I'm amused. Even on slow I didn't hear the gi- of giyersiniz - it is there on slow, but so fast and soft. I thought Siz pantolon yersiniz. is a little unusual, but we've all encountered strange sentences on Duolingo, right? So dutifully I typed it in: "Siz pantolon yersiniz."
Mariane, thank you for your input. As to acuity, I hear extremely well, often hearing the plural ending ...lar spoken as ...larsh along with other odd pronunciations. The problem in this issue is not being able to hear something that is not there, having been 'dropped'. As Alex said, "it is common in spoken Turkish to drop the first "i" sound in some words, and this is one of them. Hence my enquiry