Given the briefest of glances at a picture, most people believe they have not had time to recognize anything in it at all. Ask them whether they saw an animal and they consider themselves to be making a futile guess. Yet those guesses are right much more often than they are wrong. That is because the brain can carry out immediate visual processing even when it does not have time for any cognitive back-chatter. A neuroscientist trying to understand how people recognize objects would thus start with this simplest of systems. That is the purpose of Dr. Serre's computer. His project is nothing less than ad attempt to reverseengineer the relevant part of the brain. That part is the ventral visual pathway. Anatomy shows that it is organized into numerous areas. Experiments on monkeys, in which researchers have recorded what excites individual nerve cells in each of these areas, give strong hints about how it works. The pathway is hierarchical. Signals from the retina flow to the most basic processing area first the cells in that area fire up others in the next area, and so on. Those in the first area are fussy. They react to edges or bars in particular orientations. By combining their signals, however, cells in the second area can respond to comers or bars in any orientation. And so the system builds up. Cells in the final area can recognize general things, animals included. Dr. Serre considered his computer's processing units analogous to nerve cells, and he organized them into areas, just as they are in real brains. Then he let the machine learn in much the same way that babies do. First he mimicked early development when nerve cells are plastic. At this stage babies' brains tune their nerve cells to visual features according to how common those features am in the world around them. That is why kittens raised so that they see only vertical lines have brains that look different from those raised in an environment with purely horizontal ones. Dr. Serre's processor developed sensitivities in a similar fashion when he showed it lots of photographs. That stage complete, he then told the computer when what it 'saw' contained an animal, and when it did not. The result was a model that closely imitates the ventral visual pathway. Processing units in each area are sensitive to the same set of features as nerve cells in the brain's analogous areas, and they are linked together as they are in the brain. This artificial recognition system correctly distinguishes photographs containing animals from those without creatures 82% of the time Dr. Serre's students get it right 80% of the time. Moreover, his computer and his volunteers tend to slip up on the same images — and turning photographs on their sides makes poorer animal-recognizers out of both, by roughly the same amount. The phrase 'cognitive back-chatter' in paragraph 1 probably means ______.