Chapter 4 Sensation Perception Sensation The process by

Chapter 4 Sensation & Perception

Sensation • The process by which stimulation of a sensory receptor produces neural impulses that the brain interprets as sound, a visual image, an odor, a taste, a pain, or other sensory images. • The registration of information.

Perception • A process that makes sensory patterns meaningful.

How Do We Interpret Sensations? • STIMULUS - energy that affects what we do. • RECEPTORS – specialized cells that convert environmental energies into signals for the nervous system.

How Does Stimulation Become Sensation? The brain senses the world indirectly because the sense organs convert stimulation into the language of the nervous system: neural impulses.

Transduction Transformation of one form of energy into another – especially the transformation of stimulus information into nerve impulses.

Sensory pathways – Bundles of neurons that carry information from the sense organs to the brain.

Sensory Adaptation • Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while.

Thresholds • Absolute threshold – Amount of stimulation necessary for a stimulus to be detected. • Difference threshold – Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND).

Approximate absolute thresholds for the 5 senses: • Vision - Candle flame seen at 30 miles on a clear, dark night. • Hearing - Tick of a watch under quiet conditions at 20 feet. • Taste - 1 Teaspoon of sugar in 2 gallons of water. • Smell - 1 Drop of perfume diffused into a threeroom apartment. • Touch - A bee's wing falling on your cheek from 1 centimeter above.

Thresholds • Weber’s law – The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low.

Signal Detection Theory • Signal detection theory – Perceptual judgment as a combination of sensation and decision-making processes. Stimulus event Neural activity Comparison with personal standard Action (or no action)

Subliminal Persuasion • Studies have found that subliminal words flashed briefly on a screen can “prime” a person’s later responses. • No controlled research has ever shown that subliminal messages delivered to a mass audience can influence people’s buying habits.

THE EYE Video

The Structure of the EYE • PUPIL – an adjustable opening in the eye through which light enters. • IRIS – the colored structure on the surface of the eye.

The Structure of the EYE • CORNEA – a rigid transparent structure on the outer surface of the eyeball. • LENS – a flexible structure that can vary in thickness, enabling the eye to accommodate.

The Structure of the EYE • RETINA – a layer of visual receptors covering the back surface of the eyeball.

Visual Sensation Retina: Photoreceptors – Light-sensitive cells in the retina that convert light energy to neural impulses. Rods – Sensitive to dim light but not colors. Cones – Sensitive to colors but not dim light. Fovea – Area of sharpest vision in the retina.

Visual Receptors • Cones – color vision – daytime – detailed • 5 -10% of visual receptors in the retina are cones • 7 million

Visual Receptors • Rods – night vision – black and white • 125 million

Interactive

The Visual Pathway Optic nerve – Bundle of neurons that carries visual information from the retina to the brain.

The Visual Pathway • Blind spot – The point where the optic nerve exits the eye and where there are no photoreceptors. DO IT YOURSELF! page 122

Review from Chapter 3!!! In which area of the brain are visual signals processed? ? ?

Answer: • VISUAL CORTEX Part of the brain in the occipital lobe where visual sensations are processed.

Neural Pathways in the Human Visual System

How the Visual System Creates Color • Electromagnetic spectrum – Entire range of electromagnetic energy, including radio waves, X -rays, and visible light. • Visible spectrum – Tiny part of the electromagnetic spectrum to which our eyes are sensitive.

How the Visual System Creates Brightness Wavelength Intensity (amplitude) Color Brightness

Trichromatic Theory • The idea that colors are sensed by 3 different types of cones; explains the earliest stage of color sensation. • Blue • Green • Red

Opponent-Process Theory • We perceive color not in terms of independent colors but in terms of a system of paired opposites. • Red vs. Green • Yellow vs. Blue • White vs. Black

Afterimages • Sensations that linger after the stimulus is removed. • Most often called negative afterimages • Try the activity on page 121

Color Blindness • Vision disorder that prevents an individual from discriminating certain colors.

Red-Green Colorblindness • Difficulty distinguishing red from green and either red or green from yellow.

The Camera • When you look at an object, light rays are reflected from the object and enter the eye through the pupil. • The light rays are bent, refracted and focused by the lens. The lens' job is to make sure the rays come to a sharp focus on the retina. The resulting image on the retina is upside-down. • Here at the retina, the light rays are converted to electrical impulses which are then transmitted through the optic nerve, to the brain, where the image is translated and perceived in an upright position!

Hearing

Hearing • The Physics of Sound Amplitude – Physical strength of a wave. High Amplitude Low Amplitude

Hearing • The Physics of Sound Frequency – Number of cycles completed by a wave in a given amount of time, usually a second. Low Frequency High Frequency

Hearing • Hertz (Hz) – unit of frequency representing one cycle (vibration) per second.

How Sound Waves Become Auditory Sensations Tympanic membrane – The eardrum

How Sound Waves Become Auditory Sensations Cochlea – Where sound waves are transduced

How Sound Waves Become Auditory Sensations Cochlea Basilar membrane – Thin strip of tissue sensitive to vibrations

How Sound Waves Become Auditory Sensations Auditory nerve – Neural pathway connecting the ear and the brain

Review from Chapter 3!!! In which area of the brain are auditory signals processed? ? ?

