We are left now with two intertwined entities to deal with. The realized work as exhibited, projected, or performed, and the experiences, ideas, and emotions that the audience members experience together or separately and uniquely as they encounter the work. The art induces the experiences in the audience just by being there. Without the work, the experience does not exist, so it is a bit unusual to attempt to disentangle them from each other to the degree that this question of accessibility demands.
The work, unless it remains nothing more than an idea, presents itself to the sensory organs of the audience. The sense organs convert impressions of the object into signals that are subject to varying levels of sorting and gathering and analysis in the relevant parts of the brain engaged in perception. Once perceived, the work has a presence in the mind of the viewer as an object of cognition, something that we can think and talk about, and something that we can relate to other things we know, we feel, and we have experienced. The process is rarely unidirectional and straightforward as a good work of art will force us to look or listen again. Our initial perceptions be prove to be false, and so the sensations and signals and perceptions and conceptions often stay in a suspended and unresolved state for some time.
As we saw with Sol Lewitt, some artists claimed to pay no attention to this play in the mind and the senses of the audience when he conceived of a work. He understood and valued it but specifically did not want to consider it during the creation of a piece. Others may consider the experience of the audience completely irrelevant. Still others consciously construct their work to guide or extend this play. Work that is explicitly focussed on this sort of experience might be considered "perceptual art" as opposed to conceptual art, but as we have seen before, these categories imposed an appealing but false clarity and organization over what is an inherently unruly, lawless terrain. But at base the question clearly becomes: is the art in the object, or does it come into being only in the presence of the viewer? And then, if the art is in the object, how do we remain true to the object in our translation to a different modality. Or else if the art arises in the presence of the viewer, then how do we remain true to this experience in our translation.
There is no general answer. Each artist and indeed each artwork by that artist may occupy a different position on a continuum between these two poles. But let's examine an extreme example. Let's imagine a work created by an artist who was unambiguous about the fact that he or she felt the audience experience to be irrelevant to the work, and that the realized work was the only thing that mattered. The stance of this hypothetical artist poses a serious challenge to the whole notion of accessibility: if audience experience is declared to be irrelevant, is not accessibility irrelevant as well? I use this example only to show how intertwined the question of accessibility is with this question of object vs experience.
Image there was a machine that was able to scientifically translate every feature of a visual artwork into sound information, so that there was a complete mapping from shape, colour, spatial composition, texture, etc into perceivable parameters of sound without distortion (so that its also non-existent inverse machine could perfectly reconstruct the visuals again from the sound.) Would this device make the painting accessible to a blind person? The success of this translation would depend not on whether all the information was converted, but whether the translated information generated a coherent, perceivable thing, rather than noise. If the translation is to have any expressive value, the translation process must be designed to pay very close attention to the way that the source and target modalities process incoming sensory data... in other words, how the sensory input in a specific modality is transformed into coherent experience. Again, when thinking of accessibility, we cannot and perhaps should not avoid an emphasis on the experience side of the equation
This means that we need to gain insight into how the raw sensory stimulus generated by a piece of art or music is refracted by the sense organs, perceptual cortices, brain and body into the aesthetically, intellectually and/or emotionally-charged experience.
It is important again to understand that part of the character of many artworks comes from a kind of built-in inaccessibility. This is not out of childish contrariness. Artist's often erect barriers to comprehension, intended to draw the viewer / listener away from habitual ways of experiencing and conceiving of things. In these cases, (perhaps all cases), we are should not really be talking about making an artwork accessible, but rather of making a work's characteristic 'inaccessibility' available to people with difference sense restrictions and capabilities.