Experiencing and perceiving visual surfaces.

A theoretical framework is proposed to understand binocular visual surface perception based on the idea of a mobile observer sampling images from random vantage points in space. Application of the generic sampling principle indicates that the visual system acts as if it were viewing surface layouts from generic not accidental vantage points. Through the observer's experience of optical sampling, which can be characterized geometrically, the visual system makes associative connections between images and surfaces, passively internalizing the conditional probabilities of image sampling from surfaces. This in turn enables the visual system to determine which surface a given image most strongly indicates. Thus, visual surface perception can be considered as inverse ecological optics based on learning through ecological optics. As such, it is formally equivalent to a degenerate form of Bayesian inference where prior probabilities are neglected.

Afterimage of perceptually filled-in surface.

An afterimage induced by prior adaptation to a visual stimulus is believed to be due to bleaching of photochemical pigments or neural adaptation in the retina. We report a type of afterimage that appears to require cortical adaptation. Fixating a neon-color spreading configuration led not only to negative afterimages corresponding to the inducers (local afterimages), but also to one corresponding to the perceptually filled-in surface during adaptation (global afterimage). These afterimages were mutually exclusive, undergoing monocular rivalry. The strength of the global afterimage correlated to a greater extent with perceptual filling-in during adaptation than with the strength of the local afterimages. Thus, global afterimages are not merely by-products of local afterimages, but involve adaptation at a cortical representation of surface.

Manifestation of scotomas created by transcranial magnetic stimulation of human visual cortex.

Reduced visual performance under transcranial magnetic stimulation (TMS) of human visual cortex demonstrates suppression whose spatial extent is not directly visible. We created an artificial scotoma (region missing from a visual pattern) to directly visualize the location, size and shape of the TMS-induced suppression by following a large-field, patterned, visual stimulus with a magnetic pulse. The scotoma shifted with coil position according to known topography of visual cortex. Visual suppression resulted in pattern-dependent distortion, and the scotoma was filled in with temporally adjacent stimuli, suggesting spatial and temporal completion mechanisms. Thus, perceptual measurements of TMS-induced suppression may provide information about cortical processing via neuronal connections and temporal interactions of neural signals.

Changing objects lead briefly flashed ones.

Continuous, predictable events and spontaneous events may coincide in the visual environment. For a continuously moving object, the brain compensates for delays in transmission between a retinal event and neural responses in higher visual areas. Here we show that it similarly compensated for other smoothly changing features. A disk was flashed briefly during the presentation of another disk of continuously changing color, and observers compared the colors of the disks at the moment of flash. We also tested luminance, spatial frequency and pattern entropy; for all features, the continuously changing item led the flashed item in feature space. Thus the visual system's ability to compensate for delays in information about a continuously changing stimulus may extend to all features. We propose a model based on backward masking and priming to explain the phenomenon.

Sensory modalities are not separate modalities: plasticity and interactions.

Historically, perception has been viewed as a modular function, with the different sensory modalities operating independently of each other. Recent behavioral and brain imaging studies challenge this view, by suggesting that cross-modal interactions are the rule and not the exception in perception, and that the cortical pathways previously thought to be sensory-specific are modulated by signals from other modalities.

A framework supporting the development of a Grid portal for analysis based on ROI.

OBJECTIVES: In our research on brain function analysis, users require two different simultaneous types of processing: interactive processing to a specific part of data and high-performance batch processing to an entire dataset. The difference between these two types of processing is in whether or not the analysis is for data in the region of interest (ROI). In this study, we propose a Grid portal that has a mechanism to freely assign computing resources to the users on a Grid environment according to the users' two different types of processing requirements. METHODS: We constructed a Grid portal which integrates interactive processing and batch processing by the following two mechanisms. First, a job steering mechanism controls job execution based on user-tagged priority among organizations with heterogeneous computing resources. Interactive jobs are processed in preference to batch jobs by this mechanism. Second, a priority-based result delivery mechanism that administrates a rank of data significance. RESULTS: The portal ensures a turn-around time of interactive processing by the priority-based job controlling mechanism, and provides the users with quality of services (QoS) for interactive processing. The users can access the analysis results of interactive jobs in preference to the analysis results of batch jobs. The Grid portal has also achieved high-performance computation of MEG analysis with batch processing on the Grid environment. CONCLUSION: The priority-based job controlling mechanism has been realized to freely assign computing resources to the users' requirements. Furthermore the achievement of high-performance computation contributes greatly to the overall progress of brain science. The portal has thus made it possible for the users to flexibly include the large computational power in what they want to analyze.

