Introductory Psychology

Introductory Psychology
Chapter 4
Sensation and Perception
How We Sense and Conceptualize the World
Sensation and Perception
Sensation is the detection of physical energy by our sense organs, which send that information to the brain.
Perception is the brain’s interpretation of raw sensory data.
Sensation
Despite their differences, all our senses rely on a handful of principles.
The external stimulus is converted by a sense receptor into neural activity via transduction.
Activation is highest when stimulus is first detected, then sensory adaptation occurs.
Psychophysics
Study of how we perceive sensory stimuli based on their physical characteristics
Absolute threshold is the lowest level of a stimulus we can detect 50% of the time
A single candle 30 miles away
50 odorant molecules
The just noticeable difference is the smallest amount of stimulus change we can detect.
Weber’s law—the stronger the stimulus, the greater the change necessary for the detection of a difference.
Signal Detection Theory
Theory regarding how stimuli are detected under different conditions
Cross-Modal Effects
Phosphenes, the McGurk effect, and the rubber hand illusion all demonstrate sensory cross-modality.
This may help to explain synesthesia—the experience of cross-modal sensations, like hearing sounds when one sees colors.

The Role of Attention
Selective attention allows us to choose which sensory inputs to focus on and which to “turn down.”
The other “channels” are still being processed at some level, though.
Cocktail party effect
We’re poor at detecting stimuli in plain sight if our attention is focused elsewhere.
Inattentional blindness and change blindness are two similar phenomena.
Blinding Problem
One of the great mysteries of psychology is just how our brains combine all the various stimuli around us into a coherent whole.
The look, feel, smell, and taste of an apple all rely on different areas of the brain to process, but we just see an apple!
Light
The human visible spectrum is a narrow band of light that we respond to.
Other animals may have a more restricted or broader spectrum.
The Visible Spectrum Is a Subset of the Electromagnetic Spectrum. Visible light is electromagnetic energy between ultraviolet and infrared. Humans are sensitive to
wavelengths ranging from slightly less than 400 nanometers (violet) to slightly more than 700 nanometers (red).
We perceive brightness (intensity) and hue (color).
Mixing lights produces white (additive).
Mixing pigments produces black (subtractive).
Additive and Subtractive Color Mixing. Additive color mixing of light differs from subtractive color mixing of paint.
The Eye
Sclera is the white portion of the eye
Iris is the colored portion and controls how much light enters the eye
Pupil is the hole where light enters the eye
Cornea contains transparent cells that focus light on the back of the eye
The lens changes curvature (accommodation) to retract light onto back of eye.
Glasses change the way light enters the eye to help correct myopia or hyperopia.
The Retina
The retina is a thin membrane at the back of the eye.
The fovea in its center is responsible for acuity.
Light hits two types of sense receptors on the retina—rods and cones.
Dark adaptation
The Key Parts of the Eye
The Eye
The optic nerve exits the back of the eye and is composed of the axons of the ganglion cells.
Causes a blind spot
Most of the axons go to the thalamus and then the visual cortex, but some go to midbrain.
Perception and the Visual Cortex – Visual information from the retina travels to the visual thalamus. Next, the visual thalamus sends inputs to the primary visual
cortex (V1), then along two visual pathways to the secondary visual cortex (V2; see p. 136 ). One pathway leads to the parietal lobe, which processes visual form,
position, and motion; and one to the temporal lobe, which processes visual form and color.
Perceiving Shape and Contour
Different cortical cells respond maximally to different types of stimuli.
Feature detector cells allow us to detect lines and edges.
Simple cells—detect orientation-specific slits of light in a particular location
Complex cells—also orientation-specific, but less dependent on location than simple cells
Color Perception
Different theories of color perception explain different aspects of our ability to detect color.
Trichromatic theory says color vision is based on our sensitivity to three primary colors.
Consistent with three types of cones in eyes
Explains color blindness
Opponent process theory sees color vision as a function of complementary, opposing colors: red v. green or blue vs. yellow.
As an example, stare at the white dot in the middle of the flag on the next slide see what happens.
Opponent Processes in Action. Find a patch of blank white wall or place a blank sheet of white paper nearby before you begin. Then relax your eyes and fix your gaze on
the white dot in the image above for at least 30 seconds without looking around or away. Afterward, stare at the white wall or paper for a few seconds. What do you
see?
When We Can’t See
Blindness—results in heightened touch, reorganization of visual cortex
Blindsight—above-chance visual performance of cortically blind individuals with damage to area V1
Visual agnosia—object recognition deficit; damage to higher visual cortical areas
Hearing and Sound
Audition (our sense of hearing) is the sense we rely on most after sight.
Sound is simply vibration traveling through a medium (usually air) and has:
Pitch—wave frequency (Hz)
Loudness—amplitude of the sound waves (dB)
Timbre—complexity of sound
The Ear
The outer, middle, and inner ear do different jobs to transduce sound into neural activity.
The outer ear (pinna and ear canal) tunnels sound waves onto the eardrum.
On the other side of the eardrum, the ossicles (hammer, anvil, stirrup) vibrate and transmit sound to the inner ear.
In the inner ear, the cochlea converts vibration into neural activity.
The organ of Corti and basilar membrane convert auditory information into action potentials.
The Human Ear and Its Parts. A cutaway section through the human ear and a close-up diagram of the hair cells.
Pitch Perception
Place theory – Different tones excite different areas of the basilar membrane and primary auditory cortex. Explains perception of high-pitched tones
Frequency theory and volley theory – Neurons’ rate of firing reproduces the frequency of the sound. Explains perception of low and middle pitches
Smell and Taste
Olfaction (smell) and gustation (taste) work hand in hand. Work together to enhance liking or disliking of some foods. Described as the “chemical senses”
Odors and Flavors
Odors are airborne chemicals that interact with lining in our nasal passages.
We are sensitive to five basic tastes:
Sweet, salty, sour, bitter, umami
There is some evidence for a “fatty” taste as well.
Smell and Taste Sense Receptors
Each olfactory neuron contains a single type of receptor, which recognizes odorants based on their shape.
The tongue contains separate taste buds for each basic taste.
25% of people are supertasters, with more taste buds.
Olfactory and Gustatory Perception
Although they take different paths, our smell and taste senses converge in the orbitofrontal cortex.
Smell and Taste. Our senses of smell and taste enter the brain by different routes but converge in the orbitofrontal cortex.
Our Body Senses
Three body systems that work in tandem:
Somatosensory (touch and pain)
Proprioception (kinesthetic sense – body position)
Vestibular sense (equilibrium and balance)

