Multisensory Integration and Proprioceptive Drift During Resizing Illusions

Abstract

Bodily resizing illusions typically use visual and/or tactile inputs to produce a vivid experience of one’s body changing size. Naturalistic auditory input (input that reflects the natural sounds of a stimulus) has been used to increase illusory experience during the rubber hand illusion, whilst non-naturalistic auditory input can influence estimations of finger length. We aimed to use non-naturalistic auditory input during a hand-based resizing illusion using augmented reality, to assess whether the addition of auditory input would increase both subjective illusion strength and measures of performance-based tasks. 44 participants completed three conditions: no finger stretching, finger stretching without tactile feedback, and finger stretching with tactile feedback. Half the participants had auditory input throughout all conditions, while the other half did not. After each condition, participants were given one of three performance tasks: stimulated (right) hand dot touch task, non-stimulated (left) hand dot touch task and a ruler judgement task. Dot tasks involved participants reaching for the location of a virtual dot, whereas the ruler task concerned estimates of the participant’s own finger on a ruler whilst the hand was hidden from view. After all trials, participants completed a questionnaire capturing subjective illusion strength. The addition of auditory input increased subjective illusion strength for manipulations without tactile feedback but not those with tactile feedback. No facilitatory effects of audio were found for any performance task. We, therefore, conclude that adding auditory input to illusory finger stretching increased subjective illusory experience in the absence of tactile feedback but did not affect performance-based measures.