Biomedical subjects

G M Pace

Publications and source records attributed to G M Pace.

24 records · Page 2Linked to original sources

PubMed1982

Minimizing Nitrate Reduction during Kjeldahl Digestion of Plant Tissue Extracts and Stem Exudates : APPLICATION TO N STUDIES.

From 10 to 60% of the nitrate present in plant tissue extracts and stem exudates of corn (Zea mays L.) was found to be reduced during Kjeldahl digestion, even in the absence of added reducing agents. This reduction is of particular concern in [(15)N]nitrate assimilation studies, because it results in an overestimate of nitrate reduction. To overcome this problem, a method was developed for removing nitrate prior to Kjeldahl digestion, thereby preventing nitrate reduction. The procedure utilizes hydrogen peroxide for partial oxidation of organic matter in order to minimize the nitration of organic compounds. The free nitrates are then volatilized as nitric acid from concentrated sulfuric acid at 95 degrees C. When the proposed method was used as a pretreatment to Kjeldahl digestion, less than 0.5% of the applied nitrate was recovered in the reduced nitrogen fraction of plant tissue extracts and stem exudates.

Journal Article↗

PubMed1981

Effects of stimulus contact on the feature-positive effect.

Fourteen pigeons were taught to discriminate displays differentiated by the presence or absence of a distinctive feature. Feature-positive (FP) birds were reinforced for responses to displays containing the feature, while feature-negative (FN) birds were reinforced for responses to displays containing only the elements common to both stimulus displays. Both control and experimental birds were required to respond to a spatially separate operant key, while experimental animals were also required to contact the individual elements of the display. A planned comparisons test indicated that FP performance was superior to FN performance only for the control animals. No difference was found between the performance of the experimental FP and FN birds. Consideration of the elements of the display toward which the FN birds orient was offered as an explanation of these results.

Animals↗

PubMed1980

Comparison of two techniques for the development and maintenance of tracking behavior in monkeys.

The present study compared two methods by which animal subjects can be taught to perform a pursuit tracking task. Rhesus monkeys were trained to track in order to avoid shock (Method No. 1) or to obtain food (Method No. 2). One animal received training under both procedures. Both techniques were effective; however, the method utilizing shock produced faster learning and more efficient performance. The possible reasons for these differences are discussed along with generality of the results. These methods should have implications for tracking research in which animal models are required.

Animals↗

PubMed1980

Feature-positive and feature-negative learning in the rhesus monkey and pigeon.

In separate experiments four monkeys and eight pigeons were presented with displays containing one red and two green keys and displays containing three green keys. During feature-positive phases, responses to displays containing the one red and two green keys were reinforced on a fixed-ratio schedule, while responses to displays containing the three green keys were never reinforced. During feature-negative phases, only responses to the three green key displays were reinforced. For monkeys in Experiment 1, both between and within subject analyses indicated that the learning of feature-positive discriminations was superior to the learning of feature-negative discriminations. The within subject analysis further revealed that performance on a feature-positive discrimination was retarded following exposure to a feature-negative discrimination, while performance on a feature-negative discrimination was enhanced following exposure to a feature-positive discrimination. Experiment 2 replicated the essential aspects of these reversal effects in four experimental pigeons. Evidence that these reversal effects were not simply a function of time was provided by four control birds exposed to only a feature-positive or feature-negative discrimination.

Animals↗

PubMed1979

Generalization gradients following differential intradimensional autoshaping.

Three pigeons were trained on a differential, intradimensional autoshaped discrimination. A 45 degrees line tilt was always paired with food whereas a 15 degrees line tilt was never paired with food. All subjects learned the discrimination within 17 sessions. The pigeons were then given generalization tests in extinction over seven line tilts (0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees and 90 degrees). The subjects yielded generalization gradients with maxima at 45 degrees and minima at 15 degrees. An area shift, but no peak shift, was found for each subject.

Animals↗

PubMed1979

Temporal parameters of the feature positive effect.

Trial duration and intertrial interval duration were parametrically varied between groups of pigeons exposed to a discrimination involving the presence vs. the absence of a dot. Half the groups received the dot as the positive stimulus (feature positive groups) and half the groups received the dot as the negative stimulus (feature negative groups). Faster learning by the feature positive birds (feature positive effect) was found when the trial duration was short (5 sec) regardless of whether the intertrial interval was short (5 sec) or long (30 sec). No evidence for a feature positive effect was found when the trial duration was long (30 sec) regardless of the length of the intertrial interval (30 sec or 180 sec). The results suggest that short trial duration is a necessary condition for the occurrence of the feature positive effect, and neither intertrial interval nor trial duration/intertrial interval ratio are important for its occurrence. The suggestion that mechanisms underlying the feature positive effect and autoshaping might be similar was not supported by the present experiment since the trial duration/intertrial interval ration parameter appears to play an important role in autoshaping but not the feature positive effect.

Animals↗