Using the shifted multiplicative model to search for “separability” in crop cultivar trials

Summary The shifted multiplicative model (SHMM) is used in an exploratory step-down method for identifying subsets of environments in which genotypic effects are separable from environmental effects. Subsets of environments are chosen on the basis of a SHMM analysis of the entire data set. SHMM analyses of the subsets may indicate a need for further subdivision and/or suggest that a different subdivision at the previous stage should be tried. The process continues until SHMM analysis indicates that a SHMM with only one multiplicative term and its point of concurrence outside (left or right) of the cluster of data points adequately fits the data in all subsets. The method is first illustrated with a simple example using a small data set from the statistical literature. Then results obtained in an international maize (Zea mays L.) yield trial with 20 sites and nine cultivars is presented and discussed.Journal Article No. 91-3-171 of the Kentucky Agricultural Experiment Station published with the approval of the Director     

Leishmania mexicana and L. tropica: inhibition of growth in mice by concurrent infections of Trypanosoma brucei

Growth of the cutaneous lesions of Leishmania mexicana and L. tropica major (P strain) in CFLP mice was markedly inhibited by concurrent Trypanosoma brucei infections. Restoration of normal growth of the lesion occurred within 1 week of the mice being treated with a trypanocidal drug. The presence of the concurrent T. brucei infections did not affect the development of acquired immunity to L. tropica, manifested as ulceration and healing of the lesion, nor did it induce any detectable immunity to L. mexicana. The possible underlying mechanisms are discussed.     

Blocking of conditioned taste avoidance induced by wheel running

In Experiment 1, compared to non-reinforced presentation of a food stimulus (A → no US), the association of a food stimulus with wheel running (A → US) blocked subsequent avoidance of a distinctive flavor (X), when both the food and flavor were followed by wheel running (AX → US). Experiment 2 replicated and extended the blocking effect, demonstrating that the amount of avoidance of X after AX → wheel training depended on the correlation between A-alone trials and wheel running—the predictiveness of the A stimulus. The present study is the first to demonstrate associative blocking of conditioned taste avoidance (CTA) induced by wheel running and strongly implicates associative learning as the basis for this kind of avoidance.     

放化疗对胃肠道的损伤以及微生态制剂防治的研究进展

肿瘤患者放化疗后不良反应较多,尤其是胃肠道反应.放化疗对胃肠道的损伤主要包括:严重损伤肠粘膜,造成肠黏膜免疫功能紊乱,以及肠道菌群失调,引发腹泻或便秘.研究发现,微生态制剂可用于防治放化疗对胃肠道的损伤,减少或避免不良反应的发生.     

Four-alternative choice violates the constant-ratio rule

Six pigeons responded on a four-key concurrent variable-interval schedule in which a 27:9:3:1 distribution of reinforcers between the keys changed every 10 reinforcers. Their behaviour quickly came under the control of this changing four-way reinforcer ratio. However, preference between a pair of keys depended not only on the relative reinforcer rates on those keys, but also on the absolute levels of those rates. This contradicts the constant-ratio rule that underpins the matching approach to choice, but is predicted by a contingency-discriminability model that assumes that organisms may occasionally misattribute reinforcers to a response that did not produce them. Reinforcers produced strong preference pulses, or transient increases in responding on the just-reinforced key. Despite accurate tracking of the reinforcer ratio, reinforcers obtained late in components and from leaner keys still produced strong pulses, suggesting both extended and local control of behaviour. Patterns of switching between keys were graded and similarly controlled by the reinforcer rates on each key. Whether considered in terms of switching, local preference pulses, or extended preference, behaviour was controlled by a rapidly changing four-way reinforcer ratio in a graduated, continuous manner that is unlikely to be explained by a simple heuristic such as fix-and-sample.     

Experimental concurrent infection of Afar breed goats with Oestrus ovis (L1) and Haemonchus contortus (L3): interaction between parasite populations, changes in parasitological and basic haematological parameters

The study was conducted to examine the occurrence and interaction between Oestrus ovis and Haemonchus contortus in experimentally infected Ethiopian Afar breed of goats. Twenty goats were divided into four groups (O, OH, H, and C) of five animals each. Each animal of groups O and OH received weekly infections for 5 weeks with 66 first instar larvae (L₁) of O. ovis. Then animals of groups OH and H were infected with a single dose of 5000 third stage larvae (L₃) of H. contortus. Goats of group C were kept free of any infection as non-infected control. Faecal egg count (FEC), blood cell count, total serum protein level and body weight were recorded weekly throughout the study period. At necropsy worm burden, female worm length, fecundity and larval burden of O. ovis in the nasal-sinus cavities of infected animals were assessed. The results showed that the presence of H. contortus in the abomasum of goats of group OH had no influence on the development of O. ovis. On the contrary, a significant reduction (P < 0.05) in FEC, worm burden, fecundity and female worm length was revealed in group OH animals compared to the mono-infected animals (group H). This was associated with eosinophilia and reduced packed cell volume.     

Discrete-trial vs. continuous free-operant procedures in assessing whether reinforcement context affects reinforcement value

Pigeons were trained to respond to two alternating concurrent reinforcement schedules. The reinforcement probabilities were .05 and .10 in one component, and .10 and .20 in the other. In one condition, the pigeons received training on a discrete-trial procedure in which the keylights remained illuminated for 5s or until a response occurred. In another condition, pigeons received training on a procedure in which the reinforcement contingencies were the same as in the discrete-trial procedure, but the stimuli were not turned off after 5s or after a response. Following training in each condition, probe tests were presented. In both conditions, the .20 alternative was, overall, preferred to the .05 alternative during probe tests. Following discrete-trial training, there was no reliable preference between the two .10 alternatives. However, when the stimuli remained illuminated during the intertrial interval periods during training, probe tests results showed preference for the .10 alternative that had been presented in the leaner context during training. The pattern of results is consistent with the notion that probe preference can be influenced both by the absolute reinforcement schedules associated with each alternative, as well as changeover behavior developed during training.     

A two-stage model for concurrent sequences

Schneider and Davison [Schneider, S.M., Davison, M., 2005. Demarcated response sequences and the generalised matching law. Behav. Proc. 70, 51–61] showed that the generalised matching law applied to concurrent free-operant two-response sequences. When sufficient temporal spacing is required between the responses, however, neither the response-level nor the sequence-level forms of the generalised matching law provide good fits. An alternative “two-stage sensitivity” model with fewer free parameters features two types of sensitivity to the reinforcement contingencies on sequences. When temporal spacing between the responses is long, the “response distribution sensitivity” parameter describes sensitivity only of the individual responses to the sequence-level contingencies. At a threshold level, this sensitivity reaches a maximum. When spacing is shorter than threshold, the “response order sensitivity” parameter reflects a new sensitivity to the order of the responses within sequences. As this sensitivity approaches its maximum, sequence matching is achieved. For both stages, a changeover parameter describes bias against sequences that require changeovers between the two responses. The model fit data ranging from near-response matching with long minimum inter-response times (IRTs) to sequence matching with no minimum IRTs, using two species and a variety of sequence reinforcer distributions. Rats differed from pigeons in achieving sequence matching only at a nonzero minimum IRT. In a comparison based on pigeon data with no minimum IRT, the two-stage sensitivity model was more efficient than the generalised matching law according to the Akaike criterion. The logic of the model suggests a new way of understanding the mechanisms underlying behavioural units.