Nonvisual motor training influences biological motion perception

Experimental evidence suggests a link between perception and the execution of actions . In particular, it has been proposed that motor programs might directly influence visual action perception . According to this hypothesis, the acquisition of novel motor behaviors should improve their visual recognition, even in the absence of visual learning. We tested this prediction by using a new experimental paradigm that dissociates visual and motor learning during the acquisition of novel motor patterns. The visual recognition of gait patterns from point-light stimuli was assessed before and after nonvisual motor training. During this training, subjects were blindfolded and learned a novel coordinated upper-body movement based only on verbal and haptic feedback. The learned movement matched one of the visual test patterns. Despite the absence of visual stimulation during training, we observed a selective improvement of the visual recognition performance for the learned movement. Furthermore, visual recognition performance after training correlated strongly with the accuracy of the execution of the learned motor pattern. These results prove, for the first time, that motor learning has a direct and highly selective influence on visual action recognition that is not mediated by visual learning.     

Vision and the statistics of the visual environment

It is widely believed that visual systems are optimized for the visual properties of the environment inhabited by the organism. A specific instance of this principle is known as the Efficient Coding Hypothesis, which holds that the purpose of early visual processing is to produce an efficient representation of the incoming visual signal. The theory provides a quantitative link between the statistical properties of the world and the structure of the visual system. As such, specific instances of this theory have been tested experimentally, and have been used to motivate and constrain models for early visual processing.     

Brief daily periods of binocular vision prevent deprivation-induced acuity loss

The role of experience in the development of the central visual pathways has been explored in the past through examination of the consequences of imposed periods of continuously abnormal or biased visual input. The massive changes in the visual cortex (area 17) induced by selected early visual experience, especially monocular deprivation (MD) or experience (ME) where patterned visual input is provided to just one eye, are accompanied by profound and long-standing visual deficits. Although the use of exclusively abnormal experience permits identification of those aspects of the visual cortex and of visual function that can be influenced by visual experience during development, this approach may provide a distorted view of the nature of the role of visual experience because of the absence of any normal visual input. In this study a different approach was used whereby animals were provided daily with separate periods of normal (i.e., binocular exposure) and abnormal (monocular exposure) visual experience. We show that 2 hr of daily normal concordant binocular experience (BE) can outweigh or protect against much longer periods of monocular deprivation (MD) and permit the development of normal visual acuities in the two eyes. This result is not what would be expected if all visual input had equal influence on visual development.     

The Development of Visual Areas Depends Differently on Visual Experience

Visual experience plays an important role in the development of the visual cortex; however, recent functional imaging studies have shown that the functional organization is preserved in several higher-tier visual areas in congenitally blind subjects, indicating that maturation of visual areas depend unequally on visual experience. In this study, we aim to validate this hypothesis using a multimodality MRI approach. We found increased cortical thickness in the congenitally blind was present in the early visual areas and absent in the higher-tier ones, suggesting that the structural development of the visual cortex depends hierarchically on visual experience. In congenitally blind subjects, the decreased resting-state functional connectivity with the primary somatosensory cortex was more prominent in the early visual areas than in the higher-tier ones and were more pronounced in the ventral stream than in the dorsal one, suggesting that the development of functional organization of the visual cortex also depends differently on visual experience. Moreover, congenitally blind subjects showed normal or increased functional connectivity between ipsilateral higher-tier and early visual areas, suggesting an indirect corticocortical pathway through which somatosenroy information can reach the early visual areas. These findings support our hypothesis that the development of visual areas depends differently on visual experience.     

The Duration of a Co-Occurring Sound Modulates Visual Detection Performance in Humans

Background

The duration of sounds can affect the perceived duration of co-occurring visual stimuli. However, it is unclear whether this is limited to amodal processes of duration perception or affects other non-temporal qualities of visual perception.

