Manual Detection of Spatial and Temporal Torque Variation through a Rotary Switch

Vibrotactile Force Perception - Absolute and Differential Thresholds and External Influences

Three experiments were carried out to determine absolute and differential thresholds for vibrotactile forces and external influences in the frequency range of 5 to 1,000 Hz at the tip of the index finger. Differential thresholds were obtained for reference stimuli of 0.5, 0.25 N, and near the individual threshold. Frequency, temperature, age, fingertip size, and contact force were investigated as parameters in a full-factorial design. Experiments were conducted with at least 27 subjects and a 1up-2down staircase procedure with 3IFC paradigm. We find absolute thresholds ranging from 1.7 to 19 mN with the lowest threshold at 320 Hz. Weber fractions from 18 to 41 dB are found near the absolute threshold. For larger references, they range from 4.9 to 23 dB. ANOVA finds frequency as significant medium effect for both absolute and differential thresholds. Results imply impact of age on the absolute threshold, but no effect of motor skill, temperature, fingertip size, and contact force. Differential thresholds are affected by frequency only, which is attributed to saturation effects of the Pacinian channel. Fingertip size and motor skill are not able to explain effects on thresholds and the interpersonal variance. Results of this work are intended as requirement source for the design of task-specific haptic interfaces.

A Comparative Study of Haptic Stiffness Identification by Veterinarians and Students

Palpation is an important clinical skill in both veterinary and medical health professions. The present study compares the ability of practicing veterinarians and veterinary students to identify the stiffness of virtual surfaces through palpation. An absolute identification paradigm was used where a force-feedback haptic device rendered virtual surfaces with five levels of stiffness within a "clinically relevant" range (0.2-0.5 N/mm). The mean information transfer was 0.97 bits (almost two perfectly identifiable stiffness levels) for 12 veterinarians and 0.58 bits (one correctly identified level) for 14 veterinary students. Although the difference between the two groups was significant (p <; 0.001), neither group was able to reliably identify more than two levels of stiffness, indicating that the success of veterinarians in clinical practice probably relies on additional properties such as size, shape, and texture. Analyses of force versus time and displacement versus time recordings suggest that the superior performance of the veterinarians may be partially attributable to motor strategy. Specifically, veterinarians used a greater mean maximum force (2.0 N) compared to students (1.6 N) (p <; 0.05). However, further studies are required to investigate motor strategy in more detail. The implications of our findings for veterinary education and quantitative skill assessment are discussed.

A Frequency-Domain Analysis of Haptic Gratings

The detectability and discriminability of virtual haptic gratings were analyzed in the frequency domain. Detection (Exp. 1) and discrimination (Exp. 2) thresholds for virtual haptic gratings were estimated using a force-feedback device that simulated sinusoidal and square-wave gratings with spatial periods from 0.2 to 38.4 mm. The detection threshold results indicated that for spatial periods up to 6.4 mm (i.e., spatial frequencies >0.156 cycle/mm), the detectability of square-wave gratings could be predicted quantitatively from the detection thresholds of their corresponding fundamental components. The discrimination experiment confirmed that at higher spatial frequencies, the square-wave gratings were initially indistinguishable from the corresponding fundamental components until the third harmonics were detectable. At lower spatial frequencies, the third harmonic components of square-wave gratings had lower detection thresholds than the corresponding fundamental components. Therefore, the square-wave gratings were detectable as soon as the third harmonic components were detectable. Results from a third experiment where gratings consisting of two superimposed sinusoidal components were compared (Exp. 3) showed that people were insensitive to the relative phase between the two components. Our results have important implications for engineering applications, where complex haptic signals are transmitted at high update rates over networks with limited bandwidths.