Attentional modulation of sensorimotor processes in the absence of perceptual awareness

Attention modulates visual perception and is generally considered inextricably linked with conscious awareness: we become aware of stimuli as we attend to them, and we attend to stimuli as we become aware of them. Recent evidence suggests that attention can also modulate the effects of stimuli that remain invisible, and a natural explanation is that attention enhances weak perceptual representations, bringing them closer to conscious threshold even if they do not reach that threshold. However, there is also the possibility that attention may modulate neural processes that are entirely separate from those supporting conscious perception: sensorimotor mechanisms that do not create awareness however much they are enhanced. Here we provide evidence in support of this second hypothesis by showing that attentional cueing can modulate the behavioral response to invisible stimuli in a way that is distinct from enhancing their visibility. We used a masked-prime paradigm that produces a negative or positive compatibility effect depending on the perceptual strength (duration or brightness) of the prime. We found that attention enhanced the effect of both visible and invisible primes and also increased the likelihood of detecting the prime (i.e., boosted perceptual strength). Crucially, the pattern of attentional influence on priming could not be explained by attentional modulation of the prime's perceptual strength but was predicted by a direct attentional influence on the nonconscious priming process itself. Therefore, in addition to regulating what we perceive, attention seems to influence our behavior through sensorimotor processes that are not involved in conscious awareness.     

Task-specific disruption of perceptual learning

For more than a century, the process of stabilization has been a central issue in the research of learning and memory. Namely, after a skill or memory is acquired, it must be consolidated before it becomes resistant to disruption by subsequent learning. Although it is clear that there are many cases in which learning can be disrupted, it is unclear when learning something new disrupts what has already been learned. Herein, we provide two answers to this question with the demonstration that perceptual learning of a visual stimulus disrupts or interferes with the consolidation of a previously learned visual stimulus. In this study, we trained subjects on two different hyperacuity tasks and determined whether learning of the second task disrupted that of the first. We first show that disruption of learning occurs between visual stimuli presented at the same orientation in the same retinotopic location but not for the same stimuli presented at retinotopically disparate locations or different orientations at the same location. Second, we show that disruption from stimuli in the same retinotopic location is ameliorated if the subjects wait for 1 h before training on the second task. These results indicate that disruption, at least in visual learning, is specific to features of the tasks and that a temporal delay of 1 h can stabilize visual learning. This research shows that visual learning is susceptible to disruption and elucidates the processes by which the brain can consolidate learning and thus protect what is learned from being overwritten.     

Stereotype threat prevents perceptual learning

Stereotype threat (ST) refers to a situation in which a member of a group fears that her or his performance will validate an existing negative performance stereotype, causing a decrease in performance. For example, reminding women of the stereotype “women are bad at math” causes them to perform more poorly on math questions from the SAT and GRE. Performance deficits can be of several types and be produced by several mechanisms. We show that ST prevents perceptual learning, defined in our task as an increasing rate of search for a target Chinese character in a display of such characters. Displays contained two or four characters and half of these contained a target. Search rate increased across a session of training for a control group of women, but not women under ST. Speeding of search is typically explained in terms of learned “popout” (automatic attraction of attention to a target). Did women under ST learn popout but fail to express it? Following training, the women were shown two colored squares and asked to choose the one with the greater color saturation. Superimposed on the squares were task-irrelevant Chinese characters. For women not trained under ST, the presence of a trained target on one square slowed responding, indicating that training had caused the learning of an attention response to targets. Women trained under ST showed no slowing, indicating that they had not learned such an attention response.     

Olfactory perceptual learning requires adult neurogenesis

Perceptual learning is required for olfactory function to adapt appropriately to changing odor environments. We here show that newborn neurons in the olfactory bulb are not only involved in, but necessary for, olfactory perceptual learning. First, the discrimination of perceptually similar odorants improves in mice after repeated exposure to the odorants. Second, this improved discrimination is accompanied by an elevated survival rate of newborn inhibitory neurons, preferentially involved in processing of the learned odor, within the olfactory bulb. Finally, blocking neurogenesis before and during the odorant exposure period prevents this learned improvement in discrimination. Olfactory perceptual learning is thus mediated by the reinforcement of functional inhibition in the olfactory bulb by adult neurogenesis.     

