Why are there sometimes concreteness effects in memory for prose?

Four experiments explored on-line encoding strategies and memory for high imagery and low imagery texts. Results consistently indicated that concreteness effects in memory for text depend on how materials are presented in several different respects. Most importantly, the experiments clarified apparently contradictory results of previous studies by indicating that concreteness effects generally do not occur in memory for prose when imageability is manipulated between-subjects, and that their occurrence when imageability is manipulated within-subjects depends on the order occurrence when imageability is manipulated within-subjects depends on the order of presentation. In addition, moving window analyses of text processing strategies indicated that differential strategies observed in previous studies when subjects listened to high vs low imagery text do not generalize to reading of the same materials. Potential explanations for the pattern of results are evaluated, and implications for theories of mental imagery and memory are considered.

Origin of a gene regulatory mechanism in the evolution of echinoderms.

A rich diversity of ancient sea urchin lineages survives to the present. These include several advanced orders as well as the cidaroids, which represent the group ancestral to all other sea urchins. Here we show that all advanced groups of sea urchins examined possess in their eggs a class of maternal messenger RNA (mRNA) encoded by the evolutionarily highly conserved alpha-subtype histone genes. The maternal histone mRNAs are unique in their time of accumulation in oogenesis, their localization in the egg nucleus and their delayed timing of translation after fertilization. Cidaroid sea urchins as well as other echinoderm classes, such as starfish and sea cucumbers, possess the genes but do not have maternal alpha-subtype histone mRNAs in their eggs. Thus, although all the echinoderms examined transcribe alpha-subtype histone genes during embryogenesis, the expression of these genes as maternal mRNAs is confined to advanced sea urchins. The fossil record allows us to pinpoint the evolution of this mode of expression of alpha-histone genes to the time of the splitting of advanced sea urchin lineages from the ancestral cidaroids in a radiation which occurred in a relatively brief interval of time approximately 190-200 Myr ago. The origin of a unique gene regulatory mechanism can thus be correlated with a set of macroevolutionary events.