Are All Spatial Reference Frames Egocentric? Reinterpreting Evidence for Allocentric, Object-Centered, or World-Centered Reference Frames

The use and neural representation of egocentric spatial reference frames is well-documented. In contrast, whether the brain represents spatial relationships between objects in allocentric, object-centered, or world-centered coordinates is debated. Here, I review behavioral, neuropsychological, neurophysiological (neuronal recording), and neuroimaging evidence for and against allocentric, object-centered, or world-centered spatial reference frames. Based on theoretical considerations, simulations, and empirical findings from spatial navigation, spatial judgments, and goal-directed movements, I suggest that all spatial representations may in fact be dependent on egocentric reference frames.

Spontaneous Vicarious Perception of the Content of Another's Visual Perspective

Visual perspective taking (VPT) is a core process of social cognition, providing humans with insights into what the environment looks like from another's point of view [1-4]. While VPT is often described as a quasi-perceptual phenomenon [5, 6], evidence for this proposal has been lacking. Here, we provide direct evidence that another's perspective can "stand in" for one's own sensory input during perceptual decision making. In a variant of the classic mental rotation task, participants judged whether characters presented in different orientations were canonical or mirror inverted. In the absence of another person, we replicate the well-established positive linear relationship between recognition times and angle of orientation such that recognition becomes slower the more an item has to be mentally rotated into its canonical orientation [7]. Importantly, this relationship was disrupted simply by placing another individual in the scene. Items rotated away from the participant were recognized more rapidly the closer they appeared in their canonical orientation, not only to the participant, but also to this other individual, showing that another's visual perspective drives mental rotation and item recognition in a similar way as one's own visual perspective. The effects were large and replicated in the three independent studies. They were observed even when the other person was completely passive, enhanced when the participant was explicitly instructed to take the other person's perspective, but reduced when the persons in the scenes were replaced with objects. The content of another's perspective is therefore spontaneously derived, takes a quasi-perceptual form, and can stand in for one's own sensory input during perceptual decision making.

Cerebral Hemodynamic Responses During Dynamic Posturography: Analysis with a Multichannel Near-Infrared Spectroscopy System

To investigate cortical roles in standing balance, cortical hemodynamic activity was recorded from the right hemisphere using near-infrared spectroscopy (NIRS) while subjects underwent the sensory organization test (SOT) protocol that systematically disrupts sensory integration processes (i.e., somatosensory or visual inputs or both). Eleven healthy men underwent the SOT during NIRS recording. Group statistical analyses were performed based on changes in oxygenated hemoglobin concentration in 10 different cortical regions of interest and on a general linear analysis with NIRS statistical parametric mapping. The statistical analyses indicated significant activation in the right frontal operculum (f-Op), right parietal operculum (p-Op), and right superior temporal gyrus (STG), right posterior parietal cortex (PPC), right dorsal and ventral premotor cortex (PMC), and the supplementary motor area (SMA) under various conditions. The activation patterns in response to specific combinations of SOT conditions suggested that (1) f-Op, p-Op, and STG are essential for sensory integration when standing balance is perturbed; (2) the SMA is involved in the execution of volitional action and establishment of new motor programs to maintain postural balance; and (3) the PPC and PMC are involved in the updating and computation of spatial reference frames during instances of sensory conflict between vestibular and visual information.

The stuff that motor chunks are made of: Spatial instead of motor representations?

In order to determine how participants represent practiced, discrete keying sequences in the discrete sequence production task, we had 24 participants practice two six-key sequences on the basis of two pre-learned six-digit numbers. These sequences were carried out by fingers of the left (L) and right (R) hand with between-hand transitions always occurring between the second and third, and the fifth and sixth responses. This yielded the so-called LLRRRL and RRLLLR sequences. Early and late in practice, the keypad used for the right hand was briefly relocated from the front of the participants to 90° at their right side. The results indicate that after 600 practice trials, executing a keying sequence relies heavily on a spatial cross-hand representation in a trunk- or head-based reference frame that after about only 15 trials is fully adjusted to the changed hand location. The hand location effect was not found with the last sequence element. This is attributed to the application of explicit knowledge. The between-hand transitions appeared to induce initial segmentation in some of the participants, but this did not consolidate into a concatenation point of successive motor chunks.

