Transfer in motion perceptual learning depends on the difficulty of the training task

One hypothesis in visual perceptual learning is that the amount of transfer depends on the difficulty of the training and transfer tasks (Ahissar & Hochstein, 1997; Liu, 1995, 1999). Jeter, Dosher, Petrov, and Lu (2009), using an orientation discrimination task, challenged this hypothesis by arguing that the amount of transfer depends only on the transfer task but not on the training task. Here we show in a motion direction discrimination task that the amount of transfer indeed depends on the difficulty of the training task. Specifically, participants were first trained with either 4 degrees or 8 degrees direction discrimination along one average direction. Their transfer performance was then tested along an average direction 90 degrees away from the trained direction. A variety of transfer measures consistently demonstrated that transfer performance depended on whether the participants were trained on 4 degrees or 8 degrees directional difference. The results contradicted the prediction that transfer was independent of the training task difficulty.