ABSTRACT
If we ask ourselves, what sets the human species apart in the animal kingdom, a variety of answers come to mind. The capacity to make skilful manipulatory movements – to direct action at objects, handle objects, assemble and reshape objects – is one of the possible answers. We are amazing movers, very good at dynamic actions as well, catching and throwing objects, anticipating requirements for upcoming movements. Some other species perform amazing specialized stunts, but none is as versatile and exible as we are. Through our manipulatory skill we relate to the world in a highly differentiated way, transform some objects into tools, which we bind into our body scheme to bring about change in another object. “Homo Faber” is a very appropriate characterization of the human mind. Examine a simple, daily-life example: Your toaster has stopped ejecting the slices of toast once done. In the hope of a cheap solution, you try to repair this defect by opening the toaster and searching for a dislocated spring. This will mean concretely that you will take the toaster toward a convenient workplace, the bench of your workshop if you are ambitious about such things. You will explore the toaster visually, turning it around while observing it to identify screws to undo, setting the toaster down, nding an appropriate screwdriver, loosening the screws, setting the toaster upright again, and carefully lifting up its cover. Some further examination leads you to, in fact, nd a loose spring (your lucky day), which you attach back to the obvious hook on to which it ts. You ret the cover and nd, insert, and turn each screw in succession. You carry the toaster back to the kitchen and test it out on an old piece of toast, and happily announce to all members of the household your heroic deed. Now this action involves a lot of cognition. First, there is an indenable amount of background knowledge (Searle 1983) that is used in multiple ways and at different
levels during the repair. Knowing that a repair involves opening a device by taking off its cover and that screws need to be undone to that end are examples of highlevel knowledge. Knowing what springs look like and that removing a screw means turning the screwdriver in counter-clockwise direction are examples of a lower level of knowledge, meaning knowledge more closely linked to the sensory or motor surfaces. Some of the background knowledge may have the discrete, categorical form of whether to turn a screwdriver to the left or to the right. Other background knowledge is more graded and fuzzy in nature, such as how much force to apply to a plastic vs. to a metallic part. Visual cognition is required to detect the screws against the background and to categorize the screws so as to select the appropriate type of screwdriver. During active visual exploration, we may memorize where the screws are located, together with the pose and viewing angle of the toaster required to return to each screw, to work on it in the unscrewing phase. At a more global level, we need to retain stably in our mind that we are trying to repair the toaster as we go about all these detailed actions and explorations. That overall goal was selected in light of predictions about its duration (e.g., short enough to make it to the cinema 30 minutes later), the worthiness of this project compared with alternatives, and the probability of success. The whole project of repairing the toaster takes place in a concrete setting, which provides surfaces to work on, visual structure that helps orient, and mechanical structure that facilitates motor control by providing force feedback and stabilization through friction. Performing the action while situated in a structured and familiar environment alleviates some of the cognitive load of the task. For instance, working memory is less taxed, because the visual context provides cues to the screws’ locations, or even just because they may always be found again by our re-exploring. In addition to this sensory interaction, the task situation is central to the generation of movements as well. Sensorimotor coordination is required when turning the toaster around for one to be able to examine it from different angles and later to hold the toaster while attempting to loosen the screws. This entails generating just the right amount of torque so that the frictional force is overcome but slipping is avoided. That torque must continuously and rapidly be adjusted as the screw starts to turn and static friction is replaced by dynamic friction. As we move ahead with the task, we need to smoothly switch from one motor state to another. For instance, while unscrewing a screw, we xate the toaster with one hand and control the screwdriver with the other. Then we must release the toaster from xation and move both hands into a coordinated grasp of the whole object as we reposition it, probably performing at the same time some nger acrobatics to hold on to the screwdriver. This simple process of repairing a toaster clearly shows how a cognitive system can benet from having a body and being in a specic situation. Compare the ease of performing this situated action with the much more challenging variant in which an engineer provides a robot with a sequence of detailed commands to achieve the same end.
