text: Caitlin pushed the button on her eyePod, switching back to simplex mode. The glowing lines of webspace were replaced by what she'd dubbed "worldview"—the reality she shared with the rest of humanity, which, just then, consisted of her blue-walled bedroom with multicolored autumn leaves visible through the window.
  
  Her mother entered, having crossed the hallway from her office.
  
  Blue letters were glowing in her notebook's IM window: Thank you, Caitlin!
  
  Caitlin typed back, Whew! You're welcome! You OK now?
  
  I believe so.
  
  Don't do that again. Don't try to multitask, or form multiple links.
  
  I won't. But I would like to know what went wrong.
  
  So would I, Caitlin typed—but her mom gave it more direct voice, demanding: "What the hell happened?"
  
  Kuroda was still on the speakerphone from Tokyo. "As Miss Caitlin said, it was multitasking."
  
  "So?" replied her mom. "Computers do that all the time."
  
  "Forgive me, Barb," Kuroda said, "but, first, Webmind is not a computer, and, second, no, they don't."
  
  Dr. Kuroda is explaining, Caitlin sent to Webmind. Here—I'll type in what he says.
  
  "A typical computer," continued Kuroda, "seems to be doing many different things at once, but it's only an illusion due to its incredible speed. Up until recently, few computers had more than one processor, and that single processor only ran one program at a time. In order to apparently multitask, the processor switched rapidly between programs, devoting little slices of time to each program in succession, but it never actually did multiple things simultaneously."
  
  Caitlin was a fast typist; typing what the teacher said was how she took notes in school, so transcribing Kuroda for Webmind, with only a few omissions, wasn't hard.
  
  He went on: "More modern computers do have multicore processors or multiple processors which can, to a very limited degree, do more than one job at once... provided that the programs have been written to take advantage of this ability, which often isn't the case. But computers are dumb as posts; they don't think, and they aren't conscious. And consciousness, you see—and I mean precisely that: you see—is incompatible with multitasking."
  
  Her mom walked over to the desk and sat on the swivel chair. "How come?" she said.
  
  "I'm a vision researcher," Kuroda said, "so my take on all this is perhaps skewed." But then his tone changed, as if he were tiptoeing around a delicate subject. "I know you are Americans, and, um, you're from the South, I believe."
  
  Caitlin paused typing long enough to say, "Don't mess with Texas."
  
  "Um, do you... do you believe in evolution?"
  
  She laughed, and so did her mom. "Of course," her mom said.
  
  Kuroda sounded relieved. "Good, good, I—forgive me; I'm sure we don't get an accurate picture of America here in Japan. You know we evolved from fish, right?"
  
  "Right," said Caitlin, and then she went back to typing.
  
  "Well," said Kuroda, "let's consider that ancestral fish: it had two eyes, one on each side of its head. And it therefore had two different fields of view—and they didn't overlap at all. It simultaneously had two perspectives on its world, yes?"
  
  "Okay," said her mom.
  
  "Somewhere along the line," Kuroda continued, "evolution decided that it was better to have those fields of view overlap, because that gave depth perception. Prior to that, our fishy ancestor pretty much had to assume that if two other fish were in its fields of view, the bigger one was closer. But, in fact, the bigger one might actually be bigger but be farther away; the small one might be close by, and be about to take a bite out of you. By the time that fish had evolved into a mammal-like reptile, it had overlapping fields of vision, and that gave it depth perception. And even though overlapping visual fields meant a narrowing of the angle of view, the advantages of perceiving depth outweighed that loss."
  
  "Hang on a minute," Caitlin said. "I'm transcribing what you're saying for Webmind... okay, go on."
  
  "Along with stereoscopic vision," Kuroda said, "suddenly the notion of looking at this as opposed to that—of shifting one's gaze, of concentrating one's attention—was born. Our very words for describing consciousness come from this: attention, perspective, point of view, focus."
  
  Caitlin paused typing long enough to think about the book she'd recently read at the suggestion of Bashira's dad: The Origin of Consciousness in the Breakdown of the Bicameral Mind by Julian Jaynes. It wasn't quite the same argument, but it amounted to the same thing: until all thought was integrated—until there was just one point of view—real consciousness couldn't exist.
  
  Maybe Kuroda was contemplating the same thing because he said, "In fact, although our brains consist of two hemispheres, they go out of their way to consolidate thought into a single perspective. You know what they say: the left hemisphere is the analytical or logical side, and the right hemisphere is the artistic or emotional side, yes?"
  