Somatosensory System – Responds to pressure, temperature, and injury. We sense these with specialized nerve endings in the skin and with free nerve endings.
The Sense of Touch. The skin contains many specialized and free nerve endings that detect mechanical pressure, temperature, and pain.
Somatosensory Pathways – Somatic nerves carry info to spinal cord -> Spinal reflexes may be activated -> Connects in brain stem, thalamus -> Touch: somatosensory,
association cortices -> OR -> Pain: somatosensory cortex, limbic areas
Pain Sensations
Pain comes in many types, usually related to the pain-causing stimulus.
Gate control model – pain is blocked from consciousness by neural mechanisms in the spinal cord.
Pain is influenced by emotional and cultural factors.
Body Position and Balance
Proprioception, our kinesthetic sense, helps us keep track of where we are, allowing us to move efficiently.
Muscle stretch receptors vs. tendon force detectors
Vestibular sense, our sense of equilibrium, enables us to sense and maintain our balance as we move about.
Due to three fluid-filled semicircular canals in the inner ear. Our awareness of this sense is limited.
Ergonomics: Human Engineering
Human factors – field that optimizes technology to better suit our sensory and perceptual capabilities. Uses what we know about psychology and sensory systems to build
more ergonomic gadgets and tools.
When Senses Meet the Brain
After being transduced, our brains then organize the sensory data into meaningful concepts.
Our brains piece together:
What’s in our sensory field
What was there a moment ago
What we remember from our past

