Chapter 4: Sensation & Perception

Chapter 4: Sensation & Perception

1. Psychophysics:Basic Concepts & Issues

   • Psychophysics
     •  is the study of how physical stimuli are translated into psychological experience.
     • Gustav Fechner(1860)
       • Wanted to know: For any given sense, what is the weakest detectable stimulus?
     • Thresholds: Looking for limits
       • Stimulus
         • Any detectable input from the environment.  subjectable...
       • Threshold
         • - is a dividing point between energy levels that do and do not  have a detectable effect.
         • Absolute Threshold
           • -an absolute threshold for a specific type of sensory input is the minimum amount of stimulation that an organism can detect. -define the boundaries of an organism's sensory capabilities. -stimulus intensity increases, subject's probability of responding to stimuli gradually increases
           • stimulus intensity detected 50% of the time
       • Just Noticeable Difference (JND)
         • - is the smallest difference in the amount of stimulation that a specific sense can detect.
         • JND varies by sense
         • Weber's Law
           • -states that the size of the Just Noticeable Difference is a constant proportion of the size of the initial stimulus. -this constant proportion is called the WEBER FRACTION
     • Signal Detection Theory
       • -proposes that the detection of stimuli involves decision processes as well as sensory processes, which are both influenced by a variety of factors besides stimulus intensity.
       • Detectability
         • - is measured in terms of probability and depends on decision making processes as well as sensory processes
         • Hits
           • detecting signals when they are present
         • Misses
           • failing to detect signals when they are present
         • False Alarms
           • detecting signals when they are not present
         • Correct Rejections
           • not detecting signals when they are absent
       • "Noise" in the system
         • -performance will also depend on the level of "noise" in the system. -Noise comes from all of the irrelevant stimuli in the environment and the neural activity they elicit. -analogous to background static on the radio station.
     • Subliminal Perception
       • - The registration of sensory input without conscious awareness. -LIMEN is another term for threshold, so subliminal means below threshold
       • stimulation generally produces weak effects.
     • Sensory Adaptation
       • - is a gradual decline in sensitivity due to prolong stimulation
       • is automatic
         • - is a built in process that keeps people tuned into the changes rather than the constants in their sensory input.
       • Focus on change in the environment that may signal threats to saftey.

2. Our Sense of Sight:the Visual System

   • The Stimulus:Light
     • For people to see, there MUST be Light
       • Lightwaves
         • Amplitude (height)
           • affects perception of brightness
         • Wavelength(distance between peaks)
           • affects perception of color
         • Purity influences perception of saturation or richness of color
           • How varied the mix of light waves is.
   • The Eye: A Living Optical Instrument
     • 2 Main Purposes
       • Channel light to the neural tissue that receives it (retina)
       • they house that tissue
     • light enters the eye through the CORNEA
       • -the cornea and lens(located behind it) form an upside down image of objects on the retina.
       • LENS focuses the light rays falling on the retina
         • capable of adjustments that facilitate a process called ACCOMMODATION. -Accommodation occurs when the curvature of the lens adjusts to alter visual focus.
         • IRIS is the coloured ring of muscle around the pupil
           • PUPIL is the opening in the centre of the iris
             • - it helps regulate the amount of light passing into the rear chamber of the eye -it constricts to let less light into the eye but sharpens the image falling on the retina -it dilates to let more light in but the image is less sharp.
             • Saccades
               • When we are looking at something, our eyes are scanning the visual environment and making brief fixations at various parts of the stimuli these movements are saccades.
               • See parts of the eye diagram on pg 135
   • The Retina: The Brain's Envoy in the Eye
     • RETINA processes images
       • - the RETINA is the neural tissue lining the inside back surface of the eye; it absorbs light, processes images and sends visual information to the brain. -part of the central nervous system -paper thin sheet of neural tissue.
       • OPTIC DISK a hole in the retina where optic nerve fibres exit the eye.
         • -Axons that run from the retina to the brain converge here -Because the optic disk is a hole in the retina, you cannot see the part of an image that falls on it. therefore it is known as the blind spot. -each eye compensates for the blind spot of the other
         • Retina has 2 types of receptors, named based on their shape
           • Rods
             • elongated shape
               • out number cones
                 • Specialized receptors - key role is night vision & peripheral vision
                   • more sensitive to dim light than cones
           • Cones
             • Stubby shaped
             • Specialized receptors-key role daylight vision & color vision
               • do not respond well in low illumination
                 • Provide better visual acuity(sharpness) than rods
                   • FOVEA only contains cones
                     • -is a tiny spot in the centre of the retina that contains only cones;visual acuity is greatest here
           • Dark Adaptation
             • the process in which the eyes become more sensitive to light in low illumination
           • Light Adaptation
             •  is the process whereby the eyes become less sensitive to light in high illumination
       • sends impulses along the OPTIC NERVE, which connect the eye to the brain
         • Receptive Field
           • the receptive field of a visual cell is the retinal area that, when stimulated, affects the firing of that cell.
   • Vision and the Brain
     • visual input is meaningless until it is processed in the brain
     • Visual pathways to the Brain
       • optic nerve travels to the OPTIC CHIASM
         • - the point at which the optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain.  - this arrangement ensures that signals from both eyes go to both hemispheres of the brain.
         • At the optic chiasm the optic nerve fibres diverge along two pathways
           • Main pathway projects into the THALAMUS
             • Here about 90% of the axons from the retinas synapse in the (LGN) lateral geniculate nucleus
             • visual signals processed in LGN
               • then distributed in the Occipital Lobe that make up the primary visual cortex
           • Second pathway branches off to an area in the mid brain called the SUPER COLLICULUS
             • Then it travels through the thalamus and on to the occipital lobe
               • Principle function appears to be the coordination of visual inpuy with other sensory input
     • Information processing in the Visual Cortex
       • Cells in the visual cortex seem to be highly specialized -FEATURE RECEPTORS
         • are neurons that respond selectively to very specific features of more complex stimuli
         • Visual input is often routed to other cortical areas travelling through two streams
           • VENTRAL STREAM
             • processes the details of what objects are out there
               • eg the perception of form and color
               • associated with our perception of the world
           • DORSAL STREAM
             • processes where the objects are
               • eg perception of motion and depth
               • associated with vision for action
                 • - control of goal directed movements
     • Viewing the World in Color
       • Colour is a psychological interpretation
         • - it is NOT a physical property of light itself
         • Wave length is related to HUE, AMPLITUDE to BRIGHTNESS, and PURITY to SATURATION
           • 2 kinds of colour mixure
             • SUBTRACTIVE
               • subtractive colour mixing works by removing some of the wavelengths of light, leaving less light than was originally there. mixing yellow and blue to get green
             • ADDITIVE
               • additive colour mixing works by superimposing lights, putting more light in the mixture than exists in any one light by itself.
       • Trichromatic Theory of Colour Vision
         • Holds that the human eye has three types of receptors with differing sensitivities to different light wavelengths.
         • tri for three and chroma for colour
           • Specialized receptors sensitive to red, green and blue
             • Colour Blindness
               • encompasses a variety of deficiencies in the ability to distinguish among colours More frequent in males than females
       • Opponent Process Theory of Colour vision
         • Complementary Colours
           • are pairs of colors that produce grey tones when mixed together.
         • Afterimage
           • a visual image that persists after a stimulus is removed
           • the colour of the afterimage will be the complement of the colour you orginally stared at.
         • Opponent Process Theory
           • colour perception depends on receptors that make antagonistic responses to three pairs of color
             • red vs green
             • yellow vs blue
             • black vs white

