Greater discrimination difficulty during perceptual learning leads to stronger and more distinct representations.

Despite the conventional wisdom that it is more difficult to find a target among similar distractors, this study demonstrates that this disadvantage is short-lived, and that high target-to-distractor (TD) similarity during visual search training can have beneficial effects for learning. Participants with no prior knowledge of Chinese performed 12 hour-long sessions over 4 weeks, where they had to find a briefly presented target character among a set of distractors. At the beginning of the experiment, high TD similarity hurt performance, but the effect reversed during the first session and remained positive throughout the remaining sessions. This effect was due primarily to reducing false alarms on trials in which the target was absent from the search display. In addition, making an error on a trial with a specific character was associated with slower visual search response times on the subsequent repetition of the character, suggesting that participants paid more attention in encoding the characters after false alarms. Finally, the benefit of high TD similarity during visual search training transferred to a subsequent N-back working-memory task. These results suggest that greater discrimination difficulty likely induces stronger and more distinct representations of each character.