 Contact lenses that produce curved retinal input were placed on the right eye of three observers, who were instructed to scan a horizontally oriented line with their left eye covered for 40 minutes. The experimenters reported that there was an average of 44% adaptation when the line was physically straight but retinally curved, and an average of 18% adaptation when the line was physically curved but retinally straight (see Miller &amp; Festinger 1977, however, for conflicting results).