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991.
Susana Maia 《Behavioural processes》2009,81(2):280-285
We examined if the representation of time intervals in a temporal discrimination task is based not only on their absolute but also on their relative durations. Six pigeons learned two temporal discriminations. In the first, red and green choices were correct following 2-s and 8-s samples, respectively. In the second, vertical and horizontal bar choices were correct following 4-s and 16-s samples, respectively. In a previous study [Zentall, T.R., Weaver, J.E., Clement, T.S., 2004. Pigeons group time intervals according to their relative duration. Psychon. Bull. Rev. 11, 113-117.], tests with 4-s samples and red/green comparisons revealed a bias for red, whereas tests with 8-s samples with vertical/horizontal comparisons revealed a bias for horizontal. These results were interpreted in terms of relative encoding of sample durations. We attempted to replicate this finding but instead of testing with only 4-s or 8-s samples, we tested with several other sample durations to obtain a psychometric function. Results were inconsistent with the relative encoding hypothesis. 相似文献
992.
Cassandra D. Gipson Holly C. Miller Jrme J.D. Alessandri Thomas R. Zentall 《Behavioural processes》2009,82(2):126-132
There is evidence that pigeons prefer conditioned reinforcers that are preceded by greater effort over those that are preceded by less effort (an effect that has been attributed to within-trial contrast). In past research the probability of reinforcement for correct choice of the conditioned reinforcer has been 100%, however, the high level of reinforcement for both alternatives in training may result in a performance ceiling when choice between those alternatives is provided on test trials. In the present study we tested this hypothesis by including a group for which the probability of reinforcement in training was only 50%. Pigeons were trained on two simultaneous discriminations, one that was preceded by a 30 peck requirement the other by a single peck requirement. On test trials, we found a significant preference for the S+ that required the greater effort in training for pigeons trained with 100% and a small but nonsignificant effect for pigeons trained with 50% reinforcement. Although the hypothesis that the within-trial contrast effect was constrained by a performance ceiling was not confirmed, we did find a reliable within-trial contrast effect with 100% reinforcement. 相似文献
993.
Comparison of hamstring neuromechanical properties between healthy males and females and the influence of musculotendinous stiffness 总被引:2,自引:0,他引:2
J. David R. Marc F. Jeff D. Lauren A. 《Journal of electromyography and kinesiology》2009,19(5):e362-e369
The hamstrings limit anterior cruciate ligament (ACL) loading, and neuromuscular control of these muscles is crucial for dynamic knee joint stability. Sex differences in electromechanical delay (EMD) and rate of force production (RFP) have been reported previously, and attributed to differences in musculotendinous stiffness (MTS). These characteristics define the neuromechanical response to joint perturbation, and sex differences in these characteristics may contribute to the greater female ACL injury risk. However, it is unclear if these differences exist in the hamstrings, and the relationship between MTS and neuromechanical function has not been assessed directly. Hamstring MTS, EMD, the time required to produce 50% peak force (Time50%), and RFP were assessed in 20 males and 20 females with no history of ACL injury. EMD did not differ significantly across sex (p = 0.788). However, MTS (p < 0.001) and RFP (p = 0.003) were greater in males, Time50% (p = 0.013) was shorter in males, and Time50% was negatively correlated with MTS (r = −0.332, p = 0.039). These results suggest that neuromechanical hamstring function in females may limit dynamic knee joint stability, potentially contributing to the greater female ACL injury risk. However, future research is necessary to determine the direct influences of MTS and neuromechanical function on dynamic knee joint stability and ACL injury risk. 相似文献
994.
