Tanky Jr.

Tanky Jr. is an experimental platform for implementing strategies of positive phototaxis utilizing a single light sensor[...]. Tanky Jr. has three motors: two drive the left and right wheels respectively and the third is utilized to scan Tanky Jr.'s single light sensor left and right. To implement a feedback strategy to monitor the position of the scanning light sensor, Tanky Jr. has as additional inputs two touch sensors mounted to the left and right of the light sensor. When the robot is first turned on, its wheels remain stationary while it performs a scanning procedure. The first part of the scanning procedure is to scan the light sensor to the right until the touch sensor dedicated to that side is activated. The program then updates a variable that serves as a record of the light sensor activity at that position. Next, the sensor is scanned in the opposite direction until the other touch sensor is activated. The reading of the light sensor in this position is then compared to the previous reading. If the difference in the light readings from the left and right positions are relatively negligible, the robot then moves straight forward a brief amount, otherwise, the robot will turn a bit in the direction of the greatest light reading before making its forward motion. The robot then stops and begins another run of the scanning procedure. The alternating repetition of the above steps is quite effective in getting the robot to move toward a light stimulus such as spot of light shone on the floor from a flashlight. Equally successful is a strategy that forgoes sensory feedback in favor of efference copies. In this latter condition, Tanky Jr.'s touch sensors are removed and the program is altered so that the commands involved in the scanning procedure do not specify that the scanning motion be ceased when the touch sensors are activated, but instead be ceased after a fraction of a second. The left and right light sensor variables are updated not as a response to touch sensor feedback but instead as a response to a record of what commands have been sensed. Thus is this latter strategy describable as implementing a system that utilizes efference copies. The equivalence in performance of the efference copy and feedback solutions shows that the efference copy solution is no less representational than the feedback solution.