The role of scene type and priming in the processing and selection of a spatial frame of reference

The selection and processing of a spatial frame of reference (FOR) in interpreting verbal scene descriptions is of great interest to psycholinguistics. In this study, we focus on the choice between the relative and the intrinsic FOR, addressing two questions: (a) does the presence or absence of a background in the scene influence the selection of a FOR, and (b) what is the effect of a previously selected FOR on the subsequent processing of a different FOR. Our results show that if a scene includes a realistic background, this will make the selection of the relative FOR more likely. We attribute this effect to the facilitation of mental simulation, which enhances the relation between the viewer and the objects. With respect to the response accuracy, we found both a higher (with the same FOR) and a lower accuracy (with a different FOR), while for the response latencies, we only found a delay effect with a different FOR.

Screen Position Preference Offers a New Direction for Action Observation Research: Preliminary Findings Using TMS

Action observation has been suggested to be an effective adjunct to physical practice in motor (re)learning settings. However, optimal viewing conditions for interventions are yet to be established. Single-pulse transcranial magnetic stimulation (TMS) was used to investigate the effect of two different screen positions and participants’ screen position viewing preference on the amplitude of motor evoked potentials (MEPs) during observation of a ball pinch action. Twenty-four participants observed four blocked conditions that contained either a dynamic index finger-thumb ball pinch or a static hand holding a ball in a similar position on a horizontally or vertically positioned screen. TMS was delivered to the hand representation of the left primary motor cortex and MEPs were recorded from the first dorsal interosseous muscle of the right hand. Initial analysis of the normalized MEP amplitude data showed no significant differences between conditions. In a follow-up procedure, participants engaged in individual semi-structured interviews and completed a questionnaire designed to assess viewing affect and screen position viewing preference. The MEP data were subsequently split by screen position preference and re-analyzed using a 2 × 2 repeated measures ANOVA. Main effects indicated that participants who preferred the horizontal screen position (n = 16) demonstrated significantly greater MEP amplitudes during observation of the ball-pinch action compared to the static hand condition irrespective of screen position, and during the horizontal compared to the vertical screen position irrespective of video type. These results suggest that ensuring anatomical and perceptual congruency with the physical task, alongside consideration of participants’ screen position viewing preferences, may be an important part of optimizing action observation interventions.

Age effects on processing spatial relations within different reference frames: The role of executive functions

Mental representations of space can be generated and communicated with respect to different reference frames and perspectives. The present study investigated the effects of age and individual differences in domain-general executive functions on people's ability to process spatial relations as expressed in language within different spatial reference frames (SRFs). Healthy adults aged between 18 and 85 completed a novel task involving self-, third-person-, object-, and environment-centered judgements of spatial relations between two objects, as well as standard tests of working memory, inhibition, and mental flexibility. A psychometric evaluation confirmed the test-retest reliability and the convergent and divergent validity of the new task. Results showed that the lifespan trajectories varied depending on the SRF. Processing from a self-centered perspective or an object-centered frame remained intact throughout the adult-lifespan. By contrast, spatial processing from a third-person-centered perspective or within an environment-centered frame declined in late adulthood. Mediation regression models showed that mental flexibility accounted for a significant part of the age-related variance in spatial processing across all allocentric SRFs. The age effects on environment-centered processing were also partially mediated by age-related changes in visuospatial working memory capacity. These findings suggest that at least partially distinct systems are involved in mentally representing space under different SRFs, which are differentially affected by typical aging. Our results also highlight that people's ability to process spatial relations across different SRFs depends on their capacity to employ domain-general effortful cognitive resources.