Interocular transfer in perceptual learning of a pop-out discrimination task.

The specificity of the improvement in perceptual learning is often used to localize the neuronal changes underlying this type of adult plasticity. We investigated a visual texture discrimination task previously reported to be accomplished preattentively and for which learning-related changes were inferred to occur at a very early level of the visual processing stream. The stimulus was a matrix of lines from which a target popped out, due to an orientation difference between the three target lines and the background lines. The task was to report the global orientation of the target and was performed monocularly. The subjects' performance improved dramatically with training over the course of 2-3 weeks, after which we tested the specificity of the improvement for the eye trained. In all subjects tested, there was complete interocular transfer of the learning effect. The neuronal correlate of this learning are therefore most likely localized in a visual area where input from the two eyes has come together.     

Perceptual learning depends on perceptual constancy

Perceptual learning refers to experience-induced improvements in the pick-up of information. Perceptual constancy describes the fact that, despite variable sensory input, perceptual representations typically correspond to stable properties of objects. Here, we show evidence of a strong link between perceptual learning and perceptual constancy: Perceptual learning depends on constancy-based perceptual representations. Perceptual learning may involve changes in early sensory analyzers, but such changes may in general be constrained by categorical distinctions among the high-level perceptual representations to which they contribute. Using established relations of perceptual constancy and sensory inputs, we tested the ability to discover regularities in tasks that dissociated perceptual and sensory invariants. We found that human subjects could learn to classify based on a perceptual invariant that depended on an underlying sensory invariant but could not learn the identical sensory invariant when it did not correlate with a perceptual invariant. These results suggest that constancy-based representations, known to be important for thought and action, also guide learning and plasticity.     

视知觉感知学习在弱视治疗中的应用

目前对于弱视形成的神经学基础、心理和物理学检测的特征性异常以及运用相关工程化平台进行治疗等方面发展迅速,已与传统诊断治疗理念有显著区别,现就该方面进展做一综述.     

An integrated reweighting theory of perceptual learning

Improvements in performance on visual tasks due to practice are often specific to a retinal position or stimulus feature. Many researchers suggest that specific perceptual learning alters selective retinotopic representations in early visual analysis. However, transfer is almost always practically advantageous, and it does occur. If perceptual learning alters location-specific representations, how does it transfer to new locations? An integrated reweighting theory explains transfer over retinal locations by incorporating higher level location-independent representations into a multilevel learning system. Location transfer is mediated through location-independent representations, whereas stimulus feature transfer is determined by stimulus similarity at both location-specific and location-independent levels. Transfer to new locations/positions differs fundamentally from transfer to new stimuli. After substantial initial training on an orientation discrimination task, switches to a new location or position are compared with switches to new orientations in the same position, or switches of both. Position switches led to the highest degree of transfer, whereas orientation switches led to the highest levels of specificity. A computational model of integrated reweighting is developed and tested that incorporates the details of the stimuli and the experiment. Transfer to an identical orientation task in a new position is mediated via more broadly tuned location-invariant representations, whereas changing orientation in the same position invokes interference or independent learning of the new orientations at both levels, reflecting stimulus dissimilarity. Consistent with single-cell recording studies, perceptual learning alters the weighting of both early and midlevel representations of the visual system.     

Attentional and perceptual contributions to the identification of extrafoveal stimuli: adult age comparisons

Gerontological researchers have been cautioned that conclusions about age differences in attention may have been inferred from data that, in fact, reflected age differences in perceptual processing of stimuli falling outside the fovea (Cerella, 1985). Presumably, the experimental manipulations on which Cerella based his caution induced a broad focus of attention so that changes in perceptual processing would not be confounded with changes in attention. Experiment 1 tested this by comparing a condition similar to Cerella's with another in which attention was narrowly focused at fixation. The results replicated Cerella's findings. In addition, there were greater age differences when attention had been narrowly focused, showing that attentional effects can be separated from the effects reported by Cerella. Experiment 2 showed that age differences in extrafoveal perception could be removed by increasing the duration of the target from 200 to 2000 ms, suggesting that the perceptual deficits in older adults are due to differentially lengthened processing of stimuli outside the fovea.     

