When attention interrupts learning: Inhibitory effects of attention on TIPL

While task-irrelevant perceptual learning (TIPL) suggests that perceptual learning of a feature occurs without focused attention to the feature, some kind of attentional involvement was implied by recent findings that TIPL occurred only when a task-irrelevant stimulus was paired with a main task target. Here, during training, two task-irrelevant stimuli with different coherent motion directions were exposed, one on an attended side and the other on an unattended side. We found no performance improvements for the direction on the attended side. These results suggest that while attention facilitates task-relevant learning, it can suppress TIPL.     

Learning to suppress task-irrelevant visual stimuli with attention

While the importance of attention in perceptual learning is widely recognized, the mechanisms through which it affects learning are poorly understood. Here we show that attentional mechanisms themselves are modified during learning. Attentional suppression of task-irrelevant stimuli becomes more efficient with practice. Attentional learning was found to be stimulus-specific and to persist for several weeks, suggesting that the plasticity of attentional mechanisms is an inherent component of visual perceptual learning.     

Low-level sensory plasticity during task-irrelevant perceptual learning: Evidence from conventional and double training procedures

Studies of perceptual learning have focused on aspects of learning that are related to early stages of sensory processing. However, conclusions that perceptual learning results in low-level sensory plasticity are controversial, since such learning may also be attributed to plasticity in later stages of sensory processing or in readout from sensory to decision stages, or to changes in high-level central processing. To address this controversy, we developed a novel random dot motion (RDM) stimulus to target motion cells selective to contrast polarity by ensuring the motion direction information arises only from signal dot onsets and not their offsets, and used these stimuli in the paradigm of task-irrelevant perceptual learning (TIPL). In TIPL, learning is achieved in response to a stimulus by subliminally pairing that stimulus with the targets of an unrelated training task. In this manner, we are able to probe learning for an aspect of motion processing thought to be a function of directional V1 simple cells with a learning procedure that dissociates the learned stimulus from the decision processes relevant to the training task. Our results show direction-selective learning for the designated contrast polarity that does not transfer to the opposite contrast polarity. This polarity specificity was replicated in a double training procedure in which subjects were additionally exposed to the opposite polarity. Taken together, these results suggest that TIPL for motion stimuli may occur at the stage of directional V1 simple cells. Finally, a theoretical explanation is provided to understand the data.     

The role of perceptual learning on modality-specific visual attentional effects

Morrone et al. [Morrone, M. C., Denti, V., & Spinelli, D. (2002). Color and luminance contrasts attract independent attention. Current Biology, 12, 1134-1137] reported that the detrimental effect on contrast discrimination thresholds of performing a concomitant task is modality specific: performing a secondary luminance task has no effect on colour contrast thresholds, and vice versa. Here we confirm this result with a novel task involving learning of spatial position, and go on to show that it is not specific to the cardinal colour axes: secondary tasks with red-green stimuli impede performance on a blue-yellow task and vice versa. We further show that the attentional effect can be abolished with continued training over 2-4 training days (2-20 training sessions), and that the effect of learning is transferable to new target positions. Given the finding of transference, we discuss the possibility that V4 is a site of plasticity for both stimulus types, and that the separation is due to a luminance-colour separation within this cortical area.     

Boosting perceptual learning by fake feedback

How does the brain control its sensory plasticity using performance feedback? We examined this question using various types of fake feedback in perceptual learning paradigm. We demonstrated that fake feedback indicating a larger performance improvement facilitated learning compared with genuine feedback. Variance of the fake feedback modulated learning as well, suggesting that feedback uncertainty can be internally evaluated. These results were explained by a computational model which controlled the learning rate of the visual system based on Bayesian estimation of performance gradient incorporating an optimistic bias. Our findings suggest that sensory plasticity might be controlled by high-level cognitive processes.     

Decoupling location specificity from perceptual learning of orientation discrimination

Perceptual learning of orientation discrimination is reported to be precisely specific to the trained retinal location. This specificity is often taken as evidence for localizing the site of orientation learning to retinotopic cortical areas V1/V2. However, the extant physiological evidence for training improved orientation turning in V1/V2 neurons is controversial and weak. Here we demonstrate substantial transfer of orientation learning across retinal locations, either from the fovea to the periphery or amongst peripheral locations. Most importantly, we found that a brief pretest at a peripheral location before foveal training enabled complete transfer of learning, so that additional practice at that peripheral location resulted in no further improvement. These results indicate that location specificity in orientation learning depends on the particular training procedures, and is not necessarily a genuine property of orientation learning. We suggest that non-retinotopic high brain areas may be responsible for orientation learning, consistent with the extant neurophysiological data.     

