Quality-specific differences in rat taste detection performance as a function of stimulus volume

Taste detection performance for representatives of the four taste qualities as a function of stimulus volume (5 x 10(-4) to 1 x 1(-1) ml) was examined in rats using high-precision gustometry, computer-controlled operant procedures, nonparametric signal detection measures of sensitivity and responsivity, and blind control procedures. The overall sensitivity index was positively related to stimulus volume (rs = .60), with optimal detection performance attained with a 5 x 10(-3) ml stimulus volume for salty tastants and a 1 x 10(-2) ml stimulus volume for the other taste qualities. The overall responsivity index was inversely related to stimulus volume (rs = -.47), especially for sour and bitter tastants. These results are consistent with prior observations and demonstrate that operant methods using small tastant samples produce sensitive estimates of the rat's taste detection performance and response bias.