1 sensation and perception chapter 5. 2 sensation and perception basic principles of sensation and...

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Sensation and Perception

Chapter 5

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Basic Principles of Sensation and Perception From Energy to Neural Impulse

Thresholds

Sensory Adaptation

Perceptual Set

Context Effects

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Vision Light Energy: From the Environment into the

Brain

The Eye Visual Information Processing

Visual Organization

Visual Interpretation

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The Nonvisual Senses Hearing

Touch

Pain

Taste

Smell

Body Position and Movement

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How do construct our representations of the world?

• Sensation: the process by which our sensory receptors and nervous system take in stimuli from the environment

• Perception: The process by which our brain organizes and interprets that information and interprets that information as meaningful objects and events

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From Energy to Neural Impulse

The senses…– Receive sensory stimulation– Transform that stimulation into neural

impulses (transduction)– Deliver the neural information to the brain

Tranduction: the process of converting one form of energy into another; in this case, from photons and sound waves into neural signals.

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Which stimuli do we sense? • We are ignorant of many stimuli

– X-rays, radio waves, ultraviolet and infrared light

– Very high and very low frequency sounds

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How much stimuli does it take to have a sensation?

• Absolute threshold: minimum stimulation needed to detect a particular stimulus 50% of the time

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Detecting Stimuli, Finding Thresholds

Audiologists can find the volume level you can detect 50% of the time for a given frequency.

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Thresholds

• Difference threshold: the minimum difference between two stimuli required for detection 50% of the time– For example, parents needs to distinguish their own

child’s voice from others

• Weber’s Law: to be perceived as different, two stimuli must differ by a constant minimum proportion (rather than a constant amount)

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Weber’s Law

By what proportion must different types of stimuli differ to be perceived as different?

Stimulus Constant

Light (intensity)

8%

Weight 2%

Tone (frequency)

0.3%

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Sensory Adaptation

• Sensory adaptation: reduced sensitivity in response to constant stimulation– We eventually cease to notice a room’s bad

smell after we’ve been there for a while

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Perceptual Set

• The perceptual set is a mental predisposition to perceive one thing rather than another

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Context Effects: Culture and Cues

Box and tree? Window and column?

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Vision Light Energy: From the Environment Into

the Brain

The Eye

Visual Information Processing

Visual Organization


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Visible Light

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Light Energy: From the Environment into the Brain

• Light’s wavelength determines its hue, the color we experience.

• The amplitude, or height, determines the light’s intensity.

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Visible Light

• Other organisms see different portions of the light spectrum. For example, bees cannot see red, but can see ultraviolet.

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The Eye

• The retina, on the inner surface of the eye contains the photoreceptors (rods and cones) plus neurons that begin the processing of visual stimuli.

• Light is inverted by the lens, and is interpreted by the brain as upright vision

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The Eye

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Test Your Blind Spot

• There are no receptor cells where the optic nerve leaves the eye, creating a blind spot

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The Retina: Rods and Cones

• Rods detect blacks, whites, and grays, and are necessary for peripheral and twilight vision

• Cones are clustered near the center of the retina, they detect fine detail and allow color vision •

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Differences Between Rods and Cones

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• How does the brain turn light stimuli into useful information about the world?

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Visual Information Processing: The Crossover

Information from the right visual field goes to the left hemisphere, information from the left visual and vice

versa.

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Feature Detection

• The visual cortex contains specialized feature detection cells, which respond to specific features– Such as edges, lines, and angles

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Parallel Processing

• The brain uses parallel processing to assign different teams of cells to simultaneously process many aspects of scene or problem

• “

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Visual Organization

• How do we organize and interprets the shapes and colors into meaningful perceptions?

• People have the tendency to organize pieces of information into an organized whole, or gestalt.

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Gestalt Principles

• Our brain does more than just register information about the world. We filter incoming information and we construct perceptions.

• Over the years, Gestalt psychologists have identified principles we use to organize our sensations into perception.– Form perception – Depth perception – Perceptual constancy

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Form Perception

• How do we know where one object begins and another ends? – Figure-ground: organization of visual field

into objects that stand out from their surroundings

– Grouping: the perceptual tendency to organize stimuli into meaningful groups

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Figure and Ground

• When seeing or hearing a scene, we identify figures, objects and events that stick out and hold our attention against the background. Example: following one conversation at a party.

• To the right: a scene with two options for seeing figures. Arrows? People?

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Grouping: Seeing Gestalts/Wholes

• Our minds use these grouping strategies to see patterns and objects

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Depth Perception

• Although the images that strike the retina are two dimensional, depth perception allows us to create mental images of objects in 3-D, and to judge distance

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The Visual CliffEleanor Gibson and Richard Walk (1960)

• Test of early 3-D perception

• Most infants refuse to crawl across the visual cliff. Depth cue: Pattern on floor

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Seeing Depth: Binocular Cues

• Binocular cues: Our two eyes help us perceive depth

• Retinal disparity: By comparing images from the two eyeballs, the brain can calculate the distance – the greater the disparity, the close the object – Used by 3-D film makers

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Monocular Cues

• Retinal disparity can differentiate between 1 and 10 feet away, but not between 10 and 100 feet

• As such, we must rely on monocular cues, depth cues available to either eye alone

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Monocular Cues

Light and Shadow

A

A A rotated 180 degrees

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Linear Perspective

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Perceptual Constancy

• Things look different depending on the angle, distances, and lighting. How do we generate perceptual constancy, perceiving objects as unchanging?

