External Reference Frame Research Articles

Disentangling the External Reference Frames Relevant to Tactile Localization.

Different reference frames appear to be relevant for tactile spatial coding. When participants give temporal order judgments (TOJ) of two tactile stimuli, one on each hand, performance declines when the hands are crossed. This effect is attributed to a conflict between anatomical and external location codes: hand crossing places the anatomically right hand into the left side of external space. However, hand crossing alone does not specify the anchor of the external reference frame, such as gaze, trunk, or the stimulated limb. Experiments that used explicit localization responses, such as pointing to tactile stimuli rather than crossing manipulations, have consistently implicated gaze-centered coding for touch. To test whether crossing effects can be explained by gaze-centered coding alone, participants made TOJ while the position of the hands was manipulated relative to gaze and trunk. The two hands either lay on different sides of space relative to gaze or trunk, or they both lay on one side of the respective space. In the latter posture, one hand was on its "regular side of space" despite hand crossing, thus reducing overall conflict between anatomical and external codes. TOJ crossing effects were significantly reduced when the hands were both located on the same side of space relative to gaze, indicating gaze-centered coding. Evidence for trunk-centered coding was tentative, with an effect in reaction time but not in accuracy. These results link paradigms that use explicit localization and TOJ, and corroborate the relevance of gaze-related coding for touch. Yet, gaze and trunk-centered coding did not account for the total size of crossing effects, suggesting that tactile localization relies on additional, possibly limb-centered, reference frames. Thus, tactile location appears to be estimated by integrating multiple anatomical and external reference frames.

Microstructural study of the mechanical response of compacted graphite iron: An experimental and numerical approach

Graphite is an important microstructural constituent in cast irons, which plays a key role in determining the material performance. This work aims at understanding the microstructural phenomena taking place in compacted graphite cast iron (CGI), and in particular the effect of the anisotropy of graphite particles on the microscale strain partitioning. To this end, an experimental–numerical approach is followed. First, in situ micro-tensile tests on CGI samples are carried out in the scanning electron microscope (SEM). From these tests, high resolution images of deforming graphite particles within CGI are obtained. These images are then used to calculate the strains within the graphite particles via the Global Digital Image Correlation (GDIC) procedure. To correct for the inherent SEM imaging artifacts the use of external reference frame is proposed. The results from the tests confirm the mechanical anisotropy of compacted graphite particles in cast irons. Next, the strain partitioning is studied numerically through a 2D microstructural model based on the SEM micrographs. Good qualitative agreement is found between the computed and measured strains within the graphite particles, validating the hypothesis on graphite mechanical anisotropy. Moreover, the numerical study reveals that graphite anisotropy has a high impact on the elasto-plastic response of the matrix material and the CGI as a whole.

Blind individuals represent the auditory space in an egocentric rather than allocentric reference frame

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.

Relative contributions of visual and auditory spatial representations to tactile localization

Spatial localization of touch is critically dependent upon coordinate transformation between different reference frames, which must ultimately allow for alignment between somatotopic and external representations of space. Although prior work has shown an important role for cues such as body posture in influencing the spatial localization of touch, the relative contributions of the different sensory systems to this process are unknown. In the current study, we had participants perform a tactile temporal order judgment (TOJ) under different body postures and conditions of sensory deprivation. Specifically, participants performed non-speeded judgments about the order of two tactile stimuli presented in rapid succession on their ankles during conditions in which their legs were either uncrossed or crossed (and thus bringing somatotopic and external reference frames into conflict). These judgments were made in the absence of 1) visual, 2) auditory, or 3) combined audio-visual spatial information by blindfolding and/or placing participants in an anechoic chamber. As expected, results revealed that tactile temporal acuity was poorer under crossed than uncrossed leg postures. Intriguingly, results also revealed that auditory and audio-visual deprivation exacerbated the difference in tactile temporal acuity between uncrossed to crossed leg postures, an effect not seen for visual-only deprivation. Furthermore, the effects under combined audio-visual deprivation were greater than those seen for auditory deprivation. Collectively, these results indicate that mechanisms governing the alignment between somatotopic and external reference frames extend beyond those imposed by body posture to include spatial features conveyed by the auditory and visual modalities – with a heavier weighting of auditory than visual spatial information. Thus, sensory modalities conveying exteroceptive spatial information contribute to judgments regarding the localization of touch.

