# INST 354 Lecture Notes - Lecture 3: Biological Neuron Model, Mental Calculation, Steven Pinker

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There has been a modest revolution in the sciences of the mind during the past half-

century. A new field has emerged, named cognitive science, with a new

conceptual paradigm for theorizing about human thought and behavior (Gardner, 1985;

Pinker, 1997). The computational model of the mind is based on the assumption that

the essence of thinking can be captured by describing what the brain does as

manipulating symbols. (Note that we say, “the essence of thinking.” We do not mean to

imply that the brain itself literally manipulates symbols.) The computational model is

obviously inspired by an analogy between the computing machine and the computing

brain, but it is important to remember that it is an analogy. The two devices, brains and

computers, perform similar functions, relating input information to output information (or

actions) in an amazingly flexible manner, but their internal structures are quite different

(most obviously, electronic circuits and biological neurons operate quite differently).

The central concept in the notion of a computational model is the manipulation of

symbolic information. Perhaps the classic example of a cognitive process is the

performance of a mental arithmetic task. Suppose we ask you to solve the following

addition problem “in your head”: 434 + 87 = ???

If we asked you to think aloud, we might hear something like the following: “Okay, I

gotta add those numbers up, uh ... 4 + 7, that’s 11 ... write down the 1, and let’s see,

carry the 1 ... ummmm ... so 3 + 8 equals 11, again, but I gotta add the carry, so that’s

12, and uhhhh ... write down the 2 and I gotta carry a 1 again. Now 4, that’s 4, but I

have to add the carry, which was 1, so that’s 5, write down the 5. So, that’s 521. Does

that look okay? Yeah, the answer is 521.”

Another controlled, deliberate method that one of us (Dawes) uses is to “work down”

from the highest multiples of 10, while making a list of “remainders” in “another part of

the head.” Thus, 434 + 87 is equal to 400, with 34 and 87 remaining. The 87, being

larger, is attacked first as 100 minus 20, with a 7 left over. So we now have 400 + 100 –

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