Is navigation in virtual reality with fMRI really navigation?

Identifying the neural mechanisms underlying spatial orientation and navigation has long posed a challenge for researchers. Multiple approaches incorporating a variety of techniques and animal models have been used to address this issue. More recently, virtual navigation has become a popular tool for understanding navigational processes. Although combining this technique with functional imaging can provide important information on many aspects of spatial navigation, it is important to recognize some of the limitations these techniques have for gaining a complete understanding of the neural mechanisms of navigation. Foremost among these is that, when participants perform a virtual navigation task in a scanner, they are lying motionless in a supine position while viewing a video monitor. Here, we provide evidence that spatial orientation and navigation rely to a large extent on locomotion and its accompanying activation of motor, vestibular, and proprioceptive systems. Researchers should therefore consider the impact on the absence of these motion-based systems when interpreting virtual navigation/functional imaging experiments to achieve a more accurate understanding of the mechanisms underlying navigation. © 2013 Massachusetts Institute of Technology

Orientation and metacognition in virtual space

Cognitive scientists increasingly use virtual reality scenarios to address spatial perception, orientation, and navigation. If based on desktops rather than mobile immersive environments, this involves a discrepancy between the physically experienced static position and the visually perceived dynamic scene, leading to cognitive challenges that users of virtual worlds may or may not be aware of. The frequently reported loss of orientation and worse performance in point-to-origin tasks relate to the difficulty of establishing a consistent reference system on an allocentric or egocentric basis. We address the verbalisability of spatial concepts relevant in this regard, along with the conscious strategies reported by participants. Behavioural and verbal data were collected using a perceptually sparse virtual tunnel scenario that has frequently been used to differentiate between humans' preferred reference systems. Surprisingly, the linguistic data we collected relate to reference system verbalisations known from the earlier literature only to a limited extent, but instead reveal complex cognitive mechanisms and strategies. Orientation in desktop VR appears to pose considerable challenges, which participants react to by conceptualising the task in individual ways that do not systematically relate to the generic concepts of egocentric and allocentric reference frames

Enhancing the Ecological Validity of fMRI Memory Research Using Virtual Reality

Functional magnetic resonance imaging (fMRI) is a powerful research tool to understand the neural underpinnings of human memory. However, as memory is known to be context-dependent, differences in contexts between naturalistic settings and the MRI scanner environment may potentially confound neuroimaging findings. Virtual reality (VR) provides a unique opportunity to mitigate this issue by allowing memories to be formed and/or retrieved within immersive, navigable, visuospatial contexts. This can enhance the ecological validity of task paradigms, while still ensuring that researchers maintain experimental control over critical aspects of the learning and testing experience. This mini-review surveys the growing body of fMRI studies that have incorporated VR to address critical questions about human memory. These studies have adopted a variety of approaches, including presenting research participants with VR experiences in the scanner, asking participants to retrieve information that they had previously acquired in a VR environment, or identifying neural correlates of behavioral metrics obtained through VR-based tasks performed outside the scanner. Although most such studies to date have focused on spatial or navigational memory, we also discuss the promise of VR in aiding other areas of memory research and facilitating research into clinical disorders

Testing the acquisition and use of navigation strategies in humans using a virtual environment

Testing the acquisition and use of navigation strategies in humans using a virtual environment Navigation is the area of spatial cognition related to how people move through space. Agents represent this space using reference frames fixed relative to the agent (egocentric) or the environment (allocentric). Research into how reference frames are used and interact has revealed many variables that can affect navigation. The thesis aim was to assess some of these variables and observe the important, modulatory roles of environment structure and complexity. For this a virtual Morris water maze analogue was designed to flexibly assess allocentric, intrinsic information-based and sequential response-based navigation. This research focussed on four facets of the interaction between environment and navigation: 1) How different reference systems knowledge develops over time in an environment; 2) What information drives improvements in navigation; 3) How reference systems interact when they suggest competing responses; 4) The relationship between the preceding points and environmental complexity. The results showed successful allocentric navigation after little training. Successful self-referential knowledge took longer to develop. Allocentric knowledge was centred on landmarks, overshadowing other cues, while egocentric knowledge was idiothetic. Conflict tests showed a strong preference for allocentric navigation that related to training maze complexity. A simpler training maze produced more egocentric navigators with relatively accurate route knowledge. These results provide further evidence for the multiple types of spatial navigation information that can be acquired and utilised, and demonstrate the importance of consideration of environment design for navigation research. The strong correspondence between these results and the real world navigation of human and non-human animals also suggest this virtual reality setup as a promising way to assess navigation in future

Three-dimensional space representation in the human brain

Brain structures that support spatial cognition by encoding one’s position and direction have been extensively studied for decades. In the majority of studies, neural substrates have been investigated on a horizontal two-dimensional plane, whereas humans and other animals also move vertically in a three-dimensional (3D) world. In this thesis, I investigated how 3D spatial information is represented in the human brain using functional MRI experiments and custom-built 3D virtual environments. In the first experiment, participants moved on flat, tilted-up or tilted-down pathways in a 3D lattice structure. Multivoxel pattern analysis revealed that the anterior hippocampus expressed 3D location information that was similarly sensitive to the vertical and horizontal axes. The retrosplenial cortex and posterior hippocampus represented direction information that was only sensitive to the vertical axis. In the second experiment, participants moved in a virtual building with multiple levels and rooms. Using an fMRI repetition suppression analysis, I observed a hierarchical representation of this 3D space, with anterior hippocampus representing local information within a room, while retrosplenial cortex, parahippocampal cortex and posterior hippocampus represented room information within the wider building. As in the first experiment, vertical and horizontal location information was similarly encoded. In the last experiments, participants were placed into a virtual zero-gravity environment where they could move freely along all 3 axes. The thalamus and subiculum expressed horizontal heading information, whereas retrosplenial cortex showed dominant encoding of vertical heading. Using novel fMRI analyses, I also found preliminary evidence of a 3D grid code in the entorhinal cortex. Overall, these experiments demonstrate the capacity of the human brain to implement a flexible and efficient representation of 3D space. The work in this thesis will, I hope, serve as a stepping-stone in our understanding of how we navigate in the real – 3D – world