Sensation & Perception

Chapter 4

Transduction

•

Transduction

: Transformation of one form of energy into another – especially the transformation of stimulus information into nerve impulses •

Receptors

: Specialized neurons that are activated by stimulation and transduce (convert) it into a nerve impulse •

Sensory pathway

: Bundles of neurons that carry information from the sense organs to the brain

Sensation and Perception

•

Sensation

: An early stage of perception in which neurons in a receptor create an internal pattern of nerve impulses that represent the conditions that stimulated it – either inside or outside the body •

Perception

: A process that makes sensory patterns meaningful and more elaborate • Stimulation  Transduction  Sensation  Perception

Sensory Adaptation

•

Sensory adaptation

: Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while • Examples???

Thresholds

• •

Absolute threshold

: Amount of stimulation necessary for a stimulus to be detected (50% of time)

Difference threshold

: Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND)

• •

Looking at the JND

Weber’s law

: The JND increases with the magnitude of the stimulus. – The JND is large when the stimulus intensity is high, and small when the stimulus intensity is low • TV (volume high – turn down a lot, volume low – turn down little) • Groceries (50 pound bag, add 1 lb., 25 pound bag, add .5 lb)

Steven’s power law

: – Used for wider array of stimuli (shock, temperature) – Fills in gaps left by Weber and Fechner

Signal Detection Theory

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Signal detection theory

: Perceptual judgment as combination of sensation and decision-making processes – based on each individual’s sensitivity and response criterion – Explanation example: holiday weekend on the interstate • False Alarm (brakes and no cop) • Hit (brakes and cop) • Miss (no brakes and cop) • Correct Rejection (no brakes and no cop) – Lowers response criterion and raises hit rates • Flawed merchandise off the assembly line, TSA putting weapons in bags – Cocktail Party Effect: when you hear your name across a room you will involuntarily switch attention to it

Subliminal Persuasion

• Studies have found that words flashed subliminally on a screen can “prime” a person’s later responses.

– scary faces activate amygdala.

• No controlled research has ever shown that subliminal messages delivered to a mass audience can influence people’s buying habits.

•

The Anatomy of Visual Sensation

Cornea  Cells  Pupil  Retina  Rods/Cones Ganglion Cells (Optic Nerve)  Bipolar

The Anatomy of Visual Sensation

• • • • • 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 • Dark adaptation: increased visual sensitivity that develops when it gets dark http://www.youtube.com/watch?v=x6Ua5d3wlA0 (6:32) Fovea: area of sharpest vision on the retina Optic nerve: Bundle of neurons that carries visual information from the retina to the brain Blind spot: Where the optic nerve exits the eye; there are no photoreceptors (money in bank demo)

•

Color Blindness & Afterimages

Color blindness

: Vision disorder that prevents an individual from discriminating certain colors –

Red –green most common

•

Afterimages

: Sensations that linger after the stimulus is removed – Flag activity

How the Visual System Creates Color

• • • • •

Visual cortex

: Part of the brain – the occipital cortex – where visual sensations are processed

Brightness

: Sensation caused by the intensity of light waves

Color

: Psychological sensation derived from the wavelength of visible light – color, itself, is not a property of the external world

Electromagnetic spectrum

visible light : Entire range of electromagnetic energy, including radio waves, X-rays, microwaves, and

Visible spectrum

: Tiny part of the electromagnetic spectrum to which our eyes are sensitive

How the Visual System Creates Brightness

Wavelength Color Intensity (amplitude) Brightness

Sensing Colors

• •

Trichromatic Theory

: Idea that colors are sensed by three different types of cones sensitive to light in the red, blue and green wavelengths.

– Explains the earliest stage of color sensation.

Opponent-process Theory

: Idea that cells in the visual system process colors in complimentary pairs, such as red or green or as yellow blue.

– Explains color sensation from the bipolar cells onward in the visual system.

Hearing: How Sound Waves Become Auditory Sensations Pinna  Bones  Ear Canal  Tympanic Membrane Oval Window   Middle Ear Cochlea (Basilar Membrane)  Auditory Nerve

Tympanic membrane

: The eardrum

Hearing: How Sound Waves Become Auditory Sensations

Cochlea

: Where sound waves are transduced

Hearing: How Sound Waves Become Auditory Sensations Cochlea

Basilar membrane

: Thin strip of tissue with hairs sensitive to vibrations

Hearing: How Sound Waves Become Auditory Sensations

Auditory nerve

: Neural pathway connecting the ear and the brain

Deafness

• •

Conduction deafness

: Results from damage to structures of the middle or inner ear – Disruption in converting sound into nerve energy

