Multisensory integration mechanisms in haptic space perception

It has been argued that representations of peripersonal space based on haptic input are systematically distorted by egocentric reference frames. Interestingly, a recent study has shown that noninformative vision (i.e., freely viewing the region above the haptic workspace) improves performance on the so-called haptic parallel-setting task, in which participants are instructed to rotate a test bar until it is parallel to a reference bar. In the present study, we made a start at identifying the different sensory integration mechanisms involved in haptic space perception by distinguishing the possible effects of orienting mechanisms from those of noninformative vision. We found that both the orienting direction of head and eyes and the availability of noninformative vision affect parallel-setting performance and that they do so independently: orienting towards a reference bar facilitated the parallel-setting of a test bar in both no-vision and noninformative vision conditions, and noninformative vision improved performance irrespective of orienting direction. These results suggest the effects of orienting and noninformative vision on haptic space perception to depend on distinct neurocognitive mechanisms, likely to be expressed in different modulations of neural activation in the multimodal parietofrontal network, thought to be concerned with multimodal representations of peripersonal space.     

Differential effects of non-informative vision and visual interference on haptic spatial processing

The primary purpose of this study was to examine the effects of non-informative vision and visual interference upon haptic spatial processing, which supposedly derives from an interaction between an allocentric and egocentric reference frame. To this end, a haptic parallelity task served as baseline to determine the participant-dependent biasing influence of the egocentric reference frame. As expected, large systematic participant-dependent deviations from veridicality were observed. In the second experiment we probed the effect of non-informative vision on the egocentric bias. Moreover, orienting mechanisms (gazing directions) were studied with respect to the presentation of haptic information in a specific hemispace. Non-informative vision proved to have a beneficial effect on haptic spatial processing. No effect of gazing direction or hemispace was observed. In the third experiment we investigated the effect of simultaneously presented interfering visual information on the haptic bias. Interfering visual information parametrically influenced haptic performance. The interplay of reference frames that subserves haptic spatial processing was found to be related to both the effects of non-informative vision and visual interference. These results suggest that spatial representations are influenced by direct cross-modal interactions; inter-participant differences in the haptic modality resulted in differential effects of the visual modality.     

Visuospatial memory computations during whole-body rotations in roll

We used a memory-saccade task to test whether the location of a target, briefly presented before a whole-body rotation in roll, is stored in egocentric or in allocentric coordinates. To make this distinction, we exploited the fact that subjects, when tilted sideways in darkness, make systematic errors when indicating the direction of gravity (an allocentric task) even though they have a veridical percept of their self-orientation in space. We hypothesized that if spatial memory is coded allocentrically, these distortions affect the coding of remembered targets and their readout after a body rotation. Alternatively, if coding is egocentric, updating for body rotation becomes essential and errors in performance should be related to the amount of intervening rotation. Subjects (n = 6) were tested making saccades to remembered world-fixed targets after passive body tilts. Initial and final tilt angle ranged between -120 degrees CCW and 120 degrees CW. The results showed that subjects made large systematic directional errors in their saccades (up to 90 degrees ). These errors did not occur in the absence of intervening body rotation, ruling out a memory degradation effect. Regression analysis showed that the errors were closely related to the amount of subjective allocentric distortion at both the initial and final tilt angle, rather than to the amount of intervening rotation. We conclude that the brain uses an allocentric reference frame, possibly gravity-based, to code visuospatial memories during whole-body tilts. This supports the notion that the brain can define information in multiple frames of reference, depending on sensory inputs and task demands.     

Impaired distance perception and size constancy following bilateral occipitoparietal damage

Accurate distance perception depends on the processing and integration of a variety of monocular and binocular cues. Dorsal stream lesions can impair this process, but details of this neurocognitive relationship remain unclear. Here, we tested a patient with bilateral occipitoparietal damage and severely impaired stereopsis. We addressed four related questions: (1) Can distance and size perception survive limitations in perceiving monocular and binocular cues? (2) Are egocentric (self-referential) and allocentric (object-referential) distance judgments similarly impaired? (3) Are distance measurements equally impaired in peripersonal and extrapersonal space? (4) Are size judgments possible when distance processing is impaired? The results demonstrate that the patient’s lesions impaired both her distance and size perception, but not uniformly. Her performance when using an egocentric reference frame was more impaired than her performance when using an allocentric reference frame. Likewise, her distance judgments in peripersonal space were more impaired than those in extrapersonal space. The patient showed partial preservation in size processing of novel objects even when familiar size cues were removed.     

