Integration Of Visual Information Research Articles

Integration of Contour and Terminator Signals in Visual Area MT of Alert Macaque.

The integration of visual information is a critical task that is performed by neurons in the extrastriate cortex of the primate brain. For motion signals, integration is complicated by the geometry of the visual world, which renders some velocity measurements ambiguous and others incorrect. The ambiguity arises because neurons in the early stages of visual processing have small receptive fields, which can only recover the component of motion perpendicular to the orientation of a contour (the aperture problem). Unambiguous motion signals are located at end points and corners, which are referred to as terminators. However, when an object moves behind an occluding surface, motion measurements made at the terminators formed by the intersection of the object and the occluder are generally not consistent with the direction of object motion. To study how cortical neurons integrate these different motion cues, we used variations on the classic "barber pole" stimulus and measured the responses of neurons in the middle temporal area (MT or V5) of extrastriate cortex of alert macaque monkeys. Our results show that MT neurons are more strongly influenced by the unambiguous motion signals generated by terminators than to the ambiguous signals generated by contours. Furthermore, these neurons respond better to terminators that are intrinsic to a moving object than to those that are accidents of occlusion. V1 neurons show similar response patterns to local cues (contours and terminators), but for large stimuli, they do not reflect the global motion direction computed by MT neurons. These observations are consistent with psychophysical findings that show that our perception of moving objects often depends on the motion of terminators.

Joint Audio-Visual Tracking Based on Dynamically Weighted Linear Combination of Probability State Density

This paper proposes a method that can be applied to speaker tracking under stabilized, continuous conditions using visual and audio information even when input information is interrupted due to disturbance or occlusion caused by the effects of noise or varying illumination. Using this method, the position of a speaker is expressed based on a likelihood distribution that is obtained through integration of visual information and audio information. First, visual and audio information is integrated as as a weighted linear combination of probability density distribution, which is estimated as a result of the observation of the visual and audio information. In this case, the weight is taken as a variable, which varys in proportion to the maximum value of probability density distributions obtained for each type of information. Next, the result obtained as described above and the weighted linear combination of the distribution in the past are obtained, and the result thus obtained is taken as the likelihood distribution related to the position of the speaker. By changing the weight dynamically, it becomes possible to select the type of information freely or to add weight and, accordingly, to conduct stabilized, continuous tracking even when the speaker cannot be detected momentarily due to occlusion, voice interruption, or noise. We conducted a series of experiments on speaker tracking using circular microphone array and an omni-directional camera. In this way, we have succeeded in confirming it possible to perform stabilized tracking on speakers continuously in spite of occlusion or voice interruption.

Audio and Visual Information Integration for Speaker's Localization in Automatic Shooting of Lecture

It is useful for automatic video shooting in a lecture room to estimate the location of a speaker in the lecture room. The captured videos are used for distance learning and lecture archiving systems. In order to estimate the location of a speaker in a wide lecture room, multiple cameras and multiple microphones are used. However, it is difficult to estimate the precise location of a speaker using only visual or acoustic sensors because of calibration problems, noise, and other interference. Therefore, we propose a method that integrates audio and visual information from a speaker in the lecture room. A lecturer’s cell and a student’s cell ared introduced as a unit of estimation of the location of a speaker. We defined 120 cells in a real lecture room and our multi-modal method were applied to the cells. The estimation accuracy of the location of a speaker is sufficient for automatic video shooting of a speaker in a lecture room by our integrating method.

Visually guided performance of simple tasks using simulated prosthetic vision.