Nerve deafness

: Linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain – Usually involves the auditory nerve or higher auditory processing centers, but can be from life damage – Most born deaf have this

Hearing: The Physics of Sound

• Loudness: produced by the amplitude of a sound wave

- Amplitude

: Physical strength of a wave High Amplitude Low Amplitude

Hearing: The Physics of Sound

• Pitch: produced by the frequency of a sound wave –

Frequency

: Number of cycles completed by a wave in a given amount of time Low Frequency High Frequency

How Sound Waves Become Auditory Sensations •

Pitch:

–

Place Theory: different places on the basilar membrane send neural codes for different pitches

–

Frequency Theory: neurons have different firing rates for different sound wave frequencies

• •

Timbre

: Quality of a sound wave that derives from the wave’s complexity

Auditory cortex

: Portion of the temporal lobe that processes sounds

Position and Movement

• • •

Vestibular sense

: Sense of body orientation with respect to gravity http://www.youtube.com/watch?v=x6Ua5d3wlA0 (7:21)

Kinesthetic sense

: Sense of body position and movement of body parts relative to each other

Smell

• • •

Olfaction

: Sense of smell • Chemical sense, just like taste

Olfactory bulbs

: Brain sites of olfactory processing

Pheromones

: Chemical signals released by organisms to communicate with other members of the species

Smell

Taste

•

Gustation

: The sense of taste • Chemical sense

Taste buds

: Receptors for taste (primarily on the upper side of the tongue)

The Skin Senses and Pain

•

Gate-control Theory

: An explanation for pain control that proposes we have a neural “gate” that can, under some circumstances, block incoming pain signals.

•

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

• • The Machinery of Perceptual Processing

Percept

: Meaningful product of a perception •

Selective attention:

Focused awareness of only a limited amount of all you are capable of experiencing •

Feature detectors

: Cells in the cortex that specialize in extracting certain features of a stimulus

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 begins with the sense receptors and works up to the brain’s integration of sensory information; focuses on characteristics of stimuli, not internal concepts http://www.youtube.com/watch?v=x6Ua5d3wlA0 (50 seconds)

Top-down processing

: Analysis guided by higher-level mental processes - emphasizes perceiver's expectations, memories, and other cognitive factors http://www.youtube.com/watch?v=x6Ua5d3wlA0 (1:44)

Perceptual Constancies

•

Perceptual constancy

: Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location • Shape, color, size

Perceptual Ambiguity and Distortion

• •

Illusions

: Distortion of a stimulus pattern, shared by others in the same perceptual environment – More likely when: • stimulus is unclear • info is missing • elements combined in unusual ways • familiar patterns aren’t apparent

Ambiguous figures

: Images that are capable of more than one interpretation

The Gestalt Approach

• • •

Gestalt psychology

: View that much of perception is shaped by innate factors built into the brain – Nature view: programmed to find patterns – The whole pattern is greater than the sum of its parts.

Figure

: Part of a pattern that commands attention

Ground

: Part of a pattern that does not command attention; the background

The Gestalt Approach

•

Subjective contours

: Boundaries that are perceived but do not appear in the stimulus pattern •

Closure:

Tendency to fill in gaps in figures and see incomplete figures as complete

The Gestalt Laws of Perceptual Grouping

Proximity Similarity Closure Continuity Common Fate Prägnanz

Law of Prägnanz A BIRD IN THE THE HAND

Binocular Cues – two eye depth cues

• •

Binocular Convergence

: lines of vision from each eye converge at different angles on objects at different distances

Retinal Disparity

: difference in perspectives of the 2 eyes (greater disparity for nearby objects – provides us with depth information)

Monocular Cues – one eye depth cues

• Monocular Cues: –

Linear Perspective

: parallel lines appear to meet in the distance

Monocular Cues – one eye depth cues

• Monocular Cues: –

Relative Motion

: objects closer to you move faster than those further away from you

Monocular Cues – one eye depth cues

• Monocular Cues: –

Relative Size

: two objects the same size; if one appears larger then it’s closer to us

Monocular Cues – one eye depth cues

• Monocular Cues: –

Interposition

: hidden objects are more distant than those objects that hide them

Monocular Cues – one eye depth cues

• Monocular Cues: –

Texture Gradient

: as object gets further away from us, the texture gets smoother

Theoretical Explanations for Perception • •

Learning-based inference

: View that perception is primarily shaped by learning, rather than innate factors (nurture); opposite of Gestalt • Context, expectation and perceptual set

Perceptual set

: Readiness to detect a particular stimulus in a given context

Muller-Lyer Illusion

• When 2 objects make the same size image on the retina, and we judge one to be farther away than the other, we assume that the more distant one is larger.