An actor who is involved in collaboration with other actors in natural presence, or in mediated presence, will have an image of the other collaborating actors. Whether it is informed by curiosity and attention, or whether it is just an uninformed stereotypical image. People judge each other's presence in relation to their own presence. Whether well-informed or full of prejudice, or not, it influences the interaction between different actors. Thomas Kuhn, in his last writing, explores the notion of incommensurability in relation to witnessed presence, even though he does not use the word as such. Thomas Kuhn never managed to finish his book before he died, so we can only guess where his argument might have led. However, Kuhn's suggestion is in tune with the latest insights in brain research by scientists like Antonio Damasio and Luc Steels, and it resonates with the proposed understanding of the sense of presence of Riva, Waterworth and Waterworth.

"A final remark will close this sketch of my current views on incommensurability. I have described those views as concerned with words and with lexical taxonomy, and I shall continue in that mode: the sort of knowledge I deal with comes in explicit verbal or related symbolic forms. But it may clarify what I have in mind to suggest that I might more appropriately speak of concepts than of words. What I have been calling a lexical taxonomy might, that is, better be called a conceptual scheme, where the 'very notion' of a conceptual scheme is not that of a set of beliefs but of a particular operating mode of a mental module prerequisite to having beliefs, a mode that at once supplies and bounds the set of beliefs it is possible to conceive. Some such taxonomic module I take to be prelinguistic and possessed by animals. Presumably it evolved originally for the sensory, most obviously for the visual, system. In the book I shall give reasons for supposing that it developed from a still more fundamental mechanism which enables individual living organisms to reidentify other substances by tracing their spatiotemporal trajectories." (Kuhn 2000, 94).

Witnessing the presence of others informs us about the identity of others and these identities are, among other things, formed by 'conceptual schemes'. This quote from Kuhn has inspired me to reflect upon the effect of performing a practice over time and how this performing of a practice will actually change the structures in the brain, even the conceptual structures in the brain that influence perception and behaviour. What is the difference between doing the dishes every day or loading and emptying the dishwasher? If people work with hard materials like stone, steel or wood using their hands, how does it influence their conceptual framework? Does a nurse have a very different brain structure to a composer of music or a London cab driver? Brain research suggests that our actions continually influence how our neurons develop, and not only in childhood. Older people's brains also continue developing according to the actions they perform. As an actor, the acts that I perform will affect my brain structure. I would argue that these brain structures, together with other input, influence the images we have of ourselves and others. Damasio points out that scientifically we do not know how we go from sensory input to conceiving images, even though the fact that we conceive images is well-established (Damasio 2004). Kuhn's idea that a fundamental mechanism 'enables living organisms to reidentify other substances by tracing their spaciotemporal trajectories' may be proven to be very worthwhile because it would explain how we often 'recognize' other actors intuitively before we know how our communication with this person will work out. Kuhn's words can be understood as an insight into witnessed presence. This may also imply that when confronted with incommensurability, the clash between intention and realization does not only occur cognitively, but physical and emotional input may also 'shape' the actor as much as the cognitive clash does.

Kuhn's suggestion is also interesting when reflecting on the thinking actor in mediated presence. Any act executed in mediated presence also feeds back into the brain: how do these mediated movements feed back into the brain, and is this process different from movements in natural presence? How does seeing a result in mediated presence, whether successful or not, influence our consciousness? And how does acquired technological or editorial skill influence our way of thinking? What does mediated collaboration do to us, whether it is pleasant and fruitful, or not?

These questions are not the subject of this study, but they have been raised to encourage follow up research. Kuhn's suggestion does resonate with the experiences of online collaborations. It is very difficult to mediate the possible pre-linguistic conceptual frameworks that characterize an actor, and which are perceived by other actors. The limited sensorial repertoire of mediated presence limits communication on very fundamental levels. Just as context is extremely difficult to mediate, up to the logical point where it is impossible, any conceivable inner pre-linguistic conceptual frameworks face the same (impossible) challenge.

Incommensurability is a significant hurdle that has to be tackled in the collaborations between actors. Actors, unlike scientists, whose taxonomies may differ completely, share certain areas of commensurability as well as certain areas of incommensurability. Some parts of their work may use very different taxonomies than other parts of their work. In collaborations, meta-cognitive skills are important to structure collaboration. By using transitional words or objects, or boundary objects, people from different disciplines can conduct structured conversations that they can derive input from in order to carry out their own work. In interdisciplinary collaborations, where incommensurability plays a significant role, meeting in natural presence is even more important when engaging in contextual reflexivity. Even though project management can orchestrate a great number of fruitful interactions, when ethical implications are discussed people have to be physically present. Kuhn suggests that pre-linguistic conceptual frameworks facilitate actors recognizing each other's spacio-temporal identities. To continue his argument, he actually suggests that performing actions changes brain structures and therefore changes identities, and different actors can recognize these different identities and thus each other's different activities. There are numerous social, economic and political reasons why, and how, people identify others. The suggestion that we may identify a deeper structure of thinking, a conceptual framework that is reflected in a lexical taxonomy, could add to the understanding of why certain actors work well together while others do not. To mediate such nuances of enacted identities is difficult and may even be impossible.

In moments of conceptual innovation as regards both product and process, the ethical impact of a process, even when it is not so formulated, requires the physical presence of the actors involved to achieve the aggregation of knowledge from the varieties of taxonomies, which contribute to the innovation process. Such presence is necessary for the input of ideas, and also people from different disciplines make different analyses of the same situation. Outside the bounds of their own expertise everybody is a layperson and will formulate 'common sense' insights about each other's expertise. When more than two disciplines collaborate and the process is not clearly structured 'common sense' may rule the debate. The challenge for interdisciplinary collaborations like this is to transcend this level of 'common sense' communication and really encourage the variety of expertises and insights to work together even though the actors involved do not speak each other's languages. Anyone who has experienced collaborations like this can tell stories about the inspiration they felt or the frustration they experienced. It is a delicate process, in which all other elements of the thinking actor play a role to facilitate the transcendence of the variety of taxonomies that are gathered.