视知觉学习的时间进程及其与睡眠的关系

视知觉学习是指通过反复训练视觉任务而使知觉表现获得改善的现象。经典的视知觉学习进程表现为起始快速上升、后逐渐缓慢提高的“渐近线”式的过程,该过程涉及“临界训练量”和学习规则对知觉学习效果的影响、学习效果的记忆性巩固、干扰现象以及睡眠在其中所起到防止干扰和促进巩固作用。对视知觉学习的上述内容进行系统介绍,并从应用角度探讨知觉学习治疗弱视的策略。     

Interference and feature specificity in visual perceptual learning

Perceptual learning (PL) often shows specificity to a trained feature. We investigated whether feature specificity is related to disruption in PL using the texture discrimination task (TDT), which shows learning specificity to background element but not to target element. Learning was disrupted when orientations of background elements were changed in two successive training sessions (interference) but not in a random order from trial to trial (roving). The presentation of target elements seemed to have reversed effect; learning occurred in two-parts training but not with roving. These results suggest that interference in TDT is feature specific while disruption by roving is not.     

The dependence of visual scanning performance on saccade, fixation, and perceptual metrics

We sought to understand the basis of performance variability and perceptual learning in saccadic visual search. Four subjects searched for a target based on its shape in a linear array of densely packed, regularly spaced items, a configuration used to simplify the analysis of performance and to minimize search strategy variability. We measured the dependence of performance-search speed-on the oculomotor variables of fixation duration and saccade amplitude, both within and across experimental sessions. We also measured perceptual span, the area in visual space in which subjects could identify the target above chance, with a modified version of the task using a gaze-contingent display with transiently appearing targets. The principal finding of this study was that both within and across sessions, saccade metrics accounted for much more of the variability and improvement in performance than did fixation duration. Increases in search speed were due primarily to subjects processing information from a greater area of the visual field, rather than processing information from a fixed area more quickly, though there was a small but consistent decrease in fixation duration across sessions. The increase in performance derived from an increase in perceptual span and not merely from an increase in subjects' efficiency in 'tiling' the search array with regions of visibility.     

Treatment of children with amblyopia by perceptual learning

Recent studies have shown that perceptual learning has the potential to treat amblyopia. In this study we tested whether a recent perceptual learning technique that improved visual functions in adults can be applied to improve the vision of children after the conventional treatment of patching has failed. A prospective clinical pilot study was carried out in children who were non-compliant with patching or in whom patching had failed despite good compliance. Each child underwent a complete eye examination before and after treatment. The treatment was based on a perceptual learning technique that was similar to the adult study [Polat, U., Ma-Naim, T., Belkin, M., & Sagi, D. (2004). Improving vision in adult amblyopia by perceptual learning. Proceedings of the National Academy of Sciences of the United States of America, 101(17), 6692–6697]. Between blocks, children played a computer game to engage and maintain their attention in order to increase compliance. Each child received two treatment sessions a week, with a total of not more than 40 sessions. Each session lasted for about 1 h and included a total practice time of about 30 min. The age of the children (n = 5) was between 7 and 8 years (mean 7.3 years). For the whole group, the average improvement in visual acuity was 1.5 Snellen lines or 2.12 ETDRS lines. The training improved the contrast sensitivity, which reached the normal range after treatment. Thus, the perceptual learning technique can be successfully used to treat children with amblyopia even after the conventional treatment of patching fails.     

知觉学习改善屈光参差性弱视视功能的临床观察

目的探讨知觉学习训练在改善青少年及成人屈光参差性弱视患者视功能方面的效果。方法前瞻性自身对照研究。共纳入18例青少年和成年单眼屈光参差性弱视患者,弱视眼在截止空间频率下进行对比度检测任务的训练,对侧相对健眼作为对照。患者随访3～6个月。分别观察患者训练前后的最佳矫正视力和对比度阈值改变,立体视改变以及试验组训练前后视觉诱发电位改变。数据进行t检验、相关性分析。结果弱视眼与相对健眼相比,其在训练前后的视力改变,截止空间频率下的对比度阈值改变,以及所有空间频率下的对比度阈值改变差异均有统计学意义（t=2.731,P<0.05;t=5.108,P<0.01;t=3.700,P<0.01）,弱视眼及对侧眼在训练前后潜伏期变化,振幅变化差异均无统计学意义,并且18例中有8例立体视得到改善。12例患者随访3个月,弱视眼视力平均保持了99.3%,对侧眼视力改善平均保持了50%。结论知觉学习能改善青少年及成年屈光参差性弱视患者的视功能,可用于治疗大龄弱视。     