Loss of photoreceptor cells is one of the major causes of blindness. Several groups are exploring the functional replacement of photoreceptors by a retinal prosthesis. The goal of this study was to simulate the vision levels that recipients of retinal prostheses with 4 x 4, 6 x 10, and 16 x 16 electrode arrays may experience, and to test the functionality of this vision. A PC video camera captured images that were converted in real time into dots ("pixels"). The PC monitor and a head-mounted display worn by test subjects displayed the pixelized images. To assess performance of normally sighted individuals with each array, we designed a set of tasks including: four-choice orientation discrimination of a Sloan letter E, object recognition and discrimination, a cutting task, a pouring task, symbol recognition, and two reading tasks. In the letter E task, subjects were found to have visual acuities of 20/1,810, 20/1,330, and 20/420 with the 4 x 4, 6 x 10, and 16 x 16 arrays, respectively. Most subjects were able to read fonts as small as 36 point with the 16 x 16 array, corresponding with a visual acuity of 20/600 in our system. The test subjects partially overcame the visual limitation of the system by scanning the video camera over the letters allowing spatial and temporal integration of visual information. In all categories, subjects performed best with the 16 x 16 array and least well with the 4 x 4 array. Even with the lowest resolution array, however, some subjects could recognize simple objects and symbols.

Contextual processing deficits in schizophrenia: Poor integration of visual information or reduced storage capacity

Contextual processing deficits in schizophrenia: Poor integration of visual information or reduced storage capacity

Temporal integration of astigmatic blur information

Purpose: The accommodation response has recently been shown to improve visual acuity (VA) in the presence of astigmatism in some individuals. This improvement could potentially result from the accommodation system exhibiting a cyclic tracking response. This type of response would allow the integration of target features over time, resulting in an improvement in VA. In this study we measure VA in simulated astigmatic blur conditions, with the magnitude of astigmatic blur being temporally modulated over a range of astigmatic blur intervals. Improvement of VA with increased range of astigmatic blur would support the integration of visual information over time hypothesis.Methods: Three fully corrected subjects participated in a 3‐Alternative Force Choice method of constant stimuli paradigm where they were asked to identify one of three randomly chosen letters (K, R or X). The stimuli (Arial, font size 18) were subjected to varying amounts of Gaussian blur along the horizontal and vertical meridian and presented at a distance of 1.3 m. On any trial, the stimuli were randomly presented to the subjects at one of six astigmatic blur intervals. Each blur interval revolved at a temporal frequency of 2 Hz around the circle of least confusion with the smallest interval presenting the stimuli at the circle of least confusion and the largest oscillating the stimuli across the full interval, i.e. from the most horizontally to vertically blurred meridian.Results: From the resulting psychometric functions it was shown that all subjects exhibit a progressive improvement in letter recognition with increasing astigmatic blur interval.Conclusions: The improvement of VA with increased astigmatic blur interval strengthens the hypothesis that visual information can be integrated over a period of time.

Posterior parietal cortex control of reach-to-grasp movements in humans.

The aim of the present study was to ascertain the neural correlates for the integration of visual information with the control of the reach-to-grasp action in the healthy human brain. Nine adult subjects (18-38 years; four females and five males) were scanned using functional magnetic resonance imaging while reaching-to-grasp a three-dimensional target. Results demonstrated differential activation of the parietal cortices according to the number of potential targets to be taken into account before movement initiation and the variability of target location. Comparing conditions where a target object that can appear at an unpredictable location with conditions where the target object appears at a predictable location revealed activations in the left superior parietal lobule, the left parieto-occipital sulcus and the right intraparietal sulcus. Results are discussed in terms of visual selective attention and action planning.

Modification of a functional motor task by non-consciously perceived sensory stimuli.

In recent years it has been suggested that processing of visual information is divided between a ventral stream, responsible for object recognition and conscious processing of object properties, and a dorsal stream mediating automatic integration of visual information into a motor task. We used metacontrast masking to prevent conscious perception of visual cues concerning the load of an object to be lifted in a precision grip. It was found that when such non-consciously perceived cues warned of a load change, they allowed the subjects to produce the grip force profile appropriate to the new load. It is concluded that non-consciously perceived visual information can be utilised to adapt a functional motor task to actual conditions.

