The haptic oblique effect in the perception of rod orientation by blind adults

The haptic perception of vertical, horizontal, +45° oblique, and +135° oblique orientations was studied in completely blind adults. The purpose was to determine whether the variations of the gravitational cues provided by the arm-hand system during scanning would affect the manifestation of the oblique effect (lower performance in oblique orientations than in vertical-horizontal ones) as they did in blindfolded sighted people (Gentaz & Hatwell, 1996). In blindfolded sighted adults, the oblique effect was reduced or absent when the magnitude of gravitational cues was decreased. If visual experience participated in the haptic oblique effect, we should observe no oblique effect in early blind subjects in the conditions of manual exploration where late blind and blindfolded sighted manifest this effect. The magnitude of gravitational cues was therefore varied by changing gravity constraints, whereas the variability of these cues was varied by changing the plane in which the task was performed: horizontal (low variability) and frontal (high variability). Early and late blind adults were asked to explore haptically a rod and then to reproduce its orientation ipsilateraUy in one of two exploratory conditions in each plane. In the horizontal plane, the oblique effect was absent, whatever the gravity constraints, in both groups (early and late blind subjects). In the frontal plane, the oblique effect was present, whatever the gravity constraints, in both groups. Taken together, these results showed that, in blind people, the variability of gravitational cues played a role in the haptic oblique effect; no effect of previous visual experience was observed.     

The Poggendorff illusion: Amputations,rotations, and other perturbations

Studies of the Poggendorff illusion (a transversal interrupted by parallel lines) showed that illusory effects increased linearly with increasing separation between the parallels, increased in inverse proportion to the tangent of the angle of intersection between transversal and parallels, decreased whenever line segments (other than a transversal segment) were omitted, decreasing to zero when the segment of a parallel forming the obtuse angle with the transversal was omitted, and varied systematically with the tilt of the whole display, approaching zero when the transversal was oriented in a horizontal or vertical position. Hypothesis: The Poggendorff illusion involves at least three kinds of effects on the perceived orientation of a segment: distortion by other segments (especially a segment intersecting at an obtuse angle), stability of vertical and Horizontal orientations, and assimilation towards vertical or horizontal.     

Visual and haptic matching of perceived orientations of lines

In this study we investigated the perception and production of line orientations in a vertical plane. Previous studies have shown that systematic errors are made when participants have to match oblique orientations visually and haptically. Differences in the setup for visual and haptic matching did not allow for a quantitative comparison of the errors. To investigate whether matching errors are the same for different modalities, we asked participants to match a visually presented orientation visually, haptically with visual feedback, and haptically without visual feedback. The matching errors were the same in all three matching conditions. Horizontal and vertical orientations were matched correctly, but systematic errors were made for the oblique orientations. The errors depended on the viewing position from which the stimuli were seen, and on the distance of the stimulus from the observer.     

Auditory psychomotor coordination and visual search performance

In Experiments 1 and 2, the time to locate and identify a visual target (visual search performance in a two-alternative forced-choice paradigm) was measured as a function of the location of the target relative to the subject's initial line of gaze. In Experiment 1, tests were conducted within a 260 degree region on the horizontal plane at a fixed elevation (eye level). In Experiment 2, the position of the target was varied in both the horizontal (260 degrees) and the vertical (+/- 46 degrees from the initial line of gaze) planes. In both experiments, and for all locations tested, the time required to conduct a visual search was reduced substantially (175-1,200 msec) when a 10-Hz click train was presented from the same location as that occupied by the visual target. Significant differences in latencies were still evident when the visual target was located within 10 degrees of the initial line of gaze (central visual field). In Experiment 3, we examined head and eye movements that occur as subjects attempt to locate a sound source. Concurrent movements of the head and eyes are commonly encountered during auditorily directed search behavior. In over half of the trials, eyelid closures were apparent as the subjects attempted to orient themselves toward the sound source. The results from these experiments support the hypothesis that the auditory spatial channel has a significant role in regulating visual gaze.     