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• Color constancy: we perceive familiar objects as having consistent color, even if changing illumination alters the reflected wavelengths

• Below is the same process, opposite effect: The color with the same wavelength is perceived as brighter in the shadows.

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Shape and Size Constancy

• We perceive the shape of objects as constant while our retinas receive changing images

• We perceive the size of an object as constant from different distances

• However, context matters: consider the Moon illusion

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• Is our perceptual knowledge inborn?

• Or do we learn to perceive the world through our experiences?

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• Is our perceptual knowledge inborn?

YES, to some extent. We come equipped to process sensory information

• Or do we learn to perceive the world through our experiences?

YES, to some extent. For example, we learn to associate distance with size.

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Experience and Visual Perception

• What does research reveal about the effects of experience on perception?

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Sensory Deprivation and Restored Vision

• Some adults were born blind (clouded lenses from cataracts) then had surgery to remove cataracts– Patients could sense colors

• but, they could not visually recognize objects

• infant kittens and monkeys wore translucent goggles from birth– later they could not detect shape

• In both cases, the retinas still sent signals to the brain, but visual cortex had not developed its normal associations

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Perceptual Adaptation

• We can adapt to an artificially displaced or inverted visual field

• George Stratton (1896) wore goggles that flipped images upside down and backwards

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The Nonvisual Senses Hearing (or audition)

Touch

Pain

Taste

Smell


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Hearing

The Stimulus Input: Sound Waves

Sound waves are compressing and expanding air molecules.

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Sound Characteristics• As with light waves, amplitude (height)

determines intensity (loudness)

• Compression frequency: Low frequency = long wavelength = low pitch

• Sound is measured in decibels (dB)– 0 dB is the absolute threshold (not the absence of

sound, just less than we can hear)– 60 dB is normal conversation– 85+ dB: prolonger exposure can cause hearing loss

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Decoding Sound Waves

1. Sound waves strike the ear drum, causing it to vibrate

2. Tiny bones in the middle ear pick up the vibrations and transmit them to the cochlea, a coiled, fluid-filled tube in the inner ear

3. Ripples in the fluid of the cochlea bend the hair cells lining the surface, which trigger impulses in nerve cells

4. Axons from these nerve cells transmit a signal to the auditory cortex

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The Ear is Sensitive!

• A neural response is triggered when the tiny bundles of cilia on top of even one of the 16,000 hair cells on the cochlea are moved even the width of an atom!

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How Do We Locate Sounds?

The placement of our two ears helps us in two ways. Sounds to the closer ear…

1. Are more intense

2. Arrive sooner

That’s why it’s hard to tell if a sound is directly behind or in front of you

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TouchOur “sense of touch” is actually a mix of four distinct skin senses: – Pressure– Warmth– Cold– Pain

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Pain

• Pain is your body’s way of saying “something has gone wrong”

• No one type of stimulus produces pain. At low intensities, the same stimulus that produces pain can cause other sensations, such as warmth or coolness, roughness or smoothness.

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Controlling Pain• Pain is where body meets mind• Built-in controls: endorphins + distraction• Virtual reality distraction helps a burn victim feel

less pain (below)• Pain is a combination of body and mind

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Hypnosis and Pain Relief

• Hypnosis: a social interaction in which one person suggests to another that certain thoughts, feelings, perceptions, or behaviors will spontaneously occur– Useful for relieving pain

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Taste

•Traditionally, taste sensations consisted of sweet, salty, sour, and bitter tastes. •Some have claimed that there is a fifth taste called umami.

• But most sensory psychologists say--nay

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Tastes Exist for a Purpose

[Insert table 5.2]

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Taste Is A Chemical Sense

• Inside each little bump on the top and sides of the tongue are 200+ taste buds

• Each bud contains a pore with 50-100 taste receptors, each of which react to different types of food molecules and send messages to the brain

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Taste is Psychological

• Perceptual bias can influence taste– People thought a $10 bottle of wine tasted better

when told it cost $90

• Sensory interaction: one sense may influence anotherSmell + texture + taste = flavor

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Other Examples of Sensory Interaction

• A person with hearing loss can “hear” a video when subtitles are include

• People are more likely to rate someone as “warm” and treat them more generously after holding a warm vs. a cold drink

Seeing a face forming words helps someone hard of hearing to understand spoken words

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Smell

• Like taste, smell is a chemical sense– Smell occurs when molecules in the air reach

the cluster of 5 million olfactory receptor cells at the top of each nasal cavity

• There are hundreds of different receptors– Different combinations of receptors identify

different smells

• Odors can evoke strong memories

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Taste, Smell, and Memory

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• Kinesthesis: The system for sensing the position and movement of individual body parts– Interacts with vision

• Vestibular sense: the sense of body movement and position, including the sense of balance

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Where Sensory Information Goes

•Sensory nerves carry sensory information to the brain.

• where it is processed to form perceptions.

1 sensation and perception chapter 5. 2 sensation and perception basic principles of sensation and...

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