Methodology/Principal Findings

Here, we tested the hypothesis that visual sensitivity - rather than only the perceived duration of visual stimuli - can be affected by the duration of co-occurring sounds. We found that visual detection sensitivity (d’) for unimodal stimuli was higher for stimuli of longer duration. Crucially, in a cross-modal condition, we replicated previous unimodal findings, observing that visual sensitivity was shaped by the duration of co-occurring sounds. When short visual stimuli (∼24 ms) were accompanied by sounds of matching duration, visual sensitivity was decreased relative to the unimodal visual condition. However, when the same visual stimuli were accompanied by longer auditory stimuli (∼60–96 ms), visual sensitivity was increased relative to the performance for ∼24 ms auditory stimuli. Across participants, this sensitivity enhancement was observed within a critical time window of ∼60–96 ms. Moreover, the amplitude of this effect correlated with visual sensitivity enhancement found for longer lasting visual stimuli across participants.

Conclusions/Significance

Our findings show that the duration of co-occurring sounds affects visual perception; it changes visual sensitivity in a similar way as altering the (actual) duration of the visual stimuli does.     

Attention and visual perception

Somewhere between the retina and our conscious visual experience, the majority of the information impinging on the eye is lost. We are typically aware of only either the most salient parts of a visual scene or the parts that we are actively paying attention to. Recent research on visual neurons in monkeys is beginning to show how the brain both selects and discards incoming visual information. For example, what happens to the responses of visual neurons when attention is directed to one element, such as an oriented colored bar, embedded among an array of other oriented bars? Some of this research shows that attention to the oriented bar restricts the receptive field of visual neurons down to this single element. However, other research shows that attention to this single element affects the responses of neurons with receptive fields throughout the visual field. In this review, these two seemingly contradictory results are shown to actually be mutually consistent. A simple computational model is described that explains these results, and also provides a framework for predicting a variety of additional neurophysiological, neuroimaging and behavioral studies of attention.     

Neural mechanism of visual information degradation from retina to V1 area

The information processing mechanism of the visual nervous system is an unresolved scientific problem that has long puzzled neuroscientists. The amount of visual information is significantly degraded when it reaches the V1 after entering the retina; nevertheless, this does not affect our visual perception of the outside world. Currently, the mechanisms of visual information degradation from retina to V1 are still unclear. For this purpose, the current study used the experimental data summarized by Marcus E. Raichle to investigate the neural mechanisms underlying the degradation of the large amount of data from topological mapping from retina to V1, drawing on the photoreceptor model first. The obtained results showed that the image edge features of visual information were extracted by the convolution algorithm with respect to the function of synaptic plasticity when visual signals were hierarchically processed from low-level to high-level. The visual processing was characterized by the visual information degradation, and this compensatory mechanism embodied the principles of energy minimization and transmission efficiency maximization of brain activity, which matched the experimental data summarized by Marcus E. Raichle. Our results further the understanding of the information processing mechanism of the visual nervous system.     

Work of the human visual system. II. Color]

In the first part of this work [1] the author presented the expression for so called adequate visual stimulus. This expression describing the change of relative space - time differences of light actions in different retinal points defines the conditions necessary for producing visual sensations. In this paper author makes a statement that the quality of visual sensation (the percieved colour) can be evaluated by integrating the expression for the adequate visual stimulus both in time and in space. The integration in space is fulfilled starting from the extreme periphery of the retina, which is usually illuminated by scattered light averaged over the whole visual field. Human visual system works in such a way that the light action in the extreme periphery plays a role of the unit for scaling of visual sensations.     

Online learning and stimulus-driven responses of neurons in visual cortex

In understanding how visual scene is processed in visual cortex, it has been an intriguing problem for theoretical and experimental neuroscientists to examine the relationship between visual stimuli and the induced responses of visual cortex. In particular, it is less explored whether and how the collective responses of visual neurons are patterned to reflect the geometrical regularities. In this paper, through a computation model and statistical analysis, we show that the orientation preference maps induced from correlated visual stimuli exhibit geometrical regularities similar as observed in natural images.     