Using Object Knowledge in Visual Tracking and Reaching

AbstractNine‐month‐old infants were presented with an engaging and challenging task of visually tracking and reaching for a rolling ball that disappeared and reappeared from behind an occluder. On some trials, the infant observed the experimenter place a barrier on the ball's track; the barrier remained partially visible above the occluder throughout the remainder of the trial. When the task involved only predictive tracking, infants' anticipatory gaze shifts were faster when no barrier was present. When the task involved both tracking and reaching, there were more reaches when no barrier was present. If the infant reached, the timing and extension of the reach and the accompanying gaze shift did not differ with regard to the barrier. Because catching the ball was quite difficult for these infants, task demands interfered with the integration of visual information and visuospatial reasoning about the barrier with the reaching action.

Visual interhemispheric transfer to areas 17 and 18 in cats with convergent strabismus

Commissural connections between primary visual cortical maps of the two hemispheres are essential to unify the split representation of the visual field. In normal adult cats, callosal connections are essentially restricted to the border between areas A17 and A18, where the central vertical meridian is projected. In contrast, early convergent strabismus leads to an expanded callosal-receiving zone, as repeatedly indicated by anatomical experiments. We investigated here the functional correlates of this widespread distribution of callosal terminals by analysing transcallosal visual responses in five anaesthetized and paralysed 4-10-month-old cats whose right eye had been surgically deviated on postnatal day 6. After acute section of the optic chiasm, single-unit activity was recorded from A17 and A18 of the right hemisphere while the left eye was visually stimulated. A total of 108/406 units were transcallosally activated. While they were more frequent at the 17/18 border (46% of the units recorded within this region), numerous transcallosally activated units were located throughout A17 (16%), A18 (27%) or within the white matter (17%). In all regions, transcallosally driven units displayed functional deficits usually associated with strabismus, such as decreased binocularity and ability to respond to fast-moving stimuli, and increased receptive field size. Many units also displayed reduced orientation selectivity and increased position disparity. In addition, transcallosal receptive fields were manifestly located within the hemifield ipsilateral to the explored cortex, with almost no contact with the central vertical meridian. Comparison with data from normal adults revealed that strabismus induced a considerable expansion of the callosal receiving zone, both in terms of the cortical region and of the extent of the visual field involved in interhemispheric transfer, with implications in the integration of visual information across the hemispheres.

When does inter-hemispheric integration of visual events emerge in infancy? A developmental study on 19- to 28-month-old infants

Simultaneous attention in the two visual fields and interhemispheric integration of visual information was studied in 19–23 and 24–28-month-old infants. The stimuli were schematic faces within which the pair of eyes was made of either two identical (two circles or two triangles) or two different eyes (triangle–circle, circle–triangle). The faces were presented either in one visual hemifield, on the right or left side of a central fixation point (unilateral presentation), or across the two visual hemifields (bilateral presentation), with one eye of the stimulus on each side of the fixation point. The task was an operant conditioning task where the children had to decide whether the shapes of the two eyes were identical or not. The results show that even the younger subjects were able to perform the task when presented in the unilateral presentation condition, whereas only children aged 24 months and older could learn the task when presented in the bilateral condition. It is concluded that simultaneous attention to the two visual fields and inter-hemispheric co-ordination of visual information emerge very late in development at about the age of 24 months.

Functional Architecture of Synapses in the Inner Retina: Segregation of Visual Signals by Stratification of Bipolar Cell Axon Terminals