The effect of visuo-haptic congruency on haptic spatial matching

Eye-hand coordination is crucial for everyday visuo-haptic object-manipulation. Noninformative vision has been reported to improve haptic spatial tasks relying on world-based reference frames. The current study investigated whether the degree of visuo-haptic congruity systematically affects haptic task performance. Congruent and parametrically varied incongruent visual orientation cues were presented while participants manually explored the orientation of a reference bar stimulus. Participants were asked to haptically match this reference orientation by turning a test bar either to a parallel or mirrored orientation, depending on the instruction. While parallel matching can only be performed correctly in a world-based frame, mirror matching (in the mid-sagittal plane) can also be achieved in a body-centered frame. We revealed that visuo-haptic incongruence affected parallel but not mirror matching responses in size and direction. Parallel matching did not improve when congruent visual orientation cues were provided throughout a run, and mirror matching even deteriorated. These results show that there is no positive effect of visual input on haptic performance per se. Tasks, which favor a body-centered frame are immune to incongruent visual input, while such input parametrically modulates performance on world-based haptic tasks.     

Hard and fast rules about the body: contributions of the action stream to judging body space

Analogously to the visual system, somatosensory processing may be segregated into two streams, with the body constituting either part of the action system or a perceptual object. Experimental studies with participants free from neurological disease which test this hypothesis are rare, however. The present study explored the contributions of the two putative streams to a task that requires participants to estimate the spatial properties of their own body. Two manipulations from the visuospatial literature were included. First, participants were required to point either backward towards pre-defined landmarks on their own body (egocentric reference frame) or to a forward projection of their own body (allocentric representation). Second, a manipulation of movement mode was included, requiring participants to perform pointing movements either immediately, or after a fixed delay, following instruction. Results show that accessing an allocentric representation of one’s own body results in performance changes. Specifically, the spatial bias shown to exist for body space when pointing backward at one’s own body disappears when participants are requested to mentally project their body to a pre-defined location in front space. Conversely, delayed execution of pointing movements does not result in performance changes. Altogether, these findings provide support for a constrained dual stream hypothesis of somatosensory processing and are the first to show similarities in the processing of body space and peripersonal space.     

Delay improves performance on a haptic spatial matching task

Systematic deviations occur when blindfolded subjects set a test bar parallel to a reference bar in the horizontal plane using haptic information (Kappers and Koenderink 1999, Perception 28:781–795; Kappers 1999, Perception 28:1001–1012). These deviations are assumed to reflect the use of a combination of a biasing egocentric reference frame and an allocentric, more cognitive one (Kappers 2002, Acta Psychol 109:25–40). In two experiments, we have examined the effect of delay between the perception of a reference bar and the parallel setting of a test bar. In both experiments a 10-s delay improved performance. The improvement increased with a larger horizontal (left–right) distance between the bars. This improvement was interpreted as a shift from the egocentric towards the allocentric reference frame during the delay period. Electronic Publication     

Pointing at targets by children with congenital and transient blindness

The study investigated pointing at memorized targets in reachable space in congenitally blind (CB) and blindfolded sighted (BS) children (6, 8, 10 and 12 years; ten children in each group). The target locations were presented on a sagittal plane by passive positioning of the left index finger. A go signal for matching the target location with the right index finger was provided 0 or 4 s after demonstration. An age effect was found only for absolute distance errors and the surface area of pointing was smaller for the CB children. Results indicate that early visual experience and age are not predictive factors for pointing in children. The delay was an important factor at all ages and for both groups, indicating distinct spatial representations such as egocentric and allocentric frames of reference, for immediate and delayed pointing, respectively. Therefore, the CB like the BS children are able to use both ego- and allocentric frames of reference.     

