FM depth detection thresholds were worse in animals with CHL. A, Example psychometric functions from a single test session for a control (black) and P10 CHL (red) animal. FM depth threshold was estimated by fitting a psychometric function (solid line) to the percent-correct data (individual points). The fitted psychometric function was transformed into sensitivity (d′) using the fitted FA rate. Threshold was defined as the FM depth where d′ = 1. The slope is indicated next to both curves. B, FM depth threshold for each session for a representative control (black) and adult CHL animal (orange). The first session was devoted to test cage habituation (dark gray), followed by several sessions of procedural learning (i.e., training at a single FM depth of 500 Hz, light gray). Filled markers indicate the three best sessions. C, Average of the three best FM depth thresholds for each animal. Bars indicate ± SEM. The aged adult CHL group is plotted separately (diamond marker). In all other panels and figures, the aged adult CHL group was combined with the adult CHL group. D, Average FM depth threshold for each group. Bars indicate ± SEM.