This problem, which occurs frequently in papers by UCI students, fits into several categories including redundancy and unclear pronoun reference. Think about it. We don't know who that extra he is. It doesn't have to be Slater. Perhaps the problem occurs so frequently because academic essays require that ideas be attributed to their source, and students aren't sure how to do this. Here are two possibilities.

Correction #1: According to Slater, Americans are blind.
Correction #2: Slater argues that Americans are blind.

Check the following resources for useful practice material: 1) Guide to Grammar and Writing, 2) Colleen Hildebrand's UCI Correction Symbols with hyperlinks.