Perception of Vibrotactile Cues in Musical Performance

We suggest that studies on active touch psychophysics are needed to inform the design of haptic musical interfaces and better understand the relevance of haptic cues in musical performance. Following a review of the previous literature on vibrotactile perception in musical performance, two recent experiments are reported. The first experiment investigated how active finger-pressing forces affect vibration perception, finding significant effects of vibration type and force level on perceptual thresholds. Moreover, the measured thresholds were considerably lower than those reported in the literature, possibly due to the concurrent effect of large (unconstrained) finger contact areas, active pressing forces, and long-duration stimuli. The second experiment assessed the validity of these findings in a real musical context by studying the detection of vibrotactile cues at the keyboard of a grand and an upright piano. Sensitivity to key vibrations in fact not only was highest at the lower octaves and gradually decreased toward higher pitches; it was also significant for stimuli having spectral peaks of acceleration similar to those of the first experiment, i.e., below the standard sensitivity thresholds measured for sinusoidal vibrations under passive touch conditions

Efficiency of a Column Supported Embankment in Sabkha Soil

This thesis report presents an investigation of a soil improvement technique that is being executed for a Van Oord project in Kuwait. The soil is improved by the use of a column supported embankment, consisting of sand columns installed in a soft soil layer and a sand platform. The efficiency of this method is defined in terms of stress transfer and settlement reduction. When the soil improvement is finished and the land will be used, there are conditions concerning bearing capacity and settlement behavior. To this extent two important parameters were defined. i.e. the incremental efficiency (the load increase in a sand column over the total surface load increase) and incremental settlement reduction ratio (the settlement of the improved soil over the settlement of the unimproved soil (i.e. soil that has not been improved by sand columns), under loading). To determine the efficiency of the soil improvement, a number of tests were performed on site. Tests included plate load tests (in this thesis referred to as zone load tests). The load tests were simulated in Plaxis, with the known load/settlement results the model could be benchmarked. Furthermore soil samples were taken and tested to determine the local soil characteristics. The parameters derived from the soil tests are also used in the Plaxis calculations. Plaxis allows for a step-by-step consolidation of the soft soil in which the columns were installed. It can be seen that the stress distribution changes for different stages of consolidation. The columns are first constrained by the very stiff soft soil layer (due to high excess pore pressures under loading). When the pore pressures dissipate the constraining stress is lowered and the column head expands. Under vertical loading the stress in the column head has a funnel shape, due to the displacements in the outer ring of the column head. Based on the Plaxis calculations it can be concluded that when a load is activated on top of a surface of soil that has been improved by the use of sand columns (with a center-to-center distance of three meters), given that the platform is thick enough, 60% of that load is transferred to the column. With a greater center-to-center distance between the columns that percentage decreases, e.g. 28% for a column spacing of five meters. Compared to existing theories by Hewlett and Randolph (1988) and Zaeske (2001) (it should be noted that most existing theories assume presence of geosynthetic reinforcement, which is not the case for this project) the calculated column force is relatively low. A minimal thickness of the sand platform is needed to facilitate maximum efficiency. The thickness as determined by the Plaxis calculations are lower compared to existing literature. With platform heights of up to seven meters no full arching was observed, however partial arching did occur as evidenced by the efficiency values.Section Geo-EngineeringCivil Engineering and Geoscience

Vibrotactile Thresholds on the Mastoid and Forehead Position of Deaf Patients Using Radioear B71 and B81

Objectives: The main objective of this study was to measure the vibrotactile thresholds on the mastoid process and forehead positions using patients with bilateral deafness and to compare the results from the two bone conduction vibrators Radioear B71 and B81. Design: There is a possibility that the vibrotactile sensation on the skin makes it difficult to discriminate between sound and vibration. The risk is highest for patients who have bone conduction hearing thresholds in proximity to or worse than their vibrotactile thresholds. All measurements were performed similar to regular bone conduction threshold testing using an audiometer-driven bone conduction vibrator and pulsed warble tones, but the patients were instructed to respond only when feeling vibrations of the bone conduction vibrator instead of when hearing sound. Both the posterior forehead position and the mastoid process position on the temporal bone were tested for comparative reasons. In total, 16 patients participated in the study, 31% females and 69% males of age 29 to 77 years. All subjects were cochlear implant recipients, either uni-or bilaterally implanted. They were selected based on their audiogram data showing unmeasurable unaided hearing. Results: The force level at which the vibrotactile thresholds were reached, increased with frequency from 125 up to 500 Hz, but remained constant for higher frequencies up to 2 kHz. A statistically significant difference was found between the 2 devices at 125 Hz at both the mastoid process and forehead position, where the vibrotactile threshold seem to be more sensitive for B71, possibly due to contribution of distortion components. There was no statistically significant difference in vibrotactile thresholds between the mastoid process and forehead position in absolute values (force level in dB re 1 mu N), but in terms of hearing levels (dB HL) there was an average difference of 10 and 9 dB for B71 and B81, respectively. Conclusions: The results indicate that the vibrotactile thresholds can be confounded with bone conduction hearing thresholds measurements up to 500 Hz when using a standard audiometer and in particular when measuring on the forehead position