We correlated the morphology of salamander bipolar cells with characteristics of their light responses, recorded under voltage-clamp conditions. Twelve types of bipolar cells were identified, each displaying a unique morphology and level(s) of axon terminal stratification in the inner plexiform layer (IPL) and exhibiting light responses that differed with respect to polarity, kinetics, the relative strengths of rod and cone inputs, and characteristics of spontaneous EPSCs (sEPSCs) and IPSCs. In addition to the well known segregation of visual information into ON and OFF channels along the depth of the IPL, we found an overlying mapping of spectral information in this same dimension, with cone signals being transmitted predominantly to the central IPL and rod signals being sent predominantly to the margins of the IPL. The kinetics of bipolar cell responses correlated with this segregation of ON and OFF and of rod and cone information in the IPL. At light offset, rod-dominated cells displayed larger slow cationic current tails and smaller rapid overshoot responses than did cone-dominated cells. sEPSCs were generally absent in depolarizing bipolar cells but present in all hyperpolarizing bipolar cells (HBCs) and larger in rod-dominated HBCs than in cone-dominated HBCs. Inhibitory chloride currents, elicited both at light onset and light offset, tended to be larger for cone-dominated cells than for rod-dominated cells. This orderly segregation of visual signals along the depth of the IPL simplifies the integration of visual information in the retina, and it begins a chain of parallel processing in the visual system.

Selective suppression of horizontal propagation in rat visual cortex by norepinephrine.

The release of norepinephrine in the cerebral cortex from axon terminals of locus coeruleus neurons was suggested to be involved in the control of attention. Accumulating data indicate that the responses of cortical neurons are varied when norepinephrine is applied iontophoretically in the vicinity of the cells being recorded. However, it is not known how the pattern of excitatory propagation is modified when norepinephrine is applied over a wide area in the visual cortex. By applying optical imaging to rat visuocortical slices, we found a new mode of norepinephrine action; a prominent suppression of the horizontal propagation in layers II/III. This action of norepinephrine was confirmed by the simultaneous recording of field potentials from multiple sites by use of a multi-electrode dish. Furthermore, our electrophysiological recordings showed that this norepinephrine action is exerted through suppression of excitatory neural transmission and enhancement of inhibitory transmission to the pyramidal neurons in these layers. Because the release of norepinephrine in the visual cortex is regulated by the level of attention, the neural basis of visual attention may relate partially to the suppression of the integration of visual information by norepinephrine resulting in a state-dependent restructuring of the receptive field.

Dynamics of spatial summation in primary visual cortex of alert monkeys.

One of the fundamental tasks of the visual cortex is to integrate input from different parts of the retina, parsing an image into contours and surfaces, and then assembling these features into coherent representations of objects. To examine the role of the primary visual cortex in the integration of visual information, we measured the response properties of neurons under different stimulus conditions. Surprisingly, we found that even the most conventional measures of receptive field (RF) size were not fixed, but could vary depending on stimulus contrast and foreground-background relationships. On average, the length of the excitatory RF was 4-fold greater for a low-contrast stimulus than for a stimulus at high contrast. Embedding a high-contrast stimulus in a textured background tended to suppress neuronal responses and produced an enlargement in RF size similar to that observed by decreasing the contrast of an isolated stimulus. The results show that RF dimensions are regulated in a dynamic manner that depends both on local stimulus characteristics, such as contrast, and on global relationships between a stimulus and its surroundings.

Bilateral field advantage and evoked potential interhemispheric transmission in commissurotomy and callosal agenesis

The role of the corpus callosum versus other cerebral commissures in the interhemispheric integration of visual information was studied in four individuals with complete agenesis of the corpus callosum, two individuals with partial agenesis, one total commissurotomy patient, and normal individuals. Evoked potential (EP) indices of interhemispheric transmission of visual sensory responses were observed during matching of unilateral and bilateral visual field letters and patterns. Neither the commissurotomy nor any of the acallosal patients had ipsilateral hemisphere visual EPs (P1 and N1), demonstrating that the posterior callosum is necessary for interhemispheric transmission of these components of visual evoked potentials. While the commissurotomy patient could not compare bilaterally presented letters, the anterior commissure of the acallosal patients appeared to be sufficient for interhemispheric comparison of single letters. However, bilateral comparison of more complex visual patterns resulted in considerable difficulty for complete agenesis patients, while comparison of patterns was more nearly normal when anterior callosal fibers were present (partial agenesis).

