The word "bias" usually has a bad connotation, as some hurtful deviance that must be fixed. But this becomes less the case when talking about electronic circuits where bias simply means some voltage or current that is deliberately applied to make the circuit operate properly. And probably with that context in mind, bias was the word that David Tudor used sometimes to paraphrase what he often called the nature of material. Now the interesting thing about this paraphrase is that it turns the positivity of nature into a negativity, for bias does not identify but constrain. It is not about what something is, but what something is not.
Generalizing this notion of bias provides a different way to see things like scores or instructions and their relationship to performance which is described by terms like indeterminacy. Because if scores are biases telling the performer the constraints to be imposed in the realization of a performance, then even the most detailed score would still be indeterminate in the sense that there will always be some liberty within any given constraint—a positive leeway in the sea of negativity. As a consequence, indeterminacy becomes a matter of degree.
But there are other materials that impose bias on what can be done. And that is precisely what instruments are, including the body of the performer. But the kind of bias implemented by instruments is usually different from that of the score or written instructions since it does not operate by language or symbols but through their distinct physicality. So one can distinguish between textual bias and physical bias.
The negativity of bias is reminiscent of cybernetics, especially in relation to the way Gregory Bateson formulates it. According to Bateson, whereas causal explanation is positive and describes events as being produced by one thing moving another, the cybernetic explanation is negative in that it considers first a universe of possibilities and then asks why so many of those possibilities did not materialize, and what kind of restraints stopped them from occurring. This is very similar to the model of performance where there is some material that provides a universe of possibilities which is biased in multiple ways to produce a specific realization. "Universe of possibilities" actually happens to be the term that Cage used to describe the status of parameters before they were subjected to chance operation. And this connection can be explored further because one of the things I found out recently is that the term "performance" starts proliferating in various disciplines after Norbert Wiener, the founder of cybernetics, started using it in the early 1940s as a paraphrase of the word "behavior," when he was trying to translate the model of behaviorism from humans to machines.
Some of this (although none of the connection with cybernetics) is laid out in a chapter titled "Material Bias" in the anthology Material Cultures of Musical Notation to be published in 2022 from Routledge.