Hemispheric Asymmetry in the Auditory Facilitation Effect in Dual-Stream Rapid Serial Visual Presentation Tasks

Even though auditory stimuli do not directly convey information related to visual stimuli, they often improve visual detection and identification performance. Auditory stimuli often alter visual perception depending on the reliability of the sensory input, with visual and auditory information reciprocally compensating for ambiguity in the other sensory domain. Perceptual processing is characterized by hemispheric asymmetry. While the left hemisphere is more involved in linguistic processing, the right hemisphere dominates spatial processing. In this context, we hypothesized that an auditory facilitation effect in the right visual field for the target identification task, and a similar effect would be observed in the left visual field for the target localization task. In the present study, we conducted target identification and localization tasks using a dual-stream rapid serial visual presentation. When two targets are embedded in a rapid serial visual presentation stream, the target detection or discrimination performance for the second target is generally lower than for the first target; this deficit is well known as attentional blink. Our results indicate that auditory stimuli improved target identification performance for the second target within the stream when visual stimuli were presented in the right, but not the left visual field. In contrast, auditory stimuli improved second target localization performance when visual stimuli were presented in the left visual field. An auditory facilitation effect was observed in perceptual processing, depending on the hemispheric specialization. Our results demonstrate a dissociation between the lateral visual hemifield in which a stimulus is projected and the kind of visual judgment that may benefit from the presentation of an auditory cue.     

Am I seeing my hand? Visual appearance and knowledge of controllability both contribute to the visual capture of a person's own body

When confronted with complex visual scenes in daily life, how do we know which visual information represents our own hand? We investigated the cues used to assign visual information to one''s own hand. Wrist tendon vibration elicits an illusory sensation of wrist movement. The intensity of this illusion attenuates when the actual motionless hand is visually presented. Testing what kind of visual stimuli attenuate this illusion will elucidate factors contributing to visual detection of one''s own hand. The illusion was reduced when a stationary object was shown, but only when participants knew it was controllable with their hands. In contrast, the visual image of their own hand attenuated the illusion even when participants knew that it was not controllable. We suggest that long-term knowledge about the appearance of the body and short-term knowledge about controllability of a visual object are combined to robustly extract our own body from a visual scene.     

Visual field asymmetries in attention and learning

It has been suggested that attentional resolution is greater in the lower than in the upper visual field. As there is no corresponding asymmetry between the areas in the primary visual cortex where the input from upper and lower visual fields is processed, an 'attentional filter' has been proposed to act in one or more higher visual cortical areas in order to constrict the availability of visual information to the level of awareness. To investigate this, a visual search array was presented to the entire visual field and reaction times from upper and lower visual fields compared. In a second experiment, subjects were trained in detecting targets in different visual fields. There was no significant difference between reaction times for targets presented in either upper or lower visual fields when the array was presented to the entire visual field. However, when the array was restricted to either the upper or lower visual fields, reaction times were significantly slower for detection in the upper visual field.     

Neuronal mechanisms for visual stability: progress and problems

How our vision remains stable in spite of the interruptions produced by saccadic eye movements has been a repeatedly revisited perceptual puzzle. The major hypothesis is that a corollary discharge (CD) or efference copy signal provides information that the eye has moved, and this information is used to compensate for the motion. There has been progress in the search for neuronal correlates of such a CD in the monkey brain, the best animal model of the human visual system. In this article, we briefly summarize the evidence for a CD pathway to frontal cortex, and then consider four questions on the relation of neuronal mechanisms in the monkey brain to stable visual perception. First, how can we determine whether the neuronal activity is related to stable visual perception? Second, is the activity a possible neuronal correlate of the proposed transsaccadic memory hypothesis of visual stability? Third, are the neuronal mechanisms modified by visual attention and does our perceived visual stability actually result from neuronal mechanisms related primarily to the central visual field? Fourth, does the pathway from superior colliculus through the pulvinar nucleus to visual cortex contribute to visual stability through suppression of the visual blur produced by saccades?     

