Evaluation of the parallel coupling constitutive model for biomaterials using a fully coupled network-matrix model.

In this article we discuss the effective properties of composites containing a crosslinked athermal fiber network embedded in a continuum elastic matrix, which are representative for a broad range of biological materials. The goal is to evaluate the accuracy of the widely used biomechanics parallel coupling model in which the tissue response is defined as the additive superposition of the network and matrix contributions, and the interaction of the two components is neglected. To this end, explicit, fully coupled models are used to evaluate the linear and non-linear response of the composite. It is observed that in the small strain, linear regime the parallel model leads to errors when the ratio of the individual stiffnesses of the two components is in the range 0.1-10, and the error increases as the matrix approaches the incompressible limit. The data presented can be used to correct the parallel model to improve the accuracy of the overall stiffness prediction. In the non-linear large deformation regime linear superposition does not apply. The data shows that the matrix reduces the stiffening rate of the network, and the response is softer than that predicted by the parallel model. The correction proposed for the linear regime mitigates to a large extent the error in the non-linear regime as well, provided the matrix Poisson ratio is not close to 0.5. The special case in which the matrix is rendered auxetic is also evaluated and it is seen that the auxeticity of the matrix may compensate the stiffening introduced by the network, leading to a composite with linear elastic response over a broad range of strains.

Influence of response similarity on interference in perceptual motor learning.

Motor interference was measured in terms of average response time in sorting 15 pairs of cards, each pair containing words which were either unrelated or identical but printed in different colors. The two words of each pair were used in labeling two cubicles in such a way that they were apart by 0, 1, 2, or 3 intervening cubicles in quasirandomly chosen directions. Interference was inversely related to response similarity, but this relationship may not appear in the absence of sufficient stimulus similarity. The findings are interpreted in the light of a hypothesis which views motor interference as a tendency for responses to deflect from their own courses and be pulled towards those of other responses with which they are at conflict.

Anagram solution speed as a joint function of manifest anxiety and number of category sets.

Anagrams constructed from words in 1,2,3, or 4 conceptual categories were administered in random sequences to subjects scoring at the extremes of the Taylor Manifest Anxiety Scale. Scince explicit instructions were given to the subjects concerning the nature of the categories involved, it is assumed that sets for responding with words from these categories were present from the start. The results demonstrate a negative relation of solution rate to number of category sets and an interaction of this variable with manifest anxiety. Anxiety facilitates performance in the presence of a single category set but inhibits performance when multiple sets are concurrently operative. The latter finding is consistent with the drive interpretation of manifest anxiety by Taylor and Spence.

Interactions of Manifest Anxiety score with anagram letter transition probability and Thorndike-Lorge frequency of solution word.

In an experiment designed for further exploration of the effects of manifest anxiety upon anagram problem solving, two levels each of manifest anxiety score, letter transition probability of anagram, and Thorndike-Lorge frequency of solution word were factorially combined (N = 40 male and 40 female freshmen and sophomores). While corroborating the previous findings that anagram solving rate is positively related to solution word frequency and negatively related to anagram letter transition probability, the results have demonstrated a significant interaction of solution word frequency, though not of anagram letter transition probability, with manifest anxiety score. This interaction, as shown in the facilitative effect of manifest anxiety with anagrams derived from high-frequency words and the inhibitory effect with anagrams derived from low-frequency words, is consistent with Taylor's interpretation that manifest anxiety, as an emotionally based drive, multiplicatively interacts with habit strength.