The cognitive psychology of categorizing the animate and inanimate
When I think of my interests as a preschooler and kindergartner certain images form in my head, most of them recalling my avant-garde portraiture, a somewhat violent obsession with dinosaurs, and frequent daydreaming about bringing my pet lizards (carefully named “lizard” and “lizzy”) into class and unleashing them into a frenzied, screaming room. Like most children, I was keenly interested in living things.
There is no doubt that early in their lives, children show a certain distinct concern for animate objects. That’s not to say they don’t show an eager interest in inanimate objects as well. At any rate, research has shown that children as young as 4 years old have a rather sophisticated understanding of the difference between what is alive and what is not (though they surely make mistakes…see Piaget’s 1929 work on “animism”). Young children usually understand that plastic shovels do not feel sad or run away from home, that’s the business of cats and dogs; and pigeons are not meant to be picked up and used to displace sand, that‘s the business of plastic shovels.
There is a good deal of debate about the structure, evolution, and development of the inanimate-animate distinction. It is generally thought to be an evolved cognitive mechanism, though there is some strong backlash to that idea (Farah et al resolutely referred to the idea of an evolved ability to distinguish animate and inanimate objects as, “an a priori implausible hypothesis.” backlash, indeed). Either way, many cognitive scientists aspire to achieve a more thorough understanding of this ability, and some compelling new research out of Harvard has produced some strange, though telling, results.
It is known that separate regions of the ventral visual pathway categorize objects as nonliving and living. Different groups of cells in different regions of the ventral visual pathway respond to either inanimate (medial ventral stream) or animate (occipital-temporal cortex) objects. Furthermore, while other sensory modes play a role (like hearing and touch), visual cues, especially about the movement of objects, are thought to be central to the animate/inanimate categorization ability. Whether this “neural specialization” is formed by sensory experience or is built into the architecture of the brain is not known, though new work by Mahon et al (2009) implies the latter.
By comparing groups of blind and seeing adults, Mahon et al came to the startling conclusion that living vs. non-living categorization in the ventral visual pathway does not require visual experience. When prompted to think about living and non-living objects, subjects who were blind since birth showed overlapping fMRI BOLD (blood oxygen-level dependent) responses with the sighted subjects; that is, the areas of the visual cortex that categorize differences between inanimate and animate objects in seeing adults appears to function identically in congenitally blind adults. How is this possible? How can an individual that has never seen a dog, a person, or a chair (or anything at all) show object categorization in the visual areas of their brain?
Mahon et al believe they’re close to an answer. They write:
“One framework that can accommodate our findings views category-specific regions of the ventral stream as parts of broader neural circuits within the brain that are innately disposed to handle information about different domains of objects (Mahon et al, 2009, emphasis added).”
In other words, the brain doesn’t need visual experiences to categorize living and non-living things because it is built to do so before birth. Visual experience may act to increase the resolution of this categorization and provide the individual with real-world examples, but it is not required to initially shape the visual cortex.
This idea is inspired by the “domain-specific” approach to cognitive psychology, which maintains that evolution shapes specific cognitive programs that help elicit specific behaviors in the animal that are relevant to specific pressures from the environment.
According to this line of thought, the brain is much like a cluster of machines within a machine. These machines communicate with and rely on each other, but also have their own distinct functions. Each “machine” helps to enhance the evolutionary fitness of the animal: One machine helps us recognize faces in order to facilitate complex social interactions, another machine helps us recognize depth so we avoid fatal falls (my “depth machine” is particularly sensitive), and perhaps another builds animate vs. inanimate categories into our visual system, thus making it easier for us to notice that important difference in the world, and tell, say, predator from landscape.
To end with a digression, I propose that the amusing nature of an erroneous or confused calculation by our “animacy machine” could be a product of the machine’s innateness. Moments when we swear our clocks are looking at us, sigh at wilting flowers, or believe our computers are malicious villains meant to tirelessly test our patience, are exceptionally resonant, and that may be because they go against the grain of a normal pattern of thought. Perhaps it is due to our instinctual and skillful classification of the living and non-living that we find wit in animating the inanimate.