Specificity of perceptual learning increases with increased training

Perceptual learning often shows substantial and long-lasting changes in the ability to classify relevant perceptual stimuli due to practice. Specificity to trained stimuli and tasks is a key characteristic of visual perceptual learning, but little is known about whether specificity depends upon the extent of initial training. Using an orientation discrimination task, we demonstrate that specificity follows after extensive training, while the earliest stages of perceptual learning exhibit substantial transfer to a new location and an opposite orientation. Brief training shows the best performance at the point of transfer. These results for orientation-location transfer have both theoretical and practical implications for understanding perceptual expertise.     

Perceptual learning and attention: Reduction of object attention limitations with practice

Perceptual learning has widely been claimed to be attention driven; attention assists in choosing the relevant sensory information and attention may be necessary in many cases for learning. In this paper, we focus on the interaction of perceptual learning and attention - that perceptual learning can reduce or eliminate the limitations of attention, or, correspondingly, that perceptual learning depends on the attention condition. Object attention is a robust limit on performance. Two attributes of a single attended object may be reported without loss, while the same two attributes of different objects can exhibit a substantial dual-report deficit due to the sharing of attention between objects. The current experiments document that this fundamental dual-object report deficit can be reduced, or eliminated, through perceptual learning that is partially specific to retinal location. This suggests that alternative routes established by practice may reduce the competition between objects for processing resources.     

Robust perceptual learning of faces in the absence of sleep

This study examines the effects of sleep on learning in a face identification task. Five groups of subjects performed a 1-of-10 face identification task in two sessions separated by 3, 12, and 24 h. Session 1 consisted of four blocks of 105 trials each; Session 2 consisted of eight blocks of trials. All groups exhibited significant improvement in response accuracy within each session. Furthermore, between-session learning – defined as the difference in proportion correct between sessions 1 and 2 – was significant for all groups. Between-session learning was greater in groups that slept between sessions, but the effect was small and affected performance only in the first block of trials in Session 2. Overall, we find that sleep’s contribution is a small proportion of the total amount learned in face identification, with improvements continuing to accrue in its absence.     

A link between perceptual learning, adaptation and sleep

Between-sessions gains in the texture discrimination task have been attributed to memory consolidation. A strong dependence of consolidation on sleep was suggested though not always supported by experimental results. Here we suggest that the interaction between consolidation and sleep depends on the adaptation level obtained during the training session. We find that both discrimination thresholds and learning depend on the number of trials used during training, with more trials producing higher discrimination thresholds due to suppressive processes related to adaptation. In addition, while learning benefits from increasing number of trials, a further increase in number of trials reduces learning. Consolidation may benefit from between-session sleep in the adapted states.     

Identification of contrast-defined letters benefits from perceptual learning in adults with amblyopia

Amblyopes show specific deficits in processing second-order spatial information (e.g. Wong, Levi, & McGraw (2001). Is second-order spatial loss in amblyopia explained by the loss of first-order spatial input? Vision Research, 41, 2951-2960). Recent work suggests there is a significant degree of plasticity in the visual pathway that processes first-order spatial information in adults with amblyopia. In this study, we asked whether or not there is similar plasticity in the ability to process second-order spatial information in adults with amblyopia. Ten adult observers with amblyopia (five strabismic, four anisometropic and one mixed) were trained to identify contrast-defined (second-order) letters using their amblyopic eyes. Before and after training, we determined observers' contrast thresholds for identifying luminance-defined (first-order) and contrast-defined letters, separately for the non-amblyopic and amblyopic eyes. Following training, eight of the 10 observers showed a significant reduction in contrast thresholds for identifying contrast-defined letters with the amblyopic eye. Five of these observers also showed a partial transfer of improvement to their fellow untrained non-amblyopic eye for identifying contrast-defined letters. There was a small but statistically significant transfer to the untrained task of identifying luminance-defined letters in the same trained eye. Similar to first-order spatial tasks, adults with amblyopia benefit from perceptual learning for identifying contrast-defined letters in their amblyopic eyes, suggesting a sizeable degree of plasticity in the visual pathway for processing second-order spatial information.     