Lossless Frame Memory Compression Using Pixel-Grain Prediction and Dynamic Order Entropy Coding

Power constraints constitute a critical design issue for the portable video codec system, in which the external dynamic random access memory (DRAM) accounts for more than half of the overall system power requirements. With the ultrahigh-definition video specifications, the power consumed by accessing reference frames in the external DRAM has become the bottleneck for the portable video encoding system design. To relieve the dynamic power stresses introduced by the DRAM, a lossless compression algorithm is devised to reduce the external traffic and the memory requirements of reference frames. First, pixel-granularity directional prediction is adopted to decrease the prediction residual energy by 54.1% over the previous horizontal prediction. Second, the dynamic $k$ th-order unary/Exp-Golomb rice coding is applied to accommodate the large-valued prediction residues. With the aforementioned techniques, an average data traffic reduction of 68.5% for the off-chip reference frames is obtained, which consequently reduces the dynamic power requirements of the DRAM by 42.3%. Based on the high data reduction ratio of the proposed compression algorithm, a partition group table-based storage space reduction scheme is provided to improve the utilization of row buffers in the DRAM. Consequently, an additional 14.5% of the DRAM dynamic power can be saved by reducing the number of row buffer activations. In total, a 56.8% decrease in the dynamic power requirements of the external reference frame access can be obtained using our strategies. With TSMC 65-nm CMOS logic technology, our algorithm was implemented in a parallel VLSI architecture based on a compressor and decompressor at the cost of 36.5k and 34.7k, respectively, in terms of gate count. The throughputs of the proposed compressor and decompressor are 1.54 and 0.78 Gpixels/s, which are suitable for quad full high definition (4K) @ 94 frames/s real-time encoding with the level-D reference data reuse scheme.

Retrosplenial cortex maps the conjunction of internal and external spaces.

Intelligent behavior demands not only multiple forms of spatial representation, but also coordination among the brain regions mediating those representations. Retrosplenial cortex is densely interconnected with the majority of cortical and subcortical brain structures that register an animal's position in multiple internal and external spatial frames of reference. This unique anatomy suggests that it functions to integrate distinct forms of spatial information and provides an interface for transformations between them. Evidence for this was found in rats traversing two different routes placed at different environmental locations. Retrosplenial ensembles robustly encoded conjunctions of progress through the current route, position in the larger environment and the left versus right turning behavior of the animal. Thus, the retrosplenial cortex has the requisite dynamics to serve as an intermediary between brain regions generating different forms of spatial mapping, a result that is consistent with navigational and episodic memory impairments following damage to this region in humans.

Oscillatory activity reflects differential use of spatial reference frames by sighted and blind individuals in tactile attention

Touch can be localized either on the skin in anatomical coordinates, or, after integration with posture, in external space. Sighted individuals are thought to encode touch in both coordinate systems concurrently, whereas congenitally blind individuals exhibit a strong bias for using anatomical coordinates. We investigated the neural correlates of this differential dominance in the use of anatomical and external reference frames by assessing oscillatory brain activity during a tactile spatial attention task. The EEG was recorded while sighted and congenitally blind adults received tactile stimulation to uncrossed and crossed hands while detecting rare tactile targets at one cued hand only.In the sighted group, oscillatory alpha-band activity (8–12Hz) in the cue–target interval was reduced contralaterally and enhanced ipsilaterally with uncrossed hands. Hand crossing attenuated the degree of posterior parietal alpha-band lateralization, indicating that attention deployment was affected by external spatial coordinates. Beamforming suggested that this posture effect originated in the posterior parietal cortex. In contrast, cue-related lateralization of central alpha-band as well as of beta-band activity (16–24Hz) were unaffected by hand crossing, suggesting that these oscillations exclusively encode anatomical coordinates. In the blind group, central alpha-band activity was lateralized, but did not change across postures. The pattern of beta-band activity was indistinguishable between groups. Because the neural mechanisms for posterior alpha-band generation seem to be linked to developmental vision, we speculate that the lack of this neural mechanism in blind individuals is related to their preferred use of anatomical over external spatial codes in sensory processing.

Irrelevant tactile stimulation biases visual exploration in external coordinates.

We evaluated the effect of irrelevant tactile stimulation on humans’ free-viewing behavior during the exploration of complex static scenes. Specifically, we address the questions of (1) whether task-irrelevant tactile stimulation presented to subjects’ hands can guide visual selection during free viewing; (2) whether tactile stimulation can modulate visual exploratory biases that are independent of image content and task goals; and (3) in which reference frame these effects occur. Tactile stimulation to uncrossed and crossed hands during the viewing of static images resulted in long-lasting modulation of visual orienting responses. Subjects showed a well-known leftward bias during the early exploration of images, and this bias was modulated by tactile stimulation presented at image onset. Tactile stimulation, both at image onset and later during the trials, biased visual orienting toward the space ipsilateral to the stimulated hand, both in uncrossed and crossed hand postures. The long-lasting temporal and global spatial profile of the modulation of free viewing exploration by touch indicates that cross-modal cues produce orienting responses, which are coded exclusively in an external reference frame.

