Internal frame of reference as a determinant of the oblique effect.

Studied the oblique effect (preference for stimuli that are oriented vertically or horizontally over those oriented obliquely) using single dots as stimuli in 2 experiments with 20 graduate students and staff of a university and 10 undergraduates, all with normal or corrected vision. These dots were surrounded by either a square or a circle frame that provided information about their position in the visual field. Results of classification, focusing, and discrimination tasks show that the processing of these dots followed the same pattern of results as it did with line stimuli: Dots located on the main axes (vertical and horizontal) were easier to classify than dots located on the oblique axes. The same pattern of results was found in both the square- and circle-frame experiments. It is suggested that an internal frame of reference, aligned with vertical and horizontal, facilitates processing of stimuli located on those axes. (21 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Vertebral osteomyelitis due to salmonellae: report of two cases and review

A static or kinetic visual disturbance affects subjects' ability to estimate the direction of the gravitational vertical. This kind of error is increased by a head roll inclination. In two experiments, we combined head orientation with a static (Experiment 1: tilted frame) versus kinetic (Experiment 2: rotating disk) visual disturbance. The results showed that with a static visual disturbance, the increase of errors in the inclined head condition was mainly the consequence of a postural head effect like an Aubert effect. On the contrary, with a kinetic visual disturbance, it appears that the disk effect increases with head inclination. However, individual errors observed with the head inclined in front of a stationary disk were systematically correlated with the errors triggered by the same head inclination in front of a rotating disk. These observations confirm that the head axis spatial reference plays an important role in orientation perception, whatever the head position and the kind of visual display.     

Visual Search for Object Orientation Can Be Modulated by Canonical Orientation.

The authors studied the influence of canonical orientation on visual search for object orientation. Displays consisted of pictures of animals whose axis of elongation was either vertical or tilted in their canonical orientation. Target orientation could be either congruent or incongruent with the object's canonical orientation. In Experiment 1, vertical canonical targets were detected faster when they were tilted (incongruent) than when they were vertical (congruent). This search asymmetry was reversed for tilted canonical targets. The effect of canonical orientation was partially preserved when objects were high-pass filtered, but it was eliminated when they were low-pass filtered, rendering them as unfamiliar shapes (Experiment 2). The effect of canonical orientation was also eliminated by inverting the objects (Experiment 3) and in a patient with visual agnosia (Experiment 4). These results indicate that orientation search with familiar objects can be modulated by canonical orientation, and they indicate a top-down influence on orientation processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Paediatric reference values for urinary catecholamine metabolites evaluated by high performance liquid chromatography and electrochemical detection

This report summarizes our experiences with the subjective visual vertical (SVV) as a clinical neuro-otological tool. In the SVV test, patients have to orient a dim light bar in an otherwise dark surrounding earth-vertical, using a remote-control. Normal subjects in an upright position did not deviate more than 2 degrees from true vertical. After vestibular neurectomy, the SVV was consistently tilted by some 12 degrees toward the affected ear. Smaller tilts (approximately 7 degrees) of the SVV occurred in patients with spontaneous peripheral vestibular diseases. This shift in SVV disappeared within weeks to months, similar to the spontaneous nystagmus. After stapes surgery slight deviations of the SVV towards the unoperated ear were seen in about 20% of the patients, indicating a slight irritation of the otolith organs. Assessed in an upright position, the SVV thus may be regarded as reflecting tonic otolithic input differences between the two ears. Asymmetries in the shifts of the SVV induced by roll tilts of the gravito-inertial vector by eccentric rotations of the subject have been proposed as a test for otolithic sensitivity. In our studies such asymmetries in the shifts of the SVV could not be induced by 26 degrees or 90 degrees roll tilts of subjects towards the affected or healthy ears. A simple clinical test to reveal unilateral otolithic sensitivity (comparable to an otolithic "caloric test") thus still has to be found.     

