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Mental Maps and Images

Steven Kosslyn of Harvard is also famous for studies of mental imagery. Kosslyn found that the size of an imagined image influenced how quickly subjects could "move around" the image in memory. If subjects memorized a map, the time it took them to make a mental jump from one location to another depended upon the distance on the imagined map.

What did Kosslyn find, concerning scanning of mental maps? When he had subjects imagine a rabbit next to a fly?

In one experiment, Kosslyn (1975) asked subjects to imagine animals standing next to one another, such as a rabbit next to an elephant or a rabbit next to a fly. Then subjects were asked questions such as, "Does the rabbit have two front paws?" People took longer to answer such questions when the rabbit was imagined next to an elephant, because the rabbit's image was so small. When the rabbit was imagined next to a fly, its imagined image was large, and subjects were quicker to answer questions about the image. Kosslyn concluded that visual imagination produces "little models, which we can manipulate much like we do actual objects."

When asked to imagined a rabbit next to a fly, people were quick to answer questions about the rabbit's appearance. They were slower when first asked to imagine it next to an elephant.

What are two types of mental imagery? What is evidence that they are distinct?

Researchers have identified two types of mental imagery, one for pictures (for example, visualizing the rabbit next to the fly) and one for spatial representation (for example, rotating shapes in imagination). Kosslyn's work focused on imagined pictures. Shepard and colleagues focused on imagined rotation of shapes in space. The two involve different brain areas, and the two skills can be doubly dissociated by brain injury (you can lose one but not the other). The ability to imagine pictures can be lost after damage to the back of the brain, near the occipital lobe. The ability to imagine space is lost after damage to the middle of the right hemisphere, near the parietal lobe.

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