Space and time in the sighted and blind

Across many cultures people conceptualize time as extending along a horizontal Mental Time Line (MTL). This spatial mapping of time has been shown to depend on experience with written text, and may also depend on other graphic conventions such as graphs and calendars. All of this information is typically acquired visually, suggesting that visual experience may play an important role in the development of the MTL. Do blind people develop a MTL? If so, how does it compare with the MTL in sighted? In this study we tested early blind, late blind and sighted participants in a space–time congruity task. Participants had to classify temporal words by pressing a right and a left key, either with crossed or uncrossed hands. We found that the MTL develops in the absence of vision, and that it is based on the same external frame of reference in sighted and blind people. Reading braille may provide the same experiential link between space and time in the manual modality as reading printed text provides in the visual modality. These results showing a similar MTL in sighted and blind participants contrast with previous results showing that the Mental Number Line (MNL) depends on different spatial coordinates in the sighted and the blind, and suggest that spatial representations of time and number may have different experiential bases.

Event-related potential evidence for a dynamic (re-)weighting of somatotopic and external coordinates of touch during visual-tactile interactions.

The localization of touch in external space requires the remapping of somatotopically represented tactile information into an external frame of reference. Several recent studies have highlighted the role of posterior parietal areas for this remapping process, yet its temporal dynamics are poorly understood. The present study combined cross-modal stimulation with electrophysiological recordings in humans to trace the time course of tactile spatial remapping during visual-tactile interactions. Adopting an uncrossed or crossed hand posture, participants made speeded elevation judgments about rare vibrotactile stimuli within a stream of frequent, task-irrelevant vibrotactile events presented to the left or right hand. Simultaneous but spatially independent visual stimuli had to be ignored. An analysis of the recorded event-related potentials to the task-irrelevant vibrotactile stimuli revealed a somatotopic coding of tactile stimuli within the first 100ms. Between 180 and 250ms, neither an external nor a somatotopic representation dominated, suggesting that both coordinates were active in parallel. After 250ms, tactile stimuli were coded in a somatotopic frame of reference. Our results indicate that cross-modal interactions start before the termination of tactile spatial remapping, that is within the first 100ms. Thereafter, tactile stimuli are represented simultaneously in both somatotopic and external spatial coordinates, which are dynamically (re-)weighted as a function of processing stage.

Recollection and unitization in associating actors with extrinsic and intrinsic motions.

Four experiments provide evidence for a distinction between 2 different kinds of motion representations. Extrinsic motions involve the path of an object with respect to an external frame of reference. Intrinsic motions involve the relative motions of the parts of an object. This research suggests that intrinsic motions are represented conjointly with information about the identities of the actors who perform them, whereas extrinsic motions are represented separately from identity information. Experiment 1 demonstrated that participants remembered which actor had performed a particular intrinsic motion better than they remembered which actor had performed a particular extrinsic motion. Experiment 2 replicated this effect with incidental encoding of actor information, suggesting that encoding intrinsic motions leads one to automatically encode identity information. The results of Experiments 3 and 4 were fit by Yonelinas's (1999) source-memory model to quantify the contributions of familiarity and recollection to memory for the actors who carried out the intrinsic and extrinsic motions. Successful performance with extrinsic motion items in Experiment 3 required participants to remember in which scene contexts an actor had appeared, whereas successful performance in Experiment 4 required participants to remember the exact path taken by an actor in each scene. In both experiments, discrimination of old and new combinations of actors and extrinsic motions relied strongly on recollection, suggesting independent but associated representations of actors and extrinsic motions. In contrast, participants discriminated old and new combinations of actors and intrinsic motions primarily on the basis of familiarity, suggesting unitized representations of actors and intrinsic motions.

Shearing-induced asymmetry in entorhinal grid cells.

Grid cells are neurons with periodic spatial receptive fields (grids) that tile two-dimensional space in a hexagonal pattern. To provide useful information about location, grids must be stably anchored to an external reference frame. The mechanisms underlying this anchoring process have remained elusive. Here we show in differently sized familiar square enclosures that the axes of the grids are offset from the walls by an angle that minimizes symmetry with the borders of the environment. This rotational offset is invariably accompanied by an elliptic distortion of the grid pattern. Reversing the ellipticity analytically by a shearing transformation removes the angular offset. This, together with the near-absence of rotation in novel environments, suggests that the rotation emerges through non-coaxial strain as a function of experience. The systematic relationship between rotation and distortion of the grid pattern points to shear forces arising from anchoring to specific geometric reference points as key elements of the mechanism for alignment of grid patterns to the external world.