Apparent body tilt and postural aftereffect

Apparent orientation of the body tilted laterally in the frontal plane was studied with the methods of absolute judgments in four experiments. In Experiment 1, 17 subjects, who maintained the normal adaptation of body to gravity, estimated their body tilts under the condition of seeing the gravitational vertical and under the condition of eliminating it. The results showed that (1) there was not a significant difference between the two conditions and (2) the small tilts of less than 45 degrees were exactly estimated, whereas the large tilts of 45 degrees-108 degrees were overestimated. In Experiment 2, 10 subjects estimated their body tilts under three velocities of a rotating chair on which each subject was placed. Although both body tilt and chair velocity were found to influence tilt estimation, the effect of body tilt was overwhelmingly greater than that of chair velocity. In Experiment 3, 11 subjects adapted their bodies to a 72 degrees left tilt for 10 min and then estimated various body tilts around the adapting tilt. The estimations obtained under the 72 degrees adaptation were lower than those obtained under the 0 degree adaptation, and this reduction was greater for the test tilt that was farther away from the adapting tilt. In Experiment 4, 11 subjects adjusted their own body tilts to designated angles. The results confirmed the outcomes of absolute estimation in Experiments 1-3. From these findings and past literature, the judgments of body tilt were considered to be subserved by a single sensory process that was based on the cutaneous and muscular proprioceptors, rather than the vestibular and joint proprioceptors.     

Frame-of-reference and hierarchical-organisation effects in the rod-and-frame illusion

Two hypotheses proposed as alternatives by Rock--frame of reference and hierarchical organisation of perception--were tested in a series of experiments with the use of the rod-and-frame illusion. This illusion produces errors in the apparent vertical due to the presence of a tilted frame surrounding the test rod. The apparent vertical is shifted in the direction of the frame tilt. When an upright square was added inside the tilted frame, rod-setting errors varied according to the visual characteristics of the display. In the case of a large display presented in the dark (experiment 1), there continued to be large errors in the direction of the outer-square tilt. This finding supports the frame-of-reference hypothesis, which proposes that the orientation of all objects in the visual field is dominated by the most peripheral reference. In the case of a small display presented in a lit environment (experiments 2 and 3), the direction of errors was the opposite. This latter finding was taken to indicate that the rod was set with reference to the perceived tilt of the inner upright square. Thus, according to a hierarchical-organisation hypothesis, the orientation of an object in the visual field is influenced by objects in the immediate surroundings not by outermost reference. Overall, the results confirm the presence of two qualitatively different classes of orientational phenomena: one is concerned with the definition of egocentric coordinates and one with an object-centred visual representation.     

Spatial and physical frames of reference in positioning a limb

Splints attached to the right forearm were used to rotate the forearm's physical reference frame, as defined by the eigenvectors of its inertia tensor, relative to its spatial reference frame. In two experiments, when subjects were required to orient the forearm parallel to, or at 45 degrees to, the environmental horizontal, they produced limb orientations that were systematically deflected from the forearm's longitudinal spatial axis in the direction of the forearm's physical axes. The position sense seems to be based on inertial eigenvectors rather than on joint angles or gravitational torques.     

Convergence of ampullar and macular inputs on vestibular nuclei unit of the rat

181 vestibular nucleus neurons were examined for their responsiveness to rotation about the vertical axis and static tilts in roll and pitch planes in the rat. 68 of these units were sensitive to rotation and tilts (canal-otolith cells). In other words, 41.0% of the neurons responded to rotation (68/166). There was no significant difference in percentage of canal-otolith cells in type I and II neurons, which were 48.6% and 37.0% respectively. Vertical axis rotation when the head was tilted produced a simultaneous stimulation of the canal and otoliths. Using this stimulus method, the bias effect was observed in 72.5% of the canal-otolith cells (29/40). Furthermore, since vertical axis rotation with the head tilted elicited vertical canal responses, the rate of ampullary convergence was estimated by analysing response profiles obtained such rotations. The results obtained in the rat were compared with those in other species.     

