Previous experiments performed on monkey and human fingertips suggested that the skin surface and stimulus probe decouple for sinusoidal displacements applied perpendicularly to the skin surface. From these observations, it was concluded that sinusoidal vibration may not be a suitable stimulus for understanding and modeling the tactile system. We repeated these experiments on human observers using stimulus frequencies ranging from 0.5 to 240 Hz and with displacement amplitudes up to 1 mm peak-to-peak (p-p). The skin and probe movements were measured in the steady-state using stroboscopic illumination and video microscopy. Contrary to previous conclusions, we found that decoupling did not occur for amplitudes less then 0.25 mm p-p, regardless of stimulus frequency. Decoupling was only observed for stimulus amplitudes greater than 0.25 mm over the stimulus-frequency range investigated. To further investigate this effect, a modified stimulus contactor was used, which permitted the measurement of the skin's movement using reflected light. Measurements were made on both the index fingertip and the thenar eminence. Regardless of body site, no decoupling between the skin and stimulus probe was observed for frequencies ranging from 20 to 100 Hz up to displacements of 0.25 mm p-p. These levels are well within the range used in most human psychophysical experiments performed on these parts of the body. We conclude that sinusoidal vibration can be used reliably to stimulate the tactile system and is an appropriate stimulus for developing models of touch.

The interaction of excitation and inhibition in responses due to attentional mechanisms in the visual system has been investigated. The studies reported herein use the tactile system of humans to test a specific hypothesis about the processes of attention that have never been directly addressed. Both exogenous and endogenous Inhibition of Return (IOR) reaction-time paradigms with a 100 Hz, 35 microm of peak displacement amplitude were used. In these experiments multiple Stimulus Onset Asynchronies were tested which made it difficult for subjects to learn timing patterns. We tested whether a detection time to a target which is to be attended to is a composite of at least two underlying mechanisms. These mechanisms were explored using exogenous and endogenous IOR experiments. It is hypothesized that these mechanisms work in a push-pull fashion: one deploying attention when new events occur, and the other withdrawing attention ("Disengagement") after it has been deployed. Based on the results, a new hypothesis is proposed stating that one form of attention (selective attention) competes with IOR in determining the time taken to detect a target in the tactile system.

Children's ability to discriminate nonsymbolic number (e.g., the number of items in a set) is a commonly studied predictor of later math skills. Number discrimination improves throughout development, but what drives this improvement is unclear. Competing theories suggest that it may be due to a sharpening numerical representation or an improved ability to pay attention to number and filter out non-numerical information. We investigate this issue by studying change in children's performance (N = 65) on a nonsymbolic number comparison task, where children decide which of two dot arrays has more dots, from the middle to the end of 1st grade (mean age at time 1 = 6.85 years old). In this task, visual properties of the dot arrays such as surface area are either congruent (the more numerous array has more surface area) or incongruent. Children rely more on executive functions during incongruent trials, so improvements in each congruency condition provide information about the underlying cognitive mechanisms. We found that accuracy rates increased similarly for both conditions, indicating a sharpening sense of numerical magnitude, not simply improved attention to the numerical task dimension. Symbolic number skills predicted change in congruent trials, but executive function did not predict change in either condition. No factor predicted change in math achievement. Together, these findings suggest that nonsymbolic number processing undergoes development related to existing symbolic number skills, development that appears not to be driving math gains during this period.• Children's ability to discriminate nonsymbolic number improves throughout development. Competing theories suggest improvement due to sharpening magnitude representations or changes in attention and inhibition.• The current study investigates change in nonsymbolic number comparison performance during first grade and whether symbolic number skills, math skills, or executive function predict change.• Children's performance increased across visual control conditions (i.e., congruent or incongruent with number) suggesting an overall sharpening of number processing.• Symbolic number skills predicted change in nonsymbolic number comparison performance.

The effectiveness of using vibrotactile threshold measures to aid in the diagnosis of carpal tunnel syndrome (CTS) was evaluated. Thresholds for detecting 1-, 10-, and 300-Hz vibratory stimuli were measured on the fingertips of 24 CTS patients and 20 healthy control subjects. There were no significant differences in threshold for 1- and 300-Hz between the two groups. Although there were significant differences for 10-Hz stimuli, the mean patient threshold was within 1 standard deviation of the mean threshold for the control group. These results indicate that threshold testing is not a suitable diagnostic tool for CTS. Additionally, we examined whether thresholds were elevated in the presence of pain. Seven patients reported experiences of pain and no pain sessions. No significant differences in threshold were found between the two pain conditions, indicating that the presence of pain related to CTS does not affect threshold.

The implementation of tactile aids for the deaf and blind has progressed largely through the development of new technologies and strategies adapted to adequately and efficiently activate previously understood tactile mechanisms and processes. In the past decade, however, important new discoveries have been made relating to the basic mechanisms of taction such as the effects of aging and disease, submodality interactions, skin mechanics, and learning and cortical plasticity. These advances in our knowledge will impact heavily on future developments and applications of tactile aids. Several of these new discoveries will be described in the context of basic tactile mechanisms and in their implications for significant improvements in the effectiveness of aids for tactile communication. [Work supported by NIH.]