Foveal increment thresholds were measured in young, middle-aged, and older observers. These thresholds, which involved the detection of a small test flash as a function of the intensity of a larger background adapting field (AF), were measured at the instant of onset of the AF (transient condition) and when the eye had been fully light adapted to the AF (steady-state condition). All stimuli were presented to the left eye in a free-viewing system through a 2 mm artificial pupil. For the steady-state condition for all age groups, the functions were similar, but for the transient condition, the slope for the older observers was significantly less steep than that for the younger observers. These findings are consistent with an hypothesis of a selective loss of transient (Y) channels in the aging visual system.