Cellular kinetic differences between Hodgkin''s and anaplastic large cell lymphomas: relation to the expression of p34cdc2 and cyclin B-1

Normal human subjects were tested for their ability to discriminate the orientation of a square plaque tilted in depth, using two different tasks: a grasping task and a perceptual matching task. Both tasks were given under separate monocular and binocular conditions. Accuracy of performance was measured by use of an opto-electronic motion analysis system, which computed the hand orientation (specifically, a line joining the tips of the thumb and index finger) as the hand either approached the target during grasping or was used to match the target. In all cases there was a very strong statistical coupling between hand orientation and target orientation, irrespective of viewing conditions. However, the matching data differed from the grasping data in showing a consistent curvature in the hand-target relationship, whereby the rate of change of hand orientation as a function of object orientation was smaller for oblique orientations than for those near the horizontal or vertical. The results are interpreted as reflecting the operation of two different mechanisms for analysing orientation in depth: a visuomotor system (assumed to be located primarily in the dorsal cortical visual stream) and a perceptual system (assumed to be located in the ventral stream). It may be that the requirements of visuomotor control dictate a primary need for absolute orientation coding, whereas those of perception dictate a need for more categorical coding.     

The role of categorization in visual search for orientation.

Visual search for 1 target orientation is fast and virtually independent of set size if all of the distractors are of a single, different orientation. However, in the presence of distractors of several orientations, search can become inefficient and strongly dependent on set size (Exp 1). Search can be inefficient even if only 2 distractor orientations are used and even if those orientations are quite remote from the target orientation (e.g., 20° or even 40° away, Exp 2). Search for 1 orientation among heterogeneous distractor orientations becomes more efficient if the target orientation is the only item possessing a categorical attribute such as steep, shallow (Exp 3), tilted left or tilted right (Exp 4), or simply tilted (Exps 5 and 6). Orientation categories appear to be 1 of several strategies used in visual search for orientation. These serve as a compromise between the limits on parallel visual processing and the demands of a complex visual world. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception and discrimination as a function of stimulus orientation: The "oblique effect" in man and animals.

A review of both behavioral and neurophysiological studies of orientation preferences indicates that performance for a large variety of perceptual tasks is superior for stimuli aligned in horizontal or vertical orientations, as compared to stimuli in oblique orientations. This phenomenon appears in the human adult and child and throughout the animal kingdom. Neurophysiological mechanisms for orientation analysis have been found in the higher visual pathways of many animals, and the suggestive evidence is compelling that these mechanisms underlie the orientation preferences reported behaviorally. Additional methods for determining the cause of these effects are suggested. (11 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coordinate frames for naming misoriented chimerics: a case study of visuo-spatial neglect

A persistent line of inquiry for the students of visuo-spatial neglect has involved the perceptual frame of reference respect to which the neglected region of space is defined. On standard testing conditions viewer-centered and object-centered systems of coordinates are confounded. In order to disambiguate these two reference frames FB, a patient with severe left visual neglect consequent upon a right parieto-temporal haemorrhage, was asked to identify chimeric figures presented at different orientations. FB continued to recognize poorly the left side of chimeric figures even when the display was rotated 90 degrees clockwise or anticlockwise so that the 'left' of the chimeric fell on the patient's egocentric up or down, respectively. The result suggests that, at least under the present testing conditions, unilateral neglect is tied to the principal (top-bottom) axis of the object. Object-centered vs. (viewer-centered) representational accounts of this finding are discussed.     

The detection of bilateral symmetry: Effects of surrounding frames.

