"eğer önündeki kapılar bir daha yüzüne kapanacak olursa, hayatının sona ermediğini düşün. sona eren şey yalnızca hayatlarının birincisidir ve diğeri başlamak üzere sabırsızlanmaktadır. o zaman bir gemiye bin, seni bekleyen bir kent vardır."

(bkz: tanios kayası)

once information is "in mind," protected from temporal decay, can it enter into specific operations? do some cognitive operations require consciousness and lie beyond the scope of our unconscious thought processes? the answer seems to be positive: in humans at least, consciousness gives us the power of a sophisticated serial computer.

for instance, try to compute 12 times 13 in your head.

finished?

whatever strategy we use, we can consciously report it. and our report is accurate: it can be cross-validated by behavioral measures of response time and eye movements.

such accurate introspection is unusual in psychology. most mental operations are opaque to the mind's eye; we have no insight into the operations that allow us to recognize a face, plan a step, add two digits, or name a word. but somehow multidigit arithmetic is different: it seems to consist of a series of introspectable steps. i propose that there is a simple reason for it. complex strategies, formed by stringing together several elementary steps -- what computer scientists call "algorithms" -- are another of consciousness's uniquely evolved functions.

would you be able to calculate 12 times 13 unconsciously if the problem was presented to you in a subliminal flash? no, never. a slow dispatching system seems necessary to store intermediate results and pass them on to the next step.

the brain must contain a "router" that allows it to flexibly broadcast information to and from its internal routines.

this seems to be a major function of consciousness: to collect the information from various processors, synthesize it, and then broadcast the result to other, arbitrarily selected processors.

these processors, in turn, apply their unconscious skills to this symbol and the entire cycle may repeat a number of times.

together with the physicists, i have begun to explore the computational properties that such a device would possess. it closely resembles what computer scientists call a "production system," a type of program introduced in the 1960s to implement artificial intelligence tasks.

with its massively parallel, self-modifiable organization, capable of computing over entire probability distributions rather than discrete symbols, the human brain departs radically from contemporary computers.

when we zoom in on human behavior, we see deviations from its predictions. instead of being neatly separate in time, successive stages slightly overlap and create an undesired cross-talk among operations. during mental arithmetic, the second operation can start before the first one is fully finished. jerome sackur and i studied one of the simplest possible algorithms: take a number n, add 2 to it (n + 2), and then decide if the result is larger or smaller than 5 (n + 2 > 5?) we observed interference: unconsciously, participants started to compare the initial number n with 5, even before they had obtained the intermediate result n + 2. in a computer, such a silly error would never occur; a master clock controls each step, and digital routing ensures that each bit always reaches its intended destination.

the brain, however, never evolved for complex arithmetic. its architecture, selected for survival in a probabilistic world, explains why we make so many errors during mental calculation. we painfully recycle our brain networks for serial calculations, using conscious control to exchange information in a slow and serial manner.

if one of the functions of consciousness is to serve as a medium for the flexible routing of information across otherwise specialized processors, then a simple prediction ensues: a single routinized operation may unfold unconsciously, but unless the information is conscious, it will be impossible to string together several such steps. in the domain of arithmetic, for instance, our brain might well compute 3 + 2 unconsciously, but not (3 + 2) ^3, (3 + 2) - 1, or 1 / (3 + 2). multi-step calculations will always require a conscious effort.

sackur and i set out to test this idea experimentally. we flashed a target digit n and masked it, so that our participants could see it only half the time. we then asked them to perform a variety of operations with it. in 3 different blocks of trials, they attempted to name it, to add 2 to it (the n + 2 task), and compare it with 5 (the n > 5 task). a fourth block required a two-step calculation: add 2, then compare the result with 5 (the n + 2 > 5 task).

on the first 3 tasks, people did much better than chance. even when they swore they hadn't seen anything, we asked them to venture an answer, and they were surprised to discover the extent of their unconscious knowledge. they could name the unseen digit much better than chance alone would predict: nearly half of their verbal responses were correct, whereas with 4 digits, guessing performance should have been 25 percent. they could even add 2 to it, or decide, above chance level, whether the digit was larger than 5. all these operations, of course, are familiar routines. there is a lot of evidence that they can be partially launched without consciousness.

crucially, however, during the unconscious two-step task (n + 2 > 5?), the participants failed: they responded at random. this is strange, because if they had just thought of naming the digit, and used the name to perform the task, they would have reached a very high level of success! subliminal information was demonstrably present in their brains, since they correctly uttered the hidden number about half of the time -- but without consciousness, it could not be channeled through a series of two successive stages.

all together, then, these experiments point to a crucial role for consciousness. we need to be conscious in order to rationally think through a problem. the might unconscious generates sophisticated hunches, but only a conscious mind can follow a rational strategy, step after step. by acting as a router, feeding information through any arbitrary string of successive processes, consciousness seems to give us access to a whole new mode of operation -- the brain's turing machine.

in brief, within the human brain lies a set of neural structures uniquely adapted to the representation of our social knowledge. we use the same database to encode our self-knowledge and to accumulate information about others. these brain networks build a mental image of our own self as a peculiar character sitting next to others in a mental database of our social acquaintances. each of us represents "oneself as another".

if this view of the self is correct, then the neural underpinnings of our own identity are built u in a rather indirect manner. we spend our life monitoring our behavior as well as that of others, and our statistical brain constantly draws inferences about what it observes, literally "makign up its mind" as it proceeds.

learning who we are is a statistical deduction from observation. having spent a lifetime with ourselves, we reach a view of our own character, knowledge, and confidence that is only a bit more refined than our view of other people's personalities. furthermore, our brain does enjoy privileged access to some of its inner workings. introspection makes our conscious motives and strategies transparent to us, while we have no sure means of deciphering them in others. yet we never genuinely know our true selves. we remain largely ignorant of the actual unconscious determinants of our behavior, and therefore we cannot accurately predict what our behavior, will be in circumstances beyond the safety zone of our past experience. the greek motto "know thyself," when applied to the minute details of our behavior, remains an inaccessible ideal.

our "self" is just a database that gets filled in through our social experiences, in the same format with which we attempt to understand other minds, and therefore it is just as likely to include glaring gaps, misunderstandings, and delusions.

consciousness is the mind's virtual reality simulator. but how does the brain make up the mind?