Improving vision in adult amblyopia by perceptual learning

Practicing certain visual tasks leads, as a result of a process termed "perceptual learning," to a significant improvement in performance. Learning is specific for basic stimulus features such as local orientation, retinal location, and eye of presentation, suggesting modification of neuronal processes at the primary visual cortex in adults. It is not known, however, whether such low-level learning affects higher-level visual tasks such as recognition. By systematic low-level training of an adult visual system malfunctioning as a result of abnormal development (leading to amblyopia) of the primary visual cortex during the "critical period," we show here that induction of low-level changes might yield significant perceptual benefits that transfer to higher visual tasks. The training procedure resulted in a 2-fold improvement in contrast sensitivity and in letter-recognition tasks. These findings demonstrate that perceptual learning can improve basic representations within an adult visual system that did not develop during the critical period.     

Perceptual learning in clear displays optimizes perceptual expertise: learning the limiting process

Human operators develop expertise in perceptual tasks by practice or perceptual learning. For noisy displays, practice improves performance by learned external-noise filtering. For clear displays, practice improves performance by improved amplification or enhancement of the stimulus. Can these two mechanisms of perceptual improvement be trained separately? In an orientation task, we found that training with clear displays generalized to performance in noisy displays, but we did not find the reverse to be true. In noisy displays, the noise in the stimulus limits performance. In clear displays, performance is limited by noisiness of internal representations and processes. Our results suggest that training in one display condition optimizes the limiting factor(s) in performance in that condition and that noise filtering is also improved by exposure to the stimulus in clear displays. The asymmetric pattern of transfer implies the existence of two independent mechanisms of perceptual learning, which may reflect channel reweighting in adult visual system. These results also suggest that training operators with clear stimuli may suffice to improve performance in a range of clear and noisy environments by simultaneous learning by two mechanisms.     

Independent perceptual learning in monocular and binocular motion systems

Eye-transfer tests, external noise manipulations, and observer models were used to systematically characterize learning mechanisms in judging motion direction of moving objects in visual periphery (Experiment 1) and fovea (Experiment 2) and to investigate the degree of transfer of the learning mechanisms from trained to untrained eyes. Perceptual learning in one eye was measured over 10 practice sessions. Subsequent learning in the untrained eye was assessed in five transfer sessions. We characterized the magnitude of transfer of each learning mechanism to the untrained eye by separately analyzing the magnitude of subsequent learning in low and high external noise conditions. In both experiments, we found that learning in the trained eye reduced contrast thresholds uniformly across all of the external noise levels: 47 +/- 10% and 62 +/- 8% in experiments 1 and 2, respectively. Two mechanisms, stimulus enhancement and template retuning, accounted for the observed performance improvements. The degree of transfer to the untrained eye depended on the amount of external noise added to the signal stimuli: In high external noise conditions, learning transferred completely to the untrained eye in both experiments. In low external noise conditions, there was only partial transfer of learning: 63% in experiment 1 and 54% in experiment 2. The results suggest that template retuning, which is effective in high external noise conditions, is mostly binocular, whereas stimulus enhancement, which is effective in low external noise displays, is largely monocular. The two independent mechanisms underlie perceptual learning of motion direction identification in monocular and binocular motion systems.     

