can reliably detect stimulation in a given sense. Differential threshold or just noticeable difference (JDS) is the smallest detectable difference between A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of stimuli. During sensation, sense organs collect various stimuli (such as a sound or smell) for transduction, meaning transformation into a form that can be understood by the brain. Sensation and perception are fundamental to nearly every aspect of Perception occurs when nerves that lead from the sensory organs (e.g. eye) to the brain are stimulated, even if that stimulation is unrelated to the target signal of the sensory organ. For example, in the case of the eye, it does not matter whether light or something else stimulates the optic nerve, that stimulation will results in visual perception, even if there was no visual stimulus to begin with. (To prove this point to yourself (and if you are a human), close your eyes (preferably in a dark room) and press gently on the outside corner of one eye through the eyelid. You will see a visual spot toward the inside of your visual field, near your nose.)

Light and the immature visual system. Preterm neonates are cared for in an environment which is continuously and brightly lit, and is very different to that experienced at any other time of life. The amount of light reaching the neonatal eye is governed by two groups of factors. Physical factors include intensity, spectral characteristics and duration of light exposure. Physiological factors are: Frequency of eyelid opening, transmission of light through the closed eyelid, pupil reactivity and area, transmission by the ocular tissues and retinal surface area. Retinal irradiance declines with increasing postmenstrual age. Mechanisms by which light may affect the neonatal eye and clinical conditions in which light have been implicated are considered. Published in Eye (London, England) (1992)

lids. When this stage is reached, one can focus, with the aid of the sun glass, the light on the closed eyelids , which at first is very disagreeable. When