Answer: • Auditory cortex – Portion of the temporal lobe that processes sounds.

ANSWERS • • • (a) outer ear (pinna) (b) ear canal (c) eardrum (d) hammer, anvil, and stirrup (e) cochlea (f) auditory nerve

The Psychology of… • Pitch – Sensory characteristic of sound produced by the frequency of the sound wave. • Loudness – Sensory characteristic of sound produced by the amplitude (intensity) of the sound wave. Video Clip • Timbre – Quality of a sound wave that derives from the wave’s complexity.

Hearing Loss • Conduction Deafness – An inability to hear resulting from damage to structures of the middle or inner ear.

Hearing Loss • Nerve Deafness – An inability to hear that is linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve.

The Senses: Smell, Taste, & Touch

Position and Movement • Vestibular sense – Sense of body orientation with respect to gravity. – Tells us how our bodies are positioned. – Movement and motion. 3 semicircular canals

Position and Movement • Kinesthetic sense – Sense of body position and movement of body parts relative to each other. – Makes you aware when you are crossing your legs. – Provides constant sensory feedback.

Olfaction • Sense of smell. • Smell can influence mood, memory, emotions, mate choice, and the endocrine system (hormones).

Olfaction • Olfactory bulbs – Brain sites of olfactory processing.

Olfaction

Taste • Gustation – The sense of taste. Taste buds – Receptors for taste (primarily on the upper side of the tongue)

Taste Receptors • • Sweet Salty Sour Bitter – Umami • Savory sensation

TASTE & SMELL • Our sense of smell is responsible for about 80% of what we taste. • All other flavors that we experience come from smell. This is why, when we have a cold, most foods seem bland or tasteless. • Our sense of smell becomes stronger when we are hungry.

The Skin Senses • • • Touch Warmth Cold Texture Pain

Review from Chapter 3!!! Sensory information related to the skin senses is processed within which part of the brain? ? ?

Answer: • SOMATOSENSORY CORTEX

Pain Gate-control theory • An explanation for pain control that proposes we have a neural “gate” that can, under circumstances, block incoming pain signals.

Pain • Placebos – Substances that appear to be drugs but are not. • Placebo effect – A response to a placebo caused by subjects’ belief that they are taking real drugs.

What is the Relationship Between Perception and Sensation? Perception brings meaning to sensation, so perception produces an interpretation of the external world, not a perfect representation of it.

Perception and Sensation? • Percept – Meaningful product of a perception. • What we perceive.

The Machinery of Perceptual Processing • Feature detectors – Cells in the cortex that specialize in extracting certain features of a stimulus.

The Machinery of Perceptual Processing • Binding problem – A major unsolved mystery in cognitive psychology, concerning the physical processes used by the brain to combine many aspects of sensation to a single percept.

Bottom-Up and Top-Down Processing • Bottom-up processing – Analysis that emphasizes characteristics of the stimulus, rather than internal concepts (stimulus-driven processing). • Top-down processing – Emphasizes perceiver's expectations, memories, and other cognitive factors (conceptually-driven processing).

Perceptual Constancy • Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location. Size Color Shape

ILLUSIONS • An incorrect experience of a stimulus pattern, shared by others in the same perceptual environment. Muller-Lyer Illusion

Ponzo Illusion

Muller-Lyer Illusion

Ambiguous Figures • Images that are capable of more than one interpretation.

Gestalt Psychology The whole is greater than the sum of its parts.

The Gestalt Approach • Gestalt psychology – An approach to psychology that seeks to explain how we perceive overall patterns. • Figure – Part of a pattern that commands attention. • Ground – Part of a pattern that does not command attention; the background.

The Gestalt Approach • Closure – Tendency to fill in gaps in figures and see incomplete figures as complete.

The Gestalt Laws of Perceptual Grouping Similarity Proximity Continuity Common fate Prägnanz

The Gestalt Approach • Similarity – we tend to group similar objects together in our perceptions.

The Gestalt Approach • Proximity – we tend to group objects together when they are near each other.

The Gestalt Approach • Continuity – we prefer perceptions of connected and continuous figures to disconnected and disjointed ones.

The Gestalt Approach • Common Fate – we tend to group similar objects together that share a common motion or destination.

The Gestalt Approach • Law of Prägnanz – The simplest organization, requiring the least amount of cognitive effort, will emerge as the figure. A BIRD IN THE HAND

Depth Perception • Visual Cliff Experiment • Develops around 6 months of age

Depth Perception • Binocular cues – information taken in by both eyes that aids in depth perception, including convergence and retinal disparity.

Depth Perception • Monocular Cues – information about depth that relies on just one eye; includes relative size, light and shadow, interposition, relative motion, and atmospheric perspective.

Theoretical Explanations for Perception • Learning-based inference – View that perception is primarily shaped by learning, rather than innate factors. • Perceptual set – Readiness to detect a particular stimulus in a given context.

End of Chapter 4