Funded Grants

The Perception of Animate Form: Probing the Neural Basis of Cognition

Movement is a fact of life. Try to imagine living in a world where neither you, nor anything around you, were animate. Even if you could fathom such a world, it would be senseless, literally, because there would be no way to affect your surroundings and thus there would be no need to sense anything at all. Of course no organism lives in such conditions. To be capable of perceiving one's place in the world and the actions and behaviors of other objects is of immense importance to all animals. It turns out that of the six senses (we include kinesthesia, or the sense of body position and movement, which is often overlooked as a primary sense), primates have become particularly dependent on the sense of sight, and a disproportionate amount of the primate brain appears to be involved in vision.

Because humans are so dependent on vision, significant scientific effort has been directed at understanding how we perceive the world through our sense of sight. The process of vision, of course, begins at the eye, and as far as the brain is concerned, at the eye's retina. From this starting point, many people conceive of the problem of vision as converting the retinal image into percepts and then into recognized wholes. This snapshot view of vision, where the eye is likened to a camera and the brain likened to a computer, may be an intriguing analogy, but it largely ignores the fact that we live in a dynamic, not a static, world. What makes the world's great photographers special is that they are uniquely capable of capturing the essence of their subject in a single frame. Fortunately, since most of us are rather amateur photographers, we don't have to depend on these once in a lifetime snapshots. Instead, we are adept at appreciating the subtle, or not so subtle, dynamics present in the world.

How our nervous systems extract a coherent view of a complex, dynamic world is still unknown. Observations of children with autism, a pervasive developmental disorder, suggest that these individuals may lack the kind of global coherence most people simply take for granted. Consider the description of Jerry, a young boy with autism, by Uta Frith (from Autism: Explaining the Enigma): "Nothing seemed constant; everything was unpredictable and strange. Animate beings were a particular problem". Frith argues that the central deficit in autism is an inability to cope with the sensory complexities encountered in everyday life, which stems from a fragmented perception of the world. The social and communicative difficulties presented by autistic individuals emphasize the importance of creating a coherent, or unified, impression from a dynamic array of sensory impressions. The research objectives presented in this project are aimed at addressing this relatively neglected aspect of brain science. In particular, we will explore how primates, both human and non-human, abstract meaningful events from the animate actions of other forms. We stress that perceiving the actions of others is by no means a capacity unique to humans. Many animals live in environments where the activity of prey, predators, or conspecifics must be constantly evaluated. In primate social groups, individuals can clearly make use of the behavioral cues of others to guide their own actions. Vervet monkeys, for example, elicit characteristic calls following detection of a predatory eagle, leopard, or python, and the acoustic properties of the call is used by other monkeys seek safe haven depending on the particular enemy's natural route of attack. Similarly, primates are keenly sensitive to the gestural signals displayed by others, the properties of which can be used to predict impending behavior or to assess social status.

Our goal in the proposed research program will be to walk the fine line between ecologically valid fieldwork and traditional laboratory science. We believe that to uncover the mechanisms involved in the processing of dynamic, realistic events, like those encountered in the real world, an animal must be tested in these conditions. The technology boom of the last twenty years has brought with it the possibility of creating at least virtual renditions of these complex worlds in the laboratory. Virtual three-dimensional objects, with associated animate behaviors, can be created and presented on graphics hardware in a way that subjects can learn to identify these objects based on their structural composition or their actions. Because these stimuli are computer generated, subtle aspects of their form and articulated motion can be systematically manipulated, and an observer's ability to detect these changes can be assessed. One look at a child engrossed in any current video game adventure and it is clear that these environments, and their associated inhabitants, can be very real indeed.

Our initial aim will be to demonstrate that monkeys are inherently capable of learning to recognize the actions of novel, realistic objects. From this starting point we will embark upon the second component of our research plan, which is to better understand the role the brain plays in this process. Significant progress has been made in describing the basic properties of individual neurons--the nervous system's building blocks--in the primate brain. One of the great discoveries in the last forty years is that is possible to record, in a pain-free way, the activity of these cells in the behaving brain. In this way, it has been possible to directly relate the response of single cells to the perceptual and motor activity of the whole animal. Currently, however, most of this information has been acquired under extremely simplified conditions. This cautious approach is understandable, since it seems hardly believable that the actions of single cells could ever be directly linked to more complex situations. We have recently found, though, that in the domain of vision, the activity of single neurons in the temporal lobes of monkeys is clearly related to the act of noticing familiar targets, even when these objects are hidden in complex naturalistic scenes. Furthermore, these findings were made under conditions where monkeys could freely scan these scenes. The results augmented data from our earlier work, which showed that neural activity in these areas was best correlated with the perceptual state of the animal, and not the physical stimulus imaged by the eyes.

Encouraged by these findings, we believe it will be possible to relate the activity of single neurons, and groups of neurons, to some of the fundamental problems in visual cognition. By studying the problem of perceiving animate form, we will be forced to think about how the brain groups dynamic patterns of optical information into coherent acts. By training monkeys to differentiate between behaviors like BOUNCING or FLIPPING or FROWNING, can we then determine how the brain encodes these recognized actions? Will these representations be independent of the underlying objects performing the actions? Can these representations be detected in the activity of single cells, or only in the conjoint activity of populations of cells? Can we watch these representations develop as new objects and actions are first encountered and then learned? And if we do find answers to these questions, can they help us understand how such circuitry may malfunction?

One might ask whether the physiologist's reductionist methodology is appropriate for asking questions of cognitive function. How can the records of neural activity from a tiny proportion of nerve cells hope to offer any insights that cannot be deduced from behavior alone? Our view is that if these studies are carried out at the very same time that the capacities at issue are being demonstrated, we do have a chance of observing not just that, but also how, the brain makes sense of a complex world. In doing so, we hope to better understand what Huxley called "Man's place in nature".