As behavioral sciences develop, however, researchers find the importance of speech has been overestimated. (Para. 4)
Meaning: However, with the development of behavioral science, researchers find that the role of speech has been thought to be more important than it really is.
overestimate: vt. think something is bigger or more important, etc. than it really is
The sales manager overestimated the demand and the company was as a result left with 20,000 unsold copies. 销售经理过高地估计了需求，公司因此有两万册书没有售出去。
The failing of the project forced us to conclude that we had overestimated his abilities. 项目的失败使我们得出结论：我们过高估计了他的能力。