Simultaneous modulation of pulse charge and burst period elicits two differentiable referred sensations

Objective. To investigate the feasibility of delivering multidimensional
feedback using a single channel of peripheral nerve stimulation by
complementing percepts of intensity with percepts of flutter frequency
controlled by burst period modulation. Approach. Two dimensions
of a distally referred sensation were provided simultaneously: intensity
was conveyed by the modulation of the pulse charge rate inside short
discrete periods of stimulation referred to as bursts, and frequency was
conveyed by the modulation of the period between bursts. For this approach
to be feasible, intensity percepts must be perceived independently of
frequency percepts. Two experiments investigated these interactions. A
series of two alternative forced choice tasks (2AFC) were used to
investigate burst period modulation's role in intensity
discernibility. Magnitude estimation tasks were used to determine any
interactions in the gradation between these frequency and intensity
percepts. Main Results. The 2AFC revealed that burst periods can
be individually differentiated as a gradable frequency percept in
peripheral nerve stimulation. Participants could correctly rate a
perceptual scale of intensity and frequency regardless of the value of the
second, but the dependence of frequency differentiability on charge rate
indicates that frequency was harder to detect with weaker intensity
percepts. The same was not observed in intensity differentiability as the
length of burst periods did not significantly alter intensity
differentiation. These results suggest that multidimensional encoding is a
promising approach for increasing information throughput in sensory
feedback systems as long as intensity ranges are selected properly.
Significance. This study provides valuable insights into haptic
feedback through the peripheral nervous system and demonstrates an
encoding approach that may offer enhanced information transfer for use in
virtual reality applications and in sensory-enabled prosthetic systems.
The feasibility of the multidimensional encoding approach in performing
control tasks opens new avenues for developing enriched sensory feedback
systems.