Fact 5. Relational concepts have a category structure

Other research indicates that relational concepts seem to be like object concepts in having a graded similarity structure. For example, Logan and Sadler logan+sadler asked adults to rate the goodness of representations such as those shown in Figure 11 as instances of the spatial terms above, below, over, under, left of and RIGHT OF. The adults' judgments were highly organized and consistent, and as shown in Figure 12; various instances of trajector-landmark relatedness are better and worse instances of the concepts.

**Figure:** Stimuli used by Logan & Sadler to study adults' ratings of the goodness of spatial terms. The Xs represent trajectors, the circles landmarks.
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**Figure:** Average ratings for *above*, *below*, *left of*, *right of* in Logan & Sadler's goodness rating task.
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Children's acquisition of relational terms also exhibit a graded category structure. Smith, Cooney & McCord (1986; see also Ryalls, Winslow & Smith, in press) investigated children's understanding of the words higher and lower. Three- and four-year-old children were presented with two objects at a time and asked to indicate ``which is higher?'' or on other trials ``which is lower?'' The objects were discs about a foot in diameter that were positioned (above the ground) at 1' vs. 2', 3' vs. 4' or 5' vs. 6'. The results are shown in Figure 13. When presented with the discs at the two highest locations (5' vs. 6'), young children chose correctly when asked ``which is higher?'' but chose incorrectly when asked ``which is lower?'' Conversely, when presented with the discs at the two lowest locations (1' vs. 2'), young children chose correctly when asked ``which is lower?'' but chose incorrectly when asked ``which is higher?'' Judgments at the mid-height locations were intermediate. These results strongly suggest a categorical representation of higher and lower in which the best exemplar of higher is an object that is very high and the best exemplar of lower is an object that is very low. Notice also that these judgments suggest that children do not represent higher and lower as opposites -- that they can know that A IS HIGHER THAN B without knowing that B IS LOWER THAN A.

**Figure:** Children's accuracy in selecting the *lower* or *higher* of two discs placed at different heights (Smith, Cooney, & McCord, 1986).
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It is not only children's representations that are categorical in this way. In comparative judgment tasks, adults show the same pattern in reaction time that children show in errors [PetrusicPetrusic1992]. For both children and adults, some instances of a relation are better instances.