Scott C. Kelly A. Cheryl L. William D. Kevin J. 《Journal of electromyography and kinesiology》2009,19(5):e370-e379
Non-contact ACL injuries generally occur as the foot contacts the ground during cutting or landing maneuvers and the non-contact ACL injury rate is 2–8 times greater in females compared to males. To provide insight into the gender bias of this injury, this study set out to identify gender differences in the neuromuscular response of the quadriceps, hamstrings and gastrocnemii muscles in elite adolescent soccer players during the pre-contact and early stance phases of an unanticipated side-cut and cross-cut. For the early stance phase of the two maneuvers, females demonstrated greater rectus femoris activity compared to males. Throughout the pre-contact phase of the maneuvers, a rectus femoris activation difference was identified with females having an earlier and more rapid rise in muscle activity as initial ground contact approached. Females demonstrated greater lateral and medial gastrocnemii activity for the pre-contact and early stance phases of the side-cut and greater lateral gastrocnemii activity during early stance of the cross-cut. Timing of hamstring activity also differed between genders prior to foot contact. The differences suggest that the activation patterns observed in females might not be providing adequate joint protection and stability, thereby possibly having a contributing role towards increased non-contact ACL injuries in females. 相似文献
995.
Christopher J. Welch 《Chirality》2020,32(7):961-974
Professor William H. Pirkle (1934–2018) made a profound impact on modern chemistry by inventing and popularizing widely used techniques for the analysis and purification of enantiomers, contributions that paved the way for the subsequent advances in the discovery, development, and manufacture of enantiopure pharmaceuticals, agrochemicals, and specialty chemicals. Pirkle's pioneering 1966 demonstration of the use of chiral solvating agents for the nuclear magnetic resonance determination of enantiopurity led to a lifelong interest in understanding the supramolecular interactions responsible for enantiodifferentiation. Ongoing research into the chromatographic resolution of stereoisomers throughout the 1970s led in 1981 to the very first commercialization of a chiral stationary phase for the high-performance liquid chromatography (HPLC) separation of enantiomers. The availability of this and subsequent “Pirkle columns” had a deep and lasting impact, becoming widely embraced by the chemical sciences research community worldwide and spearheading the wholesale changeover to HPLC as the preferred technique for measuring enantiopurity. Doc Pirkle was a highly creative, independent, and fun-loving collaborator whose circle of friends extends around the globe. His research group at the University of Illinois, often referred to as The Pirkle Zoo, became a refuge for an interesting assembly of characters who flourished under his mentorship and guidance. 相似文献
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Association of protein intakes and variation of diet‐scalp hair nitrogen isotopic discrimination factor in Papua New Guinea highlanders 下载免费PDF全文
Yuichi I. Naito Ayako Morita Kazumi Natsuhara Kiyoshi Tadokoro Jun Baba Shingo Odani Eriko Tomitsuka Katsura Igai Takumi Tsutaya Minoru Yoneda Andrew R. Greenhill Paul F. Horwood Kevin W. Soli Suparat Phuanukoonnon Peter M. Siba Masahiro Umezaki 《American journal of physical anthropology》2015,158(3):359-370
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Manganese (Mn) is an essential trace element involved in the formation of bone and in amino acid, lipid and carbohydrate metabolism. Mn excess may be neurotoxic to humans, affecting specific areas of the central nervous system. However, relatively little is known about its physiological and/or toxicological effects, and very few data are available concerning the role of Mn in chronic renal failure (CRF). This paper describes a 12-month study of the evolution of plasma Mn levels in predialysis patients with CRF and the relationship with energy and macronutrient intake. The participants in this trial were 64 patients with CRF in predialysis and 62 healthy controls. Plasma levels of creatinine, urea, uric acid, total protein and Mn were measured. The glomerular filtration rate (GFR) was calculated using the Cockcroft-Gault index. The CRF patients had higher plasma levels of creatinine, urea, uric acid and Mn and a lower GFR than the controls. Plasma Mn was positively correlated with creatinine, plasma urea and plasma uric acid and was negatively correlated with the GFR and the intake of energy and macronutrients. In conclusion, CRF in predialysis patients is associated with increases in circulating levels of Mn. 相似文献