▁forms ▁of ▁life ▁that ▁might ▁never ▁be ▁seen , ▁or ▁even ▁be ▁imag in able , ▁in ▁their ▁absence ." ▁See ing ▁Vo ices , ▁S acks ' s ▁ 1 9 8 9 ▁book , ▁covers ▁a ▁variety ▁of ▁topics ▁in ▁de af ▁studies . ▁ ▁In ▁his ▁book ▁The ▁Island ▁of ▁the ▁Color bl ind ▁S acks ▁wrote ▁about ▁an ▁island ▁where ▁many ▁people ▁have ▁ach rom at ops ia ▁( total ▁colour bl ind ness , ▁very ▁low ▁visual ▁ac u ity ▁and ▁high ▁phot oph ob ia ). ▁The ▁second ▁section ▁of ▁this ▁book , ▁entitled ▁Cy c ad ▁Island , ▁describes ▁the ▁Cham or ro ▁people ▁of ▁Gu am , ▁who ▁have ▁a ▁high ▁inc idence ▁of ▁a ▁ne uro de gener ative ▁disease ▁locally ▁known ▁as ▁L yt ico - B od ig ▁disease ▁( a ▁dev ast ating ▁combination ▁of ▁A LS , ▁de ment ia ▁and ▁par kin son ism ). ▁Later , ▁along ▁with ▁Paul ▁Alan ▁C ox , ▁S acks ▁published ▁papers ▁suggesting ▁a ▁possible ▁environmental ▁cause ▁for ▁the ▁disease , ▁namely ▁the ▁to x in ▁beta - m eth yl am ino ▁L - al an ine ▁( B MA A ) ▁from ▁the ▁cy c ad ▁nut ▁accum ulating ▁by ▁bi om agn ification ▁in ▁the ▁flying ▁fo x ▁bat . ▁ ▁In ▁November ▁ 2 0 1 2 ▁S acks ' s ▁book ▁Hall uc in ations ▁was ▁published . ▁In ▁it ▁he ▁exam ined ▁why ▁ordinary ▁people ▁can ▁sometimes