An Introduction to "The Neuroscience of Perceptual Integration"

An important goal in the study of object, word, and face perception is to understand how the brain integrates various visual features- the binding process. Along with the progress of knowledge of the neurophysiological properties of integration processes in cortical areas, a number of psychophysical, neuropsychological, and computational studies have provided information about how and in what conditions the visual system combines different signals across time and space, the factors that modulate integration processes, the local processes that control larger scale integration, and how the mechanisms can be implemented physiologically. This special issue is aimed at summarizing recent data about integration processes based on investigations ranging from the neurochemical substrate of integration processes, the role of attention in integrating characteristics, the spatial and temporal integration of local signals into coherentpercepts, the integration of visual information during the programming of saccade, and what remains when integration fails in neurologically impaired patients.

Judgements of visual precedence by strabismics

Strabismus induced early in the life of cats results in disruption of the normal development of the posterior corpus callosum. In human strabismic amblyopic subjects a similar disruption in callosal development may cause poor interhemispheric integration of simple visual information. To examine this possibility judgements of visual target onset precedence were made for targets presented in bilateral and unilateral viewing conditions using a method of constants psychophysical procedure. In one condition, with targets presented in opposite visual fields requiring integration between the two hemispheres, the subjects having strabismic amblyopia had significantly larger just noticeable difference values (JNDs) than those found for the non-strabismic controls. In a second condition, with targets presented within a visual field requiring integration within only a single hemisphere, the JNDs for the two groups were not significantly different. The results suggest that strabismic amblyopes have poor integration of visual information between the cerebral hemispheres, and that this reflects disruptions in the development of the posterior corpus callosum.

Research in perceptual development: history, methods, and recent directions

Over the past four decades, numerous investigators have examined the perceptual and cognitive capabilities of young infants, and how these skills develop. The contributors to this Special Issue on Perceptual Development take divergent, and complementary, approaches to this problem. Their work has revealed important new evidence for early competence in intermodal perception and the sense of self, as well as developmental processes in infants and children involving categorization, manual exploratory activity, visual object segregation, coordination of visual and body-centred knowledge, and integration of visual information over space and time. There are also theoretical contributions from experienced researchers in speech perception and imitation. Together, this collection of articles illustrates the wide-ranging character of research in perceptual development, and continues the tradition of revealing fundamental and often surprising abilities in infants and children. ©1997 John Wiley & Sons, Ltd.

Congenital Nystagmus Image Motion

In persons with congenital nystagmus (CN), the ability to integrate visual information over time can be limited by two factors--the duration of foveation periods and the temporal integration period of the visual system. The purpose of this study was to assess the relative importance of these two factors for visual acuity for targets of different luminances. We measured visual acuity using Landolt C targets at 5 luminance levels (50 to 0.005 cd/m2) in 6 observers with CN, and in 6 normal observers with comparable motion of the retinal image. To allow comparison, normal observers viewed the targets during image motion simulating jerk CN, with "foveation durations" ranging from 20 to 160 ms. In the normal observers, acuity improves as a function of the simulated foveation duration at all luminance levels. However, this improvement is larger and occurs at a faster rate at high than at low luminances. The more gradual improvement in acuity with simulated foveation durations at low luminances is consistent with a prolongation of the temporal integration period, which we estimate to range from approximately 140 to 380 ms over the 4 log unit range in luminance that we tested. In observers with CN, the change in acuity with luminance is similar, but not identical, to that in normal observers when the duration of the foveation periods is matched. We conclude that the integration of visual information may be limited by either the period of temporal integration or the duration of the foveation period in persons with CN, depending upon which is shorter at the luminance level under consideration.

29-2 注視点移動前後の視覚情報統合過程における注意とサッカード潜時の解析

29-2 注視点移動前後の視覚情報統合過程における注意とサッカード潜時の解析