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. 銷售經理過高地估計了需求，公司因此有兩萬冊書沒有售出去。
The failing of the project forced us to conclude that we had overestimated his abilities. 項目的失敗使我們得出結論：我們過高估計了他的能力。