Identification of ground materials with the aid of tapping sounds and vibrations of long canes for the blind

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Abstract
One of the functions of the long cane for the blind is to inform the user about the ground he or she is walking on. Three experiments were conducted to study to what extent sounds and vibrations from long canes make it possible to identify ground materials. The first experiment investigated how observers could identify four materials by sounds made, when tapping the long cane. The correlations of these behavioural data with the spectral contents of the tappings showed that the materials were characterized by different frequency bands. The most important frequency range resided between 500 and 2500 Hz with a preponderance in the higher frequencies. In the second experiment learning effects were studied and resulted in the same conclusions. The third experiment was designed to study how canes differ in their capacity to make available to the hand useful vibratory information on the hardness, or impedance, of the material, but no statistically significant differences were found between them. The ranking order of the canes from the first two experiments suggested that the overall elasticity should be an important factor, when constructing an acoustically adequate cane.

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