What is more interesting, I think, is that the distinction that his experimental

many
Navigation and Spatial Reasoning 209
subsequent researchers have been unwilling to accept—is not (at least for
my purposes) the most interesting aspect of Tolman’s experiment. What
is more interesting, I think, is that the distinction that his experimental
paradigm brings out offers an excellent operational illustration of a minimal
condition that has to be fulfilled before one can even start to enquire
whether or not a creature’s behavior is governed by an integrated representation
of its environment. The minimal condition is simply that the
behavior cannot be understood in terms of learned responses that can be
coded in terms of bodily movements rather than their distal targets.
This initial baseline condition cannot stand alone, however. There is a
second condition on the class of navigation-behaviors driven by spatial
representation of the environment. Although the contrast between response
learning and place learning is clear enough to illustrate how
behavior driven by information coded in terms of chained movement sequences
cannot count as driven by spatial representation of the environment,
it is not clear that we are in a position to affirm the converse
proposition, namely, that all behavior that resists explanation in terms
of learned responses is ipso facto driven by spatial representation of the
environment. In other words, the distinction on which the first minimal
condition rests is not exhaustive. This can be appreciated by considering
the possibility that a creature’s navigational behavior might be driven neither
by coded movement responses nor by the representation of places
but instead by sensitivity to features of the environment that covary with
spatial features. Let me give an example.
Animal behaviorists puzzled by the extraordinary homing abilities of
birds, particularly of homing pigeons, have put forward several different
explanations of how a bird released into completely unfamiliar territory
hundreds of miles from its home can almost immediately set a fairly direct
course for home. On the widely accepted assumption that homing behavior
cannot be explained in terms of any form of dead reckoning, the
birds must be reacting to stimuli that convey spatial information, and the
challenge is to identify those stimuli and how they are registered. The explanations
put forward fall into two broad categories (Gallistel 1990,
144–148). One set of explanations propose that the birds are registering
the angle of arrival of nonvisual stimuli propagated from their home posi-
210 Chapter 8
tion, such as odors or low frequency sounds. A second class of explanations
appeals to the possibility of bicoordinate navigation. Bicoordinate
navigation is navigation in terms of stimuli that can be perceived from
any point on the earth’s surface and that covary with latitude and longitude,
such as the position of the sun and stars and/or the earth’s magnetic
field. Bicoordinate navigation on the basis of magnetic information can
illustrate the difference between sensitivity to spatial features of the environment
and sensitivity to features of the environment that covary with
spatial features. Although we are obviously dealing with navigation that
is representationally far richer than learned movement responses, in neither
case do we yet have behavior driven by direct sensitivity to spatial
features of the environment. The fact that the magnetic field increases
in strength toward the poles, for example, might perhaps offer a way of
obtaining compass orientation, but it is not itself a spatial feature of the
environment. Nor are odors or low frequency sounds emanating from the
home position spatial features of that home position. If navigation behavior
is driven by the computation of magnetic information, then there is
no need to appeal to the distal target in explaining what is going on.
And if the behavior is explained through quite extraordinary sensitivity
to nonspatial stimuli then, even though the distal target will play a crucial
role in the explanation, those features of it involved in the explanation
will not be spatial features.
This gives us two minimal necessary (negative) conditions that must be
satisfied before there is any possibility of describing a creature’s behavior
as driven by representations of the spatial features of its environment. It
must be the case both that the behavior in question is not reducible to
coded sequences of bodily movements and that it is not driven by sensitivity
to features of the environment that merely covary with spatial features.
While noting that it does not seem to be true that the conjunction
of these conditions provides a sufficient condition for the existence of
behavior driven by representation of spatial features of the environment,
let me pass over the question of how exactly to specify such a sufficient
condition and turn to the further question of how one might build up
from behavior that satisfies these two minimal necessary conditions to
behavior that reflects possession of an integrated representation of the
Navigation and Spatial Reasoning 211
world. Here it seems that there are three further and more sophisticated
conditions that capture the core of this more advanced form of spatial
representation.
Possessing an integrated representation of the world involves appreciating
a system of simultaneous spatial relations. This entails that, for any
given route between two places, a subject who possesses an integrated
representation of the world will appreciate that the route is not the only
possible route. In fact, it seems to be a central aspect of appreciating that
something is a route between two points that one appreciate that there are
other possible routes between those same two points. This is, of course, a
vital element in appreciating the connectivity of space. One key way of
giving practical significance to the idea that all places are connected with
each other is by appreciating that there are multiple routes between any
two places. But how are we to understand this in operational terms? What
navigational abilities would count as practical manifestations of the grasp
that any given route between two points is merely one of a set of possible
routes?
In general terms, the relevant navigational ability is the capacity to
think about different routes to the same place. This navigational ability
can, of course, take many specific practical forms. One very obvious such
practical form is the capacity to navigate around obstacles. A good index
of a creature’s possession of an integrated representation of a given spatial
environment is that, should it find its customary route to a particular
place (say a source of water) blocked for some reason, it will try to navigate
around that obstacle. An interesting illustration of how the capacity
to think about different routes to the same place and the capacity to navigate
around obstacles can come together can be found in a set of experiments
carried out by Tolman and Honzik (1930a). Tolman and Honzik
ran rats through a maze in which three different routes of varying length
led from the starting point to a food reward. Unsurprisingly, the rats
quickly learned to follow the shortest route to the reward, and when the
shortest route was blocked, they quickly learned to use the middle-length
route. The interesting result occurred when the shortest route was
blocked at a point after the middle-length route had rejoined it. According
to Tolman and Honzik, in such a situation their rats did not attempt to
take the middle-length route but instead moved straight from the shortest