Chapter 4: Sensation and Perception

Chapter Outline Basic Principles of Sensation Vision Hearing Your Other Senses Perception

Definitions of Sensation and Perception Sensation is the process that detects stimuli from our bodies and our environment. Perception is the process that organizes those stimuli into meaningful objects and events.

Perception (1) Bottom-up processing is building a perceptual experience from smaller pieces of information. Top-down processing occurs when perception of the whole is based on our memories, experiences, and expectations, which shape our perception of smaller sensory features of stimulus.

Basic Principles of Sensation (Slide 1 of 2) Transduction occurs when sensory receptors convert energy from stimuli into neural impulses. Absolute threshold describes the lowest level of intensity of a given stimulus that a person can detect half the time. Signal detection theory explains that detection of a stimulus is influenced by the observer’s decision- making strategy.

Basic Principles of Sensation (Slide 2 of 2) Difference threshold is the smallest difference between two stimuli that can be detected half the time. Weber’s Law explains that to be noticed, two stimuli must differ by a constant minimum percentage rather than by a constant amount.

Sensory Receptors Sensory adaptation is the tendency for our sensory receptors to have decreasing responsiveness to stimuli that continue without change.

Vision (Slide 1 of 2) Light is a form of energy that travels in waves. Wavelength: the distance between two peaks of adjacent waves Cornea: clear membrane covering the front of the eyeball Iris: a ring of muscles that dilate the pupil Pupil: A hole in the center of the iris that regulates the amount of light entering the eye

Vision (Slide 2 of 2) Lens: a clear disk-shaped structure that focuses light Retina: a light-sensitive structure at the back of the eye where light is projected Rods: receptor neurons that detect black, white, and gray Cones: receptor neurons that detect color Optic nerve: a nerve bundle that carried information from the retina to the brain

Color Vision Trichromatic theory: three types of color receptors in the retina produce the primary color sensations red, green, and blue Color blindness: a deficiency in the ability to distinguish among colors Afterimage: visual images that persist after the image is removed Opponent-process theory: color perception depends on receptors that make opposing responses

Hearing (Slide 1 of 2) Sound waves: pressure changes in a medium caused by vibrations of molecules Cochlea: coiled, fluid-filled tube containing hair- like receptors Eardrum: membrane at the end of the ear canal that vibrates in sequence with sound waves

Hearing (Slide 2 of 2) Sound localization: the ability to locate objects on the basis of the sounds they make Place theory: different sound waves trigger the hair cells on different portions of the cochlea’s basilar membrane Frequency theory: pitch is determined by the frequency at which the basilar membrane vibrates Volley theory: neurons work in groups and alternate firing so frequency corresponds to sound wave frequency

Smell Olfaction: sense of smell Pheromones: airborne chemicals released and detected by animals; can affect behavior

Taste Gustation: sense of taste Taste buds: sensory receptors located on the tongue

Touch Sense of touch is a combination of three senses: Pressure: passive and dynamic touch Temperature: warm and cold receptors Gate-control theory of pain: small and large nerve fibers open and close gateways for pain

Perception (2) Gestalt: the mind organizing stimuli into a coherent whole Sensations organized into meaningful shapes and patters forms perception Figure-ground relationship: when people focus on an object in their perceptual field that automatically distinguishes it from its surroundings

Figure 4-15: Gestalt Laws of Grouping

Figure 4-14: Reversible Figure and Ground

Depth Perception Depth perception: ability to perceive objects three-dimensionally Binocular cues: depth cues which require information from both eyes Monocular cues: depth cues that require information from only one eye

Perceptual Constancy and Illusions Perceptual constancy: tendency to perceive objects as relatively stable despite continually changing information Perceptual illusions: misperception of reality Induces movement: illusory movement of a stationary object cased by the movement of another nearby object

Figure 4-21: The Müller-Lyer Illusion