storage of the on-line the link are willing to tum it on. I am dual-processor machine with two beyond economical limits. not ready to trust any computer accumulators, memory buffers, Now that you have been convinced center that much, and I quite prefer memory address registers, instruction that, for my purposes and doubtless the role of standard batch-processing registers, and program counters. The for many of yours, communication user. Cheaper off-line media are core memory is shared between two with the central campus facility is unfeasible in general. Cards bend, tear, processors. The one processor can essential, why do it off-line via warp, jam machines, get out of order, function as a stand-alone PDP-S. compatible magnetic tape? Why not and go through keypunch machines Interfacing to external devices is done do it on-line, as Aiken and Millward incredibly slowly. Punched paper tape through the PDP-S processor, and the have, or via a cheaper off-line is refused handling in many computer interface described below is applicable medium? At Stony Brook, and centers and despised for its slow-down to any PDP-S computer. The doubtless at other institutions, a data characteristics by the rest. Hand advantage of using the LINC processor link to the central facility is transcription is slow, unreliable, and is in a more advanced instruction set dangerous. It ties you to the vagaries costly. and direct access to the display of scheduling, down time, routine oscilloscope, relays, sense lines, and maintenance, etc., in the central So, if you need large core memory LINCtape. facility at the best of times, and puts capacity for experimental setup or The LINC-S used in our you at the mercy of unsympathetic data analysis, but only a small capacity experiments is equipped with a 32K computer center administrations, to actually run the experiments, I urge disk, incremental tape and financial stringencies, etc., at less good your consideration of a magnetic user-designed interface.2' The times. Baldly put, a data link can only tape-drive system compatible with incremental tape is used to transfer work at those times when both ends of your central campus computer. large blocks of data (10-50K) to a larger machine for data analysis. The disk is used for storing programs, subroutines, and data during a run. The interface consists of two independent 12-bit buffered clocks. Each clock is driven by a multivibrator with one of four clock rates selected Hardware and software considerations in using by a front panel control. Each clock can generate a program-interrupt request and can be preset to any value, a LINC-8 computer in a behavioral which facilitates programming countdown procedures. The clocks can toxicology laboratory* also be run with the program-interrupt capability disabled. The behavioral interface is buffered with flip-flops so G. A. VAN GELDER and RON MUNSINGER that external events are stored until College of Veterinary Medicine, Iowa State University, Ames, Iowa 50010 the computer is ready to accept the information. This is of importance A LINC-S! computer is utilized in spindle analysis. Following when two or more independent the Behavioral Toxicology Laboratory presentation of the CS, 2 sec of EEG paradigms are being run for data acquisition and analysis from from each of the four leads were simultaneously. When anyone of the electrophysical and behavioral digitized and stored on LINC tape. flip-flops is set, i.e., an external event experiments and for real-time control The Ss' behavioral responses were also has occurred, a program-interrupt of behavioral experiments. Two monitored. Computer sense lines were request is generated and a flag is set. examples are given below. used to interface to the behavioral Control of the computer is In one experiment, the computer control system. A 500-Hz square-wave automatically shifted to the PDP-S was used to present a conditioned generator connected to one of the AID processor, and the interface servicing stimulus (CS, tone) to a sheep upon channels was used as a clock to program entered. detection of simultaneous determine latency. The user determines interrupt high-amplitude, slow-wave spindles in In another experiment, the priorities in the sequence of two leads of cortical computer logged data from a LAB-K instructions which check the device electroencephalogram (EEG). The control system (Digital Equipment flags, Because of the dual-processor sheep was placed in the operant Corporation). The LAB-K was shared-memory structure of the chamber, and four leads of EEG were instrumented for a visual LINC-S, the interface-servicing radiotelemetered to the control room. discrimination matching-to-sample subroutine transfers the status of the A paper record of the EEG was task. The hardware and software were device flags, clock values, and data obtained on a polygraph. The four developed to accommodate the buffer to specific core locations EEG signal leads were connected to following options: (1) use of a pacing addressable by the LINC processor. the inputs of the computer lever, and (2) selection of one to four The LINC program determines what analog-to-digital converter (AID). The possible visual images on any of three external event has occured and what tone source was coupled to one of the projectors. The following tasks could action needs to be implemented. The computer relays. The frequency and be implemented: (1) delayed LINC instruction group, EXC NN, amplitude EEG spindle criteria were matching-to-sample task, Operation Codes 0740-0777, has been set at the console and could be varied (2) mismatching-to-sample task, (3) a utilized to provide control of the while the program was running. Two two-choice visual discrimination task, clocks and interface from the LINC of the four EEG leads were selected at and (4) a two-choice, processor. Subroutines reside in the console for on-line, slow-wave, visual-discrimination, reversal-learning memory which interpret the particular task. Criteria for terminating a session EXC instruction, generate the *Development SUPPorted by NIH Grant ROI-ES-00122 and EPA Community were user specified and could be either necessary PDP-S lOT instructions, and Pesticide Studies Program Contract total trials or session time. return control to the LINC processor. 