14 Patrick Suppes Lucie Stern Professor of Philosophy, Emeritus Stanford University, USA 1. Why were you initially drawn to computational or in­ formational issues? I begin with some history. I am not sure just when I first thought about the use of computers for computation, but I do remember the late 1950s when Dick Atkinson and I were writing a book on applications of learning models and stimulus-response reinforce­ ment concepts to simple game situations. The book is full of ex­ tended computations supported by use of the I.B.M. 650 Com­ puter at Stanford, which was one of the very earliest made avail­ able to academic communities to have the possibility of going be­ yond the old days of computing with hand calculators. We say this in the preface of Suppes and Atkinson (1960): "Evan Linick has been indispensable in programming many problems for the I.B.M. 650 Computer at Stanford; we are also indebted to Richard Hill of the Western Data Processing Center for his cooperation." This brief acknowledgement is all we had to say about what was really a first, big-time, move into computing from my own standpoint. At that time, the only task was facilitating the many statistical estimates of parameters and the like for the models introduced in the book. It is important to realize how fundamental the change was in feasible applications of statistics with the introduction of digital computers in the 1950s. Even very simple formulations of linear-programming or linear-regression problems, that were prac­ tically unsolvable, could now be used to address all kinds of inter­ esting questions in theories of behavior and social interaction. I was pleased to be on the initial wave of this range of applications (for those reading this that do not know much about my back­ ground, I have spent as much of my:time as a scientist as I have as a philosopher.) 144 14. Patrick Suppes The next step was a significant one, and in fact an important predecessor in a long career of being concerned with the use of computers for instruction. The shift from data analysis to in­ struction is conceptually a big one: this direction involved a much deeper commitment to thinking about computation in many dif­ ferent ways. It began with something rather simple: the deliv­ ery of elementary exercises in arithmetic, mainly in the form of drill and practice, initially to students in elementary schools close to Stanford. In fact, the very first experiments began early in the 1960s when John McCarthy and I, with grants we had avail­ able, shared the expense of purchasing one of the early PDP-1's from Digital Equipment Corporation. To give a flavor of early work on computers, where we were concerned with the real-time performance for instructional purposes, I quote from an early book I co-authored on these matters (Suppes, Jerman, and Brian, 1968) recounting experiences in 1965-1966. In fact, the book's title is Computer-Assisted Instruction: Stanford's 1965-66 Arithmetic Program. Here is a quotation from Chapter 9 on the nature of the time-sharing system and CAl programming: This chapter briefly describes the operating system and programming language used to implement the drill­ and-practice system. The complete process of coding, inputting, and debugging is described in connection with several examples. This description is of the op­ erating system in effect during 1966-67, which is an improvement on that running during 1965-66. For a detailed description of the general time-sharing system in effect during 1965-66, see McCarthy et al (1967). The hardware used is a highly modified PDP-1 made by Digital Equipment Corporation. The PDP-1 is a small to medium-sized binary computer with 32,000 words of 5-microsecond core memory. The system op­ erates in a general time-sharing mode. The heart of the time-sharing system is a 131,000 word­ swapping drum. Each user program is normally read into memory in turn and allowed to run for a short period of time. Then the program is re-written on the drum and the next program is brought in. This process of interchanging two user programs from core memory to drum is known as program swapping. The process takes 32 milliseconds on the PDP-l. The new program 14. Patrick Suppes 145 swapped in is commonly allowed to run for 64 millisec­ onds if it does not create some situation causing it to be terminated early. Normal early terminations will consist of things such as waiting for input or output to be completed. For example, if a program tries to read a keyboard but there has been no input on the key­ board, the program will be dismissed until the input becomes available. A program so terminated will not be swapped into memory until the cause for its termi­ nation is removed. When input which was unavailable becomes available, the program is marked active and is put back in line to be run when its turn comes. To introduce the system response cycle, we take as an example a program which reads input (such as check­ ing for a correct single character answer to a question), and then responds with some output to the teletype. The period from the time the key is struck until the printer responds with the next message from the pro­ gram is known as the system response time. This time should be fast enough to give a human user the impres­ sion that there was little or no system response time. This system response time can be compared with re­ sponse times in devices such as automatic self-service elevators and telephones (for example, dial or busy tones). A system response time longer than 1-2 sec­ onds will create impatience and disinterest, and will be very annoying to users. The 131D data channel is connected to an IBM 1301 model II random-access disk file. The total capacity of this file is on the order of 336 million bits (56 million 6-bit characters of 1S-1/2 million IS-bit words). Two independent-access arms are provided. Maximum seek (arm movement) time is 180 millisec­ onds. When the appropriate arm is positioned there is a rotational delay of 0-34 milliseconds before the transfer may begin. The average delay is 17 millisec­ onds. The transfer rate is one IS-bit word about every 35 microseconds or every seventh memory cycle. The rate is comparable with that of high-speed magnetic tape drive~. However, the relatively fast random ac­ cess has a very distinct advantage over (serial-access) magnetic tape units in a time-sharing environment, 146 14. Patrick Suppes because of the rapid switching between user programs and hence between users' files (Suppes, Jerman, and Brian, 1968, pp. 291-92). These paragraphs seem really quaint forty years later. Just about every computing device, including current cell phones, has more computer power than we had available then. There is more progress between the PDP-1 and current computer facilities widely available than there is between the earlier introduction of the Model-T Ford in the 1920s and current automobiles, a much more radical conceptual evolution over a much shorter period. Notice however, that I am still concerned here with using com­ puters to deliver a product that is different, of course, than it could ever be delivered by other means, but still delivered as a rather standard product. To emphasize how differences are possi­ ble, I stress that the important psychological measure of response latency (i.e. the time it takes for a student to make each response), can be measured and studied carefully, something that is not pos­ sible in the classroom or even, really, by an individual tutor with no computer facilities. I can elaborate on this point, but will not here. In any case, practical involvement with computers had its theo­ retical consequences, however, and during the 1960s my thinking about many conceptual questions relevant to computing changed forever. One of the things I got involved in was the controversy between behaviorists and cognitivists, or linguists such as Noam Chomsky, on the nature of the mind, about which more in answer to the next question. 2.What examples from your work (or the work of others) best illustrate the fruitful use of computational and/or in­ formational approach for foundational researches and/or applications? The appearance of Chomsky's famous review (1959) of Skinner's Verbal Behavior (1957), marked a change that proved permanent in the acceptance of behaviorism, in particular the learning theory, of the stimulus-response variety that was dominant in American psychology from the 1920s to the latter part of the 1950s. Skin­ ner's Verbal Behavior, with its non-mathematical formulation, but with rather strong claims made in much too qualitative and vague a way, was an easy target for Chomsky's detailed critique. One of 14. Patrick Suppes 147 the primary effects was to disturb, again in a way that was a per­ manent change, the theoretical complacency of many behavioral psychologists. Since I followed this development rather closely, because of my attempts with Bill Estes and others to give a sharp mathematical formulation of stimulus-response theory, I was sometimes called "the white knight of behaviorism". Very early in the 1960s, I re­ member a famous public debate I had on these questions with Chomsky at Stanford. The aisles were crowded, there was no place to sit down, the students were enthralled, not because of me, but because of Chomsky.