Intelligence and Sensory Capacities

Sir Francis Galton, cousin of Charles Darwin, was a highly respected scientist and inventor. He proposed a hypothesis stating that intelligence is the by-product of sensory our sensory capacity. In other words, Galton claimed that people with highly sensitive capacities, such as better eyesight and hearing, acquire more knowledge than others. Although Galton's hypothesis was later disproved, with the help from cases such as Helen Keller and how great of a scholar and successor she was, this hypothesis is important because it gives a relationship between biological factors about our sensory system and intelligence. It also initiated research about the correlation between biology and intelligence and excavated our understanding about the relationship between the two.
There is a correlation vs causation issue that goes along with this hypothesis that could explain a 3rd variable that I thought of when reading this section in the textbook. In earlier times, where poor eyesight, hearing, taste and other senses couldn't be fixed with the technology we have now, people with poor senses may have been less motivated than others to learn. Now that we have ways to adapt, such as glasses and hearing aids, people with poor senses can bring in more information and have the sensory capacity of a normal person.
This is particularly interesting to me because my sister, one of the smartest people I have ever met, has very poor vision. Although Galton's theory was disproven, new research suggests that although sensory capacities and intelligence don't go hand in hand they do have some relation to one another. From this, I wonder if she was born in a different time without the technology we have now, would the third variable I stated above cause her to not fulfill her intellectual potential? Again, there may be some correlations but there are always cases such as Helen Keller (blind and deaf), Ray Charles (Blind), and Beethoven (deaf) proved to be very successful in their practices.