Does adaptation of motion-direction detectors affect bias or sensitivity of direction judgments?

The question how channels tuned to different motion directions contribute to motion perception has been investigated by using motion adaptation to silence certain channels, and then measuring performance in a fine motion-discrimination task. To help constrain models of how the channels become integrated, we examined whether changes in performance stem from reduced accuracy (bias) or from reduced precision (sensitivity) in direction judgments. On a given trial, the observer first adapted to a field of dots moving coherently in a given direction (ranging +/-180 degrees from upward), then judged whether the motion of an ensuing test stimulus (ranging +/- 3 degrees) was left or right of reference.