Glossary I

Isomerization refers to a change in shape of the retinal part of the visual pigment molecule that occurs when the molecule absorbs a quantum of light. Isomerization triggers the enzyme cascade that results in transduction from light energy to electrical energy in the retinal receptors .

Isometric contraction is defined as a type of contraction with little or no shortening of the muscle resulting in no appreciable change in the joint angle.

Isometric exercise refers to exercise performed by contracting muscles against an immovable object.

Isotonic is a contraction in which a muscle shortens against a constant load or tension, resulting in movement; contraction occurring in which there is either shortening or lengthening in the muscle under tension Isotonic also known as a Dynamic contraction, and classified as being either concentric or eccentric.

Isotonic exercise is defined as an exercise that requires the contraction of muscles and the movement of joints, as in weight lifting.

Item refers to a specific stimulus to which a person responds overtly and that can be scored or evaluated.

Item analysis refers to an assessment of whether each of the items included in a composite measure makes an independent contribution or merely duplicates the contribution of other items in the measure. Moreover, Item analysis is a set of methods used to evaluate test items. The most common techniques involve assessment of item difficulty and item discriminability .

Item characteristic curve refers to a graph prepared as part of the process of Item analysis . One graph is prepared for each test item and shows the total test score on the X axis and the proportion of test takers passing the item on the Y axis.