Glossary — Page 448, Lesson 700

I want to walk you through the glossary terms that are essential for understanding human performance in aviation. Let's start with Percept — that's the immediate interpretation of the information sitting in your sensory store. It's the very first meaning your brain assigns to raw sensory data, but here's the key: it is not necessarily a complete representation of that information. Your brain grabs a quick impression, not the full picture. Perception is the broader, active process. Through perception, you use your knowledge and understanding of the world to interpret those sensations as meaningful experiences. So percept is the instant snapshot; perception is the ongoing work of making sense of it all. Now let's talk about vision, because your eyes are your primary instrument in the cockpit. Peripheral Vision is vision that comes from areas away from the fovea — that's the central spot of sharpest vision — and it relies on the rod cell receptors of the eye. Rods are your low-light specialists, and they're packed outside the fovea. Photopic Vision is the opposite: it's vision through the functioning of the cone light-sensitive cells. Cones handle bright light and colour, and they're concentrated in the fovea. Scotopic Vision is vision through the rods — the rod light-sensitive cells. So photopic is daylight, colour vision; scotopic is night, black-and-white, low-light vision. Let's move to hearing. Presbycusis — the glossary simply says "See Hearing loss." That's age-related hearing loss, and we'll cover it when we get to that entry. Presbyopia is a form of long-sightedness. It's caused by the lens of your eye losing its elasticity with age. That loss of elasticity means the lens can no longer accommodate fully — it can't change shape to focus on near objects — so close objects become blurred. This is a common condition in people more than 45 years of age, but it's easily corrected with a weak convex lens. Psychosomatic — this refers to a psychological reaction to an outside stimulus that causes physiological changes. It's about the interrelationships of the mind and body. A stressful thought can produce a real physical response — that's psychosomatic. Pulmonary simply means referring to the lungs. So the pulmonary artery takes blood from the heart to the lungs, and the pulmonary vein carries oxygenated blood from the lungs back to the heart. That's the basic pulmonary circulation. Regression is a symptom of stress. Under stress, correct actions are forgotten and substituted with procedures learnt in the past — you regress to older, more familiar behaviours even if they're wrong for the current situation. REM stands for Rapid Eye Movements. It's a term used in sleep studies to define a stage of sleep. In REM sleep, the EEG — that's the brain wave recording — becomes irregular, and the EOG — the eye movement recording — shows the eyes rapidly darting back and forth, while the EMG — the muscle activity recording — shows the muscles to be relaxed. It's suggested that during REM sleep, your memory is strengthened and organized. REM sleep is sometimes referred to as Paradoxical Sleep. Residual Volume is the volume of air remaining in the lungs even after the most forceful expiration. No matter how hard you breathe out, you cannot empty your lungs completely — that leftover air is the residual volume. Retina — this is the light-sensitive screen on the inside of the eye to which images are focused. The retina has light-sensitive cells: rods and cones. These cells convert the image into nerve impulses, which are then interpreted by the brain. Rods are those light-sensitive cells on the retina. They are sensitive to lower levels of light than the cones, and they are not sensitive to colour. To adapt completely to dark conditions takes the rods about 30 minutes, and that adaptation can be destroyed by even a transitory bright light. That's why a quick flash of light in the cockpit at night can ruin your night vision for a while. Saccade — here's an important one for visual scanning. The eye cannot be moved continuously and smoothly when searching for a target. Instead, it moves in jerks, known as saccades, with rests between them. The external world is sampled only during those resting periods. An eye movement/rest cycle takes about one third of a second, which means the amount of the external world that can be examined in detail is strictly limited. So when you're scanning the instrument panel or the sky, your eyes are making these rapid jerky movements and only gathering information during the brief pauses. Semantic Memory is a part of long-term memory that stores general knowledge of the world — facts, concepts, meanings — not personal experiences, but knowledge about how things work.