视知觉学习对屈光不正性学龄前儿童视力改善作用的近期观察

目的观察视知觉学习对屈光不正性学龄前儿童的视力改善作用。方法采用回顾性自身对照试验方法选择2009-01～2010-03在广西视光中心接受视知觉学习的屈光不正儿童53例,其中男28例,女25例,年龄(5.4±0.9)岁;矫正视力0.3～0.1 LogMAR。所有受试者均戴矫正眼镜接受视知觉学习,临床随访观察5个月,记录每月的矫正视力,视力检测结果对照LogMAR视力进行转换。采用SPSS13.0统计软件进行方差分析比较视知觉学习前、后各时间点的矫正视力差异。结果 (1)53例最佳矫正视力正常的屈光不正儿童在视知觉学习前和视知觉学习后1～5个月的矫正视力分别为(0.163±0.068)、(0.079±0.066)、(0.060±0.063)、(0.042±0.055)、(0.037±0.056)、(0.028±0.047)LogMAR。(2)重复测量资料的方差分析结果显示:视知觉学习后各时间点的矫正视力与视知觉学习前相比差异均有统计学意义(F=164.655,P0.01),即所有受试者的矫正视力均较训练前得到明显改善。(3)LSD法进行各时间点间的两两比较结果显示,视知觉学习后第1个月、第2个月、第3个月两两之间差异均有统计学意义(P0.01),但第3个月、第4个月之间差异无统计学意义(P=0.167)、而第4个月与第5个月之间差异亦有统计学意义(P0.05)。结论视知觉学习可在短期内迅速改善学龄前儿童的矫正视力。     

Attentional integration between anatomically distinct stimulus representations in early visual cortex

Vision often requires attending to, and integrating information from, distant parts of the visual field. However, the neural basis for such long-range integration is not clearly understood. Here, we demonstrate a specific neural signature of attentional integration between stimuli in different parts of the visual field. Using functional MRI, we found that a task requiring the integration of information between two attended but spatially separated stimuli actively modulated the degree of functional integration (in terms of effective connectivity) between their retinotopic representations in visual cortical areas V1, V2, and V4. Spatial attention enhanced long-distance coupling between distinct neuronal populations that represented the attended visual stimuli, even at the earliest stages of cortical processing. In contrast, unattended stimulus representations were decoupled both from attended representations and particularly strongly from each other. Furthermore, enhanced functional integration between cortical representations was associated with enhanced behavioral performance. Attention may thus serve to "bind" together cortical loci at multiple levels of the visual hierarchy that are commonly involved in processing attended stimuli, promoting integration between otherwise functionally isolated cortical loci.     

Seeing what is not there shows the costs of perceptual learning

Perceptual learning is an improvement in one's sensory abilities after training and is thought to help us to better adapt to the sensory environment. Here, we show that perceptual learning also can lead to misperceptions, such that subjects actually perceive stimuli when none are physically presented. After learning, subjects not only showed enhanced performance when tested with the motion direction of the trained stimulus but also often reported seeing dots moving in the trained direction when no stimulus was displayed. We further show that these misperceptions are not attributable to a response bias. These results show that there are costs as well as benefits to perceptual learning and that performance enhancements for a specific feature also can be accompanied by misperceptions of the visual environment.     

Attentional demands and postural control: the effect of sensory context

BACKGROUND: This study used a dual task design to examine the effect of sensory context on postural stability during the concurrent performance of an attentionally demanding cognitive task in young and older adults with and without a history of imbalance and falls. METHODS: A choice reaction time auditory task was used to produce changes in attention during quiet stance in six different sensory conditions that changed the availability of accurate visual and somatosensory cues for postural control. Postural stability was quantified by using forceplate measures of center of pressure in 18 young adults, 18 healthy older adults, and 18 older adults with balance impairments and a history of recent falls. Reaction time and accuracy of verbal response to the auditory task were quantified by using a repeated measures analysis of variance. RESULTS: In young adults the auditory task did not affect postural stability in any of the sensory conditions. However, in the older adults the effect of the auditory task depended on sensory context. For healthy older adults, the addition of an auditory tone task significantly affected sway only when both visual and somatosensory cues for postural control were removed. In the balance-impaired older adults, the addition of the auditory task significantly affected postural stability in all sensory conditions. In addition, as sensory conditions became more difficult, older adults who had been able to maintain stability in a single task context lost balance when performing a secondary task. CONCLUSION: Results suggest that with aging, attentional demands for postural control increase as sensory information decreases. In addition, the inability to allocate sufficient attention to postural control under multitask conditions may be a contributing factor to imbalance and falls in some older adults.     

