Feeling the difference: discrimination of vibration frequency and acceleration magnitude in the tactile channels

Abstract

The sense of touch translates indentation of the skin into information about the physical properties of the world, including texture, shape, weight, hardness and motion. This complex system depends on subsystems of mechanoreceptive nerves that can be characterised as ‘tactile channels’. Like any sensory system, the tactile system is vulnerable to damage and degradation from illness or environmental exposure. Characterising the relationship between physical vibrations that indent the skin and the subjective perception of those vibrations (“vibrotactile psychophysics”) provides us with a powerful tool for understanding the tactile system, and therefore for diagnosing sensorineural disorders that affect it. However, our current methods are marked by profound limitations in sensitivity, validity, and capacity to characterise the full action of the tactile channels. The aims of the research presented in this thesis are to: 1) design a vibrotactile psychophysical paradigm that measures the sensitivity of the tactile channels beyond the capacity of current methods, 2) advance and extend the model of the tactile channels, and 3) make substantive links to applications of vibrotactile stimulation to the diagnosis and treatment of sensorineural disorders. Four main experiments are reported. The first experiment instantiates and tests a two alternative forced choice paradigm for vibrotactile frequency discrimination and investigates whether contact area affects the sensitivity of two tactile channels. The second experiment builds on this work to evaluate the effect of recruiting additional channels on the sensitivity to frequency differences. The third experiment investigates whether these effects are paralleled in the discrimination of acceleration magnitude. The final experiment completes the series by investigating how sensitivity to vibrotactile frequency changes across the boundaries between channels. The results of these studies are combined to build a novel suprathreshold, diagnostic model of the tactile channels. This is then applied to improve the effectiveness of vibrotactile applications in translational medical science as haptic aids for CI users.

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ORCID for Sean R Mills: orcid.org/0000-0001-7866-7225

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