Backward and forward masking for direct electrical stimulation of the VIIIth nerve in two profoundly deaf subjects

Abstract

Stanford Electronics Laboratories, Stanford, CA 94305 Two profoundly deaf multielectrode implant subjects were required to detect a probe signal (10 ms in duration) in a temporal gap between two pulse‐train maskers (each 300 ms in duration). The detection threshold was measured for a probe centered temporally in the gap, as well as for a probe offset from center by up to 97.5%. Also presented were the pure backward and pure forward masking cases. Qualitatively, both subject's forward and backward masking functions approximated those observed for normal hearing subjects [L.L. Elliott, J. Acoust. Soc. Am. 34, 1116–1117 (1962)] in that forward masking decayed more gradually than backward masking as a function of probe‐masker separation. Because mechanical (cochlear) contributions to masking [H. Duifhuis, J. Acoust. Soc. Am. 54, 1471–1488 (1973)] can be excluded in the case of direct VIIIth nerve stimulation, these data support the attribution of nonsimultaneous masking phenomena to VIIIth nerve or higher neural mechanisms. [Work supported by NIH.]