A lower visual field advantage for endpoint stability but no advantage for online movement precision

It has been proposed that visually guided reaching movements performed in the lower visual field (LVF) of peripersonal space are more effective and efficient than their upper visual field (UVF) counterparts (Danckert and Goodale 2001). In the present investigation we sought to determine whether this purported visual field asymmetry reflects advantaged processing of online visual feedback. To accomplish that objective, participants performed discrete reaching movements to each of three target locations in the LVF and UVF. In addition, reaches were completed under conditions wherein target location remained constant throughout a reaching response (i.e., control trials) and a separate condition wherein target location unexpectedly perturbed at movement onset (i.e., experimental trials). We reasoned that the target perturbation paradigm would provide a novel means to assess a possible superior-inferior visual field asymmetry for online reaching control. In terms of the impact of a target perturbation, both visual fields demonstrated equal proficiency integrating visual feedback for online limb adjustments. Interestingly, however, the spatial distribution of movement endpoints in the LVF was less than UVF counterparts (cf. Binsted and Heath 2005). Taken together, the present findings suggest that although LVF and UVF reaches readily use visual feedback to accommodate an unexpected target perturbation, reaches in the LVF elicit advantaged spatial benefits influencing the effectiveness of online limb corrections.     

Effects of aging on visual recognition memory in the rhesus monkey

As part of an effort to develop a primate model of human age-related memory dysfunction, performance by six rhesus monkeys 26 to 27 years of age was compared to that of six young adult monkeys (four to five years of age) on a trial unique delayed nonmatching to sample (DNMS) task. This task assesses the monkey's ability to identify a novel from a familiar stimulus over a delay and resembles closely clinical tests that are used to assess memory function in geriatric patients. The task was presented in three stages: acquisition, delays and lists. As a group, aged monkeys were impaired relative to the young adult group on all three conditions. However, within the aged group, individual cases of efficient performance were observed. Error analyses of item positions of the lists condition revealed the absence of enhanced performance for items presented at the end of a list by aged animals, suggesting an abnormal sensitivity to proactive interference. The finding of a recognition impairment with age is in parallel with studies of normal human aging and lends support to the notion that the rhesus monkey is a suitable animal model of human aging.     

The effect of early visual experience on spatial maze learning in rats

In the 1st of 2 experiments on spatial ability, groups of sighted and blind, light-reared (LR) and dark-reared (DR) rats were tested on a series of (Hebb-Williams) maze problems and their reversals under appetitive and aversive reinforcement conditions. Significant effects due to early rearing conditions, vision at time of testing, and problem were found. Dark-reared rats learned the problems whose solution depended on nonvisual cues more slowly than LR animals. Blindness at time of testing had a significantly adverse effect on the performance of LR and DR rats on all problems, but a significantly greater effect in the DR animals. In a 2nd experiment DR rats were also found to perform less effectively than LR rats on a 17-arm radial maze throughout a 36-day period during which variations in the task were introduced. The results reveal the impact of early visual experience on the development of the ability to acquire spatial concepts.     

虚拟现实视觉体验对脑功能网络的影响

随着虚拟现实(VR)技术的广泛应用和相关设备的迅速普及,长时间使用VR技术引起的脑疲劳问题受到广泛关注。本研究结合主观疲劳量表与脑电信号脑功能网络特征参数,研究VR技术引起的脑疲劳问题。随机选取16名健康受试者,同步采集观看相同题材的传统平面(TP)视频及VR视频时的脑电信号,观看视频前后填写主观疲劳量表,利用互相关方法对所采集到的脑电信号进行关联特性分析,构建两种视觉体验前后的脑功能网络,并从复杂网络的角度,对比分析平均度、平均聚类系数、平均路径长度、平均全局效率和"小世界"属性等脑网络特征参数。结果发现,观看视频后的量表分值均大于观看前,并且从主观感受上,受试者观看VR视频比观看TP视频更容易产生疲劳感;观看VR和TP视频后,脑网络互相关系数、平均度值、平均聚类系数和平均全局效率值均比观看视频前显著降低,平均路径长度值显著升高,"小世界"属性显著减小;并且相比观看TP视频,观看VR视频后脑网络特征参数变化量更大,且差异具有统计学意义(P <0.05)。通过本研究结果,或可为分析和评价VR视觉体验引发的脑疲劳提供理论依据和试验参考。     