Task-specific perceptual learning on speed and direction discrimination

Twenty-two nai;ve undergraduates participated in a psychophysical experiment designed to elucidate the neural events that allow us to see subtle motion differences. Half of the subjects practiced extensively on a direction-discrimination task while the other half practiced extensively on a speed-discrimination task. The stimulus conditions in the two groups were identical. The results indicated that the learning curves for direction discrimination were significantly steeper than those for speed discrimination. Additionally, the significant practice-based improvements on each motion task did not transfer to the other motion task. The different learning rates and the lack of transfer suggest that the neural events mediating speed discrimination are at least partially independent from those mediating direction discrimination, and vice versa, even under identical stimulus conditions.     

Mirror symmetrical transfer of perceptual learning by prism adaptation

Recent study of [Sugita, Y. (1996) Global plasticity in adult visual cortex following reversal of visual input. Nature, 380, 523-526.] demonstrated that prism adaptation to reversed retinal input generates the transfer of neuronal activities in monkey V1 to the opposite visual cortex. This raises the question if perceptual learning on one side of the visual field can transfer to the other side. We tested this in using the Gabor lateral masking paradigm. Before adaptation, long-range interaction was induced vertically on one side (i.e., the right) of the visual field with training (perceptual learning). Prism adaptation was achieved by wearing right-left reversing goggles. During adaptation period, perceptual learning transferred to a mirror symmetrical region across the vertical meridian. Results in the post adaptation period revealed that both learning and transfer persisted for over three months. These results provide direct evidence of transferred perceptual plasticity across the visual field, the underlying mechanism of which is supported by the mirror symmetrical connection between the right and left cortices.     

Transfer of perceptual learning of depth discrimination between local and global stereograms

Several previous studies reported differences when stereothresholds are assessed with local-contour stereograms vs. complex random-dot stereograms (RDSs). Dissimilar thresholds may be due to differences in the properties of the stereograms (e.g. spatial frequency content, contrast, inter-element separation, area) or to different underlying processing mechanisms. This study examined the transfer of perceptual learning of depth discrimination between local and global RDSs with similar properties, and vice versa. If global and local stereograms are processed by separate neural mechanisms, then the magnitude and rate of training for the two types of stimuli are likely to differ, and the transfer of training from one stimulus type to the other should be minimal. Based on previous results, we chose RDSs with element densities of 0.17% and 28.3% to serve as the local and global stereograms, respectively. Fourteen inexperienced subjects with normal binocular vision were randomly assigned to either a local- or global- RDS training group. Stereothresholds for both stimulus types were measured before and after 7700 training trials distributed over 10 sessions. Stereothresholds for the trained condition improve for approximately 3000 trials, by an average of 0.36 ± 0.08 for local and 0.29 ± 0.10 for global RDSs, and level off thereafter. Neither the rate nor the magnitude of improvement differ statistically between the local- and global-training groups. Further, no significant difference exists in the amount of improvement on the trained vs. the untrained targets for either training group. These results are consistent with the operation of a single mechanism to process both local and global stereograms.     

Level and mechanisms of perceptual learning: learning first-order luminance and second-order texture objects

Perceptual learning is an improvement in perceptual task performance reflecting plasticity in the perceptual system. Practice effects were studied in two object orientation tasks: a first order, luminance object task and a second-order, texture object task. Perceptual learning was small or absent in the first-order task, but consistently occurred for the second-order (texture) task, where it was limited to improvements in low external noise conditions, or stimulus enhancement [Dosher, B., & Lu, Z. -L. (1998). Perceptual learning reflects external noise filtering and internal noise reduction through channel reweighting. Proceedings of the National Academy of Sciences of the United States of America, 95 (23) 13988-13993; Dosher, B., & Lu, Z. -L. (1999). Mechanisms of perceptual learning. Vision Research, 39 (19) 3197-3221], analogous to attention effects in first- and second-order motion processing [Lu, Z. -L., Liu, C. Q., & Dosher, B. (2000). Attention mechanisms for multi-location first- and second-order motion perception. Vision Research, 40 (2) 173-186]. Perceptual learning affected the later, post-rectification, stages of perceptual analysis, possibly localized at V2 or above. It serves to amplify the stimulus relative to limiting internal noise for intrinsically noisy representations of second-order stimuli.