EFFECTS OF UNDERWATER ENVIRONMENTAL-CONDITIONS ON VIBROTACTILE THRESHOLDS

The effects of low-frequency, water-borne vibration upon the cutaneous surface of swimmers and divers are virtually unknown. It has been rep orted that divers can ''feel'' underwater sounds on various parts of t heir bodies. The current experiments were conducted in two parts as in itial investigations of these reports. The first experiments were to d etermine if changes in barometric pressure and breathing mixture have an effect on vibrotactile thresholds measured in air. Vibrotactile thr esholds at the thenar eminence were measured on eight divers during tw o saturation dives in a dry hyperbaric chamber. Measurements were made on four subjects before and after a 6-day saturation dive that simula ted an excursion to 300 feet of seawater (fsw). Measurements on anothe r four subjects were made at 1 atmosphere absolute (ATA) before and af ter an 8-day simulated 300-fsw dive, and at 5, 7, and 10.1 ATA (300 fs w). The gas mixture in which the divers lived was varied according to standard procedures to prevent adverse body reactions during compressi on and decompression. Vibrotactile thresholds were measured by standar d psychophysical methods at 1, 10, 100, and 250 Hz. Results suggest th at neither increased atmospheric pressure nor breathing gas had any ef fect on vibrotactile thresholds within any of the four mechanoreceptor channels that innervate normal skin. The second set of experiments wa s performed to assess the effect of complete seawater hydration of the skin upon vibrotactile threshold sensitivity measured at the thenar e minence and the volar surface of the forearm. In-air thresholds of thr ee subjects were measured by standard psychophysical methods at 1, 10, 100, and 250 Hz. The measurements were repeated underwater after the forearm and hand were submerged for 20 min in a seawater solution. Wit h the exception of 1 Hz, no statistically significant changes were fou nd at either site when compared to threshold measured in air. At 1 Hz there appears to be an increase in sensitivity of approximately 3 dB w hen the skin is hydrated with seawater. (C) 1996 Acoustical Society of America.