Interleaving bisection stimuli - randomly or in sequence - does not disrupt perceptual learning, it just makes it more difficult

Presenting stimuli of two or more stimulus types randomly interleaved, so called roving, disrupts perceptual learning in many paradigms. Recently, it was shown that no disruption occurs when Gabor stimuli were presented interleaved in sequence, instead of randomly. Here, using bisection stimuli, we found the opposite pattern of results. Presenting bisection stimuli in a sequence disrupted perceptual learning, whereas we found improvement under roving conditions. A meta-analysis showed that parts of this deviation from previous studies is possibly caused by the initial performance level of participants. These results do not prove previous results wrong, they just show that multiple factors play a crucial role in perceptual learning which cannot always be easily controlled for.