Generating an image that affords slant perception from stereo, without pictorial cues.

This paper describes an algorithm for generating a planar image that when tilted provides stereo cues to slant, without contamination from pictorial gradients. As the stimuli derived from this image are ultimately intended for use in studies of slant perception under magnification, a further requirement is that the generated image be suitable for high-definition printing or display on a monitor. A first stage generates an image consisting of overlapping edges with sufficient density that when zoomed, edges that nearly span the original scale are replaced with newly emergent content that leaves the visible edge statistics unchanged. A second stage reduces intensity clumping while preserving edges by enforcing a broad dynamic range across the image. Spectral analyses demonstrate that the low-frequency content of the resulting image, which would correspond to the pictorial cue of texture gradient changes under slant, (a) has a power fall-off deviating from 1/f noise (to which the visual system is particularly sensitive), and (b) does not offer systematic cues under changes in scale or slant. Two behavioral experiments tested whether the algorithm generates stimuli that offer cues to slant under stereo viewing only, and not when disparities are eliminated. With a particular adjustment of dynamic range (and nearly so with the other version that was tested), participants viewing without stereo cues were essentially unable to discriminate slanted from flat (frontal) stimuli, and when slant was reported, they failed to discriminate its direction. In contrast, non-stereo viewing of a control stimulus with pictorial cues, as well as stereoscopic observation, consistently allowed participants to perceive slant correctly. Experiment 2 further showed that these results generalized across a population of different stimuli from the same generation process and demonstrated that the process did not substitute biased slant cues.

Please Touch: Object Properties that Invite Touch.

Touch has received increasing interest in marketing, given research indicating that contact with products influences evaluation and the tendency to purchase. However, little is known from the marketing or psychophysical literature about visible attributes of objects that elicit touch for hedonic purposes. In these studies, participants rated the tendency of pictured objects to invite touch, or "touch-ability." Rated touch-ability varied reliably with structural attributes of objects, and the structural influences were distinct from those on other ratings such as attractiveness and apparent expense. Although the trends varied across object sets, touch-ability generally declined as surface textures became markedly rough and shape complexity became extreme. Holding stimulus factors constant, touch-ability also varied with the specific hand movements that were anticipated. Finally, mean touch-ability ratings were correlated across participants with the "Need for Touch" scale, which measures an individual's tendency to touch products. The studies point to touch-ability as a potential factor that might be incorporated into product design.

Roughness Perception in Virtual Textures.

Haptic devices allow the production of virtual textured surfaces for psychophysical experiments. Some studies have shown inconsistencies between virtual and real textures with respect to their psychophysical functions for roughness, leading to speculation that virtual textures differ in some way from real ones. We have determined the psychophysical function for roughness using textures rendered with a high-fidelity magnetic levitation haptic device. A constraint surface algorithm was used to simulate the motion of a spherical probe over trapezoidal gratings and randomly dithered cones. The shape of the psychophysical functions for roughness is consistent between subjects but varies with changes in texture and probe geometry. For dithered cones, inverted "U"-shaped functions were found nearly identical, in maxima and curvature, to those in the literature for real textures with similar geometry.

Haptic Classification of Facial Identity in 2D Displays: Configural versus Feature-Based Processing.

Participants learned through feedback to haptically classify the identity of upright versus inverted versus scrambled faces depicted in simple 2D raised-line displays. We investigated whether identity classification would make use of a configural face representation, as is evidenced for vision and 3D haptic facial displays. Upright and scrambled faces produced equivalent accuracy, and both were identified more accurately than inverted faces. The mean magnitude of the haptic inversion effect for 2D facial identity was a sizable 26 percent, indicating that the upright orientation was ¿privileged¿ in the haptic representations of facial identity in these 2D displays, as with other facial modalities. However, given the effect of scrambling, we conclude that configural processing was not employed; rather, only local information about the features was used, the features being treated as oriented objects within a body-centered frame of reference. The results indicate a fundamental difference between haptic identification of 2D facial depictions and 3D faces, paralleling a corresponding difference in recognition of nonface objects.

Haptic perception: a tutorial.

This tutorial focuses on the sense of touch within the context of a fully active human observer. It is intended for graduate students and researchers outside the discipline who seek an introduction to the rapidly evolving field of human haptics. The tutorial begins with a review of peripheral sensory receptors in skin, muscles, tendons, and joints. We then describe an extensive body of research on "what" and "where" channels, the former dealing with haptic perception of objects, surfaces, and their properties, and the latter with perception of spatial layout on the skin and in external space relative to the perceiver. We conclude with a brief discussion of other significant issues in the field, including vision-touch interactions, affective touch, neural plasticity, and applications.