Changes in visual fields associated with web reduction in the spider family uloboridae

When visual fields of the primitive orb-weaver, Waitkera waitkerensis, are reconstructed using measurements taken from intact lenses and cross and longitudinal sections of the prosoma, they show that this species has complete visual surveillance, but that none of the visual fields of its eight eyes overlap. The more advanced orb-weaver, Uloborus glomosus, also has eight eyes, but each eye has a greater visual angle, giving this species a complex pattern of overlapping visual fields. Uloborids that spin reduced webs are characterized by reduction or loss of the four anterior eyes and other carapace modifications necessary for them to effectively monitor and manipulate their reduced webs. The eyes of these uloborids have greater visual angles than those of orb-weavers, resulting primarily from perimetric expansion of their retinal hemispheres. Additionally, the axes of their visual fields are more ventrally directed due to greater dorsal than ventral retinal expansion and to ventral redirection of the entire eye. Consequently, even though the anterior lateral eyes of the triangle-weaver Hyptiotes cavatus lack retinae, the species' six functional eyes permit complete visual surveillance and exhibit visual overlap. The single-line-weaver, Miagrammopes animotus, has lost its four anterior eyes, and with them much of the anterior vision and all of the visual overlap found in the other species. However, changes similar to those of H. cavatus permit this species to retain most if its dorsal and ventral visual surveillance. Thus, ocular changes act in consort to maintain relatively complete visual surveillance in the face of eye loss and other major carapace modifications necessary for the operation of reduced webs.     

Contrast and Strength of Visual Memory and Imagery Differentially Affect Visual Perception

Visual short-term memory (VSTM) and visual imagery have been shown to modulate visual perception. However, how the subjective experience of VSTM/imagery and its contrast modulate this process has not been investigated. We addressed this issue by asking participants to detect brief masked targets while they were engaged either in VSTM or visual imagery. Subjective experience of memory/imagery (strength scale), and the visual contrast of the memory/mental image (contrast scale) were assessed on a trial-by-trial basis. For both VSTM and imagery, contrast of the memory/mental image was positively associated with reporting target presence. Consequently, at the sensory level, both VSTM and imagery facilitated visual perception. However, subjective strength of VSTM was positively associated with visual detection whereas the opposite pattern was found for imagery. Thus the relationship between subjective strength of memory/imagery and visual detection are qualitatively different for VSTM and visual imagery, although their impact at the sensory level appears similar. Our results furthermore demonstrate that imagery and VSTM are partly dissociable processes.     

Cerebral Asymmetry of fMRI-BOLD Responses to Visual Stimulation

Hemispheric asymmetry of a wide range of functions is a hallmark of the human brain. The visual system has traditionally been thought of as symmetrically distributed in the brain, but a growing body of evidence has challenged this view. Some highly specific visual tasks have been shown to depend on hemispheric specialization. However, the possible lateralization of cerebral responses to a simple checkerboard visual stimulation has not been a focus of previous studies. To investigate this, we performed two sessions of blood-oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) in 54 healthy subjects during stimulation with a black and white checkerboard visual stimulus. While carefully excluding possible non-physiological causes of left-to-right bias, we compared the activation of the left and the right cerebral hemispheres and related this to grey matter volume, handedness, age, gender, ocular dominance, interocular difference in visual acuity, as well as line-bisection performance. We found a general lateralization of cerebral activation towards the right hemisphere of early visual cortical areas and areas of higher-level visual processing, involved in visuospatial attention, especially in top-down (i.e., goal-oriented) attentional processing. This right hemisphere lateralization was partly, but not completely, explained by an increased grey matter volume in the right hemisphere of the early visual areas. Difference in activation of the superior parietal lobule was correlated with subject age, suggesting a shift towards the left hemisphere with increasing age. Our findings suggest a right-hemispheric dominance of these areas, which could lend support to the generally observed leftward visual attentional bias and to the left hemifield advantage for some visual perception tasks.     

The perceived image: efficient modelling of visual inhomogeneity.

When we fixate on a certain location in a scene, the image that our visual system provides us with is not like a snapshot of the scene. Because of visual inhomogeneity, the image we perceive is sharp and clean only around the fixation location, and it gradually blurs and loses detail with increasing distance from that location. In this paper, a procedure is presented that allows one to obtain the luminance distribution in the perceived image of a scene. The procedure is based on a stack distribution model of spatial visual processing, with parameters obtained experimentally. An application of this procedure is presented which allows an explanation of data on the decrease of visual acuity with eccentricity. The advantages of this procedure for taking visual inhomogeneity into account when seeking explanations for perceptual phenomena are also discussed.     

