M.Sc Thesis

M.Sc StudentDikovsky Larisa
SubjectNeurophysiological Correlates of Inconsistencies and Breaks
in Presence in Virtual Environment
DepartmentDepartment of Medicine
Supervisors PROFESSOR EMERITUS Hillel Pratt
Full Thesis textFull thesis text - English Version


In the study we aimed to find neurophysiological correlates of interferences in presence under virtual reality conditions. Regarding virtual environments, a ‘sense of presence’ was defined as a ‘sense of being and acting in virtual environment’, and presence is achieved if the subject’s responses to the virtual environment are similar to those in physical reality. Presence is a cognitive process provoked by the environment, and the current study focused on the neurophysiological characteristics of this cognitive process.

In the experiment subjects played an interactive game in a visuo-haptic virtual environment that was validated as creating a high sense of presence. While playing the game, anomalous events which interrupted with visual or haptic sensory stream in virtual environment , occurred. The anomalies were of three types: total cutoff of the visual sensory stream that made up the virtual scene, inconsistency across time in the haptic parameters of a virtual object and inconsistency across haptic and visual parameters of a virtual object. The anomalous events were designed to interfere with subjects’ sense of presence and served as stimuli for the evoked potentials.

Our basic hypothesis was that the cognitive processing of anomalies that interfere with the sense of presence would be detectable at the neurophysiological level, and might manifest by unusual features of the associated endogenous event related potentials and their intracranial sources.

The results showed that total cutoff of the visual sensory stream and inconsistency across time in the haptic modality evoked an unusual neurophysiological signature. The presence-interfering effect of these two events manifested in extraordinarily high amplitudes of the P3 component, the appearance of an unusual sustained positivity and substantial activation of prefrontal cortex during these potentials. The total cutoff of a visual sensory stream and inconsistency across time in haptic modality evoked similar late endogenous potentials and brain activation patterns, with graded magnitudes across conditions. This suggests that there can be different degrees of interference with the sense of presence, and that presence can be reduced by inconsistencies in haptic sensory cues within the virtual environment.

Inconsistency across haptic and visual sensory modalities elicited a very weak neurophysiological response, and evoked neither the high amplitude P3 nor the sustained positivity potentials associated with presence interference. These findings imply that this condition was not evaluated as interference in presence and, in contrast to our assumption, did not reduce presence in the virtual environment.