Hand orientation is insufficiently compensated for in haptic spatial perception

What humans haptically perceive as parallel is often far from physically parallel. These deviations from parallelity are highly significant and very systematic. There exists accumulating evidence, both psychophysical and neurophysiological, that what is haptically parallel is decided in a frame of reference intermediate to an allocentric and an egocentric one. The central question here concerns the nature of the egocentric frame of reference. In the literature, various kinds of egocentric reference frames are mentioned for haptic spatial tasks, such as hand-centered, arm-centered, and body-centered frames of reference. Thus far, it has not been possible to distinguish between body-centered, arm-centered, and hand-centered reference frames in our experiments, as hand and arm orientation always covaried with distance from the body-midline. In the current set of experiments the influence of body-centered and hand-centered reference frames could be dissociated. Subjects were asked to make a test bar haptically parallel to a reference bar in five different conditions, in which their hands were oriented straight ahead, rotated to the left, rotated to the right, rotated outward or rotated inward. If the reference frame is body-centered, the deviations should be independent of condition. If, on the other hand, the reference frame is hand-centered, the deviations should vary with condition. The results show that deviation size varies strongly with condition, exactly in the way predicted by the influence of a hand-centered egocentric frame of reference. Interestingly, this implies that subjects do not sufficiently take into account the orientation of their hands.     

Effects of age on navigation strategy

Age differences in navigation strategies have been demonstrated in animals, with aged animals more likely to prefer an egocentric (route) strategy and younger animals more likely to prefer an allocentric (place) strategy. Using a novel virtual Y-maze strategy assessment (vYSA), the present study demonstrated substantial age differences in strategy preference in humans. Older adults overwhelmingly preferred an egocentric strategy, while younger adults were equally distributed between egocentric and allocentric preference. A preference for allocentric strategy on the Y-maze strategy assessment was found to benefit performance on an independent assessment (virtual Morris water task) only in younger adults. These results establish baseline age differences in spatial strategies and suggest this may impact performance on other spatial navigation assessments. The results are interpreted within the framework of age differences in hippocampal structure and function.     

Extending or projecting peripersonal space with tools? Multisensory interactions highlight only the distal and proximal ends of tools

The effects of tool-use on the brain's representation of the body and of the space surrounding the body ('peripersonal space') has recently been studied within a number of disciplines in cognitive neuroscience, and is also of great interest to philosophers and behavioural ecologists. To date, most experimental findings suggest that tool-use extends the boundary of peripersonal space-visual stimuli presented at the tips of tools interact more with simultaneous tactile stimuli presented at the hands than visual stimuli presented at the same distance, but not associated with the tools. We studied the proposed extension of peripersonal space by tool-use by measuring the effects of three different tool-use tasks on the integration of visual and tactile stimuli at three distances from participants' hands along two hand-held tools. When the tool-use task required using the shafts or the tips of the tools, visuotactile interactions were stronger at the tips of the tools than in the middle of the shaft. When the handles of the tools were used, however, visuotactile interactions were strongest near the hands and decreased with distance along the tools. These results suggest that tools do not simply 'extend' peripersonal space, but that just the tips of tools actively manipulated in extrapersonal space are incorporated into the brain's visuotactile representations of the body and of peripersonal space.     

The haptic perception of spatial orientations

This review examines the isotropy of the perception of spatial orientations in the haptic system. It shows the existence of an oblique effect (i.e., a better perception of vertical and horizontal orientations than oblique orientations) in a spatial plane intrinsic to the haptic system, determined by the gravitational cues and the cognitive resources and defined in a subjective frame of reference. Similar results are observed from infancy to adulthood. In 3D space, the haptic processing of orientations is also anisotropic and seems to use both egocentric and allocentric cues. Taken together, these results revealed that the haptic oblique effect occurs when the sensory motor traces associated with exploratory movement are represented more abstractly at a cognitive level.     

