difficult to discern what is a figure—an object, vehicle, or building—and what is shadow or fog. Novices have that experience when looking at X-rays: what is bone, what is tissue, what is tumor?
Pattern recognition is of special significance in everyday life and in specialized knowledge domains. In everyday life, it underlies recognition of faces and places. For recognizing that something is a face, the outside contour is important; for recognizing that a face is that of a particular individual, the inside configuration is critical (Farah et al., 1998). In specialized knowledge domains, pattern recognition underlies recognition of a multitude of spatial categories from flight paths on radar screens and interactions in graphs to fault lines in aerial photographs. For shapes, it underlies object and letter recognition in everyday life, as well as recognition of rare subspecies in biology, protein molecules in chemistry, rock types in geology, and symbols in mathematics. Learning to correctly distinguish one pattern from another can take considerable experience and often depends on first discerning figure from ground. Expertise in many domains requires recognition of specific patterns, but the principles are the same as those for recognizing the objects and patterns in the world around us. For everyday and expert situations, recognizing patterns entails discerning relevant features and their appropriate spatial relations.
In everyday life, evaluating size is essential for navigation, packing, and rearranging furniture. In scientific thinking, size evaluation is used in thinking about structures in geology, biology, and many aspects of engineering. Size evaluations are subject to many perceptual illusions, so learning to overcome them is important.
Texture is one important clue to depth and distance, so evaluating texture is important in navigating the world (Gibson, 1979). It is also a clue to object recognition: the furriness of a cat, the sleekness of an automobile, and the coarseness of freshly sawed wood. Texture is also a clue to how something should be handled and interpreted. In science, texture can distinguish one kind of rock from another (see Chapter 3.6), one kind of tissue from another, or one kind of vegetation from another in a remotely sensed image.
Color evaluation is a clue to object recognition. Small round things that are orange are more likely to be apricots than plums. Similarly, in science, color distinguishes one chemical, rock, or tissue from another.
Representations: The Relations Between Static Entities Often spatial judgments, such as size, shape, distance, or direction comparisons, are not evaluations of properties of entities but rather evaluations that depend on relating an entity to a reference frame (e.g., determining whether something is upright), or relating one entity to another (e.g., deciding whether one glass is closer than another or filled higher than another). Important spatial evaluations and comparisons that depend on relating an entity to a reference frame or comparing two entities are
comparing direction, and
comparing other attributes.
Thus, in the case of determining orientation, we can ask: Is the picture on the wall upright or tilted? Evaluating orientation requires comparing the intrinsic frame of reference of an object—in this case, the picture—to the extrinsic frame of reference—in this case, the room. Determining