Vibrotactile discriminative capacity is impacted in a digit-specific manner with concurrent unattended hand stimulation.

A number of perceptual and neurophysiological studies have investigated the effects of delivering unilateral versus bilateral tactile sensory stimulation. While a number of studies indicate that perceptual discrimination degrades with opposite-hand stimulation, there have been no reports that examined the digit specificity of cross-hemispheric interactions to discriminative capabilities. The purpose of this study was to determine whether unattended hand (UH) stimulation significantly degraded or improved amplitude discriminative capacity on the attended hand (AH) in a digit-specific manner. The methods are based on a sensory perceptual task (vibrotactile amplitude discriminative capacity on the tips of the fingers D2 and D3 of the left hand) in the absence and presence of conditioning stimuli delivered to D2 and D3 of the right hand. Non-specific equal-amplitude stimulation to D2 and D3 of the UH significantly worsened amplitude discrimination (AD) performance, while delivering unequal-amplitude stimuli to D2 and D3 of the UH worsened task performance only under the condition in which the unattended stimuli failed to appropriately match the stimulus parameters on the AH. Additionally, delivering single-site stimuli to D2 or D3 of the UH resulted in degraded performance on the AD task when the stimulus amplitude did not match the amplitude of the stimulus applied to homologous digits of the AH. The findings demonstrate that there is a reduction in performance under conditions where UH stimulation least matched stimulation applied to the AH, while there was little or no change in performance when stimulus conditions on the homologous digit(s) of the contralateral sites were similar. Results suggest that bilateral interactions influence perception in a context-dependent manner that is digit specific.

An undergraduate laboratory exercise to study sensory inhibition.

Sensory inhibition was first described by von Békésy as a process in which excitation of a field of sensory neurons leads to the reduction of activity of surrounding neurons and thus promotes contrast enhancement of the excited field. In the context of somatosensory cortex, the cortical neurons excited by touch or vibration will suppress excitation of neurons from surrounding receptive fields. USING TACTILE STIMULATORS BOTH DESIGNED AND FABRICATED AT THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL, WE CONDUCTED TWO SIMPLE EXPERIMENTS IN WHICH SENSORY INHIBITION PLAYS A ROLE IN INFORMATION PROCESSING: a unilateral study in which stimuli are delivered to the digits of one hand, and a bilateral study in which stimuli are delivered to the digits of both hands. In the unilateral study, we demonstrated that threshold detection on the third digit (D3) is impacted by conditioning stimuli delivered to adjacent digits 2 (D2) and digits 4 (D4). In the bilateral study, we delivered different conditions of bilateral stimulation in order to investigate the impact that conditioning stimulation of the right hand had on amplitude discriminative capacity of the left hand. The results demonstrated that conditioning stimulation on the right hand had a significant impact on the discriminative capacity of the left hand, and this alteration in discriminative capacity was consistent with previous animal studies in which somatosensory cortical responses evoked by stimulus conditions of unilateral vs. bilateral stimulation were compared. At the conclusion of this exercise, students will appreciate the fundamentals of sensory inhibition as well as the logistics of obtaining and analyzing data from human subjects. This study is designed to help students prepare for studying other facets of sensory processing by providing a firm foundation in the experimental methods and procedures.

Methodological Problems With Online Concussion Testing.

Reaction time testing is widely used in online computerized concussion assessments, and most concussion studies utilizing the metric have demonstrated varying degrees of difference between concussed and non-concussed individuals. The problem with most of these online concussion assessments is that they predominantly rely on consumer grade technology. Typical administration of these reaction time tests involves presenting a visual stimulus on a computer monitor and prompting the test subject to respond as quickly as possible via keypad or computer mouse. However, inherent delays and variabilities are introduced to the reaction time measure by both computer and associated operating systems that the concussion assessment tool is installed on. The authors hypothesized systems that are typically used to collect concussion reaction time data would demonstrate significant errors in reaction time measurements. To remove human bias, a series of experiments was conducted robotically to assess timing errors introduced by reaction time tests under four different conditions. In the first condition, a visual reaction time test was conducted by flashing a visual stimulus on a computer monitor. Detection was via photodiode and mechanical response was delivered via computer mouse. The second condition employed a mobile device for the visual stimulus, and the mechanical response was delivered to the mobile device's touchscreen. The third condition simulated a tactile reaction time test, and mechanical response was delivered via computer mouse. The fourth condition also simulated a tactile reaction time test, but response was delivered to a dedicated device designed to store the interval between stimulus delivery and response, thus bypassing any problems hypothesized to be introduced by computer and/or computer software. There were significant differences in the range of responses recorded from the four different conditions with the reaction time collected from visual stimulus on a mobile device being the worst and the device with dedicated hardware designed for the task being the best. The results suggest that some of the commonly used visual tasks on consumer grade computers could be (and have been) introducing significant errors for reaction time testing and that dedicated hardware designed for the reaction time task is needed to minimize testing errors.