Figure 1.

Procedure and results of the perceptual learning experiment. (a) Layout of the displays. Threshold estimation by a 3/1 (b) and 2/1 staircase (c) (19). (d) Contrast thresholds for orientation discrimination were estimated at each of eight levels of environmental (external) noise. Contrasts at threshold are shown averaged over observers and pairs of days. Contrast thresholds for the more stringent criterion (e) and the less stringent criterion (f). Smooth curves are fits of the Perceptual Template Model (PTM) (Fig. 2). Perceptual learning at the two criterion levels identifies the improvements as a hybrid of external noise exclusion and signal enhancement.