Reference frames and haptic perception of orientation: Body and head tilt effects on the oblique effect

The aim of this study was to examine the effect of body and head tilts on the haptic oblique effect. This effect reflects the more accurate processing of vertical and horizontal orientations, relative to oblique orientations. Body or head tilts lead to a mismatch between egocentric and gravitational axes and indicate whether the haptic oblique effect is defined in an egocentric or a gravitational reference frame. The ability to reproduce principal (vertical and horizontal) and oblique orientations was studied in upright and tilted postures. Moreover, by controlling the deviation of the haptic subjective vertical provoked by postural tilt, the possible role of a subjective gravitational reference frame was tested. Results showed that the haptic reproduction of orientations was strongly affected by both the position of the body (Experiment 1) and the position of the head (Experiment 2). In particular, the classical haptic oblique effect observed in the upright posture disappeared in tilted conditions, mainly because of a decrease in the accuracy of the vertical and horizontal settings. The subjective vertical appeared to be the orientation reproduced the most accurately. These results suggest that the haptic oblique effect is not purely gravitationally or egocentrically defined but, rather, depends on a subjective gravitational reference frame that is tilted in a direction opposite to that of the head in tilted postures (Experiment 3).     

Reference frames and haptic perception of orientation: body and head tilt effects on the oblique effect.

The aim of this study was to examine the effect of body and head tilts on the haptic oblique effect. This effect reflects the more accurate processing of vertical and horizontal orientations, relative to oblique orientations. Body or head tilts lead to a mismatch between egocentric and gravitational axes and indicate whether the haptic oblique effect is defined in an egocentric or a gravitational reference frame. The ability to reproduce principal (vertical and horizontal) and oblique orientations was studied in upright and tilted postures. Moreover, by controlling the deviation of the haptic subjective vertical provoked by postural tilt, the possible role of a subjective gravitational reference frame was tested. Results showed that the haptic reproduction of orientations was strongly affected by both the position of the body (Experiment 1) and the position of the head (Experiment 2). In particular, the classical haptic oblique effect observed in the upright posture disappeared in tilted conditions, mainly because of a decrease in the accuracy of the vertical and horizontal settings. The subjective vertical appeared to be the orientation reproduced the most accurately. These results suggest that the haptic oblique effect is not purely gravitationally or egocentrically defined but, rather, depends on a subjective gravitational reference frame that is tilted in a direction opposite to that of the head in tilted postures (Experiment 3).     

The misperception of angles: Estimating the vertex of converging line segments

Estimates of the point of intersection of converging line segments depended upon the angle between lines and the orientation of the display. Main conclusion: The tilt of a line is perceptually altered to appear more nearly parallel to the more closely aligned axis, either horizontal or vertical, of an O’s visual field.     

Spatial coding and oblique discrimination by children

Children from five to eight years of age learned to discriminate between mirrorimage oblique lines more readily when cards bearing the obliques were presented vertically than when they were presented horizontally. The difference in performance between the vertical and horizontal planes could not be accounted for by differences in either the external visual context or the availability of asymmetrical body information (e.g., left vs right hand). The superiority of the vertical plane was attributed to the congruence of objective, bodily, and retinal vertical axes for the vertical, but not the horizontal plane, It was concluded, on this basis, that at least part of children's difficulty discriminating between mirror-image obliques is due to their difficulty establishing the internalized vertical axis necessary for the left-right spatial coding of the obliques.     

The perception and representation of orientations: A study in the haptic modality

This research examines the haptic perception of orientations in the frontal plane in order to identify the nature of their representation. Blindfolded participants inserted the tip of the index finger into a thimble mounted on the extremity of a haptic interface and manually explored the orientation of a "virtual rod". After a short delay, participants had to reproduce the scanned orientation with the same hand without the guidance of the virtual rod. The analysis of the systematic errors showed that the recalled orientations were markedly biased toward the nearest diagonal in each quadrant with the exception of the orientations nearest to the vertical, which were biased toward the vertical. The variable error was greater for the oblique orientations than for the horizontal or vertical orientation. These results are interpreted with the Category-Adjustment model, which posits that orientations are categorically represented. We show that it is necessary to assume the existence of vertical and horizontal categories in addition to the previously postulated oblique categories to predict the error patterns observed in the present and former studies. The similarity of the error patterns in the visual and haptic modalities suggests that a common mechanism is at play in perceiving and reproducing orientations in both sensory modalities.     

