Sensation and perception are parts of one continuous process.
Sensation:
Sensory receptors and nervous system receive and represent stimulus energies from our environment.
Senses receive sensory stimulation, transform it into neural impulses, and deliver this information to the brain.
Transduction
Conversion of one form of energy into another.
In sensation, it transforms stimulus energies (sights, sounds, smells) into neural impulses the brain can interpret.
Absolute Threshold
Minimum stimulus energy needed to detect a particular stimulus 50% of the time.
Tested by defining the point where half the time a stimulus is detected and half the time it is not.
Subliminal: Input below the absolute threshold for conscious awareness.
Priming: Activating associations in our mind, often unconsciously, setting us up to perceive, remember, or respond to objects or events in certain ways.
Basic Concepts
Difference threshold:
Minimum difference a person can detect between any two stimuli half the time.
Weber’s law:
For an average person to perceive a difference, two stimuli must differ by a constant minimum percentage (not a constant amount).
Subliminal Messages
Subliminal stimuli:
Too weak to detect 50 percent of the time; below the absolute threshold.
Subliminal sensation:
Exists, but such sensations are too fleeting to enable exploitation with subliminal messages.
Subliminal persuasion:
May produce a fleeting and subtle but not powerful or enduring effect on behavior (Greenwald, 1992).
Sensory Adaptation
Diminished sensitivity because of constant stimulation.
Aids focus by reducing background chatter.
Influences how the world is perceived in a personally useful way.
Perception
Perception: Brain organizes and interprets sensory information, enabling us to recognize objects and events as meaningful.
Bottom-Up vs Top-Down Processing
Bottom-up processing:
Begins with the sensory receptors and works up to the brain’s integration of sensory information.
Top-down processing:
Guided by higher-level mental processes.
Construct perceptions drawing on our experience and expectations.
Perceptual Set
Mental predisposition to perceive one thing and not another.
Affects top-down processing.
What determines our perceptual set?
Schemas organize and interpret unfamiliar information through experience.
Preexisting schemas influence top-down processing of ambiguous sensation interpretation, including gender stereotypes.
Influence of Motivation and Emotions
Walking destinations look farther away when we are fatigued.
Slopes look steeper when we are wearing a heavy backpack (or after listening to sad, heavy classical music).
Water bottles look closer when we are thirsty.
Perceiving Vision
Our eyes receive light energy and transduce (transform) it into neural messages.
Our brain then creates what we consciously see.
Wavelengths
Wavelength: distance from one wave peak to the next.
Hue: color experienced.
Amplitude: height.
Intensity: amount of contained energy; influences brightness.
Light Reflection
Components:
Pupil
Iris
Retina
Lens
Cornea
Blind spot
Fovea (point of central focus)
Optic nerve to brain's visual cortex
Rods and Cones
Cones are sensitive to detail and color.
Rods are sensitive to faint light.
Light energy triggers chemical changes in the rods and cones which activate the bipolar cells.
These cells then activate the ganglion cells of the optic nerve, which transmits the neural impulses from the eye to the brain.
Retinal Processing
Optic nerve: Carries neural impulses from the eye to the brain; highway from eye to brain.
Blind spot: The point at which the optic nerve leaves the eye, where no receptor cells are located.
Fovea: The central focal point in the retina, around which the eye’s cones cluster.
Eye must have three corresponding color receptor types, each sensitive to red, green, and blue wavelengths.
Color is seen when light stimulates these cones.
Color-deficient vision; colorblind.
Hering’s hypothesis (opponent-process theory):
Opposing retinal processes (red-green, blue-yellow, white-black) enable color vision.
Cones’ responses are then processed by opponent-process cells.
Afterimages.
Feature Detection
Specialized nerve cells in the brain respond to specific features of the stimulus, such as shape, angle, or movement.
Cells receive information from the ganglion cells in the retina and pass the information to other cortical areas, where teams of cells (supercell clusters) respond to more complex patterns.
Parallel Processing
Brain’s ability to do many things simultaneously.
Visual scene is first divided into subdimensions: form, depth, motion, perceptual constancy.
Grouping
Perceptual tendency to organize stimuli into coherent groups:
Proximity: Grouping nearby figures together.
Continuity: Perceiving smooth, continuous patterns, rather than discontinuous ones.
Closure: Filling in gaps to create a complete, whole object.