An OGSA-based integration of life-scientific resources for drug discovery.

OBJECTIVES: The rapid progress of life-scientific research has the potential to dramatically change the paradigm of drug discovery. Efficient utilization of life-scientific resources, i.e., databases and analytic software tools, poses a challenging issue with regard to the reduction of time and cost in the drug discovery process. In this paper, a variety of heterogeneous Web-based life-scientific resources are integrated toward the improvement of drug discovery performance. METHODS: For the integration of heterogeneous life-scientific resources, a database federation technique based on three-layer architecture has been utilized. With the federation technique, life-scientific resources are integrated step by step through database layers, database integration layers and analysis layers to encapsulate complexity and heterogeneity. In this study, we have taken advantage of the latest Grid technology based on OGSA (Open Grid Services Architecture) for the implementation of our approach. RESULTS: The actual case of life-scientific resources for drug discovery demonstrates that our prototype system developed with the proposed technique works well for the identification process of candidate compounds to a target protein. In other words, the prototype system allows a researcher to retrieve candidate compounds with less effort than before. CONCLUSIONS: The usefulness of the prototypic system represents the ability of our approach to integrate heterogeneous life-scientific resources, which have the potential to dramatically improve efficiency in drug discovery, resulting in the shortening of drug development. On the other hand, the system requires further consideration from the aspect of practical use. Dynamic aggregation of the resources is one example of such a consideration.

The first grid for the oral and maxillofacial region and its application for speech analysis.

OBJECTIVES: Introduction of a new grid-based method for analyzing speech functions which takes into account the related information of patients' data and the oral air flow with pronouncing analyzed by computational fluid dynamics. METHODS: An on-line speech analyzer was developed for clinical use utilizing GridPort2.3.1 based on globus2.4.2, comprising several computational tools such as unified data storage, semantic data analysis, computational fluid dynamics analysis and three-dimensional visualization of calculated results from different hardware sources with various types of operation systems. RESULTS: The power transportation layer between dental clinics and computational and storage resources could be provided by using a WWW-based portal. The backend data management system could be constructed using a storage resource broker (SRB) and extensible mark up language (XML). CONCLUSIONS: The new method allows the construction of a data warehouse through this grid-based speech function analysis in order to extract the principal factors related to speech disorders.

Preferential-looking assessment of fusion and stereopsis in infants aged 1-6 months.

The ability of infants to discriminate zero-disparity stimuli from both reverse contrast (rivalrous) and disparate (stereoscopic) stimuli was investigated in a two-alternative, forced-choice, preferential-looking paradigm. Few infants under 4 months of age demonstrated discrimination for any stimulus pairing. Of the infants tested at 4 months of age, approximately 70% preferred zero-disparity stimuli to reverse contrast stimuli, and 82% preferred stereoscopic stimuli to zero-disparity stimuli. Nearly 100% of 5- and 6-month-old infants exhibited these preferences. These findings suggest that sensory fusion is not present at birth but develops rapidly over the first 6 months of life. The time course for the development of sensory fusion was similar to the time course for the development of stereopsis in nine infants tested longitudinally.

Intuitive reasoning about probability: theoretical and experimental analyses of the "problem of three prisoners".

Among various Bayesian problems of probability, the "problem of three prisoners" (Lindley, 1971; Mosteller, 1965) is an especially good example which illustrates the drastic discrepancy between intuitive reasoning and mathematical formal reasoning about probability. In particular, it raises intriguing questions concerning the mathematical and cognitive relevance of factors such as prior probabilities and the context in which certain information is given. In the current paper, we report a new version of the problem which turned out to be even more counterintuitive. This new version was also designed so that different inferential schemes would lead to separate estimates of posterior probability. The data obtained from questionnaires and theoretical analyses of the original and modified problems suggest that: (1) The psychological processes of intuitive reasoning are qualitatively different from mathematical reasoning. (2) The tendency to neglect prior probabilities (Tversky & Kahneman, 1974, 1982) is not always the critical factor for illusory judgments. (3) Intuitive judgments can be categorized by several, distinctive propositional beliefs from which the judgments are apparently derived. We call these prototypical, crude beliefs "subjective theorems," and discuss their nature and roles in the current paper.

Orienting a spatial attention--its reflexive, compensatory, and voluntary mechanisms.

