Sentence:  They started their own research at the beginning of the seventies, after hearing of Jürgenson's voices, and since then they have indefatigably dedicated a lot of their time and energy to research, particularly in the field of <WSD>psychophony</WSD>, as the phenomenon is known in Spain. 
Meaning of the word marked with <WSD> tags:  The appearance of voices or meaningful sounds in the white noise on electronic recordings; electronic voice phenomenon (EVP).