Repetition effects in action planning reflect effector- but not hemisphere-specific coding

Action choices are influenced by future and recent past action states. For example, when performing two actions in succession, response times (RT) to initiate the second action are reduced when the same hand is used. These findings suggest the existence of effector-specific processing for action planning. However, given that each hand is primarily controlled by the contralateral hemisphere, the RT benefit might actually reflect effector-independent, hemisphere-specific rather than effector-specific repetition effects. Here, participants performed two consecutive movements, each with a hand or a foot, in one of two directions. Direction was specified in an egocentric reference frame (inward, outward) or in an allocentric reference frame (left, right). Successive actions were initiated faster when the same limb (e.g., left hand - left hand), but not when the other limb of the same body side (e.g., left foot - left hand) executed the second action. The same-limb advantage was evident even when the two movements involved different directions, whether specified egocentrically or allocentrically. Corroborating evidence from computational modeling lends support to the claim that repetition effects in action planning reflect persistent changes in baseline activity within neural populations that encode effector-specific action plans.

Repetition effects in action selection reflect effector- but not hemisphere-specific coding

Action choices are influenced by future and recent past action states. For example, when performing two actions in succession, response times (RT) to initiate the second action are reduced when the same hand is used. These findings suggest the existence of effector-specific processing for action selection. However, given that each hand is primarily controlled by the contralateral hemisphere, the RT benefit might actually reflect body side or hemisphere-specific rather than effector-specific repetition effects. Here, participants performed two consecutive movements, each with a hand or a foot, in one of two directions. Direction was specified in an egocentric reference frame (inward, outward) or in an allocentric reference frame (left, right). Successive actions were initiated faster when the same limb (e.g., left hand - left hand), but not when the other limb of the same body side (e.g., left foot - left hand) executed the second action. The same-limb advantage was evident even when the two movements involved different directions, whether specified egocentrically or allocentrically. Corroborating evidence from computational modeling lends support to the claim that repetition effects in action selection reflect persistent changes in baseline activity within neural populations that encode effector-specific action plans.

Prism adaptation speeds reach initiation in the direction of the prism after-effect.

Damage to the temporal-parietal cortex in the right hemisphere often leads to spatial neglect – a disorder in which patients are unable to attend to sensory input from their contralesional (left) side. Neglect has been associated with both attentional and premotor deficits. That is, in addition to having difficulty with attending to the left side, patients are often slower to initiate leftward vs. rightward movements (i.e., directional hypokinesia). Previous research has indicated that a brief period of adaptation to rightward shifting prisms can reduce symptoms of neglect by adjusting the patient’s movements leftward, towards the neglected field. Although prism adaptation has been shown to reduce spatial attention deficits in patients with neglect, very little work has examined the effects of prisms on premotor symptoms. In the current study, we examined this in healthy individuals using leftward shifting prisms to induce a rightward shift in the egocentric reference frame, similar to neglect patients prior to prism adaptation. Specifically, we examined the speed with which healthy participants initiated leftward and rightward reaches (without visual feedback) prior to and following adaptation to either 17° leftward (n=16) or 17° rightward (n=15) shifting prisms. Our results indicated that, following adaptation, participants were significantly faster to initiate reaches towards targets located in the direction opposite the prism shift. That is, participants were faster to initiate reaches to right targets following leftward prism adaptation, and were faster to initiate reaches to left targets following rightward prism adaptation. Overall these results are consistent with the idea that prism adaptation can influence the speed with which a reach can be planned toward a target in the direction opposite the prism shift, possibly through altering activity in neural circuits involved in reach planning.

Egocentric Asymmetric Coding in Sensory Cortical Border Cells

ABSTRACTBoth egocentric and allocentric representations of space are essential to spatial navigation. Although some studies of egocentric coding have been conducted within and around the hippocampal formation, externally anchored egocentric spatial representations have not yet been fully explored. Here we record and identify two subtypes of border cell in the rat primary somatosensory cortex (S1) and secondary visual cortex (V2). Subpopulations of S1 and V2 border cells exhibit rotation-selective asymmetric firing fields in an either clockwise (CW) or counterclockwise (CCW) manner. CW- and CCW-border cells increase their firing rates when animals move unidirectionally along environmental border(s). We demonstrate that both CW- and CCW-border cells fire in an egocentric reference frame relative to environmental borders, maintain preferred directional tunings in rotated, stretched, dark as well as novel arenas, and switch their directional firings in the presence of multi-layer concentric enclosures. These findings may provide rotation-selective egocentric reference frames within a larger spatial navigation system, and point to a common computational principle of spatial coding shared by multiple sensory cortical areas.HighlightsEgocentric border cells are present in rat S1 and V2Subtypes of border cells display egocentric asymmetric codingEgocentric and allocentric streams coexist in sensory corticesRotation-selective asymmetric firing is robust with environmental manipulations

Influence of action video gaming on spatial representation in the haptic modality

Spatial representation in the haptic domain has been shown to be prone to systematic errors. When participants are asked to make two bars haptically parallel, their performance deviates from what would be veridically parallel. This is hypothesized to be caused by the bias of the egocentric reference frame. Stimulating the use of an allocentric reference frame has previously been shown to improve performance in haptic parallelity matching. The aim of the current study was to investigate the influence of action video game experience on parallelity performance. We hypothesized that participants who extensively play action video games with a so-called ‘bird’s-eye view’ are likely to process spatial information more allocentrically, resulting in better performance in haptic parallelity matching. This was tested in two groups of male participants, 10 participants with extensive action video gaming experience (AVGPs) and 10 participants without or hardly any action video gaming experience (NAVGPs). Additionally, the effect of visual–haptic practice on haptic parallelity performance was tested. In the haptic blocks, blindfolded participants had to feel the orientation of a reference bar with their non-dominant hand and had to match this orientation on a test bar with their dominant hand. In subsequent visual–haptic blocks, they had full view of the set-up and visually paralleled both bars. As hypothesized, AVGPs performed significantly better in haptic blocks than NAVGPs. Visual–haptic practice resulted in significantly better performance in subsequent haptic blocks in both groups. These results suggest that playing action video games might enhance haptic spatial representation, although a causative relationship still needs to be established.