Effects of visual experience on activity-dependent gene regulation in cortex

There are critical periods in development when sensory experience directs the maturation of synapses and circuits within neocortex. We report that the critical period in mouse visual cortex has a specific molecular logic of gene regulation. Four days of visual deprivation regulated one set of genes during the critical period, and different sets before or after. Dark rearing perturbed the regulation of these age-specific gene sets. In addition, a 'common gene set', comprised of target genes belonging to a mitogen-activated protein (MAP) kinase signaling pathway, was regulated by vision at all ages but was impervious to prior history of sensory experience. Together, our results demonstrate that vision has dual effects on gene regulation in visual cortex and that sensory experience is needed for the sequential acquisition of age-specific, but not common, gene sets. Thus, a dynamic interplay between experience and gene expression drives activity-dependent circuit maturation.     

Neural correlates of visual recognition in 3-month-old infants: the role of experience

Early experiences contribute powerfully to the development of neural systems that underlie various perceptual and cognitive abilities in humans. In one of the first studies to systematically control infants' exposure to a familiar object, we examined the effects of controlled experience on the neural correlates of visual recognition in two groups of infants. One group received 1 month of in‐home familiarization to a 3D model of a female face. Another group received 1.5 min of in‐lab familiarization to the 3D model of a female face, creating two conditions that differed in the amount and, importantly, the context of exposure to a familiar stimulus. Following familiarization, event‐related potentials (ERPs) were recorded at 3 months of age while infants viewed pictures of the familiar face and an unfamiliar face. Results demonstrated that while both groups of infants discriminated between the familiar and unfamiliar faces, the pattern of neural processing was reversed for the two groups. Thus, the amount and context of visual exposure altered the neural correlates of recognition processes in young infants. © 2011 Wiley Periodicals, Inc. Dev Psychobiol 53:416–424, 2011.     

ERP topography and human perceptual learning in the peripheral visual field.

We studied human perceptual learning in the peripheral visual field in 16 healthy adults. Horizontal or vertical vernier stimuli were presented simultaneously at 8 locations at an eccentricity of 4 degrees . One of the stimuli displayed an offset, and subjects were asked to detect the target offset. Training was performed with either vertical or horizontal stimuli by the repeated presentation of stimuli. Discrimination performance was also measured with the untrained stimuli. Before and after the psychophysical experiment, EEG was recorded from 30 electrodes over the occipital areas (between the inion and Cz) while targets were presented at all locations as vernier onset/offset stimuli. The EEG was averaged for each orientation separately. Improvement in discrimination performance was observed in about 70% of the subjects with the trained orientation only. The evoked potential maps displayed three components occurring between 80 and 160, 180 and 260, and 280 and 340 ms. The potential field topography of the first and third component showed significant differences before and after learning. In addition, field strength (global field power) of the second and third component increased with learning. No effects were seen with the untrained stimuli in the psychophysical and electrophysiological experiments. Our findings suggest that perceptual learning in the peripheral visual field is specifically related to neurophysiological changes induced by training, and it is not caused by unspecific changes of spatial attention. The changes of electrical brain activity reflect short-term plasticity related to human perceptual learning.     

Effects of age and visual experience on [3H] MK801 binding to NMDA receptors in the kitten visual cortex

Summary We have investigated the postnatal development of N-methyl-D-aspartate (NMDA) receptors in kitten neocortex by measuring the density of [³H] MK801 binding sites. NMDA receptor density in area 17 markedly increases between postnatal day 7 and 35, and then remains at a high level into adulthood. Similar temporal changes were observed in area 6. A brief period of binocular deprivation did not alter the density of [³H] MK801 binding sites in either brain region. However, dark rearing kittens from birth resulted in a significant decrease after 35 and 120 days in both area 17 and area 6. These results demonstrate that the density of NMDA receptors does not effectively predict the capacity for visual cortical plasticity in kitten neocortex. In addition, these results show that dark rearing produces significant effects in areas of the kitten neocortex not normally associated with visual function.     

Applications of random field theory to electrophysiology

The analysis of electrophysiological data often produces results that are continuous in one or more dimensions, e.g., time-frequency maps, peri-stimulus time histograms, and cross-correlation functions. Classical inferences made on the ensuing statistical maps must control family wise error (FWE) when searching across the map's dimensions. In this paper, we borrow multiple comparisons procedures, established in neuroimaging, and apply them to electrophysiological data. These procedures use random field theory (RFT) to adjust p-values from statistics that are functions of time and/or frequency. This RFT adjustment for continuous statistical processes plays the same role as a Bonnferonni adjustment in the context of discrete statistical tests. Here, by analysing the time-frequency decompositions of single channel EEG data we show that RFT adjustments can be used in the analysis of electrophysiological data and illustrate the advantages of this method over existing approaches.     

