A statement that represents an observation in words in a parsimonious manner so as to answer ‘how’, ‘what’, ‘when’ and ‘where’ questions about objects, events and changes in events. While description can distinguished from (scientific) explanation, it cannot be separated from it. Thus, when theory changes explanatory principles, so does the way in …
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Depth perception
The ability to perceive the distance of objects from the viewer’s perspective and the three-dimensional nature of objects and space through monocular and binocular cues projected as two-dimensional on the retina. The binocular cues are ocular convergence (the degree of convergence between the eyes in fixating an object) and stereopsis, while the monocular cues include …
Dependent differentiation
The idea that activity and interaction among structures and functions is necessary to embryonic development. In the theory of embryological development by Wilhelm Roux (1850-1924), which he referred to as mosaic development, the developing organism proceeds through a stage of independent development directed almost independently of other embryonic regions (i.e., self-differentiation), to be followed by …
Dephosphorylation
See Adenosine triphosphate (ATP), Phosphorylation
Deoxyribose
The sugar in DNA, which is similar to ribose, but that lacks one oxygen atom. See DNA (deoxyribonucleic acid), DNA double helix, Nucleotide, Ribose
Denervation
Injury to a peripheral nerve, resulting in disconnection from its target (synapse), as well as fasciculation (spontaneous bursts of action potentials in degenerating motor neurons, with accompanying observable contractions in the entire motor unit) and fibrillation (spontaneous bursts of action potentials and accompanying very small twitches in isolated, denervated muscle fibers). Following denervation muscles usually …
Deoxyhemoglobin (dHB)
Means deoxygenated hemoglobin. Oxygen associates with haemoglobin by means of weak chemical bonds. However, once oxyhemoglobin encounters an environment with a low partial pressure of oxygen, the oxygen molecule releases itself from the oxyhemoglobin molecule to move into the low partial pressure environment. With this transition, oxyhemoglobin becomes dHB. See Blood Oxygenation Level Dependent Contrast …
Dendrite
Derived from the Greek word dendron meaning ‘tree’, in biology, it is a branch-like nerve cell process collecting incoming or afferent information in the form of electrical signals. It receives synapses from the axon terminals of neurons, but unlike a neuron it is not myelinated. Pyramidal neurons have a tall-tree-like apical dendrite plus some root-like …
Delphi method
A structured process for collecting and distilling knowledge from a pre-selected panel of geographically dispersed experts whose opinions or judgments are of interest by means of a series of questionnaires interspersed with anonymous controlled feedback to refine opinions. After two or three rounds, the panel‚was position is determined by averaging. Originally developed at the RAND …
Demand characteristics
The degree to which participants in an experiment experience an expectation that they should behave in a particular way. See Experimental method, Hawthorne effect, ‘Screw-you’ effect