Haptic Processing of Facial Expressions of Emotion in 2D Raised-Line Drawings.

Participants haptically (vs. visually) classified universal facial expressions of emotion (FEEs) depicted in simple 2D raised-line displays. Experiments 1 and 2 established that haptic classification was well above chance; face-inversion effects further indicated that the upright orientation was privileged. Experiment 2 added a third condition in which the normal configuration of the upright features was spatially scrambled. Results confirmed that configural processing played a critical role, since upright FEEs were classified more accurately and confidently than either scrambled or inverted FEEs, which did not differ. Because accuracy in both scrambled and inverted conditions was above chance, feature processing also played a role, as confirmed by commonalities across confusions for upright, inverted, and scrambled faces. Experiment 3 required participants to visually and haptically assign emotional valence (positive/negative) and magnitude to upright and inverted 2-D FEE displays. While emotional magnitude could be assigned using either modality, haptic presentation led to more variable valence judgments. We also documented a new face-inversion effect for emotional valence visually, but not haptically. These results suggest emotions can be interpreted from 2-D displays presented haptically as well as visually; however, emotional impact is judged more reliably by vision than by touch. Potential applications of this work are also considered.

Haptic recognition of static and dynamic expressions of emotion in the live face.

If humans can detect the wealth of tactile and haptic information potentially available in live facial expressions of emotion (FEEs), they should be capable of haptically recognizing the six universal expressions of emotion (anger, disgust, fear, happiness, sadness, and surprise) at levels well above chance. We tested this hypothesis in the experiments reported here. With minimal training, subjects' overall mean accuracy was 51% for static FEEs (Experiment 1) and 74% for dynamic FEEs (Experiment 2). All FEEs except static fear were successfully recognized above the chance level of 16.7%. Complementing these findings, overall confidence and information transmission were higher for dynamic than for corresponding static faces. Our performance measures (accuracy and confidence ratings, plus response latency in Experiment 2 only) confirmed that happiness, sadness, and surprise were all highly recognizable, and anger, disgust, and fear less so.

Shaping synergistic pinching patterns with feedback distortion in a virtual rehabilitation environment.

Individuals with chronic disabilities often use compensatory coordination patterns learned during the recovery phase, even after their individual muscular control returns. Although these compensatory movements limit their ability to complete tasks, these individuals are not able to relearn the correct synergistic coordination patterns because doing so would temporarily compromise task performance. Following our previous work using feedback distortion in a virtual rehabilitation environment to increase the strength and range of motion of disabled individuals, we address the use of this same feedback distortion environment to alter movement coordination patterns. In this paper, we present the methodology and preliminary results showing that (1) able-bodied individuals could be trained to use a different coordination pattern to produce pinching movements, and (2) feedback distortion can alter movements for individual fingers separately during a coordinated movement. These results indicate that our distorted virtual environment may be a powerful rehabilitation tool to convert compensatory movements into movements that utilize all muscles in the normal synergistic patterns.

Navigating without vision: basic and applied research.

We describe some of the results of our program of basic and applied research on navigating without vision. One basic research topic that we have studied extensively is path integration, a form of navigation in which perceived self-motion is integrated over time to obtain an estimate of current position and orientation. In experiments on pathway completion, one test of path integration ability, we have found that subjects who are passively guided over the outbound path without vision exhibit significant errors when attempting to return to the origin but are nevertheless sensitive to turns and segment lengths in the stimulus path. We have also found no major differences in path integration ability among blind and sighted populations. A model we have developed that attributes errors in path integration to errors in encoding the stimulus path is a good beginning toward understanding path integration performance. In other research on path integration, in which optic flow information was manipulated in addition to the proprioceptive and vestibular information of nonvisual locomotion, we have found that optic flow is a weak input to the path integration process. In other basic research, our studies of auditory distance perception in outdoor environments show systematic underestimation of sound source distance. Our applied research has been concerned with developing and evaluating a navigation system for the visually impaired that uses three recent technologies: the Global Positioning System, Geographic Information Systems, and virtual acoustics. Our work shows that there is considerable promise of these three technologies in allowing visually impaired individuals to navigate and learn about unfamiliar environments without the assistance of human guides.

Active control of locomotion facilitates nonvisual navigation.