Attention is a mechanism to select sensory information. It is a modulatory process which normally cannot be observed as overt responses. We have studied spatial attention using a new visual illusion of motion--line-motion effect: a line, which was presented physically at once, was perceived to be drawn from one side when attention was captured to that side of the line by a preceding visual cue stimulus. This effect was due to acceleration of visual information processing at the locus of attention. The motion illusion was produced by both stimulus-induced (bottom-up) and voluntary (top-down) attention, which suggested that the two kinds of attention act on relatively early stages of visual processing. The objective of this study was to examine how various modes of spatial attention might be represented and reorganized in the brain. Using the induction of illusory line motion as a measure we found that: (1) once attention is captured by a moving object, it follows the object as it moves; and (2) attention moves with a saccade in the retinal coordinates such that its focus remains fixed in space. We then asked whether attention acts across different sensory modalities. We found that both auditory and somatosensory cues induced focal visual attention in space where the cue was presented. Based on these findings we propose a model which would allow (1) matching of visual spatial information obtained across saccades, and (2) matching of spatial information obtained in different sensory modalities.

Stimulus-driven facilitation and inhibition of visual information processing in environmental and retinotopic representations of space.

This contribution deals with two major issues on visual/spatial attention. One is the issue of facilitation and inhibition; that is, under what conditions facilitatory modulation occurs, and under what other conditions inhibitory modulation occurs. The other issue is that of spatial representation; in what type of spatial representation do these modulations occur, retinotopic or environmental? In the first half of this article, We review the latest studies employing various psychophysical measures to assess spatially-selective modulation of visual information processing. We also summarize our latest results on reaction time, indicating a dissociation of two visual functions, detection/orientation and feature discrimination. Based on these chunks of knowledge, we raise a questions about the spatial coordinate system in which the facilitatory and/or inhibitory modulations occur. We then provide results of two reaction-time experiments which partly answer the question.

Sound alters visual evoked potentials in humans.

When a single flash is accompanied by two auditory beeps, the single flash is perceived as two flashes. We investigated whether this crossmodal influence on visual perception occurs at the level of the modality-specific visual pathway or later. We compared the visual evoked potentials (VEPs) in the presence and absence of sound. Activity was modulated extensively and with short latency in trials in which an illusory flash was perceived. In addition, the brain potentials for the illusory flash were qualitatively very similar to those for a physical flash, suggesting that the same mechanism underlies the percept of both illusory and physical flashes. These results suggest that the activity in the visual cortex can be modulated by sound. This implication challenges the general belief that the visual cortical processing is independent of other modalities.

Visual attention revealed by an illusion of motion.

Attention is a mechanism to select sensory information. It is a modulatory process which normally cannot be observed as overt responses. A new psychophysical method using an illusion of motion perception allowed us to visualize the field of the magnitude of attention and its dynamic changes. Based on our experiments using this method we suggest that (1) both passive (bottom-up) and active (top-down) attention exert their effects on the early stages of visual processing, (2) active attention can quickly and briefly be replaced by passive attention induced by an external event, but can be restored in about 400 ms, and (3) attention is directed to an object, not space, and follows the object as it moves.

The locus of visual-motor learning at the task or manipulator level: implications from intermanual transfer.

To assess the functional locus of visual-motor learning, the computational concepts of "task level" programming (determination of the trajectory of a hand during arm reaching in the Cartesian coordinates) and "manipulator level" programming (determination of the joint coordinates) was adopted. Because the former is likely to be hand nonspecific and the latter is hand specific, it is assumed that learning at the task level should be transferred to the unpracticed hand, whereas that at the manipulator level it should not. Under this assumption, the paradigm of intermanual transfer was used in an aiming task under rotated visual feedback. Nearly 100% intermanual transfer from the practiced hand to the unpracticed hand in the performance time of aiming was found, concluding that the locus of visual-motor learning should be at the task level rather than at the manipulator level.

Repetition priming reveals sustained facilitation and transient inhibition in reaction time.

Reaction time (RT) in a detection or a location discrimination task increases when a target is repeatedly presented at the same location (inhibition), whereas RT decreases in feature (color or orientation) discrimination tasks (facilitation; Y. Tanaka & S. Shimojo, 1996a). Here, the time course of inhibition and facilitation was examined, using a repetition priming paradigm. Results indicate that inhibition occurred only in the immediately successive trial, whereas facilitation accumulated over several trials with location repetition. Moreover, inhibition and facilitation occurred in a task-relevant manner: Detection-location discrimination tasks produced transient RT increase, whereas feature discrimination tasks produced cumulative RT decrease. These results suggest a functional dissociation between spatial orienting and feature analysis, as well as top-down modulations by tasks leading to different types of visual memory.

Perceived spatial organization of cutaneous patterns on surfaces of the human body in various positions.

