved by using virtual acoustic software to convert a monaural input signal into a binaural output signal (Loomis et al., 2005) and this signal is delivered via either headphones or a speaker worn near the shoulder. The sounds delivered might be synthesised speech or tones and the intensity increases as the user approaches the waypoint. The use of virtual sound imposes less of a cognitive load than does speech in a route following task (Marston et al., 2007). In this case cognitive load refers to the level of effort on working memory associated with thinking and reasoning, which has the potential to interfere with other thought processes. The use of virtual sound as a display interface would be beneficial when one considers that working memory capacity is reduced in older people. This means that less information elements can be processed (Van Gerven, Paas, Van Merrienboer, & Schmidt, 2007) and the ability to engage in demanding processes and comprehend and learn complex material is impaired (Paas, Camp, & Rikers, 2001).

An alternative display is a haptic/auditory interface that involves a simultaneous delivery of both tactile and auditory information (Marston et al., 2007). The tactile information is delivered through the use of a vibrating output device worn on the body of the user. A haptic/auditory interface is useful in noisy environments when audition alone can not be relied upon. In the older population, hearing problems as an additional disability to vision impairments is common (Morris & Ballard, 2003). In these cases speech or tone cues supplemented by tactile cues would be of benefit.

The use of vibrotactile stimulators alone are also a form of display in adapted GPS devices. A 4x4 grid of stimulators placed on the backs of the users help them navigate indoor spaces by relying on the messages relayed by pulsing vertical columns within the grid. These pulsations are prompted by detection by the GPS device of preprogrammed waypoints. Another vibrotactile display is realised by placing eight evenly spaced stimulators around the waist of the user. Pulsations within the eight stimulators indicate the direction in which the user should go. A more simplified way of receiving vibrotactile feedback is by placing a single stimulator on the wrist (or any other body part) of the user. This corresponds to an electric compass placed on a visor worn on the head. When the user is heading in the correct direction as determined by the location of the next waypoint, a signal is sent to the stimulator and a pulsation is felt. This can also be set to a certain pulse-type when the user is heading in the wrong direction (Marston et al., 2007). Vibrotactile displays worn on the torso may be cumbersome, especially when paired with a backpack used to carry the GPS receiver and other equipment. This might not be acceptable for older people who do not have the strength to carry the equipment or who prefer to look inconspicuous. It might also not be suitable if it affects balance in any way as one in three older people suffer from unsteadiness and/or dizziness at some time (Yardley, 2004). Vibrotactile stimulators worn on the wrist might not be as effective for those people who have diabetes and have a loss of sensation in their extremities. Wrist stimulators might also pose problems when accessing a refreshable Braille display.

Finally, Haptic Pointer Interface can also be used as a display for adapted GPS devices. The user holds a pointer (in the form of a small rectangular stick) to which an electronic compass is attached. When the hand points within a set range of the next way-point, either beeping tones or synthesised speech lets the user know that they are heading in the right direction. Speech updates are also provided indicating the distance to the next waypoint (Loomis et al., 2005).

Adapted GPS devices are designed to be used in conjunction with traditional orientation and mobility (O&M) skills and mobility aids such as long canes, guide dogs and soliciting aid. Older people have been found to experience some difficulties in tasks that require mental coordination and integration. Processing speed becomes slower, especially in tasks which are complex and require more mental effort and when simultaneous information is presented (Paas et al., 2001; Van Gerven et al., 2007). Hence, integrating information across several domains might be compromised (Paas et al., 2001) when an older person manipulates a long cane whilst simultaneously attending to the information provided by an adapted GPS device. Receiving both visual and auditory environmental information as well as GPS information might become overwhelming for the older user.

Using an adapted GPS device requires some level of training whether it is briefly learning simple functions or an extensive education about sophisticated applications. This need for training might be of concern when focusing on the older population as they generally experience aging-associated cognitive decline and a reduced working capacity which affects their ability to learn new tasks. When learning entirely new material, any prior experience and knowledge is expected to be unhelpful and older people are forced to rely on their working memory abilities (Van Gerven et al., 2002).

Although there are limitations to adapted GPS devices for the older user, the main benefits that might be experienced are independent mobility, increased confidence in wayfinding and a reduction in stress (Ponchillia, Rak, et al., 2007; Yardley, 2004). An additional benefit for older users is the decreased reliance on memory for navigation tasks. Memory for new and familiar environments decreases with age. Memory for landmarks remains unimpeded but older people have more difficulty with the more integrative aspects involved in the memory of layouts (Paas et al., 2001). This decline, along with other memory deficits associated with aging, has implications on the ability to learn and retain new routes. However, GPS directions can be referred to and repeated on request.

Although the advantages of adapted GPS devices for people with vision impairments are many and far reaching, the use of this technology for route planning is not generally popular with older people as some feel anxious or intimidated by it (Morris & Ballard, 2003). Currently, of the GPS devices discussed, the Trekker Breeze would probably be the most acceptable for older users as it is lighter, smaller, discreet and affordable. It also has voice output that might be more suitable than other types of displays. Further research is required to investigate the implications of GPS devices, effective GPS training methods and adaptations for the older user with vision impairment.