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Note from the Institute: Dr. Rogelio Escobar is a professor at the National Autonomous University of Mexico in Mexico City. He is an expert in not only the experimental analysis of behavior, but also instrumentation and the history of psychology. He recently co-authored a commentary for the Institute on Behavior Analysis in Mexico. In this commentary he describes his innovative creations with 3D printing and laser cutting technologies, something that we in behavior analysis have not previously taken advantage of in our work.
B. F. Skinner is well remembered for creating ingenious devices for studying behavior. The sine qua non example is the operant conditioning chamber also known as “Skinner’s box.” His chamber design is brilliantly simple. A hungry rat serves as the subject and its moving a metal level results in small bits of food. Using the operant chamber, Skinner meticulously arranged contingencies of reinforcement and punishment and observed regularities in behavior that no one had seen before.
During the decades following Skinner’s description of the operant chamber, these became a staple instrument in operant laboratories. Skinner´s instruments used sophisticated electromechanical systems to operate, but as new technologies became available, the operant chamber and control equipment evolved by integrating computers, electronic interfaces, and even custom-designed programming languages that simplified the job of researchers (see Escobar, 2014 for a review). This progress, however, came, literally, with a high price tag. Nowadays, grants from major funding agencies usually are necessary to acquire operant chambers. In some cases, especially in developing countries, such funding simply isn’t available. Because of this, it is not surprising that using costly operant chambers to teach students in laboratory courses is now rare.
Technological advances in electronics and manufacturing can be embraced by behavior analysts to help construct reliable, inexpensive equipment. I started a project some years ago in which easy-to-use electronics were used for controlling standard operant conditioning chambers. The purpose was to reduce the costs of equipment used in operant research and laboratory courses (Escobar & Pérez-Herrera, 2015). For the system to serve its purpose, however, it also was necessary to reduce the costs of operant chambers without compromising comparability with commercial chambers. The solution was found in 3D printing and laser cutting technologies.
Figure 1. A 3D printer.
Additive manufacturing or 3D printing has revolutionized manufacturing processes. Users can design and create solid tridimensional objects almost everywhere. Although 3D printing technology has been available since the 1980s, only recently 3D printers, like the one shown in Figure 1, became cost accessible worldwide. Ordinarily, 3D printing begins by using design software to create a tridimensional object. This object is automatically translated into a file in which the solid object can be sliced into numerous thin horizontal layers. This file is sent to the 3D printer. The 3D printer heats the printing material until it is melt and can be pushed or extruded through the tip of a nozzle. The material reaches a flat surface where it solidifies and creates a thin layer (usually from 0.1 to 0.3 mm) of the object. By adding slowly, one layer after another, the solid object is created. 3D printing can be done with a variety of materials. With an adequate printer even titanium can be used. Home-use 3D printers, however, generally print objects in PLA or ABS plastic.
This project started by creating with a computer program tridimensional models of all the parts of an operant conditioning chamber. Many programs are available but I use the free version of 123D Design (see Figure 2). The panels and supports were 3D printed using non-toxic PLA biodegradable plastic. To replicate commercial chambers as closely as possible, 8-mm stainless-steel rods were used in the floor grid. I chose these rods because they are used in 3D printers and can be acquired, and cut to the proper length, from any vendor of 3D-printer parts.
Figure 2. Tridimensional model of a section of the chamber.
The clear walls of the chamber were created using another technological development: laser cutting. Laser cutting machines are bigger and more expensive than 3D printers, but laser cutting services are inexpensive and fairly common. Laser cutters cut accurately flat sheet materials from a two-dimensional drawing of an object created with a computer program (e.g., AutoCAD, http://www.autodesk.com/education/free-software/autocad) . Two walls and the top cover of the chamber were laser cut from 3-mm acrylic (see Figure 3).
Figure 3. Drawings of the two walls and the top cover of the chamber in AutoCAD. Red lines indicate cuts to the Laser Cutting machine.
A lever was created using a 3D-printed case in combination with a stainless-steel plate and a miniature switch. An inexpensive solution for delivering reinforcement is a miniature peristaltic pump attached to a 3D-printed support that can deliver small quantities of water. I also created a food pellet dispenser that uses a small stepper motor. This dispenser delivers 45-mg food pellets. The final printed versions of the lever and feeder are shown in Figures 2 and 3. Once the parts for the chamber are ready, it takes a couple of hours to assemble the chamber using a screwdriver, a few metal screws, and glue.
Figure 4. Feeder dispenser on the back of the chamber (left), and the lever mounted on the panel (right).
My students and I tested the chambers in an undergraduate course on behavior analysis and learning at the National Autonomous University of Mexico (see http://3dprint.com/106669/3d-printed-lab-equipment). Students replicated well-known patterns of behavior by rats under fixed-ratio and fixed-interval schedules of reinforcement. We were concerned about rats chewing the plastic parts but, fortunately, we did not see this happening.
An important aspect of the project is that all the designs are available as free downloads. Anyone, anywhere in the world can print the parts, follow the instructions, and build a chamber. Additionally, users can modify the designs as needed. The files to print the parts and the instruction for assembling the operant conditioning chamber can be found at http://www.thingiverse.com/RogerEsc/designs (see Figure 5) The cost of building a 3D-printed chamber varies from place to place but an estimate on the high end for a basic chamber is 150 US dollars. The electronic control interface is approximately 80 US dollars (both dollar estimates as of February, 2016).
Figure 5. The operant chamber as shown in Thingiverse.com
Aside from building standard equipment, 3D printing could also be used also for creating new custom devices for studying behavior. Another foreseeable application is to help bring back to life instruments used in the history of behavior analysis that are no longer available. Although it remains to be seen if using such technology actually helps advancing our discipline, the initial applications show enormous potential for development.
Escobar, R. (2014). From relays to microcontrollers: The adoption of technology in operant research. Mexican Journal of Behavior Analysis, 40(2), 127-153.
Escobar, R., & Pérez-Herrera, C. A. (2015). Low-Cost USB interface for operant research using Arduino and Visual Basic. Journal of the Experimental Analysis of Behavior, 103, 427-435.
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