Effects of verbatim information on recognition of S-O-V sentences under incidental learning

By means of a delayed recognition task, propositions were tested about the retention of verbatim information on Japanese S-O-V sentences based on spreading activation in memory representations. Subjects studied written sentences under incidental instructions, and a recognition test was made after a 10-minute delay. In the test, subjects verified whether the sentences were true or false for (a) original sentences, (b) synonymous distractors (verbs replaced by synonyms), and (c) non-synonymous distractors (verbs replaced by non-synonyms). In Experiment I, subjects verified original sentences more accurately, faster, and more confidently than those having distractors. Results of Experiment II, in which subjects retrieved two related sentences sequentially, showed an inhibition (fan) effect for hits. In addition, there was a facilitation (priming) effect for correct rejections. These findings provide evidence in support of the spreading activation theory of memory.     

Two-dimensional mapping of the central and parafoveal visual field to human visual cortex

Primate visual cortex contains a set of maps of visual space. These maps are fundamental to early visual processing, yet their form is not fully understood in humans. This is especially true for the central and most important part of the visual field--the fovea. We used functional magnetic resonance imaging (fMRI) to measure the mapping geometry of human V1 and V2 down to 0.5 degrees of eccentricity. By applying automated atlas fitting procedures to parametrize and average retinotopic measurements of eight brains, we provide a reference standard for the two-dimensional geometry of human early visual cortex of unprecedented precision and analyze this high-quality mean dataset with respect to the 2-dimensional cortical magnification morphometry. The analysis indicates that 1) area V1 has meridional isotropy in areal projection: equal areas of visual space are mapped to equal areas of cortex at any given eccentricity. 2) V1 has a systematic pattern of local anisotropies: cortical magnification varies between isopolar and isoeccentricity lines, and 3) the shape of V1 deviates systematically from the complex-log model, the fit of which is particularly poor close to the fovea. We therefore propose that human V1 be fitted by models based on an equal-area principle of its two-dimensional magnification. 4) V2 is elongated by a factor of 2 in eccentricity direction relative to V1 and has significantly more local anisotropy. We propose that V2 has systematic intrinsic curvature, but V1 is intrinsically flat.     

Human perceptual learning in the peripheral visual field: sensory thresholds and neurophysiological correlates

Perceptual learning in the peripheral visual field was studied in 24 adults using vernier targets. The aim was to relate perceptual improvements to changes of electrical brain activity. Thresholds were measured before, during, and after training, and on the next day. During training, the subjects passively looked at suprathreshold targets, and EEG activity was recorded from 30 electrodes over the occipital brain areas. Mean evoked potentials were computed for the first and second block of 1200 stimulus presentations, and the scalp topography of visual evoked potential (VEP) activity was analysed. Only for the stimulated area, training resulted initially in increased thresholds that, however, decreased significantly after consolidation. Electrical brain activity displayed smaller field strength and altered topography after training. Some of the effects were caused by habituation or adaptation to the training stimuli resulting in less efficient neurophysiological processing. The topographical changes indicate that different neuronal elements were activated after perceptual learning.     

Effects of artificial mothers and visual experience on adrenal responsiveness of infant monkeys

Rhesus monkeys, maternally seprated at birth, were individually housed with a simple artificial mother in cages that were either completely enclosed (Enclosed Group) or had a clear plastic fron that faced the general nursery environment (Visual Group). Animals were removed from the living cage and placed for 1 hr in an enclosed carrying cage, either alone or with the artificial mother, following which blood samples were taken and analyzed for plasma cortisol levels. This procedure was repeated at monthly intervals during the first 7 months of life and at 9 and 12 months. In both groups plasma cortisol levels were higher when the animlas were alone than when the social surrogate was present. Rearing conditions were also effective, as reflected in longitudinal and diurnal contrasts between groups: cortisol levels were consistently high in the Visual Group from the 1st week of life, whereas the developmental pattern was curvilinear for the Enclosed Group. Significant diurnal variation in cortisol level was demonstrated only in the Visual Group.     