Depth Perception
Ability to see objects in three dimensions, although the images that strike the retina are two-dimensional.
Allows us to judge distance.
Is present, at least in part, at birth in humans and other animals.
Early 3-D Perception
Most infants refuse to crawl across the visual cliff.
Crawling, no matter when it begins, seems to increase an infant's fear of heights.
Cues for Depth
Two eyes help with perception of depth.
Binocular cues.
Depth cue (i.e., relative height and size available to either eye alone).
Monocular cues.
Perceptual Constancy
Objects are perceived as unchanging (having consistent color, brightness, shape, and size), even as illumination and retinal images change.
Color constancy: Seeing the color of familiar items as being constant.
Brightness constancy: Depends on context.
Shape constancy: Seeing that familiar items' shapes are constant.
Size constancy: Recognizing objects as being the same size despite changes in distance.
Sound
Sound Waves
Amplitude (height) determines intensity (loudness) in sound waves.
Intensity \propto Amplitude^2
Length (frequency) determines the pitch.
Pitch: Tone’s experienced highness or lowness (depends on frequency).
Sound is measured in decibels (dB).
Low frequency = long wavelength = low pitch.
f = \frac{v}{\lambda}, where f is frequency, v is wave velocity and \lambda is wavelength
Characteristics of Sound Waves
Bands of compressed and expanded air.
Human ears detect these changes in air pressure and transform them into neural impulses.
Brain decodes these changes as sound.
Vary in amplitude and frequency differing loudness differing pitch.
Waves and Sounds
The shorter the wavelength, the higher the frequency.
Wavelength determines the pitch of sound.
Wave amplitude influences sound intensity.
The Ear
Vibrating air (sound waves) enters the outer ear and passes through the auditory canal to the eardrum.
Middle ear: Amplifies the vibrations of the eardrum.
Cochlea: Contains nerve receptors.
Inner ear: Innermost part of the ear.
Decoding Sound Waves
Sound waves strike the eardrum, causing it to vibrate.
Tiny bones in the middle ear pick up the vibrations and transmit them to the cochlea.
Ripples in the fluid of the cochlea bend the hair cells lining the surface, which trigger impulses in nerve cells.
Axons from these nerve cells transmit a signal to the auditory cortex.
Hearing Loss
Sensorineural hearing loss (nerve deafness):
Damage to cell receptors or associated nerves.
Conduction hearing loss:
Damage to the mechanical system that conducts sound waves to the cochlea.
Cochlear implant:
A device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea.
Hearing Different Pitches (Theories)
Place theory:
Links the pitch heard with the place where the cochlea’s membrane is stimulated; best explains high pitches.
Frequency theory (temporal theory):
The rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling its pitch to be sensed; explains low pitches.
Sound Location
Sound waves strike one ear sooner and more intensely than the other.
From this information, the brain can compute the sound’s location.
Five Senses (Touch, Taste, Smell)
Touch
Sense of touch is a mix of four distinct skin senses:
Pressure
Warmth
Cold
Pain
Other skin sensations are variations of these basic four.
Cognition influences the sensory responses of the brain.
Pain
Biopsychosocial phenomenon that varies widely from group to group and person to person.
Influences of pain (biological, psychological, social-cultural).
Gate-control theory:
The spinal cord contains a neurological “gate” that either blocks pain signals or allows them to pass on to the brain.
Biopsychosocial Model & Pain
Biological influences:
Activity in spinal cord's large and small fibers
Genetic differences in endorphin production
The brain's interpretation of CNS activity
Psychological influences:
Attention to pain
Learning based on experience
Expectations
Social-cultural influences:
Presence of others
Empathy for others' pain
Cultural expectations
Senses: Taste (Gustation)
Involves several basic sensations.
Can be influenced by learning, expectations, and perceptual bias.
Has a survival function.
A chemical sense:
Sweet: Energy source
Salty: Sodium essential to physiological processes
Sour: Potentially toxic acid
Bitter: Potential poisons
Umami: Proteins to grow and repair tissue
Senses: Smell (Olfaction)
A chemical sense.
Olfactory receptor cells: Located in the olfactory bulb in the nose.
A combination of several odor molecules stimulates different receptors to detect them.
Patterns are interpreted by the olfactory cortex.
Gender, age, and expertise influence the ability to identify and remember scents.