The perceived spatial organization of cutaneous patterns was examined in three experiments. People identified letters or numbers traced on surfaces of their body when the relative spatial orientations and positions of the body surfaces and of the stimuli were varied. Stimuli on the front or back of the head were perceived with respect to a frame of reference positioned behind those surfaces, independent of the surfaces' position and orientation. This independence may relate to the way in which the sensory apparatus on the front of the head is used in planning action. Stimuli on other surfaces of the head and body were perceived in relation to the position and orientation of the surface with respect to the whole body or trunk (most of which was usually upright). Stimuli on all transverse/horizontal surfaces were perceived with respect to frames of reference associated with the head/upper chest area. These frames were also used for stimuli on frontoparallel surfaces in front of the upper body. These observations may result from the use of "central" frames of reference that are independent of the head and are associated with the upper body. Stimuli on surfaces in other positions and orientations (with two exceptions) were perceived "externally"--that is, in frames of reference directly facing the stimulated surface. The spatial information processing we found may be fairly general because several of our main findings were also observed in very young children and blind adults and in paradigms studying perception by "active touch" and the spatial organization of the motor production of patterns.

Vernier acuity is less than grating acuity in 2- and 3-month-olds.

Vernier acuity and grating acuity were measured longitudinally starting at 1 or 2 months of age in 22 infants, using a two-alternative, forced-choice preferential looking technique. For vernier acuity, the motion-sound display was employed. For grating acuity, a preferential looking method was employed. Steps of the stimulus (vernier offset and spatial frequency of the grating) and procedures were basically identical between the two acuity tests. The range of stimuli was set so as to compare the two acuities at younger ages. Results show: vernier acuity is less than grating acuity at 11-12 weeks of age or younger, and the developmental rate of vernier acuity is greater than that of grating acuity in the first half-year of life. To interpret the data, it was speculated that: the mean sampling distance (center-to-center distance between receptive fields) may influence vernier acuity more than grating acuity, whereas the size of the receptive field may influence grating acuity more than vernier acuity: when the mean sampling distance is large relative to the size of the receptive field, vernier acuity may be less than grating acuity. Thus, the neonatal visual system, just as the visual system in the periphery and in strabismic amblyopia, may be characterized by spatial undersampling.

Motion capture changes to induced motion at higher luminance contrasts, smaller eccentricities, and larger inducer sizes.

In the stimulus configuration for "motion capture" phenomenon, we varied luminance contrast of the center disk (target), eccentricity and stimulus size. The subjects had to judge the direction of perceived target motion. We found that motion capture changed to induced motion (the direction of illusory motion was reversed) at smaller eccentricities and larger stimulus sizes. At intermediate eccentricities, motion capture changed to induced motion with increasing luminance contrast of the target. By using magnitude estimation, we also found that even a luminance-defined target was captured ("homochromatic motion capture") and that a moving target was captured by a stationary inducer ("position capture"). Both motion and position capture effects were commonly observed at lower luminance contrasts of the target, larger eccentricities and smaller sizes. From these results, we propose a model of center-surround antagonistic motion contrast detectors in motion processing.

Assimilation-type and contrast-type bias of motion induced by the surround in a random-dot display: evidence for center-surround antagonism.

As a mechanism to detect differential motion, we have proposed a model of "a motion contrast detector" that has a center-surround antagonistic receptive field with respect to the direction of motion. Supporting evidence has been obtained in the studies of induced motion, motion capture, and motion aftereffect. In order to obtain further evidence in a more strictly controlled situation, we examined the perceptual bias of motion in a center stimulus induced by another, surrounding motion. By using a stochastic random-dot display configured in a center-surround concentric fashion, we measured the % signal in the center stimulus that made the stimulus perceptually stationary in the presence of a moving surround. Measurements were done for various stimulus sizes and eccentricities. The amount of bias changed as a function of stimulus size and eccentricity. At several eccentricities, smaller stimulus sizes tended to yield assimilation-type biases, whereas larger sizes tended to yield contrast-type biases. However, a spatial scaling procedure revealed that the amount of bias was a simpler function of "scaled" stimulus size that was obtained by dividing the physical size by a scaling factor at each eccentricity. In the scaled profile, assimilation-type bias changed to contrast-type bias with increasing size, reached the peak of contrast-type bias at a certain size, and decreased slightly with further increasing size. Furthermore, a model of a difference of Gaussians, DOG, function well approximated the behavior of the profile. From these results, we concluded that the process specific to perceiving relative motion is mediated by a motion contrast detector, which is possibly located in area MT.