The Multitasking Brain
We attend to multiple senses at once, called parallel processing.
Bottom-up vs. top-down processing
Perception depends on sensory data and beliefs/expectations.
What Do You See? Due to the influence of top-down processing, reading the caption “saxophone player” beneath this ambiguous figure tends to produce a different
perception than reading the caption “woman.”
Perceptual Hypotheses
Perceptual sets occur when our expectations influence our perceptions.
Perceptual constancy allows us to perceive stimuli consistency across conditions.
We don’t see the size, shape, or color of an object changing despite the objective fact that they do.
Color perception in particular derives from context.
Shape Constancy – We perceive a door as a door whether it appears as a rectangle or a trapezoid.
The Checker-Shadow Illusion – We perceive a checkerboard pattern of black and white alternating squares, and because of color constancy, we ignore the dramatic change
due to the shadow cast by the green cylinder. Believe it or not, the A and B squares are identical. (Source: © 1995 Edward H. Adelson)
Color Perception Depends on Context- Gray can appear like a color depending on surrounding colors. The blue-colored squares on the top of the cube at the left are
actually gray (see map below the cube). Similarly, the yellow-colored squares on the top of the cube at the right are actually gray (see map below the cube). (Source:
© Dale Purves and R. Beau Lotto, 2002)
Gestalt Principles
Rules that govern how we perceive objects as wholes within their overall context
Gestalt Principles of Perception- As Gestalt psychologists discovered, we use a variety of principles to help us organize the world.
Face Perception
Depends on neurons in the lower part of the temporal lobe and in the hippocampus. Though some neurons respond selectively to specific faces, face perception depends on
broad neural networks.
Motion Perception
To determine motion, the brain compares visual frames of what is to what was.
Phi phenomenon
Motion blindness—inability to perceive seamless motion
Localizing Sound
We rely on binaural cues to tell us where sounds are coming from. These cues include differences between the two ears in the timing and intensity of sound waves.
Depth Perception
Monocular depth cues rely on one eye:
Relative size, texture gradient, interposition, linear perspective, height in plane, light and shadow
Binocular depth cues require both eyes.
Binocular disparity and binocular convergence
When Perception Deceives Us
We often misperceive information around us and understanding why provides insight into how we make sense of our surroundings.
Examples of such misperception include the moon illusion; the Ames room; and the Muller-Lyer, Ponzo, vertical-horizontal, and Ebbinghaus illusions.
Subliminal Perception
We process many sensory inputs unconsciously and many of our actions occur with little to no forethought or deliberation. If we can detect stimuli without knowing it,
does that change our behavior?
The processing of sensory information that occurs below the level of conscious awareness
Can have a brief, short-term impact on behaviors and attitudes
Effect disappears when subjects are aware of or suspect subliminal influences
Subliminal Persuasion
Fairly unlikely to produce large-scale or enduring changes in attitudes or decisions
Subliminal self-help tapes have been shown to be ineffective.
Reversed subliminal messages are also ineffective.
Extrasensory Perception
The perception of events outside the known channels of sensation
According to parapsychologists, there are three major types:
Precognition
Telepathy
Clairvoyance
Evidence for ESP
Early studies by Rhine (1934) using Zener cards reported positive results.
But, methodological problems plagued the study and no one could replicate his results.
Ganzfield technique studies, fMRI studies, and others all fail to find positive effects for ESP.
ESP proponents explain away negative findings, citing such factors as experimenter effects.
These are ad-hoc explanations, though
Why People Believe
Over 40% of American adults believe in ESP.
Why?
Illusory correlations
Not understanding chance events
Underestimating the likelihood of coincidences
The “Birthday Paradox.” As we reach a group size of 23 people, the probability that at least two people share the same birthday exceeds 0.5, or 50 percent. Research
demonstrates that most people markedly underestimate the likelihood of this and other coincidences, sometimes leading them to attribute these coincidences to
paranormal events.
Failed Psychic Predictions
Specific predictions (“Nazi flag found on moon!”) do not come true.
So “psychics” use other methods to make it seem as if they are accurate.
Multiple end points
Cold reading techniques

FOR YOUR ASSIGNMENTS TO BE DONE AT A CHEAPER PRICE PLACE THIS ORDER OR A SIMILAR ORDER WITH US NOW