In the phenomenon known as blindsight, some people who have been diagnosed as completely blind through damage to their visual cortex retain the ability to make judgments and take actions that appear to require or demonstrate the use of sight, despite the fact that they consciously see nothing. Such an individual, if prompted, might catch a ball thrown to him, walk around obstacles without having been told obstacles are present, or guess with unusual accuracy whether an array of dots is moving or stationary. Individuals with blindsight are usually not surprised by these events and attribute them to coincidence.

Which of the following questions indicates the most serious weakness in the explanation described above?