Effects of learning on smooth pursuit during transient disappearance of a visual target

Previous research has demonstrated learning in the pursuit system, but it is unclear whether these effects are the result of changes in visual or motor processing. The ability to maintain smooth pursuit during the transient disappearance of a visual target provides a way to assess pursuit properties in the absence of visual inputs. To study the long-term effects of learning on nonvisual signals for pursuit, we used an operant conditioning procedure. By providing a reinforcing auditory stimulus during periods of accurate tracking, we increased the pursuit velocity gain during target blanking from 0.59 in the baseline session to 0.89 after 8 to 10 daily sessions of training. Learning also reduced the occurrence of saccades. The learned effects generalized to untrained target velocities and persisted in the presence of a textured visual background. In a yoked-control group, the reinforcer was independent of the subjects' responses, and the velocity gain remained unchanged (from 0.6 to 0.63, respectively, before and after training). In a control group that received no reinforcer, gain increased slightly after repetition of the task (from 0.63 to 0.71, respectively, before and after training). Using a model of pursuit, we show that these effects of learning can be simulated by modifying the gain of an extra-retinal signal. Our results demonstrate that learned contingencies can increase eye velocity in the absence of visual signals and support the view that pursuit is regulated by extra-retinal signals that can undergo long-term plasticity.     

Effect of visual noise on pattern recognition

We recognize objects even when they are partially degraded by visual noise. Using monkeys performing a sequential delayed match-to-sample task, we studied the relation between the amount of visual noise (5, 10, 15, 20 or 25%) degrading the eight black and white stimuli used here, and the accuracy and speed with which matching stimuli were identified. The correct response rate decreased slightly as the amount of visual noise increased for both monkeys. Even at the 25% noise level, the correct response rate was more than 80%, indicating that the monkeys can recognize the pattern they are trying to match when the pattern is masked with visual noise. In contrast, the reaction time to the match stimulus increased substantially as the amount of visual noise increased. Thus, the monkeys appear to be trading time to maintain accuracy, suggesting that the monkeys are accumulating information and/or testing hypotheses about whether the test stimulus is likely to be a match for the sample being held in short-term memory.     

Contextual modulation of synchronization to random dots in the cat visual cortex

Synchronization of neuronal activity has been proposed as a binding mechanism for integration of image properties into one coherent percept. In the present study, we investigated the contextual modulation of synchronization to random dot patterns. Coherent motion of random dots evoked well synchronized responses in area 17 of anaesthetized cats when the stimulus was presented in the compound receptive field of recorded sites. Gradually changing the directional coherence of random dots in the surround while maintaining fully coherent motion of the stimulus in the receptive field significantly suppressed synchronization of neuronal activity for some stimulus conditions. However, usually one or two peaks of increased synchronization were found in the surround coherence tuning curves with low (8–12%) and/or moderate (25–50%) coherence in the surround. At the population level, synchronization was significantly depressed with incoherent motion in the receptive field and when both the surround and the receptive field were jointly stimulated with 0% coherence. The intriguing finding was the discovery of two distinct groups of cells with opposite synchronization changes dependent on the presence or absence of significant synchronization in their spontaneous activity. The latter group of neurons showed peaks of increased synchronization with lower surround coherence, thus probably being more sensitive to the direction of the surround motion. Overall, our findings support the notion that binding of stimulus properties can be achieved by synchronized activity of cortical cells. However, our findings go further than the original hypothesis of feature binding by synchrony to show that synchronization of cortical activity may be directly related to the decision making processes, which in turn are related to the threshold of perception of coherent motion.     

Effects of lateral displacement of the visual field on the development of visual-motor abilities in cats

In this study, we test the flexibility of the cat's visual system by examining the visual-motor effects of both moderate and extreme lateral displacement of the visual field. While being reared with masks that provided either 0, 15, or 30 diopters lateral displacement of the visual field, 23 kittens received 3 tests of visual-motor abilities: a visual cliff task, a visual guiding task, and a five-alley choice task. No significant differences were found among the 0, 15, or 30 diopter displacement groups for any of the 3 tasks for either the total number of days to reach criterion performance, for the development of performance over time during the early days of testing, or for the development over time to criterion performance. After reaching criterion, kittens readapted to transposed conditions of displacement. The group changed 30 diopters did significantly worse than the group changed 15 diopters, both in error scores and in time to criterion performance. The present results with kittens are compared to those of other investigators and suggestions are made for future research.