Study of Perceptual Learning Specificity
|School||University of Science and Technology of China|
|Keywords||psychophysics perceptual learning specificity transfer motion detection discrimination|
Perceptual learning is defined as a change of performance as a result of repeated perceptual task training. The change of performance tends to persist over weeks and months. Perceptual learning is often quite specific for the exact task and stimulus attribute. Specificity is always a central topic in the perceptual field. The specificity of learning was used to support the hypothesis that perceptual learning embodies neuronal modifications in the brain’s early cortical areas and specificity was supposed to reflect the location of perceptual learning. However, different studies suggested huge variability of specificity on the same stimulus attribute. Now the low-level mechanism is facing a big challenge. Ahissar & Hochstein suggested that specificity of perceptual learning depends on task difficulty. Liu & Weinshalll found that generalization is a common phenomenon in perceptual learning.The present research studied specificity of perceptual learning on dots motion from task and stimulus attributes aspects. The study included two experiments: 1. Task transfer of perceptual learning on random dots motion. 2. The specificity of perceptual learning on speed discrimination.Experiment 1 compared task specificity of motion perceptual learning between detection and discrimination. Observers either decided which of the two stimuli contained a coherent motion signal (detection task), or whether the coherent motion direction was clockwise or counter-clockwise relative to a reference direction (discrimination task). Psychometric functions were measured before and after training. Twenty-three observers were randomly assigned to detection training group and discrimination training group. We found that the detection training improved only their detection but not discrimination sensitivity, whereas the discrimination trainees improved both. Whereas the exact direction of the coherent motion signal was irrelevant to the detection task, detection of the coherent motion signal was necessary for the discrimination task. Therefore the importance of task-relevance was demonstrated in both detection and discrimination learning. This suggests that only task-relevant information is learned in motion perceptual learning. This is an evidence that ’What is learned?’ during perceptual learning.Experiment 2 focused on specificity of perceptual learning on discriminating motion speed of radial moving dots. Observers were asked to perform a speed discrimination task. Two parts of study were included because of the different research purpose. Part 1 studied motion specificity of speed discrimination learning. Part 2 studied the specificity of learning under three speed differences. In part 1, ten observers were randomly assigned to inward training group and outward training group. Inward training group were presented with inward radial motion stimuli and outward training group were presented with outward radial motion stimuli. Also another five observers who went through no training were as controls. We found both groups improved their performance at the training direction (inward or outward), compared with control group. Moreover this improvement of performance happened at non-training direction. This means that perceptual learning of speed discrimination on radial motion dots was not specific to direction. In Part 2, twelve observers were trained at the viewing distance of 114cm. Psychometric functions were measured at three viewing distance of 57cm, 114cm and 228cm. We found that the improvement of performance happened not only at 114cm, but also at 57cm and 228cm. The speed difference doubled at 57 cm and halved at 228cm. We suggested that perceptual learning transferred between three speed differences. In summary, generalization of learning on speed discrimination was a common character.In summary, we found two main results. First, we suggested that only task-relevant information was learned in motion perceptual learning. Perceptual learning of motion was task specific. Second, perceptual learning of speed discrimination were not direction specific and speed difference specific.