For example, the text of a book must causally stimulate the reader in some way for it to be true that the reader is actually reading the book—coincidentally verbalising the same words as those in the open book while dreaming well with one's eyes open doesn't count as reading.

Eric Barnes (1991).

The object of any cognitive act must play a causally active role for it to be true that one cognizes that object. For example, the text of a book must stimulate the reader in some way for it to be true that the reader is actually reading the book (coincidentally verbalizing the same words as those in an open book while dreaming with one's eyes open doesn't count).

The Barnes argument

Barnes writes:

"One cannot read a text, I am claiming, when one's sensory organs are are dormant and unstimulated any more than one can ride a bicycle when the muscles of one's limbs are dormant and unstimulated. The causally active role of the text in the causal history of the subject's verbal activity is simply essential for the subject to be reading the text; where this condition is not met, the subject is not reading the text even when the GAA [generally appropriate activity condition for computation] condition for reading is met by this subject, and thus even when the subject's verbal activity is identical to what it would have been had the subject actually read the text" (E. Barnes, 1991, p. 313).

References

Barnes, Eric. 1991. The causal history of computationalism. The Journal of Philosophy, vol. LXXXVIII, no. 6. p. 304-316.