To the end! Distribution of attention along a tool in peri- and extrapersonal space

This study investigated the distribution of visual attention along a handheld tool depending on functional tool practice and its position in peripersonal or extrapersonal space. We created a tool with two functional parts placed at the tool’s middle and end. Participants held the tool over a display such that functional parts were aligned with stimuli for a 50/50, go/no-go, target detection task. In Experiment 1, two groups with no prior tool experience performed the task either in peripersonal (near the body; tool held horizontally) or extrapersonal space (beyond arms’ reach; tool held straight). Faster response times (RTs) were found for targets at the tool’s end and for the peripersonal space group. In Experiment 2, participants used the tool’s middle part in a hockey-like game prior to the task to assess functional practice effects. Again, faster RTs were found for targets at the tool’s end and in peripersonal space. However, a tool part × space interaction suggested that mid-tool practice reduced performance differences between tool parts but only in peripersonal space. Experiment 3 confirmed the interaction effect when mid-tool practice was constrained to only extrapersonal space. Results suggest that visual attention is naturally drawn to the tool’s end but that functional tool use can redistribute attention when positioned in peripersonal space. In extrapersonal space, no change was found suggesting that the extension of peripersonal space is not uniform in regards to visual attention and that the visual attention component is perhaps dissociable from the remapping of spatial representation by tools.     

Spatial dependency of action simulation

In this study, we investigated the spatial dependency of action simulation. From previous research in the field of single-cell recordings, grasping studies and from crossmodal extinction tasks, it is known that our surrounding space can be divided into a peripersonal space and extrapersonal space. These two spaces are functionally different at both the behavioral and neuronal level. The peripersonal space can be seen as an action space which is limited to the area in which we can grasp objects without moving the object or ourselves. The extrapersonal space is the space beyond the peripersonal space. Objects situated within peripersonal space are mapped onto an egocentric reference frame. This mapping is thought to be accomplished by action simulation. To provide direct evidence of the embodied nature of this simulated motor act, we performed two experiments, in which we used two mental rotation tasks, one with stimuli of hands and one with stimuli of graspable objects. Stimuli were presented in both peri- and extrapersonal space. The results showed increased reaction times for biomechanically difficult to adopt postures compared to more easy to adopt postures for both hand and graspable object stimuli. Importantly, this difference was only present for stimuli presented in peripersonal space but not for the stimuli presented in extrapersonal space. These results extend previous behavioral findings on the functional distinction between peripersonal- and extrapersonal space by providing direct evidence for the spatial dependency of the use of action simulation. Furthermore, these results strengthen the hypothesis that objects situated within the peripersonal space are mapped onto an egocentric reference frame by action simulation.     

Double dissociation of egocentric and allocentric space following medial prefrontal and parietal cortex lesions in the rat

Animals with medial prefrontal cortex or parietal cortex lesions and sham-operated and non-operated controls were tested for the acquisition of an adjacent arm task that accentuated the importance of egocentric spatial localization and a cheese board task that accentuated the importance of allocentric spatial localization. Results indicated that relative to controls, animals with medial-prefrontal cortex lesions are impaired on the adjacent arm task but displayed facilitation on the cheese board task. In contrast, relative to controls, rats with parietal cortex lesions are impaired on the cheese board task but show no impairment on the adjacent arm task. The data suggest a double dissociation of function between medial prefrontal cortex and parietal cortex in terms of coding of egocentric versus allocentric spatial information.     

Lesions of the dorsal hippocampus or parietal cortex differentially affect spatial information processing

The present experiments used 2 versions of a modified Hebb-Williams maze to test the role of the dorsal hippocampus (dHip) and parietal cortex (PC) in processing allocentric and egocentric space during acquisition and retention. Bilateral lesions were made to either the dHip or PC before maze testing (acquisition) or after maze testing (retention). The results indicate that lesions of the dHip impair allocentric maze acquisition, whereas lesions of the PC impair egocentric maze acquisition. During retention, lesions of the PC produced a significant impairment on both maze versions, whereas lesions of the dHip produced short-lived, transient impairments on both maze versions. These results suggest that during acquisition, the hippocampus and PC process spatial information in parallel; however, long-term retention of spatial information requires the PC with the dHIP as necessary for retrieval and/or access but not necessarily storage.     