In some navigation tasks, participants are more accurate if they view the environment beforehand. To characterize the benefits associated with visual previews, 32 blindfolded participants were guided along simple paths and asked to walk unassisted to a specified destination (e.g., the origin). Paths were completed without vision, with or without a visual preview of the environment. Previews did not necessarily improve nonvisual navigation. When previewed landmarks stood near the origin or at off-path locations, they provided little benefit; by contrast, when they specified intermediate destinations (thereby increasing the degree of active control), performance was greatly enhanced. The results suggest that the benefit of a visual preview stems from the information it supplies for actively controlled locomotion. Accuracy in reaching the final destination, however, is strongly contingent upon the destination's location during the preview.

When to inspect? Recurrent inspection decisions in a simulated risky environment.

Participants scheduled inspections to detect costly events for which they were repeatedly at constant risk (probability of event onset) within a computerized environment. They were responsive to risk variations, conveyed either in advance or by experience with inspection outcomes, although experiencing unannounced increases in risk affected inspections more than experiencing unannounced decreases. Participants responded to variations in cost (time varying or fixed) when the effects were made perceptually salient. Compared with a normative model (R. L. Klatzky, D. M. Messick, & J. Loftus, 1992), some conditions showed near-optimal inspecting or had flat payoff functions that tolerated observed departures from optimal performance. Costly departures occurred particularly when combined cost and risk levels caused optimal responses to be extreme (always or never inspect). Results assess people's processing of relevant variables and indicate circumstances in which they may set substantially nonoptimal inspection schedules.

Path integration while ignoring irrelevant movement.

Participants attempted to return to the origin of travel after following an outbound path by locomotion on foot (Experiments 1-3) or in a virtual visual environment (Experiment 4). Critical conditions interrupted the outbound path with verbal distraction or irrelevant, to-be-ignored movements. Irrelevant movement, real or virtual, had greater effects than verbal or cognitive distraction, indicating inability to ignore displacement during path integration. Effects of the irrelevant movement's direction (backward vs. rightward) and location (1st vs. 2nd leg of path) indicated that participants encoded a configural representation of the pathway and then cognitively compensated for the movement, producing errors directly related to the demands of compensation. An encoding-error model fit to the data indicated that backward movement produced downward rescaling, whereas movement that led to implied rotation (rightward on 2nd leg) produced distortions of shape and scale.

Manipulation with no or partial vision.

The present research investigated the role of vision in closed- and open-loop processing during manipulation. In Experiment 1, participants performed common manipulatory tasks with 100% accuracy in less than 1 s without vision. In Experiment 2, the effects of extensive practice of a peg-in-hole task were examined within 4 functionally significant stages of manipulation. Performance was consistently faster with than without vision in the prereach, grasp, and transport + insert stages; reverse effects were observed during the reach stage. In Experiment 3, the effects of practice with partial vision were examined: Participants initially learned the peg-in-hole task with full vision and then transferred to learning the same task with vision available only during 1 functional stage. Overall, performance was fastest when vision was limited to the prereach and reach stages.

Tactile roughness perception with a rigid link interposed between skin and surface.

Subjects made roughness judgments of textured surfaces made of raised elements, while holding stick-like probes or through a rigid sheath mounted on the fingertip. These rigid links, which impose vibratory coding of roughness, were compared with the finger (bare or covered with a compliant glove), using magnitude-estimation and roughness differentiation tasks. All end effectors led to an increasing function relating subjective roughness magnitude to surface interelement spacing, and all produced above-chance roughness discrimination. Although discrimination was best with the finger, rigid links produced greater perceived roughness for the smoothest stimuli. A peak in the magnitude-estimation functions for the small probe and a transition from calling more sparsely spaced surfaces rougher to calling them smoother were predictable from the size of the contact area. The results indicate the potential viability of vibratory coding of roughness through a rigid link and have implications for teleoperation and virtual-reality systems.

Path completion after haptic exploration without vision: implications for haptic spatial representations.

Subjects haptically explored two legs of a triangular path and responded by returning to the origin. Seven conditions were tested, varying in (1) whether the path was imaginally displaced between the initial exploration and the response; (2) the nature of the displacement, if present--rotation or translation; (3) variability in the origin location across trials; and (4) instructions to complete a triangle versus remembering the origin location. Mean distance and angle responses were modeled by the encoding-error model (Fujita, Klatzky, Loomis, & Golledge, 1993), which attributes errors to misencoding of the path legs and angle. The model failed to predict the finding of systematic errors in response distance but not response angle, a dissociation that held when the path was undisplaced or imaginally translated. Rotation before responding produced errors more consistent with the model. The data suggest use of a body-centered representation to complete undisplaced or imaginally translated paths, but adoption of an object-centered representation after imagined rotation, as is more consistent with pathway completion using whole-body locomotion.