Emergence of visual saliency from natural scenes via context-mediated probability distributions coding

Visual saliency is the perceptual quality that makes some items in visual scenes stand out from their immediate contexts. Visual saliency plays important roles in natural vision in that saliency can direct eye movements, deploy attention, and facilitate tasks like object detection and scene understanding. A central unsolved issue is: What features should be encoded in the early visual cortex for detecting salient features in natural scenes? To explore this important issue, we propose a hypothesis that visual saliency is based on efficient encoding of the probability distributions (PDs) of visual variables in specific contexts in natural scenes, referred to as context-mediated PDs in natural scenes. In this concept, computational units in the model of the early visual system do not act as feature detectors but rather as estimators of the context-mediated PDs of a full range of visual variables in natural scenes, which directly give rise to a measure of visual saliency of any input stimulus. To test this hypothesis, we developed a model of the context-mediated PDs in natural scenes using a modified algorithm for independent component analysis (ICA) and derived a measure of visual saliency based on these PDs estimated from a set of natural scenes. We demonstrated that visual saliency based on the context-mediated PDs in natural scenes effectively predicts human gaze in free-viewing of both static and dynamic natural scenes. This study suggests that the computation based on the context-mediated PDs of visual variables in natural scenes may underlie the neural mechanism in the early visual cortex for detecting salient features in natural scenes.     

宽周边视视网膜皮层映射的核磁共振研究

目的:人类视觉皮层的组织方式是视网膜皮层映射组织,先前研究已经证实视觉皮层在中心视采用这种组织方式,本文主要研究宽周边视的视觉皮层组织方式.方法:本文采用一种可以在核磁共振室中使用的光纤设备,设计了30度、40度、50度、60度的类圆环block刺激,使用1.5T的功能性核磁共振仪器,T1高分辨率图像分辨率为1*1*5.5mm,T2加权图像分辨率为4*4*5.5mm,TR反应时间为60,矩阵大小为64*64.核磁共振数据分析使用了SPM2和Brain voyager软件.结果:通过对试验者的数据处理分析,周边视的刺激的反应区域在枕叶上,主要分布在枕叶的前部,刺激反应区域随着偏心率的增大而沿着距状沟从距状沟的后部向前部移动.结论:周边视的视网膜皮层映射组织特性和中心视的特性非常相似.     

Impact of visual repetition rate on intrinsic properties of low frequency fluctuations in the visual network

Background

Visual processing network is one of the functional networks which have been reliably identified to consistently exist in human resting brains. In our work, we focused on this network and investigated the intrinsic properties of low frequency (0.01–0.08 Hz) fluctuations (LFFs) during changes of visual stimuli. There were two main questions to be discussed in this study: intrinsic properties of LFFs regarding (1) interactions between visual stimuli and resting-state; (2) impact of repetition rate of visual stimuli.

Methodology/Principal Findings

We analyzed scanning sessions that contained rest and visual stimuli in various repetition rates with a novel method. The method included three numerical approaches involving ICA (Independent Component Analyses), fALFF (fractional Amplitude of Low Frequency Fluctuation), and Coherence, to respectively investigate the modulations of visual network pattern, low frequency fluctuation power, and interregional functional connectivity during changes of visual stimuli. We discovered when resting-state was replaced by visual stimuli, more areas were involved in visual processing, and both stronger low frequency fluctuations and higher interregional functional connectivity occurred in visual network. With changes of visual repetition rate, the number of areas which were involved in visual processing, low frequency fluctuation power, and interregional functional connectivity in this network were also modulated.

Conclusions/Significance

To combine the results of prior literatures and our discoveries, intrinsic properties of LFFs in visual network are altered not only by modulations of endogenous factors (eye-open or eye-closed condition; alcohol administration) and disordered behaviors (early blind), but also exogenous sensory stimuli (visual stimuli with various repetition rates). It demonstrates that the intrinsic properties of LFFs are valuable to represent physiological states of human brains.