People Search for Thoughts Like City Rats Search for Garbage

Searching for specific memories is a universally annoying shared human experience, and also a mystery.

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Feb 15 2012, 8:26pm

You know when you're desperately trying to recall the name of that acquaintance with the lazy eye and cartoonishly high-magnification glasses, the color of your first winter jacket from when you were five, or that weird looking actor who played the villain's sidekick in that movie with the guy and the stuff? Searching for specific memories is a universally annoying shared human experience, and also a mystery – how do we search our memory? How, in the dense swamp of a human brain, can a single thought be plucked out like a scrumptious little fish?

Thomas Hills and his team at the University of Warwick in the UK, and Indiana University, have an interesting answer. They argue that the human strategy used to hunt for thoughts is eerily similar to the evolved foraging pattern used by many birds and mammals looking for a meal. Like a squirrel searching a certain patch of land for acorns, or, closer to my world in New York City, a rat inspecting a block for succulent, moist garbage, humans similarly sniff around their clusters of memories.

Mills and his team conducted an experiment that asked subjects to name as many objects in a given category (i.e. "animals" or "vehicles") as they could in three minutes. Using established statistical models of the associations of certain human thoughts (i.e. "dog" and "wolf"), they found that people who stayed in one general "patch" of associated memories weren't able to name as many objects as those that found the right time to change to new "patches" of memories. The results looked like a very familiar strategy found elsewhere in nature. Mills recounted this idea in a statement:

A bird's food tends to be clumped together in a specific patch – for example on a bush laden with berries. But when the berries on a bush are depleted to the point where the bird's energy is best focused on another more fruitful bush, it will move on. When faced with a memory task, we [humans] focus on specific clusters of information and jump between them like a bird between bushes. For example, when hunting for animals in memory, most people start with a patch of household pets—like dog, cat and hamster. But then, as this patch becomes depleted, they look elsewhere. They might then alight on another semantically distinct 'patch', for example predatory animals such as lion, tiger and jaguar.

The strategy Mills is explaining, called the marginal value theorem of foraging patterns, is nature's ace up the sleeve. It is, essentially, an evolved instinct to recognize diminishing returns, and can been seen in everything from egg sizes in birds to the curious phenomenon of optimal courtship persistence in mammals. It looks like we can add human mind-searching to the list.

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