Perceptual learning of contrast discrimination under roving: the role of semantic sequence in stimulus tagging.

Perceptual learning may occur when multiple contrasts are practiced in a fixed, but not in a roving (random), temporal sequence. However, learning may escape roving disruption when each contrast is assigned a letter tag (i.e., A, B, C, D). Because these letter tags carry not only stimulus identity information, but also semantic sequence information, here we investigated whether the semantic sequence information is necessary for learning of tagged contrasts under the roving condition. We found that assigning number tags (i.e., 1, 2, 3, 4), which also contained both identity and semantic sequence information, to four roving contrasts enabled significant learning of discrimination of each contrast, confirming previous data. However, learning became insignificant when the contrast tags were replaced with Greek letters that were familiar to our Chinese observers except their sequence or Chinese characters that carried no sequence information. In addition, assigning orientation tags, which carried no sequence information either, to roving contrasts was ineffective as well because learning occurred only with sequenced but not roving contrasts. These results suggest that semantic sequence information is necessary for stimulus tagging to effectively enable perceptual learning of multiple contrast discrimination under roving.