TransductionThe process of converting one form of physical energy from the environment into electrical energy that can be processed by the nervous system. In the visual system, this occurs when light energy stimulates the photoreceptors on the retina.
Absolute ThresholdThe minimum level of stimulus energy required for a stimulus to be detected by human senses at least 50% of the time. An example is detecting the lowest detectable amount of salt dissolved in a glass of water.
Difference ThresholdThe smallest detectable change in the intensity of a stimulus. For example, a person can easily detect the difference between a 5-kilogram and a 10-kilogram weight, but cannot distinguish between 100 kilograms and 105 kilograms.
Blind SpotThe specific area on the retina where the optic nerve exits the eye. Because this region lacks photoreceptors, light falling on it cannot be processed, creating a gap in our visual field.
ProsopagnosiaA cognitive impairment, often resulting from brain damage, characterized by the inability to recognize familiar faces, even though general visual intellectual abilities remain intact.
Trichromatic TheoryA theory of color vision stating that color perception is based on three types of receptors (cones) in the retina, each maximally sensitive to a specific wavelength: red, green, or blue.
Opponent-Process TheoryThe theory that color vision depends on three pairs of opposing physiological mechanisms: red-green, blue-yellow, and black-white. This explains why staring at a red image produces a green afterimage.
Law of ClosureA Gestalt principle of perceptual organization stating that the brain automatically fills in gaps or missing parts of a visual stimulus to perceive a complete, enclosed, and meaningful object.
AnosmiaThe partial or complete loss of the sense of smell. Individuals with this condition also experience a dramatic reduction in their ability to perceive the flavor of foods.
UmamiA savory taste category triggered by monosodium glutamate and other salts, commonly found in packaged foods and ready-made soups, complementing sweetness, sourness, saltiness, and bitterness.
Gate-Control TheoryA theory of pain asserting that non-painful input closes the nerve gates to painful input, preventing pain sensation from traveling to the central nervous system. This gate is regulated by both cognitive factors and physical skin sensations.
