Factors Influencing how Electrotactile Stimuli are Consciously Perceived

Abstract

Tactile, or touch-related, perception is critical to successfully perform activities of daily living, such as holding a cup, hugging a loved one, or learning a new skill. However, approximately 30% of individuals in the United States experience tactile perceptual impairments, or difficulty/inability detecting and interpreting tactile stimuli. In clinical settings, tactile perceptual assessments are commonly used to diagnose impairments and somatosensory function (e.g., intact dermatomes following spinal cord injury). However, these existing examination methods that focus on tactile perception can be insufficient depending on the patient population targeted. One reason why tactile examinations may be insufficient is the large number of factors that may influence intact perception are not considered and, in turn, captured. Consequently, exploring the various factors that influence intact tactile perception is of significant interest. Current literature suggest that factors which can impact intact tactile perception include arm dominance, nerve stimulated, anatomical location of stimulation, biological sex, age, and cognitive-perceptual load. In this dissertation, I provide a comprehensive examination of the factors influencing tactile perception, and how they interact, in young and older adults who are neurologically intact. By gaining a deeper understanding of the various factors that influence tactile perception, and their interactions, in individuals who are neurotypical, clinicians can more effectively examine and interpret when and why tactile impairments arise in different populations.

This work initially examines factors influencing tactile perception, and and a subset of their interactions, by having participants detect electrotactile stimuli applied at their upper limb. Findings from this body of work indicate that factors such as the nerve stimulated, anatomical location of stimulation, sex, age, and and a subset of their interactions can impact tactile perception. A novel finding from this work is the significant interaction between age and anatomical location in shaping tactile perception. While prior studies have often examined age-related or location-based differences independently, this dissertation demonstrates how the combined influence of these factors can differentially affect sensory processing. These findings suggest that aging may alter tactile perception in a location-specific manner, with important implications for sensorimotor rehabilitation strategies and age-tailored sensory assessments. However, contrary to our preliminary findings and select literature, this work did not find a consistent effect of arm dominance, highlighting the need for further research into the conditions under which dominance of the arm stimulated influences tactile perception. Combined, this work suggests that when assessing intact tactile perception, various factors and their interactions should be considered.

Next, this work explores whether the cognitive resources allocated to perceiving tactile stimuli influence tactile perception in younger adults. Participants were introduced to an additional sensory load, through auditory stimuli, during which they were instructed to complete two tasks concurrently (i.e., tactile task and auditory task). Additionally, this body of work explored whether the nature of the electrotactile stimulus (i.e., detection versus discrimination) impacted how electrotactile stimuli were perceived. Findings indicate that arm dominance significantly influenced both the accuracy of detection and discrimination of electrotactile stimuli. While performing a concurrent auditory discrimination task significantly impacted precision during tactile detection, it primarily affected accuracy during tactile discrimination. Additionally, a significant interaction between participant sex and stimulation location was observed during detection but not discrimination of the stimuli. Notably, small effect sizes were observed alongside significant p-values, raising the possibility that statistical effects may not fully reflect meaningful physiological differences. These findings indicate the importance of interpreting both statistical and physiological significance when examining the factors that influence tactile perception.

Lastly, this work explores whether the cognitive resources allocated to perceiving tactile stimuli influence tactile perception in older adults. Participants were introduced to an additional sensory load, through auditory stimuli, during which they were instructed to complete two tasks concurrently (i.e., tactile task and auditory task). Additionally, this body of work explored whether the nature of the auditory task (i.e., detection versus discrimination) and the nature of the electrotactile task (i.e., detection versus discrimination) impacted how electrotactile stimuli were perceived. This work suggests that concurrent auditory stimuli influenced participants' ability to accurately detect electrotactile stimuli when the auditory stimulus demanded greater cognitive resources (i.e., discrimination task). Furthermore, results indicate that concurrent auditory stimuli contributed to greater variability in perceiving the electrotactile stimuli when the auditory stimulus demanded less cognitive resources (i.e., detection). These results suggest that as cognitive-perceptual load increases, tactile perceptual outcomes may become impaired, particularly in older adults.

Overall, this dissertation emphasizes the importance of considering multiple contributing factors, and their interactions, when evaluating tactile perception. The results highlight that factors such as age, the anatomical location of stimulation, nerve, associated cognitive-perceptual load, and and a subset of their interactions can significantly influence how tactile stimuli are perceived in young and older adults. These findings have implications for enhancing tactile assessments, particularly in clinical settings where precise measurements are crucial for accurate diagnoses and interventions. By incorporating these factors into evaluations for tactile perception, clinicians can provide more individualized assessments, ultimately leading to more effective and personalized treatments for those with tactile impairments.