Everything that we know about the visual world is built from the sequences of discrete electrical pulses that stream from eye to brain along the roughly one million individual cables that form the optic nerve. Until recently, when scientists wanted to "listen in" on these signals, all they could do was to monitor one cable or cell at a time, getting only a very limited view of the messages being passed through the visual system. In particular, this left us literally and figuratively blind to the possibility that combinations of pulses from neighboring cells could have special meaning. The emergence of experimental techniques for recording the signals from many cells simultaneously, under reasonably natural stimulus conditions, thus offers an unprecedented opportunity to explore the full complexity of the raw data that the brain has to work with as it tries to understand what we see. Indeed, the most recent generation of multi-electrode array technologies achieves a sampling efficiency that should allow recording from nearly all of the cells in a small patch of the retina, providing access to all of the signals that the brain can use in making sense out of the corresponding small patch of the visual world. The goals of this project are to develop in tandem the experimental methods to realize this promise and the theoretical framework for understanding the problem that the brain has to solve in dealing with these data.
Even a relatively small group of twenty cells in the eye can send millions of possible signals to the brain. Just as not all combinations of twenty letters constitute real words or phrases in English, we expect that not all combinations of pulses from nearby cells actually are used. Building on preliminary results, we will develop the mathematical tools required to describe the analog of spelling rules for these neural words. What we intuitively think of as a surprising event presumably is represented by a rare word, and we will push our understanding of the relative frequencies with which the different words are used so that we can identify reliably the signals that the brain must recognize as surprising. In a similar direction we will examine how one word predicts the next, and how the brain could effectively separate the predictable from the surprising. We will compare these theoretical descriptions with what is known about brain's mechanisms for detecting such events. Improving our instruments in parallel with these mathematical developments will allow us to deal not just with twenty cells but with roughly two hundred, where the number of possibilities truly becomes astronomical.
Historically, studies of the retina have provided the conceptual foundations for work on many different areas of the brain, and we thus expect that the results of this project will help understand not just the language that the eye uses in describing the world but also provide a general set of tools for exploring the way in which many cells cooperate to shape our perceptions and thoughts.
