| Research background and aimsVisual perceptual learning is referred to as the phenomenon that adults can improve their visual perceptual skills through repeated task training. Results from psychophysical, animal electrophysiological and human brain imaging research indicate that visual perceptual learning reflects the great plasticity of adult brain. Visual perceptual learning, thus, is important to understand the general mechanism of learning and memory.In recent years, clinical research have revealed that visual perceptual learning is effective in the improvement and rehabilitation of the aging or damaged brain, such as amblyopia and hemianopia. The great success in clinic indicated the surprising application value of visual perceptual learning. It also promoted the research about how to optimize the visual training regimens and enhance the efficacy of learning acquisition and transfer. An optimal training regimen should be highly efficient. That is, the training time should be as short as possible, while the learning effect and transfer effect should be as strong as possible.However, the systematic review of the literature about the optimization of the visual perceptual training regimens shows that,1) the existing literature is still very rare; 2) it seems that training procedure and attention play important roles in improving learning and transfer efficacy; and 3) to our knowledge, there is no research exploring the long-term retention effect of the optimized training.Thus, the present study applied the classic texture discrimination training paradigm to investigate the effect of location diversity and exogenous attention on visual perceptual learning acquisition, transfer and long-term retention effect.MethodThe current study applied a 2*2 between-subjects design. The factor of location diversity included two levels:single location and cross location. The factor of exogenous attention also included two levels:valid exogenous cues and invalid exogenous cues. The two factors were manipulated orthogonally.48 undergraduate students with normal or correct-to normal vision in Southern Medical University voluntarily participated in the study. They were naive to the purpose of the study, and were randomly assigned into two experiments. The experiment 1 was about Single-Location Training, in which the texture target was always presented in a specific visual quadrant during training with the texture discrimination task. The experiment 2 was about Cross-Location Training, in which the texture target was presented randomly in either the upper-left or upper-right visual quadrant with equal probability. A central arrow before each trial cued the exact location. During the training, the background was kept constant. In each experiment, participants were further divided into two groups. That is, half of them were presented with both valid and neutral peripheral cues during training; and the other half were presented with both invalid and neutral peripheral cues. All participants completed five sessions of training, and each session consisted of 1024 trials and was finished within one day. The texture discrimination task without any cues was tested before, after and at least 6 months later. The tests include all visual quadrants and all background orientations. The method of 3-down-1-up staircase was used both during training and testing.ResultsWe found that, in single-location training experiment, (1) During the training, for the valid group, the main effect of training sessions was significant [F (4,40) =19.918, P＜0.001]. However, the main effect of cue validity was not significant [F(1,10)=0.100, P=0.759]. The interaction between cue validity and training sessions is not significant [F (4,40)=0.040 P=0.997]. For the invalid group, the main effect of training sessions was significant [F (4,40)=17.273, P＜0.001], but the main effect of cue validity was not significant[F(1,10)=0.006, P=0.940]. The interaction between cue validity and training rounds is not significant [F (4,40)=0.758, P=0.559]. (2) During the testing of the trained stimuli, for the valid group, the threshold in post-test was significantly smaller than that of the pre-test [t(10)=2.987,P=0.014]. For the invalid group, the post-test threshold was significantly smaller than that of the pre-test [t(10)=5.761, P＜0.001]. (3) During the testing of the untrained stimuli, for the valid group, the post-test threshold significantly decreased compared to the pre-test threshold [t1(10)=4.809, P1=0.001; t2 (10)=2.460, P2= 0.034; t3 (10)=2.758, P3=0.020]. For the invalid group, the post-test threshold also significantly decreased in relative to the pre-test threshold [tl (10)=2.494, P1=0.032; t2 (10)=3.342, P2=0.007; t3 (10)=5.320, P3＜0.001]. (4) During the long-term retention testing, for the valid group (n=6), there was no significant difference between the post-test threshold and the re-test threshold [t(5)=-1.311,P=0.247]. There was also no significant difference between the pre-test threshold and the re-test threshold [t(5)=1.803,P=0.131]. For the invalid group (n=7), significant difference was found between the post-test threshold and the re-test threshold [t(6)=-1.148,P=0.006], and significant difference was also revealed between the pre-test threshold and the re-test threshold [t(6)=2.200,P=0.07].In cross-location training experiment, (1) During the training, for the valid group, the main effect of training sessions was significant [F(4,44)=26.401, P＜0.001]. However, the main effect of cue validity was not significant [F(1,11)=3.700, P=0.081]. The interaction between cue validity and training sessions was not significant [F(4,44)=1.834, P=0.139]. The interaction between trained location and training sessions was not significant [F(4,44)=0.626, P=0.646]. The interaction of trained location, cue validity and training sessions was not significant [F(4,44)=0.737, P=0.572]. For the invalid group, the main effect of training sessions was significant [F(4,44)=26.600, P＜0.001], but the main effect of cue validity was not significant [F(1,11)=1.612, P=0.230]. The interaction between cue validity and training sessions was not significant[F(4,44)= 1.410, P=0.246]. The interaction between trained location and training sessions was not significant [F(4,44)=1.300, P=0.285]. The interaction of trained location, cue validity and training sessions was not significant [F(4,44)=0.211, P=0.937]. (2) During the testing of the trained stimuli, for the valid group, the main effect of test was significant [F(1,11)=61.925, P<0.001]. The interaction between trained location and test was not significant [F(1,11)=1.574, P=0.236]. For the invalid group, the main effect of test was significant [F(1,11)=73.616, P＜0.001]. The interaction between trained location and test was not significant [F(1,11)=0.042, P=0.842]. (3) During the testing of the untrained stimuli, for the valid group, the post-test threshold significantly decreased in comparison with the pre-test threshold [F1(1,11)=6.154, P1＜0.001; F2(1,11)=8.342, P2＜0.001; F3(1,11)=5.241, P3<0.001]. The main effect of trained location was not significant[Fl(1,11)=0.031, P=0.863; F2(1,11)=0.754, P=0.404; F3(1,11)=2.377, P=0.151]. The interaction between trained location and test was not significant [F1(1,11)=0.069, P=0.798; F2(1,11)=2.601, P=0.135; F3(1,11)=1.389, P=0.263]. For the invalid group, the post-test threshold significantly reduced in relative to the pre-test threshold [F1(1,11)=5.758, P1＜0.001; F2(1,11)=7.501, P2<0.001; F3(1,11)=4.544, P3<0.001]. The main effect of trained location was not significant [F1(1,11)=5.758, P1＜0.001; F2(1,11)=7.501, P2<0.001; F3(1,11)=4.544, P3<0.001]. The interaction between trained location and test was not significant [F1(1,11)=0.413, P=0.534; F2(1,11)=1.658, P=0.224; F3(1,11)=0.572, P=0.465]. (4) During the long-term retention testing, for the valid group (n=7), there was a significant difference between the post-test threshold and the re-test threshold [t(6)=-5.860, P=0.001]. There was also a significant difference between the pre-test threshold and the re-test threshold [t(6)=2.678, P=0.037]. For the invalid group(n=10), a significant difference was found between the post-test threshold and the re-test threshold [t(9)=-4.262, P=0.002]. There was also a significant difference between the pre-test threshold and the re-test threshold[t(9)=2.439, P=0.037].The combined analysis of the two experiments showed that, (1) During the training, the main effect of training sessions was significant [F(1,42)=144.275, P＜0.001].However, the interaction between cue validity and training sessions was not significant [F(1,42)=11.185, P=0.002]. The mean improvement ratio of the valid group was 50%, the mean improvement ratio of the invalid group was 40%. The improvement ratio in the valid group was marginal significantly higher than that in the invalid group [F(1)=3.921, P=0.054]. (2) During the testing of the trained stimuli, the main effect of test was significant [F(1,42)=124.216, P＜0.001]. The interaction between group and test was not significant[F(1,42)=0.108, P=0.744]. The interaction between experiments and test was not significant[F(1,42)=0.062, P=0.804]. (3) During the testing of the untrained stimuli, the main effect of test was significant [F1(1,42)=86.649, P1＜0.001; F2(1,42)=59.229, P2<0.001; F3(1,42)=75.579, P3<0.001]. The interaction between group and test was not significant [F1(1,42)=1.837, P1=0.183; F2(1,42)=0.027, P2=0.871; F3(1,42)=0.338, P3=0.564]. The interaction between experiments and test was not significant [F1(1,42)=0.135,P1=0.715;F2(1,42)=0.118,P2=0.733;F3(1,42)=0.463,P3=0.500]. (4) During the long-term retention test, the main effect of test (post-test vs. re-test) is significant [F(1,26)=32.090, P＜0.001]. The interaction between group and test was not significant[F(1,26)=0.020, P=0.889].The interaction between experiments and test was not significant [F(1,26)=3.100, P=0.090]. In addition, the main effect of test (pre-test vs. re-test) is significant [F(1,26)=15.107, P=0.001]. The interaction between group and test (pre-test vs. re-test) was not significant [F(1,26)=0.001, P=0.995].The interaction between experiments and test (pre-test vs. re-test) was not significant [F(1,26)= 1.372, P=0.252]. The mean retention ratio was 45%.ConclusionThe current study showed that, in the classic texture discrimination training paradigm, location diversity during training may enhance the acquisition efficacy of visual perceptual learning. The Cross-Location training simultaneously induces equal learning effect in two separate visual quadrants across two hemispheres with only half amount of training as in the traditional Single-Location training. In addition, the validity of the exogenous peripheral cues may promote the learning acquisition. The training effect with the valid cues was better than that with the invalid cues. Visual perceptual texture discrimination learning effect can be transferred to the stimuli with untrained background and untrained target location. The learning effect can also be partially preserved at least 6 months after training.Research significance and future directionsThe current findings are helpful to reveal the cognitive mechanisms of visual perceptual learning, and may provide insights into the improvement and rehabilitation of the aging and damaged brain in clinical settings.In future studies, it will be important,1) to add two active control groups, in order to demonstrate the role of location diversity without any exogenous cues; and 2) to carefully match the trial procedure of single-location training and cross-location training, in order to exclude the possible confounding effect. |
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