Can people mentally impose arbitrary spatial category boundaries?

When explorers like Magellan and Columbus sailed from Europe to the New World 500 years ago, they amazingly managed to navigate the open sea without terrestrial landmarks, natural boundaries or the navigational technology we have today.

Historical reports suggest that some explorers and other seafaring people did so by imagining an island just over the horizon; if they kept track of where the "virtual island" was, they knew which direction to go in the open water.

But new research from the University of Iowa suggests that people's ability to imagine virtual islands -- without any perceptual cues to help -- is quite limited. Consistent with this, studies of how seafaring people navigate on the open seas suggest they actually rely on two key perceptual cues: perception of their own motion and the boat's motion. Thus, the ability to navigate in open water stems from how the body senses motion, not on a mental ability to imagine a point.

In a paper published this month in the Journal of Experimental Psychology: Human Perception and Performance, doctoral candidate Vanessa Simmering and associate professor John Spencer, both of the Department of Psychology in the UI College of Liberal Arts and Sciences, provide evidence that adults cannot arbitrarily carve the world into spatial regions. Instead, they write, people must rely on perceptual cues for help. The paper is titled "Carving Up Space at Imaginary Joints: Can People Mentally Impose Arbitrary Spatial Category Boundaries?"

To study whether people could create a set of virtual islands, Simmering and Spencer placed test subjects at a large table with two dots dividing the table into left and right zones. The subjects' task was to remember the location of a ship and to estimate its location after a 10-second delay. In repeated trials, people remembered the ship's location relative to the visible dots -- the "real islands." They then were instructed to perform the same task, but the dots were taken away to see if subjects could maintain performance while imagining a set of virtual islands.

"When we took the dots away, suddenly people acted as if the dots had never been there, even though we had given explicit instructions to act as if the dots were there on every trial," Spencer said. "After the testing, we asked people if they had been successful at mentally imposing the dots. They all felt confident they had. People completely overestimated their mental abilities."

Spencer said the research supports a psychological concept called "embodied cognition." The idea is that while people have abstract abilities -- like using language to communicate, or understanding notions like truth and justice -- those abilities are deeply and fundamentally connected to the real world and sensory experiences.

"Rather than thinking that abstract abilities are removed from the body -- that the mind is somehow above it all -- our work suggests that what we've learned to do throughout our evolution is to use perception in very sophisticated ways, ways we are often unaware of," Spencer said. "As society moves more and more into the virtual world of technology, we need to understand how profoundly we are influenced by small details, how much we rely on sensory experience to guide our mental decisions. Our senses are not simply input devices to our big brains. Our bodies and brains are in continual dialogue, one shaping the other, in often subtle ways."