Fig. 9. Increase in relative neural gain to tactile stimulation over hydrodynamic flow for primary afferent neurons in the ventral non-pored hyomandibular canal of the stingray, Dasyatis sabina. Mean tactile sensitivity of three primary afferents from ventral non-pored canals (open circles) normalized relative to their average response to hydrodynamic flow above the canal (solid circles at 0 dB) across different stimulus frequencies are shown. Note that the average neural response is 6–20 dB greater to direct tactile stimuli compared to hydrodynamic stimuli above the canal, and are highest at the lower frequencies (10–20 Hz). Thus, non-pored canals are an average of 2–10 times more sensitive to tactile stimuli than to local water movements. Values are means ± S.E.M. and error bars are shown only in the negative direction on the 0 dB line for clarity. The broken line represents a relative neural gain of 6 dB.