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PVA Background: Transformation of the perceptual world

In his 1896 paper [15], George Stratton reported on experiments in which he wore eyeglasses that inverted his visual field of view. Upon first wearing the glasses, he reported seeing the world upside-down, but, after an adaptation period of several days, was able to function completely normally with the glasses on.

Dolezal [16] (page 19) describes ``various types of optical transformations'', such as the inversion explored by Stratton, as well as displacement, reversal, tilt, magnification, and scrambling. Kohler [17] also discusses ``transformation of the perceptual world''.

Stratton, Dolezal, and Kohler explored the use of optics (lenses, prisms, and the like). Stuart Anstis was the first to explore, in detail, an electronically mediated world. Anstis [18], using a camcorder that had a ``negation'' switch on the viewfinder, experimented with living in a ``negated'' world. He walked around holding the camcorder up to one eye, looking through it, and observed that he was unable to learn to recognize faces in a negated world. His negation experiment bore a similarity to Stratton's inversion experiment mentioned in Sec 2.1, but the important difference within the context of this article is that Anstis electronically mediated his visual world -- he experienced his world as a video signal.

Using a camcorder as a reality mediator has several drawbacks. Firstly, it is awkward (one hand is occupied constantly, and the apparatus protrudes far enough that it gets in the way of most day-to-day activities), and secondly, it makes people feel much more self-conscious Thirdly, it is not easy to insert arbitrary computational power between the camera and the viewfinder.

WearCam provided a practical solution to these three problems, by serving as a wearable, tetherless `reality mediator'. A suitable realization of WearCam, made from a battery-powered color stereo display, having 480 lines of resolution, is depicted in Fig 2.

  
Figure: Wearable-tetherless computer-mediated reality as of late 1994, showing a color stereo head-mounted display (VR4) with two cameras mounted to it. The inter-camera distance and field of view match approximately my interocular distance and field of view with the apparatus removed. The components around the author's waist comprised primarily wireless communications equipment. Antennas, etc. are located at the back of the head-mount to balance the weight of the cameras, so that the unit is not front-heavy.
\begin{figure}\figc{netcam/visualfilter1width240.ps,width=.3\figw}
\end{figure}

Here, the author mounted the cameras the correct interocular distance apart, and used cameras that had the same field of view as the display devices. With the cameras connected directly to the displays, an illusion of transparency [2] will be realized to some degree, at least to the extent that each ray of light entering the apparatus (e.g. absorbed and quantified by the cameras) will appear to emerge at roughly the same angle (by virtue of the display).

Although the apparatus provided no depth-from-focus capability there was enough depth perception remaining on account of the stereo disparity for the author to function somewhat normally with the apparatus.

The use of head-mounted displays for helping the visually handicapped, using the contrast adjustments of the video display to increase apparent scene contrast has been recently explored[19], but without the use of computational processing of the imagery. The approach described in this paper (Fig 2) also contains computational capability, and therefore extends and generalizes that recently described in [19].

A first step in using the wearable-tetherless reality mediator was to wear it for a while to become accustomed to its characteristics. Unlike in typical beam-splitter implementations of augmented reality, transparency, if desired, is synthesized, and therefore only as good as the components used to make the apparatus.

The apparatus was worn in the identity map configuration (cameras connected directly to the displays) for several days, in order to adapt to its imperfections and irregularities (the identity map is never fully achieved). It was found that one could easily walk around, up and down stairs, through doorways, etc.. Some difficulties, however, were experienced, in scenes of high dynamic range, and also in reading fine print (for example, in a restaurant, where the menu was located behind a counter, preventing a close-up look, or in a department store, where the receipt was printed in faint ink).

The attempt to create an illusion of transparency was itself a useful experiment because it established some working knowledge of what can be performed when vision is diminished or degraded to RS170 resolution and field of view is somewhat limited by the apparatus.


next up previous
Next: Video mediation Up: `Personal Visual Assistant (PVA)' Previous: `Personal Visual Assistant (PVA)'
Steve Mann
1998-09-18