Figure 3.
Schematic of the bio-robotic software algorithms and hardware, i.e., MEART's components. Commanding movement: The center of activity (CA) of neuronal action potentials was calculated from 100 ms of responses after a probe stimulation (8 × 8 box representing the MEA; increasing firing rate is black to white). Animat movement was instructed from a transformation () of the CA into a population vector. The [X,Y] movement command was sent over the internet (yellow arrows) to the robotic arms every 4 seconds. Movement: The robotic drawing machine consisted of two perpendicular arms actuated by braided pneumatic artificial muscles, allowing independent retraction (R) or extension (E) of the left (EL/RL) and right (ER/RR) arms within approximately a 30 cm by 30 cm workspace. Similarly, smaller muscles pressed the pens to the paper when at the target location (T), or optionally to trace movement trajectories (M). The supply line from an air compressor was split between three pressure regulators (green circles, one for each arm and one for the pens). 24 V AC pneumatic valves (light blue rectangles) controlled muscle air pressure. Joint encoders (purple arrows; 10 k potentiometers) tracked arm location, and a BASIC Stamp microcontroller (BS2SX-IC) modulated the relay valves to provide accurate movement as commanded by the neurons' activity. Sensory feedback: A CCD camera located above the workspace captured an image of accumulating markings every 5 minutes. The images were pixelated into 8 bit grayscale values (isomorphic to the electrodes on the MEA) and sent back over the internet to command feedback stimulation of the neurons. Training: Animat behavior was compared to the goal behavior to control training stimulation. Feedback stimuli could change neuronal activity, in turn varying subsequent animat movement and sensory feedback, thus forming a closed-loop system. TCP/IP sockets were used to communicate between the drawing robot and the neuronal network, which were often located on separate continents.