Movement Induces the Use of External Spatial Coordinates for Tactile Localization in Congenitally Blind Humans.

To localize touch, the brain integrates spatial information coded in anatomically based and external spatial reference frames. Sighted humans, by default, use both reference frames in tactile localization. In contrast, congenitally blind individuals have been reported to rely exclusively on anatomical coordinates, suggesting a crucial role of the visual system for tactile spatial processing. We tested whether the use of external spatial information in touch can, alternatively, be induced by a movement context. Sighted and congenitally blind humans performed a tactile temporal order judgment task that indexes the use of external coordinates for tactile localization, while they executed bimanual arm movements with uncrossed and crossed start and end postures. In the sighted, start posture and planned end posture of the arm movement modulated tactile localization for stimuli presented before and during movement, indicating automatic, external recoding of touch. Contrary to previous findings, tactile localization of congenitally blind participants, too, was affected by external coordinates, though only for stimuli presented before movement start. Furthermore, only the movement's start posture, but not the planned end posture affected blind individuals' tactile performance. Thus, integration of external coordinates in touch is established without vision, though more selectively than when vision has developed normally, and possibly restricted to movement contexts. The lack of modulation by the planned posture in congenitally blind participants suggests that external coordinates in this group are not mediated by motor efference copy. Instead the task-related frequent posture changes, that is, movement consequences rather than planning, appear to have induced their use of external coordinates.

Flexibly weighted integration of tactile reference frames

To estimate the location of a tactile stimulus, the brain seems to integrate different types of spatial information such as skin-based, anatomical coordinates and external, spatiotopic coordinates. The aim of the present study was to test whether the use of these coordinates is fixed, or whether they are weighted according to the task context. Participants made judgments about two tactile stimuli with different vibration characteristics, one applied to each hand. First, they always performed temporal order judgments (TOJ) of the tactile stimuli with respect to the stimulated hands that were either crossed or uncrossed. The resulting crossing effect, that is, impaired performance in crossed compared to uncrossed conditions, was used as a measure of reference frame weighting and was compared across conditions. Second, in dual judgment conditions participants subsequently made judgments about the stimulus vibration characteristics, either with respect to spatial location or with respect to temporal order. Responses in the spatial secondary task either accented anatomical (Experiment 1) or external (Experiment 2) coding. A TOJ crossing effect emerged in all conditions, and secondary tasks did not affect primary task performance in the uncrossed posture. Yet, the spatial secondary task resulted in improved crossed hands performance in the primary task, but only if the secondary judgment stressed the anatomical reference frame (Experiment 1), rather than the external reference frames (Experiment 2). Like the anatomically coded spatial secondary task, the temporal secondary task improved crossed hand performance of the primary task. The differential influence of the varying secondary tasks implies that integration weights assigned to the anatomical and external reference frames are not fixed. Rather, they are flexibly adjusted to the context, presumably through top-down modulation.

A novel 3D/dichoptic presentation system compatible with large field eye tracking

Traditional 3D and dichoptic presentation system usually uses a mirror stereoscope with a set of prisms and mirrors or colored glasses (red-green glasses) to split the view of the eyes looking at a computer display. Although these types of setups are useful in varieties of psychophysical and neuroscience studies, they have limitations. The colored glasses usually have a noticeable leak between the eyes. They also have a binocular rivalry effect over the visual field. Color glasses are hard to use for people with color deficits. Naïve subjects and clinical populations with visual impairment usually have a hard time to fuse with the mirror-prism setup. More importantly, the mirror stereoscope with a standard computer display usually does not provide a viewing angle that is big enough for a reliable measurement of fast and continuous eye movements over a large field. It is also insufficient for experiments examining visual motion and eye movements, for which it is crucial that the observers should not see the external reference frame, such as the edges of the mirrors. Although a projection system with a large screen and the active shutter glasses can provide a large viewing field, the active shutters can cause a 50% loss of the eye-tracking data. The presentation and eye-tracking system that we have developed can offer the following functions in one integrated setup: 1) No interruption of the eye tracking signals that currently occurs with active shutter glasses; 2) Large-field presentation, necessary for reliable measurement of the eye movement over a wide range of speeds and over a large distance; 3) Natural viewing experience like in movie theaters, which is important for reliable measurement in naive observers. The system is affordable and portable (except the screen), and can serve as part of other research setups, such as human brain imaging instruments. Meeting abstract presented at VSS 2014

Spatio-temporal processing of tactile stimuli in autistic children.

