16-18

Sensation & Perception Terms

• Sensation – The process by which sensory receptors and the nervous system receive and represent stimuli from the environment.

• Perception – The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.

• Bottom-up processing – Analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information.

• Top-down processing – Information processing guided by higher-level mental processes, as when we construct perceptions drawing on experience and expectations.

• Selective attention – Focusing conscious awareness on a particular stimulus.

• Inattentional blindness – Failing to notice changes in the environment, a form of inattentional blindness.

• Transduction – The conversion of one form of energy into another. In sensation, the transformation of stimulus energies, such as sights and sounds, into neural impulses our brain can interpret.

• Psychophysics – The study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them.

Thresholds & Sensory Limits

• Absolute threshold – The minimum stimulus energy needed to detect a particular stimulus 50% of the time.

• Signal detection theory – A theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Detection depends partly on experience, expectations, motivation, and alertness.

• Difference threshold – The minimum difference between two stimuli required for detection 50% of the time, also called the just noticeable difference (JND).

• Weber’s law – The principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage.

• Sensory adaptation – Diminished sensitivity as a consequence of constant stimulation.

Perceptual Processes

• Perceptual set – A mental predisposition to perceive one thing and not another.

• Extrasensory perception (ESP) – The controversial claim that perception can occur apart from sensory input (e.g., telepathy, clairvoyance, precognition).

• Parapsychology – The study of paranormal phenomena, including ESP and psychokinesis.

Vision and the Eye (Module 18)

Basic Properties of Light

• Wavelength – The distance from the peak of one light wave to the peak of the next. Determines color.

• Hue – The dimension of color determined by wavelength (e.g., blue, green, red).

• Intensity – The amount of energy in a light wave or sound wave, influencing what we perceive as brightness or loudness.

Eye Structures and Functions

• Cornea – The eye’s clear, protective outer layer, covering the pupil and iris.

• Pupil – A small adjustable opening in the center of the eye through which light enters.

• Iris – A ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.

• Lens – A transparent structure behind the pupil that changes shape to focus images on the retina.

• Retina – The light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of neurons that begin the processing of visual information.

• Accommodation – In sensation and perception, the process by which the eye’s lens changes shape to focus near or far objects on the retina.

Vision (Module 18 - Continued)

Photoreceptors & Neural Processing

• Rods – Retinal receptors that detect black, white, and gray, necessary for peripheral and night vision.

• Cones – Retinal receptors concentrated near the center of the retina that function in daylight or well-lit conditions; detect fine detail and color.

• Optic nerve – The nerve that carries neural impulses from the eye to the brain.

• Blind spot – The point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located there.

• Fovea – The central focal point in the retina, around which the eye’s cones cluster.

Color Vision Theories

• Young-Helmholtz Trichromatic (Three-Color) Theory – The retina contains three different types of color receptors (red, green, and blue), which work together to produce perception of any color.

• Opponent-Process Theory – Opposing retinal processes (red-green, yellow-blue, white-black) enable color vision. Some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green.

Feature Detection & Processing

• Feature detectors – Nerve cells in the brain’s visual cortex that respond to specific features of the stimulus, such as shape, angle, or movement.

• Parallel processing – Processing many aspects of a problem simultaneously; the brain’s natural mode of information processing for vision.