  "Yes," said her mom, and "Right," said Caitlin.
  
  "Forgive me, Miss Caitlin. I know you have vision in only one eye, but, Barb, if you were to read text with just your left eye, shouldn't you have an analytical response, while if you read it with your right eye, shouldn't the response be more emotional? Shouldn't we give each student an eye patch, and tell them to move it to the left or the right depending on whether they're reading a physics textbook or a novel for their literature class?"
  
  Caitlin thought about this. She'd once asked Kuroda why he had chosen to put his implant behind her left retina instead of her right one. He'd joked it was because Steve Austin's left eye had been the bionic one—which had sent her to Google to find out what he meant.
  
  "But we don't do that," Kuroda went on. "We don't give students eye patches—because the brain responds exactly the same way regardless of which one of the two eyes is receiving the input. That's because your left optic nerve does not feed just into your left hemisphere, nor does your right optic nerve feed just into your right hemisphere. Rather, each optic nerve splits in two in the center of the brain at the optic chiasma in what's called a partial decussation. Half the signal from the left eye goes to the left hemisphere, and the other half goes to the right. It's an awfully complex bit of wiring, and evolution doesn't do things that are complex unless they confer a survival advantage."
  
  He paused, as if waiting for Caitlin or her mom to chime in with what that advantage might be. After a moment, he went on, his voice triumphant: "And that advantage must be consciousness, must be the unification of sensory input to produce a single perspective, a single point of view."
  
  "But I was born blind," said Caitlin, letting her fingers rest. "And I've been conscious my whole life without the sharing of sight across both hemispheres."
  
  "True, but your brain was hardwired for it regardless. I've seen your MRIs, remember—you've got a perfectly normal brain; the only flaw you were born with was in your retinas. Anyway," he said, and she resumed typing, "evolution went out of its way to make sure we've only got one perspective, one point of view. A bird can't fly both left and right at the same time; a person can't think about both this and that at the same time. Consciousness is singular. It's cogito ergo sum, I think, therefore I am; it's not cogitamus ergo sumus—it's not we think, therefore we are. Even in cases of a severed corpus callosum, the brain still retains its single perspective; again, evolution has gone out of its way to make sure that unitary consciousness survives even something as traumatic as cutting the major communications trunk between the hemispheres."
  
  Caitlin's mom looked at her but said nothing. Dr. Kuroda went on. "And it's not just that a directional perspective gives rise to your own consciousness; it also gives rise to your awareness that others have consciousness, too. It's what's called theory of mind: the recognition that other people have beliefs, desires, and intentions of their own, and that those might be different from yours. And, again, that comes from you having a single point of view."
  
  "How so?" asked Caitlin's mom.
  
  "It's only because you have a limited perspective that you understand that the person facing you must be seeing something completely different from what you're seeing as you face him. Are you in Miss Caitlin's room now?"
  
  "Yes," said her mom.
  
  "Well, if we were facing each other there, you might be seeing the window and the outside world, and I might be seeing the door and the hallway beyond—not only are we seeing completely different things, but you understand that we are. Your limited perspective lets you know that my point of view is different. And there are those terms again: 'perspective, ' 'point of view'! Thought and vision are inexorably connected in our brains."
  
  "But what about blind people?" asked Caitlin, taking another break from typing.
  
  "Again, you don't actually need the vision, just the neural infrastructure geared for a single point of view." He paused. "Look, if having eyes in the back of our heads really was an improvement, we'd have them. Mutants with extra eyes are born periodically today, and probably have been throughout vertebrate history—and if that had conferred a survival advantage, the mutation would have spread. But it didn't. Having one point of view—having consciousness and being able to understand that what the predator sees is different from what you see—trumps even being able to see things approaching you from behind."
  
  Caitlin was wrestling with the implications of this, but it was her mother who got it first. "And Webmind sees through Caitlin's eye, right? Caitlin is his window on our world."
  
  Caitlin found herself looking down, pleased but a tad embarrassed that the conversation had suddenly come around to her, and—
  
  And she saw what Webmind had written at the end of her transcript of Kuroda's comments, glowing blue: You really did uplift me. You gave me the perspective and point of view and focus I needed to become truly conscious. Without you, I wouldn't exist.
  
  Caitlin looked up and allowed herself a warm, satisfied smile. "Go me!" she said.