Which group of stimuli exemplifies an arbitrary stimulus class?

• A. Photographs of a banana, watermelon, strawberry, and pineapple, which all evoke the word 'fruit'
• B. Photographs of different foods that evoke distinct labels
• C. A single photograph of fruit
• D. A set of colors that evoke color names

Answer: (A)

An arbitrary stimulus class consists of several stimuli that don’t look alike or share obvious physical properties, yet they are linked by the same response or label through learning. Here, photos of various fruits differ a lot in appearance, but they all prompt the same verbal label “fruit.” That shared function—evoking the same label despite differing visuals—defines an arbitrary class.

The other options don’t form that kind of class. One option pairs different foods with different labels, so there isn’t a single, common response binding the group. Another option shows a single photograph, which isn’t a class at all. The last option groups colors by the natural property of color and its name, which isn’t about an arbitrarily linked label across diverse stimuli.