Copyright © 1999 Massachusetts Institute of Technology
Although the term navigation originates from the Latin word for ship, the term has come to be used in a very general way. It refers to the practice and skill of animals as well as humans in finding their way and moving from one place to another by any means. Generally moving from place to place requires knowledge of where one is starting, where the goal is, what the possible paths are, and how one is progressing during the movement.
Knowledge of where one is starting in one sense is obvious; one can see the immediate surrounds. However, this is of little help if the relation of that place to the rest of the spatial layout is not known. This becomes of practical interest in the so-called drop-off situation, where one is dropped off at an unknown position and has to determine the location. Practically, this could happen in a plane crash when flying over unknown territory, or more generally if one is lost for any reason.
In such cases having a map is useful but requires matching the perception of the surrounding environment with a particular position on the map. That problem can be cognitively quite difficult. An observer has a particular viewpoint of the environment that in general is rather limited. The map typically covers a much larger area and, of course, has an infinite number of possible viewpoints. In addition, in many locales the individual features are ambiguous; limited views of any one hill, valley, or stream often look like others. Very experienced map readers have strategies that help them overcome these difficulties (Pick et al. 1995). For example, in trying to figure out where on a topographical map they are, successful readers focus initially on the terrain rather than the map. This makes sense inasmuch as knowing the details of the terrain would constrain the possibilities more than knowledge of the big picture provided by the map. Successful readers look for configurations of features. As noted, any individual feature is ambiguous; configurations provide powerful constraints as to where one might be.
Identifying possible paths from one place to another can be based on prior spatial layout knowledge (see COGNITIVE MAPS), but it can also be accomplished on the basis of maps. Depending on the type of map, constraints on possible paths will also be indicated, for example, roads on urban and highway maps; mountains, streams, and the like on topographic maps; and reefs, islands, water depths, and so forth on nautical charts. Many maps provide a very general and powerful reference system. The geographic coordinate system, as Hutchins (1995) points out, not only enables specification of the location of starting point and destination, but also permits easy determination of paths by graphic or numerical computation.
In many cases such as piloting a ship along a coast line, navigation often involves specifying position in relation to landmarks rather than the coordinate systems of maps or charts. Keeping track of one's progress during travel is particularly problematic when information about position in relation to landmarks is impoverished. One of the most impressive and cognitively interesting examples of sea navigation is that of Micronesian islanders who tradi tionally traveled from island to island across wide-open stretches of the South Pacific without navigational instruments. Their skill has been carefully studied by anthropologists (e.g., Gladwin 1970; Lewis 1978; Hutchins 1995). The islanders' knowledge of the paths from one island to another is in the form of sailing directions as to courses to steer and features that are observable along the way. By our standards, information in relation to such features is clearly impoverished. However, there are observable features to which Micronesian sailors attend that others might miss, such as slight changes of water color indicating underwater landmarks, changes in the wave patterns indicating disturbance by nearby islands, the sighting of birds flying toward or away from islands at different times of the day, and so on.
Across the open sea there are few constraints on what paths to take, so maintaining a steady course becomes quite important. Micronesian navigators have developed a form of celestial navigation in which direction at night is determined in relation to the position on the horizon at which particular stars rise and set. In fact, stars rising at the same point on the horizon all follow the same track across the sky and set at the same place in what is called a linear constellation (Hutchins 1995). During the day the direction of the sun at different times and the direction of wave patterns can be used to maintain course.
Most intriguing about the Micronesian system is how the islanders keep track of where along the journey they are. The Micronesian navigators conceptualize the trip in terms of a stationary canoe with an out-of-sight reference island moving past it. Thus the bearing from the canoe to such an island changes as the journey progresses. Because the reference islands are generally out of sight, it makes no difference if the island really exists and, in fact, if there is not an actual convenient reference island an imaginary one is used.
Because motion is relative, it makes no logical difference whether one conceptualizes travel as involving a stationary world and a moving canoe or a stationary canoe and a moving world. Hutchins and Hinton (1984) hypothesize a very interesting explanation for why this conceptualization makes sense on the basis of the sensory information available at sea to the Micronesians.
The changing bearing of a reference island is a convenient way to keep track of where one is on a journey, as is plotting one's position on a map or chart. But how does one know how fast the bearing is changing or how far to move one's chart position? If the environment is too impoverished to keep track of position with respect to features, it must be done by somehow keeping track of one's velocity and integrating over time to obtain distance moved, a procedure known as dead reckoning (Gallistel 1990). Crossing undifferentiated expanses of sea or land, dead reckoning must be relied on for registering progress between celestial fixes unless modern navigational instruments are used.
Another relevant case of impoverished environmental information is the very mundane activity of walking without vision. This is, of course, the common situation of blind people. They, like the Micronesian sailors, are able to keep track of their progress by attending to information often ignored by others, for example odors marking particular locations, and changes of air currents and acoustic resonance properties that signify open passageways and the like (Welsh and Blasch 1980). However, internal information also specifies movement, for example by proprioception and/or motor commands. There is some evidence that blind people do not use this source of information to update their position as well as do blindfolded sighted persons (Rieser, Guth, and Hill 1987; but see Loomis et al. 1993). This advantage of sighted people may be due to optical flow information when walking with vision serving to calibrate nonvisual locomotion (Rieser et al. 1995). Thus movement in nonvisual locomotion presents on a small scale some of the same problems involved in much grander global navigation .
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Copyright © 1999 Massachusetts Institute of Technology