Examined whether the detection of bilateral symmetry in the fronto-parallel plane is influenced by surrounding frames. The study was conducted with 12 Ss. When obliquely or vertically oriented rectangular frames were presented simultaneously surrounding the dot patterns, the frames influenced symmetry detection. Vertical symmetry detection was slower in the tilted frame than it was in the vertical frame, and tilted symmetry was detected faster in the tilted frame than it was in the vertical. When there was a time delay between frame and pattern onset, there was no measurable frame effect. Symmetry detection was slowed when not in line with the long axis of the frame, whereas symmetry detection was not affected when the frame axis was aligned with the symmetry axis. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In search of biased egocentric reference frames in neglect

The present study was aimed at assessing, by means of visual as well as proprioceptive-kinaesthetic straight-ahead tasks, the possible causal role of the ipsilesional deviation of the egocentric reference frame in determining neglect syndrome. The hypothesis, originally proposed by Ventre et al. [3], that an alteration of the representation of body-centred space can be a cause of asymmetrical spatial behaviour in humans has been recently revived by Karnath and co-workers [24]. The results of the present study seem to challenge the view that a systematic ipsilesional displacement of the egocentric reference is the crucial mechanism responsible for unilateral visual neglect. Under visual conditions, in which patients were required to stop a moving spot as it crossed their perceived midline, the ipsilesional deviation of the egocentric reference frame was dependent upon the direction of visual scanning. Right to left visual scanning direction produced a rightward displacement of the egocentric reference. In contrast, left to right visual scanning direction allowed neglect patients to correctly locate their perceived egocentre with an accuracy which did not differ from controls. The notion that the effect of a deviation of the egocentric reference frame is actually dependent on a bias in the visual scanning orienting response was also confirmed in the proprioceptive straight-ahead pointing tasks, in which the patients were blindfolded and therefore no visual information was available. In these conditions, in which patients were required to judge the subjective midline by using head, trunk and shoulder co-ordinate systems, the displacement of the subjective egocentric midline was not present.     

Feature-specific perceptual processing dissociates action from recognition.

Does visual processing differ for action and recognition? To address this question, the authors capitalized on research showing that color is preferred over binocular disparity in the ventral (recognition) stream, whereas disparity is preferred over color in the dorsal (action) stream. Participants searched for oblique targets among vertical distractors in displays defined only by color or disparity. Action-task participants stamped the target with a handheld block, whereas recognition-task participants lifted the block through a target-compatible gap. Analyses of reaction time and time-varying hand orientation showed that disparity and color displays were processed equally efficiently during action, but disparity was processed less efficiently than color during recognition. The results suggest that visual processing differs for action and recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Human oculomotor system accounts for 3-D eye orientation in the visual-motor transformation for saccades

A recent theoretical investigation has demonstrated that three-dimensional (3-D) eye position dependencies in the geometry of retinal stimulation must be accounted for neurally (i.e., in a visuomotor reference frame transformation) if saccades are to be both accurate and obey Listing's law from all initial eye positions. Our goal was to determine whether the human saccade generator correctly implements this eye-to-head reference frame transformation (RFT), or if it approximates this function with a visuomotor look-up table (LT). Six head-fixed subjects participated in three experiments in complete darkness. We recorded 60 degrees horizontal saccades between five parallel pairs of lights, over a vertical range of +/-40 degrees (experiment 1), and 30 degrees radial saccades from a central target, with the head upright or tilted 45 degrees clockwise/counterclockwise to induce torsional ocular counterroll, under both binocular and monocular viewing conditions (experiments 2 and 3). 3-D eye orientation and oculocentric target direction (i.e., retinal error) were computed from search coil signals in the right eye. Experiment 1: as predicted, retinal error was a nontrivial function of both target displacement in space and 3-D eye orientation (e.g., horizontally displaced targets could induce horizontal or oblique retinal errors, depending on eye position). These data were input to a 3-D visuomotor LT model, which implemented Listing's law, but predicted position-dependent errors in final gaze direction of up to 19.8 degrees. Actual saccades obeyed Listing's law but did not show the predicted pattern of inaccuracies in final gaze direction, i.e., the slope of actual error, as a function of predicted error, was only -0. 01 +/- 0.14 (compared with 0 for RFT model and 1.0 for LT model), suggesting near-perfect compensation for eye position. Experiments 2 and 3: actual directional errors from initial torsional eye positions were only a fraction of those predicted by the LT model (e. g., 32% for clockwise and 33% for counterclockwise counterroll during binocular viewing). Furthermore, any residual errors were immediately reduced when visual feedback was provided during saccades. Thus, other than sporadic miscalibrations for torsion, saccades were accurate from all 3-D eye positions. We conclude that 1) the hypothesis of a visuomotor look-up table for saccades fails to account even for saccades made directly toward visual targets, but rather, 2) the oculomotor system takes 3-D eye orientation into account in a visuomotor reference frame transformation. This transformation is probably implemented physiologically between retinotopically organized saccade centers (in cortex and superior colliculus) and the brain stem burst generator.     

