Reference frame and haptic discrimination of orientations in infants

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.

摘要： 被试在矩形房间中从两个不同的观察点学习物体场景并在多个朝向上对物体形成的空间关系进行判断，通过控制场景中物体主要内在轴相对于环境结构（房间和地毯）的方向和被试的学习顺序，探讨被试在场景空间表征中采用何种参照系和参照系选取时的影响因素。两个实验结果发现：（1）内在参照系（intrinsic reference systems）和环境参照系均可以用于物体场景的表征，两类参照系之间的关系却是影响被试物体场景表征时参照系选取的重要因素，即当内在参照系与环境参照系方向一致时，被试无论从哪个朝向学习，都选择从垂直于内在参照系和环境参照系的朝向进行表征。反之，当二者方向不一致时，表征时参照系的选择取决于被试的学习经历；（2）无论内在参照系与环境参照系方向是否一致，物体场景本身内在结构的规则性都能够促进空间记忆，即内在结构的规则性既有助于准确编码物体的相对位置，也有助于提高空间关系判断的准确性。

The haptic perception of vertical, horizontal, +45 degrees oblique, and +135 degrees 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 ipsilaterally 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.

This chapter examines the haptic perception of spatial properties (orientation, distance and localization). In normal blindfolded adults, orientations and the oblique effect (lower peformance in oblique orientations than in vertical-horizontal orientations) seem to be defined in a subjective gravitational reference frame. In patients with left visuo-spatial neglect, the orientation deficit seems to affect all values and spatial positions of orientations in the same way. In five-month-old infants, two orientations (vertical vs. diagonal) can be discriminated manually and an oblique effect was evidenced. The haptic oblique effect seems to be a general perceptual and motor phenomenon. The estimation of Euclidean distance between two points in adults is affected by the path length (including detours) only for movements spanning a limited portion of the hand-arm workspace and for paths having several points of inflexion. The inference of stimulus localization is linked to the nature of exploratory movements needed to reach it. Taken together, these studies show the coexistence of similar processes in haptic and visual modalities and specific haptic processes.

North in the head: spatial reference frame and map orientation

In clinical movement biomechanics, kinematic measurements are collected to characterise the motion of articulating joints and investigate how different factors influence movement patterns. Representative time-series signals are calculated to encapsulate (complex and multidimensional) kinematic datasets succinctly. Exacerbated by numerous difficulties to consistently define joint coordinate frames, the influence of local frame orientation and position on the characteristics of the resultant kinematic signals has been previously proven to be a major limitation. Consequently, for consistent interpretation of joint motion (especially direct comparison) to be possible, differences in local frame position and orientation must first be addressed. Here, building on previous work that introduced a frame orientation optimisation method and demonstrated its potential to induce convergence towards a consistent kinematic signal, we present the REference FRame Alignment MEthod (REFRAME) that addresses both rotational and translational kinematics, is validated here for a healthy tibiofemoral joint, and allows flexible selection of optimisation criteria to fittingly address specific research questions. While not claiming to improve the accuracy of joint kinematics or reference frame axes, REFRAME does enable a representation of knee kinematic signals that accounts for differences in local frames (regardless of how these differences were introduced, e.g. anatomical heterogeneity, use of different data capture modalities or joint axis approaches, intra- and inter-rater reliability, etc.), as evidenced by peak root-mean-square errors of 0.24° ± 0.17° and 0.03 mm ± 0.01 mm after its implementation. By using a self-contained optimisation approach to systematically re-align the position and orientation of reference frames, REFRAME allows researchers to better assess whether two kinematic signals represent fundamentally similar or different underlying knee motion. The openly available implementation of REFRAME could therefore allow the consistent interpretation and comparison of knee kinematic signals across trials, subjects, examiners, or even research institutes.

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.

EEG correlates of spatial orientation in the human retrosplenial complex

Theorists in perception have included peripheral or central factors in their explanations of the oblique effect. Studies investigating the central factors have shown that stimuli oriented vertically or horizontally have better encoding properties than do stimuli oriented obliquely and that oblique stimuli are more confusable. In the present study, the oblique effect was studied using single dots as stimuli. These dots were surrounded by either a square or a circle frame that provided information about their position in the visual field. The results of classification, focusing, and discrimination tasks showed 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. The results suggest that an internal frame of reference, aligned with vertical and horizontal, facilitates processing of stimuli located on those axes.

