CONTRAST MASKING EFFECTS CHANGE WITH PRACTICE

Contrast detection thresholds are known to increase with background co ntrast, a phenomenon called contrast masking. We found that, under som e conditions, observers improved their masked detection performance by repetitive practice of a masking experiment. This learning effect res ulted in a cancellation of suprathreshold contrast masking within the contrast range measured. A two-alternative forced-choice discriminatio n paradigm was used, with stimuli consisting of Gabor signals as maske rs and target, presented at the same location and time. Untrained obse rvers showed increased detection thresholds with increasing mask contr ast for suprathreshold mask contrasts, but perceptual learning caused an elimination of this classical effect, with masked thresholds reachi ng the no-mask level and below. Learning did not decrease, but rather somewhat increased, discrimination thresholds when target and mask sha red the same Gabor signal parameters. Performance improvement was foun d to be specific for orientation and mask configurations, though it di d transfer between mirror symmetric mask configurations and between ey es. These results argue against a static transducer function-based acc ount for contrast masking and are consistent with a theory assuming mu ltiple feature-based interactive network capable of long-term gain mod ifications. (C) 1997 Elsevier Science Ltd.