An exploratory fNIRS study with immersive virtual reality: a new method for technical implementation

Abstract

For over two decades Virtual Reality (VR) has been used as a useful tool in several fields, from medical and psychological treatments, to industrial and military applications. Only in recent years researchers have begun to study the neural correlates that subtend VR experiences. Even if the functional Magnetic Resonance Imaging (fMRI) is the most common and used technique, it suffers several limitations and problems. Here we present a methodology that involves the use of a new and growing brain imaging technique, functional Near-infrared Spectroscopy (fNIRS), while participants experience immersive VR. In order to allow a proper fNIRS probe application, a custom-made VR helmet was created. To test the adapted helmet, a virtual version of the line bisection task was used. Participants could bisect the lines in a virtual peripersonal or extrapersonal space, through the manipulation of a Nintendo Wiimote ® controller in order for the participants to move a virtual laser pointer. Although no neural correlates of the dissociation between peripersonal and extrapersonal space were found, a significant hemodynamic activity with respect to the baseline was present in the right parietal and occipital areas. Both advantages and disadvantages of the presented methodology are discussed.

Keywords: attention; brain imaging; fNIRS; line bisection; pseudoneglect; virtual reality.

Figure 1

The adapted virtual reality helmet. The helmet was created by attaching the LCDs removed from a V8 Research head mounted display to a modified bike helmet. The fNIRS optical fibers were applied to the parietal and occipital areas. A Velcro belt was attached at the back of the helmet in order to counterbalance the effect of the LCDs' weight in front of the helmet. The belt was subsequently secured to the participants back through a thoracic belt.

Figure 2

The virtual environment. On the left, a panoramic view of the virtual room is presented; the mobile chair with wheels was created to simulate and motivate the movement along the distances of line presentation, 60 and 120 cm. On the right, the participants' point of view of the virtual environment is presented; lines were presented over the white panel and could be bisected moving a red dot through the manipulation of a Nintendo Wiimote® controller.

Figure 3

The fNIRS recording. In the bottom part of the figure, the location of the regions investigated in the present study, with cerebral projections of detectors (black) and channels (white) superimposed on a template brain (occipital view). The letters of the detectors indicate the lobe (P: parietal; O: occipital) and the hemisphere (L: left; R: right). The number indicates the source. Channels are named according to the source-detector pair: for instance, detector OL and source 5 created the channel OL5. Further details can be found in Cutini et al., (2011a, b). In the top part of figure, hemodynamic response profile in symmetrical channels PR1 and PL1 (i.e., right vs. left parietal lobe) during virtual line bisection. A visual inspection of the response profiles in the two channels suggests a marked difference for what concerns the presence of task-related hemodynamic activity in the two parietal lobes.

Figure 4

Graph of the behavioral results. The graph shows the percentage error (Y axis) along the distances of line presentation, 60 and 120 cm (X axis). Negative values indicate an error on the left of the true centre of the line; positive values indicate an error on the right of the true centre of the line. Error bars represent the standard error ±SE.