No external feedback is needed for perceptual learning to occur in local and global orientation tasks.

The necessity for external reinforcement, such as response feedback, during perceptual training is a topic of debate. Additionally, internal reinforcement may act in a similar way as external reinforcement, where easy trials act as the basis for learning.  Liu et al, 2012 (Vis Res, (61) 15-24) found learning without feedback when mixing high and low accuracy trials, a result not replicated by Seitz et al, 2006, (Vis Res,(6) 966-973) using a global orientation task. A potential reason for this difference is that the stimuli used in the latter study involved low signal strength stimuli masked by background noise. To test this we performed two experiments, using local and global visual stimuli, respectively, in an orientation discrimination task. Fifty-six observers were assigned to one of four groups according to the type of task (global, local) and feedback (with or without). Detection thresholds were measured daily before and after training. A 75% detection threshold was determined for each session with training levels set daily at 65% (difficult) and 85% (easy) accuracy levels. While training thresholds were different for the feedback and no feedback conditions, significant learning occurred in all four groups. Therefore we replicate the findings of Liu et al., (2012) and extend them to global stimuli. In conclusion, interleaving high and low accuracy trials both local and global orientation tasks leads to perceptual learning independent of the external feedback. Perceptual learning occurs without feedback even for global tasks in which low strength stimuli are masked by background noise.