From pantomime to actual use: how affordances can facilitate actual tool-use

The main goal of the study was to investigate whether the presence of affordances, such as physical properties of given objects and resulting movement constraints, induce a performance increase in actual tool-use compared to demonstrating it with only the tool or pantomiming it without the tool and recipient object. In the present study the perception of affordances was manipulated by omission or supply of contextual information. The three execution modes - pantomiming, demonstration and actual use, - were investigated concerning the actions hammering and scooping in 25 patients with left unilateral brain damage and 10 healthy controls. The content of the movement, the grip formation, the direction and the location of the movement were evaluated with video-analysis. The results show that the pantomime condition is most prone to errors. The information given by the tool and the recipient object in the actual use task seems to facilitate especially scooping - the more complex tool-use action. A factor analysis and the high correlation between performance-scores show that the three execution modes of both actions have a major common factor. One possible joint commonality of the execution modes could be the nature of an action related working memory component, which is responsible for the recall and the integration of semantic information into a movement-plan. Additional analyses with a smaller group revealed a second factor, that might depict the online processing of spatial relationships of the hand, the tool and the recipient objects. The results indicate that performance improvement can be achieved by providing perceptual cues and reducing the degrees of freedom for the required action. It is concluded that manipulating affordances in a tool use context should be taken into consideration for future investigation of therapeutic approaches.