Jamie Isenstein - Arm Chair, 2006

While not activated as a relational prosthetic, since it exists as a performance/sculpture rather than as an interaction between artist/chair and audience/potential-participant, Arm Chair nevertheless could be one and is therefore worth considering.

From the artist's gallery portfolio:

David Cross - Re-Tard, 2007

All images and text from the artist's website:

3 Photographs, Assorted Sculptural Objects, Performance.

Re-tard examines the relationship between, [sic] abstraction, children’s recreational structures and the grotesque.. Utilising commercially manufactured canvas props set up as a tableaux in the gallery space, the work consists of two modes, an opening performance and a subsequent interactive installation.  Three large coloured panels are positioned diametrically across the gallery space.  The panels have slots where my body and the bodies of the performers penetrate the surface.  Each panel has two air holes where an assortment of attachable components can be fitted or removed.  As in a children’s fun house, the audience are encouraged to manipulate the pieces by attaching or removing individual components.  As well as the tableaux of objects, three large-scale photographs of the panels with my body positioned inside them are located on the gallery walls..Re-tard picks at the blurry edges of abstraction where formal concerns intercede with the popular languages of infantile play structures.

Franz Erhard Walther - Werksatz No. 1 (First Workset), 1963-69

Franz Erhard Walther, Für Zwei (Nr. 31, 1.Werksatz) [For Two], 1967.
Courtesy of fe walther foundation+archives and Peter Freeman, Inc., New York.

 From What We Want is Free: Generosity and Exchange in Recent Art:

When he began Werksatz No. 1 (First Workset) in 1963, Franz Erhard Walther created objects from fabric or other industrial materials that were intended to be brought to life by a spectator's active manipulation.  Often resembling simple-use items such as clothing, slippers, bags, pockets, and satchels, the objects offered a range of variation and playfully set off an engagement with distance, loseness, time, dimesions, and body language.  In Walther's conception, all of the components of the orkset existed to be played, worn, moved, carried, or lifted depending on the circumstances of the project.  Sometimes the works were desgned for one person at a time, sometimes several people were needed, but in each case, it was the sum of the object and the activation by the viewer that constituted the whole sculpture or work.

 http://www.cacbretigny.com/inhalt/few.html

        Walther's work offers a model for understanding the shifting role of audience participation in the process and meaning of contemporary art.  By utilizing skills required to give visual form to intellectual and emotional experience, it provides and arena for understanding how 'process' is art.  Once viewers are physically involved, they cease to be spectators and become participants (and thus a portion of the sculptures).  For Walther, this did not mean that the person/sculpture became an object; on the contrary, they remained a subject, just as the work came alive and was given bodily form. 

While Walther is clearly coming from a sculpture background and addressing/challenging issues native to that realm, the pieces in Werksatz No. 1 that involve more than one person align almost perfectly with my working definition of a relational prosthetic.  Some of his pieces also bear a striking resemblance to some of my own work.  Having learned of their existence after creating my first relational prosthetics (I'm thinking here especially of my Box intervention), it was exciting to find someone who had addressed face-to-face encounters in a somewhat similar formal manner.

Franz Erhard Walther « 1.Werksatz », 1963-1969 58 objects, Sockel, 1969 Exhibition view: Living currency, Tate Modern, London, 2007 Photos by Sheila Burnett.  From http://www.galeriewolff.com/site/artists_detail.php?uid=17&image_id=3