知觉学习中非显著性刺激视觉加工的学习机制

The mechanism of visual processing for nonsalient stimuli in perceptual learning

非显著性刺激的知觉学习研究发现成人大脑具有可塑性,但是知觉学习如何影响不同的视觉加工阶段仍不清楚。通过将眼动指标划分为3个视觉加工阶段来探究知觉学习的机制:搜索潜伏期(早期),是指从搜索屏呈现到第一次眼跳离开初始注视点位置的时间,代表了在搜索屏中选择第一个搜索位置的时间;注视点个数和平均注视时间(中期),代表搜索过程中注视加工的位置个数和平均加工时间;确定时间(后期),代表判断当前刺激是否为目标并做出反应的时间。结果发现对训练刺激的搜索正确率提高,反应时变快,同时搜索潜伏期显著增加,注视点个数和平均注视时间减少,且行为和眼动指标的变化都没有迁移至未训练刺激。说明知觉学习会影响早期和中期视觉加工阶段,可能通过增长搜索潜伏期,同时减少眼跳的次数和降低注视时间来提高搜索表现。

Previous studies have found that perceptual learning can improve the performance on visual search tasks.However,many cognitive processes are involved in visual search,and it is unclear at which visual processing stage perceptual learning facilitates search performance.The current study explored the mechanism of perceptual learning by dividing the eye movement metrics into three visual processing stages:search initiation time(the early visual processing stage),which represents the cognitive process of the time of processing the current location and selecting the next search location;scanning time(the middle visual processing stage),which includes the number and processing time of fixation positions;verification time(the late visual processing stage),which represents determining whether the current stimulus is the target and making a verification.A 2(target type:trained vs.untrained triangle)×2(test stage:pretest vs.posttest)within-subjects design was used to address the above issue.24 healthy young adults(5 males;mean age:21.23±2.02 years)participated as paid volunteers in this study.We randomly selected one of the four orientations of the triangle(Up,Down,Left,or Right)as the trained triangle,which would receive three days of training.Moreover,to ensure that the visual search training was specific to the trained triangle,the trained and untrained triangles were tested by recording the behavior results and eye movement before and after training(untrained triangle was randomly selected from the distractors).Each trial started with a fixation cross(When eye movement was recorded,the search display would not appear until the participants fixated on the center cross for more than 500 ms;when eye movement was not recorded,the central fixation cross was presented for 500 ms and then the search screen was presented).Then a search display was presented until the key response or the elapse reached 2000 ms since its onset.The response was recorded only before the fixation cross disappeared.The task of participants was to determine whether or not the target was presented as quickly as possible.Participants pressed the left arrow key to report the presence of a target or the right arrow key to report its absence.A two-way repeated-measures ANOVA was conducted with the factors of target type(trained vs.untrained triangle)and test stage(pretest vs.posttest).The behavior results found the reduced response time and increased accuracy when searching for trained stimuli after training.However,there was no significant difference in response time or accuracy between pretest and posttest for untrained stimuli.The results of eye movement tracking are as follows:(1)in the early visual processing stage,the search initiation time of the trained stimuli increased significantly after training,and there was no significant difference in the search initiation time between pretest and posttest for untrained stimuli.(2)In the middle visual processing stage,the number of fixations and the average fixation time of trained stimuli were significantly reduced after training,and there was no significant difference for untrained stimuli before and after training.(3)In the late visual processing stage,there was no significant difference in verification time between the pretest and posttest for both trained and untrained stimuli.In conclusion,the accuracy and search initiation time of searching for trained stimuli was increased,while the number of fixations and the fixation time decreased.Moreover,the changes in behavior and eye movement indexes did not transfer to untrained stimuli.It is suggested that perceptual learning can affect the early and middle visual processing stages,and search performance may be improved by increasing the search latency,reducing the number of saccades,and reducing the fixation time.