Several studies have demonstrated a dissociation of the effects of illusion on perception and action, with perception generally reported to be susceptible to illusions, while actions are seemingly immune. These findings have been interpreted to support Milner and Goodale's Two Visual Systems model, which proposes the existence of separate visual processing streams for perception and action. However, an alternative interpretation suggests that this type of behavioral dissociation will occur for any illusion that is caused by a distortion of the observer's egocentric reference frame, without requiring the existence of separate perception and action systems that are differently affected by the illusion. In this scenario, movements aimed at illusory targets will be accurate if they are guided within the same distorted reference frame used for target encoding, since the error of motor guidance will cancel with the error of encoding (hence, for actions, two wrongs do make a right). We further test this Two-Wrongs model by examining two illusions for which the hypothesis makes very different predictions: the rod-and-frame illusion (which affects perception but not actions) and the simultaneous-tilt illusion (which affects perception and actions equally). We demonstrate that the rod-and-frame illusion is caused by a distortion of the observer's egocentric reference frame suitable for the cancellation of errors predicted by the Two-Wrongs model. In contrast, the simultaneous-tilt illusion is caused by local interactions between stimulus elements within an undistorted reference frame, precluding the cancellation of errors associated with the Two-Wrongs model such that the illusion is reflected in both perception and actions. These results provide evidence for a class of illusions that lead to dissociations of perception and action through distortions of the observer's spatial reference frame, rather than through the actions of functionally separate visual processing streams.

Research in spatial navigation revealed the existence of discrete strategies defined by the use of distinct reference frames during virtual path integration. The present study investigated the distribution of these navigation strategies as a function of gender, video gaming experience, and self-estimates of spatial navigation abilities in a population of 300 subjects. Participants watched videos of virtual passages through a star-field with one turn in either the horizontal (yaw) or the vertical (pitch) axis. At the end of a passage they selected one out of four homing arrows to indicate the initial starting location. To solve the task, participants could employ two discrete strategies, navigating within either an egocentric or an allocentric reference frame. The majority of valid subjects (232/260) consistently used the same strategy in more than 75% of all trials. With that approach 33.1% of all participants were classified as Turners (using an egocentric reference frame on both axes) and 46.5% as Non-turners (using an allocentric reference frame on both axes). 9.2% of all participants consistently used an egocentric reference frame in the yaw plane but an allocentric reference frame in the pitch plane (Switcher). Investigating the influence of gender on navigation strategies revealed that females predominantly used the Non-turner strategy while males used both the Turner and the Non-turner strategy with comparable probabilities. Other than expected, video gaming experience did not influence strategy use. Based on a strong quantitative basis with the sample size about an order of magnitude larger than in typical psychophysical studies these results demonstrate that most people reliably use one out of three possible navigation strategies (Turners, Non-turners, Switchers) for spatial updating and provides a sound estimate of how those strategies are distributed within the general population.

Comparison of perceptual learning of real and virtual line orientations: An event-related potential study

Meridional variations in the line orientation discrimination of the cat

It is not clear to date how visual deprivation affects auditory spatial perception. Recent psychophysical evidences described a spatial auditory deficit in congenitally blind individuals while some others found a spatial auditory improvement. Particularly, Gori, Sandini, Martinoli, & Burr (2014) and Vercillo, Milne, Gori, & Goodale (2015) reported that people who were born blind were less efficient in localizing sound sources with respect to auditory landmarks than sighted individuals. On the other side, blind people performed similarly or even better than sighted participants during the localization of single sound sources. We investigated auditory spatial perception in early blind using different auditory spatial tasks and found that blind individuals did not succeed in localizing sound sources in an external frame of reference. The performance of early blind was severely impaired during the localization of brief auditory stimuli with respect to acoustic landmarks (allocentric frame of reference) but was comparable to that one of sighted participants when they had to localize sounds with respect to their own body (egocentric reference frame). Our results suggest that, after early visual deprivation, auditory spatial perception is centered on an egocentric reference system.

Brain damage may induce a dysfunction of upright body position termed “pusher syndrome”. Patients with such disorder suffer from an alteration of their sense of body verticality. They experience their body as oriented upright when actually tilted nearly 20 degrees to the ipsilesional side. Pusher syndrome typically is associated with posterior thalamic stroke; less frequently with extra-thalamic lesions. This argued for a fundamental role of these structures in our control of upright body posture. Here we investigated whether such patients may show additional functional or metabolic abnormalities outside the areas of brain lesion. We investigated 19 stroke patients with thalamic or with extra-thalamic lesions showing versus not showing misperception of body orientation. We measured fluid-attenuated inversion-recovery (FLAIR) imaging, diffusion-weighted imaging (DWI), and perfusion-weighted imaging (PWI). This allowed us to determine the structural damage as well as to identify the malperfused but structural intact tissue. Pusher patients with thalamic lesions did not show dysfunctional brain areas in addition to the ones found to be structurally damaged. In the pusher patients with extra-thalamic lesions, the thalamus was neither structurally damaged nor malperfused. Rather, these patients showed small regions of abnormal perfusion in the structurally intact inferior frontal gyrus, middle temporal gyrus, inferior parietal lobule, and parietal white matter. The results indicate that these extra-thalamic brain areas contribute to the network controlling upright body posture. The data also suggest that damage of the neural tissue in the posterior thalamus itself rather than additional malperfusion in distant cortical areas is associated with pusher syndrome. Hence, it seems as if the normal functioning of both extra-thalamic as well as posterior thalamic structures is integral to perceiving gravity and controlling upright body orientation in humans.