The reproduction of vertical and oblique orientations in the visual, haptic, and somatovestibular systems

This study investigates whether the vertical orientation may be predominantly used as an amodal reference norm by the visual, haptic, and somato-vestibular perceptual systems to define oblique orientations. We examined this question by asking the same sighted adult subjects to reproduce, in the frontal (roll) plane, the vertical (0°) and six oblique orientations in three tasks involving different perceptual systems. In the visual task, the subjects adjusted a moveable rod so that it reproduced the orientation of a visual rod seen previously in a dark room. In the haptic task, the blindfolded sighted subjects scanned an oriented rod with one hand and reproduced its orientation, with the same hand, on a moveable response rod. In the somato-vestibular task, the blindfolded sighted subjects, sitting in a rotating chair, adjusted this chair in order to reproduce the tested orientation of their own body. The results showed that similar oblique effects (unsigned angular error difference between six oblique orientations and vertical orientation) were observed across the three tasks. However, there were no positive correlations between the visual, haptic,     

Perception of the head transversal plane and the subjective horizontal during gondola centrifugation

The subjective visual horizontal (SVH) and the subjective head transversal plane (STP) were measured by means of an adjustable luminous line in darkness during centrifuging. Subjects (N = 10) were seated upright, facing forward in a swing-out gondola. After acceleration of the centrifuge to 2G (vectorial sum of the earth's gravity and the centrifugal force; gondola inclination 60 degrees), subjects had to set the line either so that it was perceived as gravitoinertially horizontal (SVH) or so that it was perceived as parallel with the transversal ("horizontal") plane of the head (STP). Initially after acceleration, the SVH was tilted with respect to the gravitoinertial horizontal of the gondola (M = 16.6 degrees). This tilt was compensatory with respect to the gondola inclination. However, the STP was tilted in the opposite direction (M = 12.4 degrees), which might suggest a vestibular-induced distortion of the mental representation of one's own body. Similar results were obtained when measuring the subjective visual vertical (SVV) and the subjective midsagittal plane (SSP) in 5 subjects. The perceived roll angle (obtained as SVH-STP or SVV-SSP) was considerably larger than had previously been reported. Time constants for exponential decay of the tilt of the SVH or SVV were often 2-3 min, indicating a memory for semicircular canal information on changes in head orientation--a position-storage mechanism.     

宽带宽噪音图片朝向辨识任务上的“反倾斜效应”

本研究探讨宽带宽噪音图片的反倾斜效应及短期训练对其影响。首先,我们测量被试对四个朝向(0°,45°,90°和135°)噪音图片的知觉明显度阈值。然后根据被试的阈值生成图片,让被试完成朝向辨识任务,记录正确率和反应时。结果表明人对倾斜朝向刺激的辨识显著好于主要朝向。并且,被试对所有朝向刺激的辨识经训练后都有显著提高。本研究提示人们对于这种宽带宽噪音图片的辨识能够学习,但是短期的训练不能使反倾斜效应消失。     

Body tilt effect on the reproduction of orientations: studies on the visual oblique effect and subjective orientations

Body tilt effects on the visual reproduction of orientations and the Class 2 oblique effect (E. A. Essock, 1980) were examined. Body tilts indicate whether the oblique effect (i.e., lower performance in oblique orientations than in vertical-horizontal orientations) is defined in an egocentric or a gravitational reference frame. Results showed that the oblique effect observed in upright posture disappeared in tilted conditions, mainly due to a decrease in the precision of the vertical and horizontal settings. In tilted conditions, the subjective visual vertical proved to be the orientation reproduced the most precisely. Thus, the oblique effect seemed to be not purely gravitationally or egocentrically defined but, rather, to depend on a subjective gravitational reference frame tilted in the same direction as body tilts.     