63-03-0036. The LINC-S computer is a For example, EXC 0 will disable the Behav. Res. Meth. & Instru., 1972, Vol. 4 (2) 101 interface in 164.25 microsec. EXC 16 letting the external event signal the NOTES will write the BCD character in the computer when information is 1. Digital Equipment Corporation. LINC accumulator onto the available. Any interface developed Maynard Massachusetts 01754. incremental tape in 159 mierosec, should have indicators, usually lamps, 2. Engineering drawings of the interface while EXC 3 will transfer contents of that indicate the status of each input, logic and software details can be obtained Clock 1 to the LINC accumulator in output, and control bit in order to from the author. 156.75 microsec. When an external facilitate debugging hardware and 3. Massey Dickinson. Saxonvflle, device requests a program interrupt, software. Massachusetts 01701. the device is serviced and control returned to the LINC processor within 170 microsec. These execution times can be reduced, but it has not been necessary when only two independent paradigms have been operated simultaneously. Most of the time, the computer is idling while waiting for real-time external events to occur CRT displays in the every second or two. Clock rates are usually 100 to 1,000 Hz. experimental psychology laboratory* Interfacing to a Massey Dickinson3 solid-state control system is handled through level converters and Schmitt PETER VAN GELDER triggers. Relay closures are handled University of Connecticut, Storrs, Connecticut, 06268 directly through Schmitt triggers. Interfacing the LAB-K is handled in The cathode ray tube (CRT) can be laboratories whose requirements for the same manner. Flip-flops are used used effectively as a general purpose multiple independent displays tempt in the LAB-K to isolate noise which visual stimulus presentation device. It consideration of a single centralized may be introduced on long cable runs. is possible to send information from a computer should heed Uttal's advice, Similarily, the level converters, to a CRT to draw any elsewhere in this issue, not to time Schmitt triggers, and buffer flip-flops picture using points or line segments share (see also Markowitz, 1969). In in the computer interface keep noise and to do it simply and cheaply. At general, experimental applications from entering the computer logic. A any instant, the picture consists of a with a need for general-purpose CRT major concern with the discrete bright fluorescent point appearing on displays can be implemented much component computer logic is to the phosphor-coated surface of the more cheaply, simply, and, therefore, observe rise time requirements. CRT, whose luminous intensity is quickly if a separate minicomputer is The following observations are proportional to the amount of dedicated to controlling each based on 3 years' experience of using a electron beam energy striking that experiment, refreshing the display laboratory computer in a behavioral point per unit of time. Any arbitrarily directly from its core memory. I a b oratory. Tasks should be complex picture can be drawn by implemented with stand-alone manipulating the three voltages which Selection hardware when possible. Thus, the determine horizontal (x axis) and The computer should be able to specialized computer is not tied up on vertical (y axis) components of the switch instantly (i.e., between one meaningless tasks and is free to be beam's location and its intensity (z refresh and the next) from one display exploited on tasks for which it was axis). One sweep of the beam creates to another, selected from among a intended. The potential user should the appearance of a brief flash. This large number of alternative displays. realize that if computer usage is to must be repeated (refreshed) to An advantageous solution is thus expand and become more innovative, maintain the appearance of a steady provided to the n-field tachistoscope then time on available systems must picture. problem (Eriksen, Shurman, & always be available for hardware and Richter, 1969; Lawrence & Sasaki, software development without CRITERIA 1970). This obvious criterion needs to jeopardizing current user research and Efficiency be mentioned because some displays, teaching programs. Time spent in The system should be capable of which change from one picture to learning computer hardware is a good presenting a complex picture (lines of another in a gradual roll-down fashion, investment. Initial time required can text, for example) with minimal are commercially available. be quite large but will payoff in the requirements of space for information long run as the user realizes he is not storage in the computer and of Precision locked to an existing system but can computer processing time to maintain "General purpose" implies the modify it at will to suit present and the steady picture. The latter problem ability to construct a picture precisely fu ture needs. Interfacing is can be eliminated by a "storage CRT" as specified by the E, free from straightforward once the fundamental which stores the information on the inherent restrictions on fine-grain skills are acquired. The user also gains face of the CRT itself until an erase detail. Such precision should be the ability to maintain his system, command is given, with a loss of achieved consistent with efficiency which, depending on availability of intensity control, some loss of spatial and ease of programming. local outside service, can be crucial to resolution, and timing problems, as the conduct of scientific inquiry. Our discussed below. Multiple independent Timing approach has been that downtime of displays can also be refreshed from For some applications, more than a few hours is of major their own common rotating magnetic millisecond-resolution timing concern and potentially a disaster in disk memory. However, large-scale capability is required. Different sets of experiments requiring large problems are encountered in display investments of time and money. onset and offset. A rigid 60-Hz refresh *Supported by a grant from the From the beginning, interfaces University of Connecticut Research rate may limit display initiation points should be developed with the intent of Foundation. to every 16-2/3 msec, for example,

102 Behav. Res. Meth. & Instru., 1972, Vol. 4 (2)