Altered multisensory integration has been reported in autism; however, little is known concerning how the autistic brain processes spatio-temporal information concerning tactile stimuli. We report a study in which a crossed-hands illusion was investigated in autistic children. Neurotypical individuals often experience a subjective reversal of temporal order judgments when their hands are stimulated while crossed, and the illusion is known to be acquired in early childhood. However, under those conditions where the somatotopic representation is given priority over the actual spatial location of the hands, such reversals may not occur. Here, we showed that a significantly smaller illusory reversal was demonstrated in autistic children than in neurotypical children. Furthermore, in an additional experiment, the young boys who had higher Autism Spectrum Quotient (AQ) scores generally showed a smaller crossed hands deficit. These results suggest that rudimentary spatio-temporal processing of tactile stimuli exists in autistic children, and the altered processing may interfere with the development of an external frame of reference in real-life situations.

Attention to the body depends on eye-in-orbit position.

Attentional selectivity in touch is modulated by the position of the body in external space. For instance, during endogenous attention tasks in which tactile stimuli are presented to the hands, the effect of attention is reduced when the hands are placed far apart than when they are close together and when the hands are crossed as compared to when they are placed in their anatomical position. This suggests that both somatotopic and external spatial reference frames coding the hands’ locations contribute to the spatial selection of the relevant hand. Here we investigate whether tactile selection of hands is also modulated by the position of other body parts, not directly involved in tactile perception, such as eye-in-orbit (gaze direction). We asked participants to perform the same sustained tactile attention task while gazing laterally toward an eccentric fixation point (Eccentric gaze) or toward a central fixation point (Central gaze). Event-related potentials recorded in response to tactile non-target stimuli presented to the attended or unattended hand were compared as a function of gaze direction (Eccentric vs. Central conditions). Results revealed that attentional modulations were reduced in the Eccentric gaze condition as compared to the Central gaze condition in the time range of the Nd component (200–260 ms post-stimulus), demonstrating for the first time that the attentional selection of one of the hands is affected by the position of the eye in the orbit. Directing the eyes toward an eccentric position might be sufficient to create a misalignment between external and somatotopic frames of references reducing tactile attention. This suggests that the eye-in-orbit position contributes to the spatial selection of the task relevant body part.

A Polytomous Item Response Theory Analysis of Social Physique Anxiety Scale

The present study investigated the social physique anxiety scale’s factor structure and item properties using confirmatory factor analysis and item response theory. An additional aim was to identify differences in response patterns between groups (gender). A large sample of high school students aged 11–15 years (N = 1,529) consisting of n = 562 males and n = 967 females. Confirmatory factor analysis and polytomous item response theory examined the structure of the scale. Items shown to be invariant across were identified using multidimensional differential item functioning methods. Graded response model results showed that item parameters were high with low associated standard errors. Multidimensional differential item functioning results revealed six items are biased in favor of either men (33%) or women (17%). The primary source of differential item functioning related to the item composition, and internal (male) or external (female) frames of reference.

The Prayers of Abū Muslim and al-Maʾmūn. An Exercise in Dating Ḥadīth

In usingḥadīthnarratives as historical sources, the challenge is to determine their origin. Different methods have been devised to trace the provenance ofḥadīthreports, but all these approaches lack an external frame of reference. Data retrieved from other sources, such as the historiographical genres, can be used to validate the results ofḥadīth-analysis under certain conditions. The method proposed here is exclusively applicable to traditions that describe events or support a rule that can be linked to a historical event described in the chronicles. Two case studies — concerning the festival prayer and the pronouncement of a finaltakbīrin the regular prayers — demonstrate that the results of the proposed method of datingḥadīths correspond to the dates ascribed to the events in the chronicles.

Effects of posture on tactile localization by 4 years of age are modulated by sight of the hands: evidence for an early acquired external spatial frame of reference for touch.

Adults show a deficit in their ability to localize tactile stimuli to their hands when their arms are in the less familiar, crossed posture. It is thought that this 'crossed-hands deficit' arises due to a conflict between the anatomical and external spatial frames of reference within which touches can be encoded. The ability to localize a single tactile stimulus applied to one of the two hands across uncrossed-hands and crossed-hands postures was investigated in typically developing children (aged 4 to 6 years). The effect of posture was also compared across conditions in which children did, or did not, have visual information about current hand posture. All children, including the 4-year-olds, demonstrated the crossed-hands deficit when they did not have sight of hand posture, suggesting that touch is located in an external reference frame by this age. In this youngest age group, when visual information about current hand posture was available, tactile localization performance was impaired specifically when the children's hands were uncrossed. We propose that this may be due to an early difficulty with integrating visual representations of the hand within the body schema.