Direct realist account

In opposition to sense-data theory or indirect realism and subjective idealism (representationalism or what we perceive is determined by a psychological representation of the thing), it is James J. Gibson’s theory of perception according to which the structure of the world is directly available to perception (‘what you see is what you get’).  Thus, on …

Direct (monogenesis) and indirect (metagenesis and metamorphosis) development

Monogenesis is the direct development of an embryo, without metamorphosis, into an organism similar to the parent.  Metagenesis, like the other form of indirect development, metamorphosis, consists of marked changes undergone in a series of successively produced individuals, extending from the one developed from the ovum to the final mature individual.  Unlike metamorphosis, metagenesis involves …

Direct corticomotoneuronal connections (or tracts)

The pyramidal fibers originating in the motor cortex and extending down the spinal cord where they synapse on alpha motoneurons.   They connect to the extrafusal muscles of the hand and fingers with just one synapse, and thus are referred to as being ‘monosynaptic’.  In the newborn macaque monkey, fibers of this tract have reached …

Digraphs

Combinations of letters that represent a single phoneme (e.g., ‘gh’ in ‘laugh’).  For the most part, these combinations are of consecutive letters, but sometimes they are split (e.g., the ‘o-e’ combination signifies a long ‘o’ sound, as in ‘hope’. See Diagraph, Phoneme

Diploid

From the Greek word meaning ‘double’, a cell or organism having two sets or copies (or homologs) of each somatic chromosome, usually one from the mother and one from the father, and thus twice the haploid number.  Nearly all animal cells are diploid, except for the gametes, and some are polypoid (three or more copies …

Diffusion tensor magnetic resonance imaging

As applied to neuroimaging, this magnetic resonance imaging (also known as diffusion tractography) uses information about the direction of water movement in white matter to determine the size and orientation of its constituent fiber tracts.  The underlying principle stems for the fact that when water in unobstructed at body temperature, then the water molecules move …