Mirror apraxia affects the peripersonal mirror space. A combined lesion and cerebral activation study

Mirror apraxia is a condition in which patients with lesions of the posterior parietal cortex have deficits in reaching to objects presented through a mirror. The aim of the present study was to investigate possible mechanisms underlying this disorder. First, we addressed the question of whether mirror apraxia is exhibited to the same extent in peripersonal and in body space. Four patients with lesions of the posterior parietal lobe on either side and with marked mirror apraxia were required to reach for objects that were presented to them through a mirror and located either in body space (i.e. on the body surface) or in peripersonal space (i.e. in the reaching distance). Whereas reaching for objects located in body space was flawless in all patients, the performance deteriorated when the same objects were transferred to the peripersonal space. Although the objects were located only a few centimetres above the body surface, the patients reached towards the virtual object in the mirror. Based on these results we suggest that mirror apraxia may originate from a dissociation between the representations of body schema and peripersonal space and that objects located on the body surface become integrated into the body schema. In the second part of the study, using positron emission tomography study (PET), we studied the cerebral activation pattern during reaching to objects presented through a mirror in the peripersonal space in healthy subjects. The results show that increased neural activity in the anterior part of the intraparietal sulcus and in the dorsal premotor cortex was bound to the transformation of the target position from the mirror space to the real space. In contrast, the activity related to object localization in the mirror occurred at the parieto-occipital junction. Both mirror and arm transformation involved the medial posterior part of the superior parietal lobule, putatively area V6a. The results demonstrate that acting through a mirror is processed in a number of cortical areas of the dorsal stream.     

Coordinative constraints in bimanual tool use

This study investigates coordinative constraints when participants execute discrete bimanual tool use actions. Participants moved two levers to targets that were either presented near the proximal parts of the levers or near the distal tips of the levers. In the first case, the tool transformation (i.e. the relationship between hand movement direction and target direction) was compatible, whereas in the second case, it was incompatible. We hypothesized that an egocentric constraint (i.e. a preference for moving the hands and tools in a mirror-symmetrical fashion) would be dominant when targets are presented near the proximal parts of the levers because in this situation, movements can be coded in terms of body-related coordinates. Furthermore, an allocentric constraint (i.e. a preference to move the hands in the same (parallel) direction in extrinsic space) was expected to be dominant when one of the targets or both are presented near the distal parts of the levers because in this condition, movements have to be coded in an external reference frame. The results show that when both targets are presented near the proximal parts of the levers, participants are faster and produce less errors with mirror-symmetrical when compared to parallel movements. Furthermore, the RT mirror-symmetry advantage is eliminated, when both targets are presented near the distal parts of the levers, and it is reversed, when the target for one lever is presented near its distal part and the target for the other lever is presented near its proximal part. These results show that the dominance of egocentric and allocentric coordinative constraints in bimanual tool use depends on whether movements are coded in terms of body-related coordinates or in an external reference frame.     

Prefrontal serotonin depletion impairs egocentric, but not allocentric working memory in rats

Working memory is a cognitive ability chiefly organized by the prefrontal cortex. Working memory tests may be resolved based on allocentric or egocentric spatial strategies. Serotonergic neurotransmission is closely involved in working memory, but its role in spatial strategies for working memory performance is unknown. To address this issue, prefrontal serotonin depletion was induced to adult male rats, and three days after the behavioral expression of both allocentric and egocentric strategies were evaluated in the "Y" maze and in a crossed-arm maze, respectively. Serotonin depletion caused no effects on allocentric-related behavioral performance, but lesioned rats performed deficiently when the egocentric working memory was evaluated. These results suggest that serotonin may be more closely related with the organization of working memory that uses own movement-guided responses than with that involving the use of external visuospatial signals. Further neurochemical studies are needed to elucidate possible interactions between serotonergic activity and other neurotransmitter systems in the organization of working memory-related allocentric and egocentric strategies.     

Restriction of early exploratory forays effects specific aspects of spatial processing in weanling hamsters

Normally reared hamsters, but not hamsters reared on a liquid diet, demonstrated spatial memory for the location of odor cues in an allocentric task (Experiment 1). In Experiment 2, an egocentric task, liquid-reared hamsters detected a change in the spatial location of odor cues. In Experiment 3 liquidreared hamsters detected a change in the spatial location of two visual cues under allocentric task conditions. Female hamsters on a liquid diet retrieved their pups more often than dams on solid food, resulting in reduced exploratory opportunities for their pups during the period when olfaction mediates behavior. Hamsters in Experiment 4 experienced a direct restriction of early forays. The restricted-rearing group failed to detect a change in the spatial location of odor cues in an allocentric task. These findings suggest that restriction of early exploratory experience during a narrow period of development results in specific spatial processing deficits.