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 .
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 .