Task: Question Generation
Input (English): Passage: Stereolab's music combines a droning rock sound with lounge instrumentals, overlaid with sing-song female vocals and pop melodies, and have also made use of unorthodox time signatures. It has been generally described as avant-pop, indie pop, art pop, indie electronic, indie rock, post-rock, experimental rock, and experimental pop.The band have played on vintage electronic keyboards and synthesizers from brands such as Farfisa and Vox and Moog. Gane has praised the instruments for their versatility: "We use the older effects because they're more direct, more extreme, and they're more like plasticine: you can shape them into loads of things." The 1994 album Mars Audiac Quintet prominently features Moog synthesizers.
Lætitia Sadier's English and French vocals was a part of Stereolab's music since the beginning; and would occasionally sing wordlessly along with the music.  In reference to her laid-back delivery, Peter Shapiro wrote facetiously in Wire that Sadier "display[ed] all the emotional histrionics of Nico", while some critics have commented that her vocals were unintelligible. Sadier would often trade vocals with Mary Hansen back-and-forth in a sing-song manner that has been described as "eerie" and "hypnotic", as well as "sweet [and] slightly alien". After Hansen's death in 2002, critic Jim Harrington commented that her absence is noticeable on live performances of Stereolab's older tracks, and that their newer songs could have benefited from Hansen's backing vocals.In interviews, Gane and Sadier have discussed their musical philosophy. Gane said that "to be unique was more important than to be good." On the subject of being too obscure, he said in a 1996 interview that "maybe the area where we're on dodgy ground, is this idea that you need great knowledge [of] esoteric music to understand what we're doing." Sadier responded to Gane, saying that she "think[s] we have achieved a music that will make sense to a lot of people whether they know about Steve Reich or not." The duo were up-front about their desire to grow their sound: for Gane, "otherwise it just sounds like what other people are doing", and for Sadier, "you trust that there is more and that it can be done more interesting.".
Output (English): What is the first name of the person who would often trade vocals with Mary Hansen back-and-forth in a sing-song manner?