Internal Rehearsal System

The Internal Rehearsal System is a module of the Central Executive Agent (CEA) within ISAC’s cognitive architecture. This module is based largely on Hesslow’s “simulation hypothesis”. Hesslow’s hypothesis states that human beings are able to internally perceive and manipulate their environment. Humans are able to perform internal motor movements, internally perceive objects, and anticipate or predict future events [1]. The Internal Rehearsal System (IRS) is used to predict consequences to actions if they are performed by ISAC in real life. Figure 1 shows an example of this concept.

Figure 1: Internal Rehearsal Concept

The left side of figure 1 shows ISAC observing two objects, a Barney toy and a Lego top box. ISAC is given a task “Reach to Barney”. During this time, Barney becomes the goal object and the Lego top box becomes the obstacle. ISAC must determine how to reach to the Barney without the arm colliding into the Lego object.

In order to accomplish this task, ISAC uses IRS. This is seen in the right hand side of the figure. ISAC has three reach behaviors that it can use to accomplish the reach task: a regular right reach, a reach right around, and a regular left reach. During the internal rehearsal, IRS predicts that both right reaches will lead to a collision with the Lego object, and this information is sent to the CEA. IRS uses a collision sphere technique to predict collisions inspired from Charoenseang’s research [2].

ISAC’s cognitive system (Central Executive Agent) decides to discard these first two behaviors, and use the third behavior or regular left reach. The end result is that ISAC will use its left arm to reach to Barney. This allows ISAC to completely avoid the Lego obstacle while accomplishing the task.


1. Hesslow, G. “Conscious thought as simulation of behavior and perception”. Trends in Cognitive Science, 6(6). 242-247. 2002.

2. Charoenseang, S. “A PC-Based Virtual Reality System For Dual-Arm Humanoid Robot Control”, Ph.D. Dissertation, Vanderbilt University, 1999.