Is the definite article missing before "head position"?

Question

Problems in the inner ear — where head position is perceived — are the most common cause of nystagmus, usually accompanied by vertigo. (source)

According to Macmillan Dictionary (marked as countable) and Cambridge Dictionary (most definitions say [countable] or [C usually singular] and but [C/U] also appears. All examples are countable usages), "position" is a count noun. Why is there no definite article before "head position" in this sentence? It seems the context calls for specificity. I thought the sentence should read:

Problems in the inner ear — where the head position is perceived — are the most common cause of nystagmus, usually accompanied by vertigo.

Answer 1

Although "head position" is countable in the sense that there are multiple positions the head can assume -in other words "head positions"- I think the noun phrase here has a different meaning in this context.

If we view it as one of the senses let's say sight or hearing for instance, then it is clear it is uncountable as the sense of "head position".

The inner ear is where a human being perceives how their head is positioned at any given instance. The sense of "head position". If you will allow me. Viewed in this light it is an uncountable concept. As you would not use the definite article with sight or hearing, in much the same way it would not be appropriate here either. e.g. The eye -where sight is perceived-... not The eye -where the sight is perceived-...(not correct)

Thank you