The sensorimotor integration system can be viewed as an observer attempting to estimate its own state and the state of the environment by integrating multiple sources of information. We describe a computational framework capturing this notion, and some specific models of integration and adaptation that result from it. Psychophysical results from two sensorimotor systems, subserving the integration and adaptation of visuo-auditory maps, and estimation of the state of the hand during arm movements, are presented and analyzed within this framework. These results suggest that: (1) Spatial information from visual and auditory systems is integrated so as to reduce the variance in localization. (2) The effects of a remapping in the relation between visual and auditory space can be predicted from a simple learning rule. (3) The temporal propagation of errors in estimating the hand's state is captured by a linear dynamic observer, providing evidence for the existence of an intern...

The head-direction (HD) cells found in the limbic system in freely moving rats represent the instantaneous head direction of the animal in the horizontal plane regardless of the location of the animal. The internal direction represented by these cells uses both self-motion information for inet-tially based updating and familiar visual landmarks for calibration. Here, a model of the dynamics of the HD cell ensemble is presented. The sta-bility of a localized static activity profile in the network and a dynamic shift mechanism are explained naturally by synaptic weight distribution components with even and odd symmetry, respectively. Under symmetric weights or symmetric reciprocal connections, a stable activity profile close to the known direc-tional tuning curves will emerge. By adding a slight asymmetry to the weights, the activity profile will shift continuously without 1

Adults were asked to judge the self-to-object directions in a room from novel points of observation that differed from their actual point at times only by a rotation and at other times only by a translation. The results show for the rotation trials that the errors and latencies when a novel point was imagined were worse than the baseline responses from their actual points of observation, and the latencies varied as a function of the magnitude of the to-be-imagined rotation. For the translation trials, on the other hand, the errors and latencies when a novel point was imagined were comparable to the baseline responses from their actual point and did not vary significantly across the different imagined station points. The evidence indicates that subjects know the objectto-object relations directly, without going through the origin of a coordinate system. In addition, similarities in processing during imagination on the one hand, and perception and action on the other are discussed. The spatial structure of a place consists of the distances and directions relating its objects, features, and events. Observers often produce spatially coordinated action while on the move and plan actions before reaching the station points from which

Research into the localization of virtual acoustic stimuli is often done in isolation from both acoustical and nonacoustical factors that are present in real-world environmental contexts. The fact that the commercial industry often separates "audio" from "visual" engineering is a reflection not only of hardware expertise but also of the specialization of psychophysical knowledge. For example, our collective knowledge of psychoacoustics far exceeds our knowledge of the multimodal interaction between sight, audition, and tactile sensations. However, technology developments benefit considerably when it is possible to predict how perception of an event within one sensory modality is affected by simultaneous presence of stimuli from other modalities. The study of multi-modal interaction, primarily between audition and vision, has received increased attention with the development of virtual reality systems, home theater, gaming, and teleconferencing. Several authors ha...

In four experiments involving blindfolded subjects, constant errors in the haptic judgment of extent in the horizontal plane were found to relate consistently to the time and velocity of limb movement. Radial movements, executed at a slower speed and for a longer time, are judged longer than tangential movements of equal extent. The data were considered in relation to certain physiological and kinematic properties of the actively moving limb. Taken together with additional information on judgments of movement duration, the results suggest that the illusion of extent is modulated by the perception of differential time cues. In these terms, it was noted that the haptic horizontal-vertical illusion with the L figure is another instance of the interaction of apparent space and time commonly found in studies of psychological relativity. Following Reid's (1954) documentation of the haptic horizontal-vertical illusion with an L figure, recent studies have shown that the effect is functionally related to the components of radial and tangential exploratory arm movements as described earlier by Davidon and Cheng (1964). Specifically, radial arm movements toward and away from the body, whether along the sagittal or coronal planes, are judged longer than equal tangential movements along the front or side of the body. The effect operates regardless of the spatial separation of the two extents to be judged (Cheng, 1968) and independently of two different types of movement involving different joints and muscle groups (Day & Wong, 1971). As radial movements are specific to the horizontal plane, no relative overestimation of haptic extent is found when the L figure is presented in the vertical (fronto-parallel) Experiments 1, 2, and 3 were completed at the University of Waikato in Hamilton, New Zealand, and supported by New Zealand University Grants

It is proposed in this paper that many geometrical optical illusions, as well as illusory patterns due to motion signals in line drawings, are due to the statistics of visual computations. The interpretation of image patterns is preceded by a step where image features such as lines, intersections of lines, or local image movement must be derived. However, there are many sources of noise or uncertainty in the formation and processing of images, and they cause problems in the estimation of these features; in particular, they cause bias. As a result, the locations of features are perceived erroneously and the appearance of the patterns is altered. The bias occurs with any visual processing of line features; under average conditions it is not large enough to be noticeable, but illusory patterns are such that the bias is highly pronounced. Thus, the broader message of this paper is that there is a general uncertainty principle which governs the workings of vision systems, and optical illusions are an artifact of this principle.

The quality of realism in virtual environments (VEs) is typically considered to be a function of visual and audio fidelity mutually exclusive of each other. However, the VE participant, being human, is multimodal by nature. Therefore, in order to validate more accurately the levels of auditory and visual fidelity that are required in a virtual environment, a better understanding is needed of the intersensory or crossmodal effects between the auditory and visual sense modalities. To identify whether any pertinent auditory-visual cross-modal perception phenomena exist, 108 subjects participated in three experiments which were completely automated using HTML, Java, and JavaScript programming languages. Visual and auditory display quality perceptions were measured intra- and intermodally by manipulating the pixel resolution of the visual display and Gaussian white noise level, and by manipulating the sampling frequency of the auditory display and Gaussian white noise level. Statistically significant results indicate that high-quality auditory displays coupled with highquality visual displays increase the quality perception of the visual displays relative to the evaluation of the visual display alone, and that low-quality auditory displays coupled with high-quality visual displays decrease the quality perception of the auditory displays relative to the evaluation of the auditory display alone. These findings strongly suggest that the quality of realism in VEs must be a function of both auditory and visual display fidelities inclusive of each other.

Confronted with the question of how we perceive the world, we are often taught that we have a series of distributed systems structured according to the sensory modalities that they process. We talk

Induced movement, illusory movement in a stationary stimulus resulting from adjoining movement, has received steady experimental investigation over the last 70 years or so. It is observed under different viewing conditions in a wide variety of displays that differ considerably in overall size and in form of inducing and induced stimuli. Explanations have been diverse, some being based on relations within the display and others invoking mediation by other aspects of the observer's perception. Probably, no one explanation can account for all forms of induced movement. Current knowledge about induced movement may have important implications for visual perception of object morion. Induced movement is one of a number of phenomena—including apparent movement, autokinetic movement, and movement aftereffect—in which movement is perceived, although the corresponding distal stimulus is physically stationary. It normally results from physical movement adjoining the stationary stimulus; the induced movement is in the direction opposite that of the adjoining movement. In a typical laboratory demonstration

In this paper, we propose a set of human perceptual cues used jointly to automatically detect image orientation. The cues used are: orientation of faces, position of the sky, brighter regions, and textured objects, and symmetry. We combine these cues in a Bayesian framework, and the photo acquiring model has been considered carefully as the prior knowledge of the image orientation. Results on more than a thousand different images provide a compelling argument that our approach is a viable one. 1.