Short-term adaptation does not null long-term visual aftereffects

Abstract

Four minutes of adaptation produces a tilt aftereffect (TAE) that can last for 2 weeks. One minute of adaptation can produce a large TAE but it disappears within minutes. TAE was measured using a tracking staircase method. Six naive subjects were tested during four minutes of adaptation in one direction, 1 min of adaptation in the opposite direction, and 5 min of recovery from adaptation. Four minutes of adaptation produced TAEs that reached an asymptote at 4.5° (avg). One minute of counteradaptation reversed the sign of the TAE, producing a significant −1.5° TAE. During recovery, the TAE reversed sign again, yielding a longterm TAE attributable to the initial adaptation (1.0°, p < 0.05). Two minutes of adaptation yields a 4.5° (avg) TAE but no long-term TAE. In a second experiment, 2 min adaptation was followed by 1 min counteradaptation. No TAE was seen during the recovery. There are two mechanisms and two sites of adaptation in the visual system: At the first site, fatigue of broadly tuned channels produces short-term aftereffects. At the second site, structural change in units that identify stimuli produces long-term aftereffects.