An oblique effect in aesthetics: homage to Mondrian (1872-1944)

The effect of the orientation of Mondrian's paintings on their aesthetic appeal was examined. Eight paintings, four with horizontal/vertical frames in the original and four with oblique frames, were presented in eight different orientations and rated for aesthetic appeal on a 7-point scale. There was a stronger preference for pictures presented so that their component lines were horizontal and vertical than for pictures presented with their component lines in an oblique orientation. In addition, subjects showed a preference for the original orientation, perhaps because rotation changes the lateral balance of the paintings as well as the orientation of the component lines. There was no overall preference for one frame orientation over another, but there was an interaction between frame orientation and component orientation, resulting in a preference for paintings where the components were parallel to the surrounding frame. It is suggested that the aesthetic oblique effect reported here is related to the oblique effect in orientation perception and the privileged access which horizontal and vertical lines have to the visual system. This offers a possible mechanism for aesthetic judgments of abstract patterns: we find pleasing those stimuli which are closely tuned to the properties of the human visual system.     

Effect of modality-specific experience on visual and haptic judgment of orientation

Although the 'oblique effect' (poorer performance on oblique orientations as compared to performance on vertical and horizontal orientations) is generally understood as a strictly visual phenomenon, a haptic oblique effect occurs for blindfolded subjects required to set a stimulus rod by hand. Because oblique effects are often attributed to the observer's experience with a predominantly horizontal and vertical environment, we assessed the effect of visual and haptic experience by providing subjects with modality-specific inspection periods to familiarize them with the more poorly judged obliques. Oblique error was significantly reduced in magnitude for judgments made by the modality of experience, and for judgments made across modalities. Rate of improvement, consistency of transfer, and the subjective reports of subjects indicate that this haptic oblique effect is more strongly influenced by visual experience and imagery than by haptic experience. It need not be interpreted as an effect based on factors intrinsic to the haptic modality.     

Coactivation, pop-out, and symmetry affect line discrimination

17 college students discriminated between vertical and horizontal target lines flanked by vertical and horizontal distractors. Large displays with 3.0-cm lines and small displays half this size were used. The distractors were positioned above and below the target or to the left and right of it, forming vertical and horizontal global orientations. The number of flankers sharing the target's orientation was varied. Vertical targets and small display sizes were processed more quickly. Speed of responding did not differ for the two global orientations. There was no advantage for target lines consistent with global orientation. The results were replicated in Exp. 2 with diagonal flankers. This supports an explanation using stimulus compatibility, since diagonal lines do not correspond to either of the response options and cannot induce a tendency to respond more to one target than another. Displays with multiple symmetry were responded to faster than those with a single symmetry which were faster than asymmetrical displays, supporting the idea that symmetrical axes parallel and perpendicular to the target orientation provide a facilitative frame of reference. Coactivation from same-oriented flankers, pop-out from differences in orientation, and symmetry all influenced responding in these patterns.     

Interaction of fixation point and stimulus orientation the appearance of rectilinearity

Data from two experiments indicate that the findings of Prytulak (1973) are generalizable to stimulus lines at all orientations: (a) when setting a response dot so that it appears to lie on an imaginary extension of a stimulus line, Ss misplace the dot on the side of the extension opposite the fixation point (a contralateral response, or CR) when the fixation point is in the vicinity of the stimulus line and on the same side of the extension as the fixation point (an ipsflateral response, or IR) when the fixation point is in the vicinity of the response dot; (b) CR is larger than IR; (c) fixation of the stimulus line or any point on its extension produces relatively accurate settings. New findings were: (a) the magnitude of CR decreased as the orientation of the stimulus line approached the vertical or horizontal; (b) the magnitude of CR on or near the horizontal was weaker than on or near the vertical; (c) the magnitude of IR was greater - for stimulus lines lying in the upper half of the visual field than for stimulus lines lying in the lowerhalf. The difficulty - - of accounting for fixation point effects by means of physiological optics was discussed.     