Assessing auditory distance perception using perceptually directed action.

Three experiments investigated auditory distance perception under natural listening conditions in a large open field. Targets varied in egocentric distance from 3 to 16 m. By presenting visual targets at these same locations on other trials, we were able to compare visual and auditory distance perception under similar circumstances. In some experimental conditions, observers made verbal reports of target distance. In others, observers viewed or listened to the target and then, without further perceptual information about the target, attempted to face the target, walk directly to it, or walk along a two-segment indirect path to it. The primary results were these. First, the verbal and walking responses were largely concordant, with the walking responses exhibiting less between-observer variability. Second, different motoric responses provided consistent estimates of the perceived target locations and, therefore, of the initially perceived distances. Third, under circumstances for which visual targets were perceived more or less correctly in distance using the more precise walking response, auditory targets were generally perceived with considerable systematic error. In particular, the perceived locations of the auditory targets varied only about half as much in distance as did the physical targets; in addition, there was a tendency to underestimate target distance, except for the closest targets.

Relative availability of surface and object properties during early haptic processing.

How the relative order in which 4 property classes of haptically perceived surfaces becomes available for processing after initial contact was studied. The classes included material, abrupt-surface discontinuity, relative orientation, and continuous 3-D surface contour properties. Relative accessibility was evaluated by using the slopes of haptic search functions obtained with a modified version of A. Treisman's (A. Treisman & S. Gormican, 1988) visual pop-out paradigm; the y0 intercepts were used to confirm and fine-tune order of accessibility. Target and distractors differed markedly in terms of their value on a single dimension. The results of 15 experiments show that coarse intensive discriminations are haptically processed early on. In marked contrast, most spatially encoded dimensions become accessible relatively later, sometimes considerably so.

Cognitive salience of haptic object properties: role of modality-encoding bias.

The influence of modality-encoding bias on the relative importance ('cognitive salience') of object shape, size, and material, with the last determined by weight and thermal variations, was examined. Experiment 1 confirmed that for these stimulus objects all five properties were very accessible haptically, as measured by the time to identify the property level of each designated property; however, observers were still generally faster for geometric than material properties. In experiment 2, the influence of modality-encoding bias on cognitive salience was assessed by using a task involving free sorting by similarity. As predicted, modality-encoding bias strongly influenced cognitive salience. Observers favoured sorting by material under haptic- bias instructions, and three-dimensional geometric properties (especially shape) under visual-bias instructions. Videotaped hand movements indicated that modality-encoding biases reflect long-term knowledge of the relative speed and precision of manual exploration patterns, rather than exploration of the current set of objects.

Identifying objects from a haptic glance.

Subjects identified common objects under conditions of a "haptic glance," a brief haptic exposure that placed severe spatial and temporal constraints on stimulus processing. They received no advance cue, a superordinate-level name as cue, or a superordinate and basic-level name as cue. The objects varied in size relative to the fingertip and in the most diagnostic attribute, either texture or shape. The data suggest that object recognition can occur when global volumetric primitives cannot directly be extracted. Even with no cue, confusion errors resembled the target object and indicated extraction of material and local shape information, which was sufficient to provide accuracy above 20%. Performance improved with cuing, and the effect of exposure duration was observed primarily with minimal cuing, indicating compensatory effects of top-down processing.

Planning for hand shape and arm transport when reaching for objects.

Two early components of object manipulation are shaping the hand appropriately for functional interaction and transporting the arm with appropriate force and spatial precision to the target object. Three experiments addressed whether people plan these two components before the onset of reaching and if so, how the plans are coordinated. Subjects reached for and contacted a series of objects with one of four hand configurations: pinch, poke, palm, and clench. The required configuration was signaled by the object's color; in some conditions its structure provided a redundant cue. The time from object exposure to arm liftoff (reaction time: RT) and the time from liftoff to contact (movement time: MT) were recorded. In Experiment 1, a compatible stimulus-to-hand-shape mapping substantially facilitated RT but not MT, suggesting that the appropriate hand shape was planned prior to reaching. Experiment 2 showed that contact precision, as defined by the stability of the object's support plane, affected MT; a smaller RT effect also suggested some pre-movement planning of arm transport to accommodate precision demands. Experiment 3 combined compatibility and precision manipulations in a single task to test a model which proposes that planning for hand-shape and arm transport occur in parallel, with the onset of reaching deferred until the slower planning process is completed.