Full Idea
If we don't need to have perceptual experiences in order to see things (as 'blindsight' might suggest), the causal theory of perception cannot be correct.
Clarification
'Blindsight' is where a patient picks up visual information while thinking he or she is blind
Gist of Idea
If blindsight shows we don't need perceptual experiences, the causal theory is wrong
Source
E.J. Lowe (Introduction to the Philosophy of Mind [2000], Ch. 6)
Book Reference
Lowe,E.J.: 'Introduction to the Philosophy of Mind' [CUP 2000], p.156
A Reaction
This is because the causal theory implies a chain of events culminating in experience as the last stage. There is no suggestion, though, that unconscious perception would be non-causal, as it bypasses all the problems about consciousness.