Psychoacoustic sonification for tracked medical instrument guidance

Abstract

In image-guided surgery, displays show a tracked instrument relative to a patient's anatomy. This helps the surgeon to follow a predefined path with a scalpel or to avoid risk structures. A psychoacoustically motivated sonification design is presented to help assist surgeons in navigating a tracked instrument to a target location in two-dimensional space. This is achieved by mapping spatial dimensions to audio parameters that affect the magnitude of different perceptual sound qualities. Horizontal distance and direction are mapped to glissando speed and direction of a Shepard tone. The vertical dimension is divided into two regions. Below the target, the vertical distance controls the LFO speed of an amplitude modulation to create a regular beating well below the threshold of roughness sensation. Above the target elevation, the vertical deflection controls the depth of frequency modulation to gradually increase the number and amplitudes of sidebands, affecting perceived noisiness and roughness. This redundancy is necessary because the magnitudes of each single sound quality are only differentiable with little confidence. In a preliminary study, non-surgeons successfully identified a target field out of 16 possible fields in 41% of all trials. The correct cardinal direction was identified in 84%. Based on findings and further psychoacoustic considerations, the mapping range is optimized and an implementation of an additional depth dimension is discussed.