Genetic control of early folliculogenesis in mice.

Perinatally, granulosa cells encase individual oocytes within the ovary to form primordial follicles. The initial stages of folliculogenesis are independent of gonadotropins and involve cell-autonomous and non-cell-autonomous factors. Although still poorly understood at a molecular level, successful follicle formation and initiation of follicle growth must involve genetic networks both in germ and in somatic cells. Mouse models offer useful windows into these essential processes. By investigating phenotypes of mouse lines lacking specific gene products, genetic hierarchies that regulate the initial stages of folliculogenesis are being elucidated. These investigations will provide insight into the regulation of mammalian fertility.     

视知觉学习治疗大龄儿童屈光参差性弱视的疗效观察

目的观察应用基于互联网的视知觉学习系统治疗9～13岁屈光参差性儿童弱视的疗效,分析其视力的变化,为寻找儿童弱视快速、有效的治疗方法提供参考。方法选取我院收治的弱视患儿216例(216眼),分别应用基于互联网的视知觉学习系统(视觉组)和传统综合训练方法(综合组)对大龄弱视儿童进行治疗,具体训练方案由医师基于患儿视觉表现的初始状态、功能低下的严重程度以及训练治疗过程中的进步来设计。视知觉学习系统组给予提高视觉噪声和轮廓整合、位置噪声等视觉训练方案;传统综合训练组采取红光、精细目力训练等治疗。90d为1个疗程,共3～4个疗程。对比观察两种方法在弱视治疗后1、3、9、12个月的视力变化。结果视知觉学习系统组的疗效优于传统综合训练组(P=0.000),不同程度屈光参差性弱视视知觉学习系统组的疗效优于传统综合训练组(P0.01)。视知觉学习系统组视力提升速率明显高于传统综合训练组,视知觉学习系统组在疗程第6个月已有50%的患儿进入基本治愈的平台期,而传统综合训练组50%的患儿在观察终点才进入基本治愈平台期。视知觉学习训练组治疗屈光参差性弱视平均训练13.75h可提高一行视力,其中中度弱视所需时间最短(10.78h),重度弱视次之(12h),轻度弱视所需时间最长(26.5h)。结论基于互联网的视知觉学习系统提供了强烈、活跃、有反馈的个性化视觉刺激,对超过视觉发育敏感期的9～13岁屈光参差性儿童弱视的疗效优于传统综合训练法,缩短了视功能障碍治疗的周期。此新方法能在较短时间达到最佳治疗效果,为弱视的临床治疗提供了新的可行途径。     

Recovery of stereopsis through perceptual learning in human adults with abnormal binocular vision

Stereopsis, the perception of depth based on the disparity of the images projected to the retinas of the two eyes, is an important process in our three-dimensional world; however, 3-5% of the population is stereoblind or has seriously impaired stereovision. Here we provide evidence for the recovery of stereopsis through perceptual learning, the repetitive practice of a demanding visual task, in human adults long deprived of normal binocular vision. We used a training paradigm that combines monocular cues that were correlated perfectly with the disparity cues. Following perceptual learning (thousands of trials) with stereoscopic gratings, five adults who initially were stereoblind or stereoanomalous showed substantial recovery of stereopsis, both on psychophysical tests with stimuli that contained no monocular cues and on clinical testing. They reported that depth "popped out" in daily life, and enjoyed 3D movies for the first time. After training, stereo tests with dynamic random-dot stereograms and band-pass noise revealed the properties of the recovered stereopsis: It has reduced resolution and precision, although it is based on perceiving depth by detecting binocular disparity. We conclude that some human adults deprived of normal binocular vision can recover stereopsis at least partially.