Model-guided Line Drawing in the Chimpanzee (Pan troglodytes)
Iver H. Iversen, Tetsuro Matsuzawa
Two female chimpanzees (Pan troglodytes) had been taught previously to draw straight lines on a touch-sensitive monitor with a method of electronic finger painting. Both subjects could accurately connect two guide dots on the monitor by placing the finger at one dot (startdot) and moving the finger over to the other dot (stopdot), thereby leaving a trace of “electronic ink" on the monitor that followed the orientation of the dots (horizontal, vertical, or diagonal). In Experiment 1, the subjects were connecting the two guide dots while a model (a 12-cm bar) was placed next to them. Probe trials tested whether this model would guide drawing when one or both of the dots were removed. One subject was able to draw parallel to the model on some of the test trials without the stopdot while the other subject showed no such behavior. In Experiment 2, the latter subject was explicitly trained to draw parallel to the model while the stopdot was gradually faded away. In an attempt to improve accuracy of drawing parallel to the model for both subjects, Experiment 3 presented only three models (vertical and the two diagonals) and one startdot location; in addition, the subjects could make multiple strokes on each trial. Both subjects, especially the chimpanzee given extra training in Experiment 2, were able eventually to draw a trace that was guided by and therefore parallel to the model. The results provide evidence that the chimpanzee can be taught a simple form of structured drawing guided by a model. The fully automated recording and teaching method induced quite accurate elementary copying behavior in chimpanzees without the use of verbal instruction, demonstration, or manual assistance.