Lateral entorhinal cortex lesions impair both egocentric and allocentric object–place associations

During navigation, landmark processing is critical either for generating an allocentric-based cognitive map or in facilitating egocentric-based strategies. Increasing evidence from manipulation and single-unit recording studies has highlighted the role of the entorhinal cortex in processing landmarks. In particular, the lateral (LEC) and medial (MEC) sub-regions of the entorhinal cortex have been shown to attend to proximal and distal landmarks, respectively. Recent studies have identified a further dissociation in cue processing between the LEC and MEC based on spatial frames of reference. Neurons in the LEC preferentially encode egocentric cues while those in the MEC encode allocentric cues. In this study, we assessed the impact of disrupting the LEC on landmark-based spatial memory in both egocentric and allocentric reference frames. Animals that received excitotoxic lesions of the LEC were significantly impaired, relative to controls, on both egocentric and allocentric versions of an object–place association task. Notably, LEC lesioned animals performed at chance on the egocentric version but above chance on the allocentric version. There was no significant difference in performance between the two groups on an object recognition and spatial T-maze task. Taken together, these results indicate that the LEC plays a role in feature integration more broadly and in specifically processing spatial information within an egocentric reference frame.

The Simon Effect Based on Allocentric and Egocentric Reference Frame: Common and Specific Neural Correlates

An object’s location can be represented either relative to an observer’s body effectors (egocentric reference frame) or relative to another external object (allocentric reference frame). In non-spatial tasks, an object’s task-irrelevant egocentric position conflicts with the side of a task-relevant manual response, which defines the classical Simon effect. Growing evidence suggests that the Simon effect occurs not only based on conflicting positions within the egocentric but also within the allocentric reference frame. Although neural mechanisms underlying the egocentric Simon effect have been extensively researched, neural mechanisms underlying the allocentric Simon effect and their potential interaction with those underlying its egocentric variant remain to be explored. In this fMRI study, spatial congruency between the task-irrelevant egocentric and allocentric target positions and the task-relevant response hand was orthogonally manipulated. Behaviorally, a significant Simon effect was observed for both reference frames. Neurally, three sub-regions in the frontoparietal network were involved in different aspects of the Simon effect, depending on the source of the task-irrelevant object locations. The right precentral gyrus, extending to the right SMA, was generally activated by Simon conflicts, irrespective of the spatial reference frame involved, and showed no additive activity to Simon conflicts. In contrast, the right postcentral gyrus was specifically involved in Simon conflicts induced by task-irrelevant allocentric, rather than egocentric, representations. Furthermore, a right lateral frontoparietal network showed increased neural activity whenever the egocentric and allocentric target locations were incongruent, indicating its functional role as a mismatch detector that monitors the discrepancy concerning allocentric and egocentric object locations.

Spatial Representation of Time in Backspace

Temporal information, numerical magnitude and space extension appear to share common representational mechanisms and be processed similarly in the brain. Evidence comes from the phenomenon of ‘pseudoneglect’, i.e. healthy persons’ orientation asymmetry toward the left side of space. Pseudoneglect is also evident along the mental number line which extends from small numbers on the left to large numbers on the right. In analogy to numbers, time is typically represented on a line extending from the left to the right side. It may thus be no surprise that pseudoneglect has been demonstrated in the temporal domain as well. Besides the perception of the space located anteriorly to our trunk (frontspace), we are able to represent the space behind us, which we cannot visually perceive (backspace). The translational model suggests a mapping of spatially defined information to the ipsilateral side of the egocentric reference frame in front- and backspace, while the rotational concept focuses on a 360° spatial representation around the midsagittal plane of the trunk. At the present stage of investigation, little is known about the representation of temporal information in backspace. In an attempt to fill this gap, we compared duration estimations of auditory stimuli in frontspace and backspace. Healthy right-handers were instructed to judge their duration relative to each other. We found a pseudoneglect-behavior not only in frontspace but also in backspace. The data are discussed in the context of common processing mechanisms for time, numbers and space and favor a translational over a rotational account for the representation of backspace. The results are further discussed with reference to potential consequences for the rehabilitation of hemispatial neglect.

Embodied Interaction Priority: Other's Body Part Affects Numeral–Space Mappings

Traditionally, the spatial–numerical association of response codes (SNARC) effect was presented in two-choice condition, in which only one individual reacted to both even (small) and odd (large) numbers. Few studies explored SNARC effect in a social situation. Moreover, there are many reference frames involved in SNARC effect, and it has not yet been investigated which reference frame is dominated when two participants perform the go-nogo task together. In the present study, we investigated which reference frame plays a primary role in SNARC effect when allocentric and egocentric reference frames were consistent or inconsistent in social settings. Furthermore, we explored how two actors corepresent number–space mapping interactively. Results of the two experiments demonstrated that egocentric reference frame was at work primarily when two reference frames were consistent and inconsistent. This shows that body-centered coordinate frames influence number–space mapping in social settings, and one actor may represent another actor's action and tasks.