Lower Discrimination Thresholds Research Articles

Neurophysiological evaluation of the differential response model for orientation and spatial-frequency discrimination.

Recent models have attempted to reconcile low psychophysical orientation and spatial-frequency discrimination thresholds with relatively broad orientation and spatial-frequency tuning of cortical neurons. These models have relied on the ability of the neurons to convert small stimulus changes into reliable response changes. We have examined this ability in a sample of neurons from the cat's striate cortex. We present here data from two cells that reliably signaled the smallest orientation and spatial-frequency differences. Using receiver operating characteristic analysis, we find that these cells could reliably signal orientation differences of 1.84 deg and spatial-frequency differences of 0.073 octave. We compare these single-cell results to cat and human behavioral discrimination thresholds.

Taste Responses in Ruminants. III. Reactions of Pygmy Goats, Normal Goats, Sheep and Cattle to Sucrose and Sodium Chloride

This study involved the use of the two-choice preference test to determine the taste responses of eight, each, of pygmy goats, normal goats, sheep and cattle to ascending concentrations of sucrose (Suc) and sodium chloride (NaCl). In addition, sheep and cattle were tested at 2.08 and 8.33% molasses concentrations. Each animal was individually penned and fed to appetite on a nutritionally adequate diet. Responses were expressed on the basis of percent of total fluid intake comprised by test solution. Response trends were analyzed by stepwise multiple linear regression. A 95% confidence interval was established for a theoretical mean intake of 50%. The upper confidence limit was at 60% intake and the lower was at 40% intake. They were termed, respectively, upper discrimination threshold (UDT) and lower discrimination threshold (LDT). The rejection threshold (RET) was set at 20% intake and the preference threshold (PRT) at 80% intake. Ascending or descending responses at the various threshold concentrations are identified by ↑ and ↓, respectively. Molar concentrations at the thresholds crossed by responses of the species studied were, for pygmies, Suc—UDT: .055↑ and .53↓; NaCl—UDT: .024↑ and .21↓, PRT: .10↑ and .14↓, LDT: .36↓, RET: .60↓,, for normals, Suc—UDT: .033↑, PRT: .38↑; NaCl—UDT: .027↑↓, LDT: .15↓, RET: .55↓, for sheep, Suc—LDT: .41↓; NaCl—LDT: .21↓, RET: .53↓, and for cattle, Suc—UDT: .025↑ and .41↓, PRT: .058↑ and .24↓, LDT: .56↓; NaCl—LDT: .016↓, RET: 14↓. Sheep were indifferent to 2.08 and 8.33% molasses concentrations. Cattle demonstrated strong preference responses to the 2.08% level and weak preference reactions to the 8.33% level.

Taste responses in ruminants. I. Reactions of sheep to sugars, saccharin, ethanol and salts.

The two-choice preference test technique was used to study taste responses in sheep. Data were reported on responses to various sugars, sodium saccharin, ethyl alcohol and various salts. Tests with sugars and saccharin showed adequately fed sheep to be on the average essentially indifferent to compounds evoking sweet taste sensations, although individual sheep showed pronounced preferences for some sugars. The upper discrimination thresholds (UDT), 60% intake, for glucose and sucrose were estimated to be at concentrations of 5 (.28 M) and 5% (.13 M), respectively. The lower discrimination threshold (LDT), 40% intake, for sucrose was estimated to be at a concentration of 15% (.44 M). The preference threshold (PRT), 80% intake, was never reached with any of the taste stimulants used in this study. Concentrations at the LDT and the rejection threshold (RET), 20% intake, for NaCl were .25 (.043 M) and 2.2% (.38 M), in the same order. The RET concentrations for the sodium salts of acetate, propionate and butyrate were lower than for NaCl.