Units of change in developmental velocity during a specified time interval. After having subtracted the mean velocity value at a previous age from that at a subsequent adjacent age to give one for ‘speed’ of development, then the resulting scores are again subtracted from each other (double differentiation) to give a measure of acceleration (the …
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Developmental biology
The study of mechanisms and processes of ontogenetic development, differentiation, growth and morphogenesis in animals and plants at the genetic, molecular, cellular and functional levels. Its model organisms include, for example, the round worm (Caenorhabditis elegans), the fruit fly (Drosophila melanogaster), the zebrafish (Brachydanio rerio), and the African clawed toed frog (Xenopus laevis). Starting in …
Developmental (or ontogenetic) time
The time scale long enough for developmental change to take place. For prehension, the requisite time would be weeks or months while for language it would be at least months and probably years. This time scale is contrasted with that for real time, the seconds or fractions of seconds during which immediate behavior is expressed. …
Development
A concept dating back to the Ancient Greeks used to denote progressive change or betterment to some idealized end state. In this respect, it did not differ from evolution and up to 19th century the two terms were used interchangeably, as they still are in French today. Toward the end of that century a distinction …
Determination
The developmental process in which cells and tissues of the embryo become progressively restricted in what they may become. Cells of the early embryo may be totipotent, capable of producing cells of any organ system of the adult. As development proceeds, however, cells become increasingly limited in their potential and directed toward a definite structure …
Determinism
The doctrine of linear causality, which holds that the state of a system at one moment determines its states at all subsequent times, and its roots lie in the idea that everything can be explained, at least in principle (termed universal determinism). While they are in some sense deterministic, non-linear dynamical systems do not show …
Desensitizing
A part of debriefing, it is an attempt to remove any undesirable consequences of participation in research through restoring the participant to a state of emotional well-being following deception. There is evidence that desensitizing does not always this goal as participants can be made aware of any unflattering behavior they may have revealed during an …
Design matrix
Contains vectors that specify the effects under study in (statistical) linear models. It represents independent (or explanatory) variables that account for observed data referred to as dependent variables. Such a matrix underpins a variety of statistical models analysis of variance and linear regression. See Analysis of variance (ANOVA), General linear model (GLM), …
Descriptive explanations
An intermediate category between description and explanation consisting of two parts. They can explain what something is like (e.g., what the reaching movements of a newborn look like relative to a three-month-old). In addition, they can explain a process: how something occurred in terms of events before and after its occurrence (e.g., after being placed in …
Dermomyotome
Somatic layer of lateral mesoderm tissue derived from somites that goes on to form muscle cells and dermis (see figure below). Cells in the somite differentiate in two directions: medially to form the sclerotome (eventually the vertebral column) and laterally to form the dermomytome (A). Subsequently, the dermotome (eventually the dermis) and the myotome (eventually muscle) …