A mathematical abstraction, combining several different measures in order to achieve a more precise measure of the underlying construct. See Construct, Latent factor/score/variable, Latent growth model
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Latent factor/score/variable
A hypothetical variable which is not directly measured but is presumed to have some influence on the scores of the observed or manifest variables. Put another way, it is a hidden commonality that has to be derived from the data generated by a group of measured variables . Statistical models that aim to explain observed …
Latent growth model
The representation of a longitudinal process for many individuals where the components of growth are hypothesized to be unobserved or latent scores and the errors of measurement at each occasion are independent. It is also possible to add a latent shape to this model so the changes represented by the latent slopes are not equal over …
Larynx
Referred to as the voice box and situated at the bottom of the vocal tract between the vocal cords and the oral cavity, it is part of the cartilaginous air passage structure, located above the trachea and below the pharynx, that houses the vocal folds and the various muscles serving laryngeal vocal mechanisms. Pitch and …
Lamillipodia
Lamillipodia (singular lamillipodium) are thin, but broad (‘sheet-like’) membrane extensions of cytoplasm at the leading edge of motile cells (e.g., immune cells, neurons). They lack any major organelles, but like their growth cone companions they are composed of a dense and dynamical network of actin filaments (sometimes referred to as ‘microspikes’). Cell migration (protrusion and …
Language development
The acquisition of the ability to understand the meaning of words (semantics) and to use them in ways that are grammatically correct (synthetics) relative to a child‚was linguistic environment. In general, there are two features of this process: the production and reception of language, with the latter developing in advance of the former, and perhaps even …
Lamarckism
A theory of organic evolution proposed by Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (1744-1829) that was ultimately discredited and replaced by Darwinism in the 19th century, but which is proved to be relevant for understanding cultural evolution. The theory is based on the principle that characteristics acquired by an organism during its …
Lactic acid
An acid produced by cells during chemical processes in the body that do not require oxygen. It forms in the muscles as a result of the incomplete breakdown of glucose and is associated with muscle fatigue and sore muscles. See Anerobic respiration
Lactose tolerance
Certain populations in eastern and western Africa who practise the husbandry of milk-producing animals consume large quantities of raw or unprocessed milk. For more than 70% of the world’s non-Caucasian adults, however, fresh milk is indigestible and when consumed produces gastric distress (e.g., abdominal cramps, diarrhoea, and sometimes nausea and vomiting). Among the semi-nomadic cattle herders …
Labio-dental
Speech sounds formed between the lower lip and the upper central incisors, as in the fricatives /f/ and /v/, but rarely with the upper lip touching the lower front teeth. The former is a voiceless labio-dental fricative (e.g., fan) and the latter a voiced labio-dental fricative (e.g., van). A labio-dental approximant is type of consonant, with …