Top-bottom and front-behind decisions on rotated objects.

Examined 2 tasks requiring the perception of the spatial relationship between an object and a dot. 24 undergraduates decided whether a dot was nearer the top or bottom of rotated drawings of objects in a top-bottom task, and whether a dot was at the front of or behind rotated objects in a front-behind task. These 2 tasks were performed with the head upright and with the head tilted clockwise and counterclockwise in separate blocks of trials in order to dissociate retinal from environmental perceptual frames of reference. Response times increased approximately linearly with increasing departure from the orientation of the perceptual reference frame in both tasks; the magnitude of the effect was similar across tasks. In the head-tilted conditions, the perceptual frame of reference was located midway between the environmental and retinal upright for both tasks. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parametric exploration of the Simon effect across visual space.

The Simon effect refers to the performance advantage for responding to the nonspatial identity of the target when the target's irrelevant location corresponds with the relative location of the response. The present study is a parametric examination of the magnitude of the Simon effect across visual space. Response keys were arranged along vertical, horizontal, and two diagonal axes, and stimuli were arranged in two concentric circles (near and far from fixation) along the same axes. The results show that the Simon effect is of similar magnitude regardless of stimulus-response axis. In contrast to findings from stimulus-response compatibility paradigms, there was no evidence in this study for the presence of an orthogonal compatibility effect or left-right prevalence effect, suggesting that these effects only arise when response location is relevant. The results demonstrate the robust generalizability of the Simon effect under different spatial conditions and thus broaden the relevance of the Simon effect to a variety of applications. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Children's construction of horizontals, verticals, and diagonals: An operational explanation of the "oblique effect."

Used a computer-based task to investigate the problem that young children have in constructing diagonals. The computer made it feasible to change how lines of different orientations had to be formed. It was predicted that if diagonals are difficult to construct because of the operations required to conceptualize them, then changing how they had to be formed might make it possible for children to construct diagonals better than horizontals and verticals. 20 5-yr-olds, 20 8-yr-olds, and 20 undergraduates attempted to construct horizontal, vertical, 45° left diagonal, and 45° right diagonal lines in either horizontal/vertical-easy or diagonal-easy configurations of the apparatus. Results support the operational explanation of the oblique effect. The 5-yr-olds performed in accordance with the configuration of the drawing system. On the whole, they could not make diagonals in the horizontal/vertical-easy configuration, thus demonstrating the oblique effect. When diagonals were made easy to produce, 5-yr-olds could form them but had difficulty with horizontals and verticals, indicating a nonoblique effect in the diagonal-easy configuration. There was only an oblique effect with the 8-yr-olds. Undergraduates made virtually no errors on any of the lines. Findings confirm the claim that the difficulty that the 5-yr-olds had was in combining separate spatial components. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The distribution of oriented contours in the real world

In both humans and experimental animals, the ability to perceive contours that are vertically or horizontally oriented is superior to the perception of oblique angles. There is, however, no consensus about the developmental origins or functional basis of this phenomenon. Here, we report the analysis of a large library of digitized scenes using image processing with orientation-sensitive filters. Our results show a prevalence of vertical and horizontal orientations in indoor, outdoor, and even entirely natural settings. Because visual experience is known to influence the development of visual cortical circuitry, we suggest that this real world anisotropy is related to the enhanced ability of humans and other animals to process contours in the cardinal axes, perhaps by stimulating the development of a greater amount of visual circuitry devoted to processing vertical and horizontal contours.