How configurations of binocular disparity determine whether stereoscopic slant or stereoscopic occlusion is seen

A partially occluded contour and a slanted contour may generate identical binocular horizontal disparities. We investigated conditions promoting an occlusion resolution indicated by an illusory contour in depth along the aligned ends of horizontally disparate line sets. For a set of identical oblique lines with a constant width added to one eye's view, strength, depth, and stability of the illusory contour were poor, whereas for oblique lines of alternating orientations the illusory contours were strong, indicating a reliance on vertical size disparities rather than vertical positional disparities in generating perceived occlusion. For horizontal lines, occlusion was seen when the lines were of different lengths and absolute width disparity was invariant across the set. In all line configurations, when the additional length was on the wrong eye to be attributed to differential occlusion, lines appeared slanted consistent with their individual horizontal disparities. This rules out monocular illusory contours as the determining factor.     

Integration of local features as a function of global goodness and spacing

In two experiments, the accuracy with which subjects detected a conjunction of features was examined as a function of the spacing between items and the goodness of the axis along which they were located. In each array, two items were arranged along a vertical, a horizontal, or a diagonal axis. Based on the well-established oblique effect, the vertical and horizontal axes were considered to be good global patterns and the diagonals were considered to be poor. In Experiment 1, the two items in an array could be two horizontal lines, two vertical lines, a vertical and a horizontal line, or a plus sign with one of the single lines. In Experiment 2, a positive- and a negative-diagonal line were used as the individual features, and an "X" was used as the conjunction. The results from Experiment 1 indicated that global goodness influenced only the rate of illusory conjunctions, and not of feature errors. Illusory conjunctions of vertical and horizontal line segments were more likely to occur in vertical and horizontal arrangements. The results from Experiment 2 revealed a reversal of the effect of global goodness on the rate of illusory conjunctions: Illusory conjunctions of negative- and positive-diagonal line segments were more likely to occur in diagonal arrangements. The results of both experiments taken together showed the existence of an important and new factor that influences the likelihood that features of shape will be conjoined: the ease with which line segments conjoin when they are translated along their extent toward each other. In both experiments, greater spacing between items produced more feature-identification errors and fewer feature-integration errors than did less spacing.     

Role of gravitational cues in the haptic perception of orientation

The haptic perception of vertical, horizontal, +45°-oblique, and +135°-oblique orientations was studied in adults. The purpose was to establish whether the gravitational cues provided by the scanning arm—hand system were involved in the haptic oblique effect (lower performances in oblique orientations than in vertical—horizontal ones) and more generally in the haptic coding of orientation. The magnitude of these cues was manipulated by changing gravity constraints, and their variability was manipulated by changing the planes in which the task was performed (horizontal, frontal, and sagittal). In Experiment 1, only the horizontal plane was tested, either with the forearm resting on the disk supporting the rod (“supported forearm” condition) or with the forearm unsupported in the air. In the latter case, antigravitational forces were elicited during scanning. The oblique effect was present in the “unsupported” condition and was absent in the “supported” condition. In Experiment 2, the three planes were tested, either in a “natural” or in a “lightened forearm” condition in which the gravitational cues were reduced by lightening the subject’s forearm. The magnitude of the oblique effect was lower in the “lightened” condition than in the “natural” one, and there was no plane effect. In Experiment 3, the subject’s forearm was loaded with either a 500- or a 1,000-g bracelet, or it was not loaded. The oblique effect was the same in the three conditions, and the plane effect (lower performances in the horizontal plane than in the frontal and sagittal ones) was present only when the forearm was loaded. Taken together, these results suggested that gravitational cues may play a role in haptic coding of orientation, although the effects of decreasing or increasing these cues are not symmetrical.