Feature theories

According to feature theories, a pattern consists of a set of specific features or attributes. For example, a face could be said to possess various features: a nose, two eyes, a mouth, a chin, and so on. The process of pattern recognition is assumed to begin with the extraction of the features from the presented visual stimulus. This set of features is then combined, and compared against information stored in memory.

In the case of an alphanumeric pattern such as "A", feature theorists might argue that its crucial features are two straight lines and a connecting cross-bar. This kind of theoretical approach has the advantage that visual stimuli varying greatly in size, orientation, and minor details may nevertheless be identifiable as instances of the same pattern.

Experimental evidence

The feature-theory approach has received support in studies of visual search, in which a target letter has to be identified as rapidly as possible (see also Chapter 5). Neisser (1964) compared the time taken to detect the letter "Z" when the distractor letters consisted of straight lines (e.g., W, V) or contained rounded features (e.g., O, G) (see Figure 4.1). Performance was faster in the latter condition, presumably because the distractors shared fewer features with the target letter Z.

Feature theories are based on the assumption that visual processing proceeds from a detailed analysis of a pattern or object to a global or general analysis. However, there is evidence suggesting that global processing often precedes more specific processing. Navon (1977) presented his participants with stimuli such s s s s s s s s s s

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