The Specificity And Transfer Of Motion Perceptual Learning With Double Training

Visual perceptual learning is defined as the visual system’s capability to improve signal detection, discrimination, or identification in optical stimuli via practice. Visual perceptual learning has been traditionally characterized by its specificity. Namely, learning transfers little to many untrained stimulus attributes. Recently, however, Xiao and colleagues (2008) demonstrated a double training technique that enabled complete transfer of learning in tasks that had previously been shown to be stimulus specific. The significance of this finding is that this technique has since been successful in all tasks tested, including motion direction discrimination. Their results challenge the notion that perceptual learning is retinotopic specific and takes place in low-level visual areas in the brain.To investigate the generality of this double training technique, here we test the specificity and transfer of motion perceptual learning with four experiments. In experiment 1 and 4 we investigated whether or not the double training technique can bring about complete transfer in long-term and short-term learning, using the method of constant stimuli. Only partial transfer was found both before and after the exposure, and in both long-term and short-term training. We concluded that stimulus specificity remains an inherent characteristic of motion perceptual learning even with the double training technique. In experiment 2 we first repeated the Zhang and Yang (2014)’s simultaneous experiment in exact procedure, stimuli, and task, and then we continued the double training to examine transfer in longer-term perceptual learning. To our surprise, in both our exact replication attempt and in our longer-term learning study, we could not find complete transfer. In fact, the transfer to the exposed direction was no greater than to the control directions which neither trained nor exposed. In experiment 3 we repeated the sequential experiment of Zhang and Yang (2014) using the same number of participants. We found, however, that the transfer to the exposed direction was not statistically greater than zero, and more than half of the total transfer occurred before exposure. The total transfer to the exposed and non-exposed control directions did not differ statistically. We suggest that, due to large individual difference, whether or not the new double training technique can bring about complete transfer in motion discrimination learning needs to be reconsider, and the transfer effect specifically induced by exposure maybe much weaker than previously thought.