3. The Visual System: Perceptual Processes

   • Perceiving Forms, Patterns, and Objects
     • Reversible Figure
       • - a drawing that is compatible with two interpretations that can shift back and forth
     • Perceptual set
       • is a readiness to perceive a stimulus in a particular way creates a slate in how someone interprets  sensory input
     • Form perception depends on the selection of sensory input- what people focus on
     • Change Blindness- the failure to notice a seemingly obvious change in a visual display
     • Inattentional Blindness involves the failure to see expected visible objects or events in a visual display
   • Feature Analysis: Assembling Forms
     • Feature Analysis
       • is the process of detecting specific elements in visual input and assembling them into a more complex form
       • involves bottom up processing
         • a progression from individual elements to the whole
         • crucial problem: is that form perception often does not involve bottom-up processing
           • evidence that perceptions of form frequently involve top-down processing
             • a progression from the whole to the elements
             • Subjective Contours is attributed to top-down
               • is the perceptionof contours where non actually exist.
   • Gestalt Principles
     • gestalt is German for form or shape
       • Phi Phenomenon
         • is the illusion of movement created by presenting visual stimuli in rapid succession objects merely take slightly different positions in successive frames
       • Figure & Ground
         • figure is the thing being looked at and ground is the background against which it stands
         • Proximity
           • things that are close to one another seem to belong together
         • Closure
           • people often group elements to create a sense of closure or completeness
         • Similarity
           • People also tend to group stimuli that are similar
         • Simplicity
           • most general principle the law of Pragnanz, translates as good form. people tend to organize forms in the simplest ways possible
         • Continuity
           • reflect's people's tendency to follow in whatever direction they've been led
     • Perceptual Hypothesis
       • is an inference about which distal stimuli could be responsible for the proximal stimuli sensed.
   • Perceiving Depth or Distance
     • Spatial considerations add a third dimension to visual perception
       • Depth Perception
         • involves interpretation of visual cues that indicate how near or far away objects are
       • Binocular Cues
         • are cues are clues about distance based on the differing views of the 2 eyes 3D movies use this fact
         • retinal disparity increases as object come closer, providing information about distance
           • Convergence involves sensing the eyes converging towards each other as they focus on closer objects
       • Monocular Cues
         • are clues about distance based on the image in either eye alone
           • motion paarallax
             • involves images of objects at different distances moving across the retina at different rates.
             • pictorial cues
               • clues about distance that can be given in a flat picture
               • Linear Perspective
                 • is a depth cue reflecting the fact that lines converge in the distance
               • Texture Gradients
                 • can provide information on depth. 
               • Interposition
                 • If an object comes between you and another object, it must be closer to you.
               • Relative Size
                 • closer objects appear larger
               • Height in Plane
                 • distant objects appear higher in a picture
               • Light & Shadow
       • Perceptual Constancy
         •  is a tendency to experience a stable perception in the face of continually changing sensory input.
       • Optical Illusion
         • involves an apparently inexplicable discrepancy between the appearance of a visual stimulus and its physical reality perceptions are based on inappropriate assumptions

4. Our Sense of Hearing: The Auditory System

   • The Stimulus:Sound
     • Sound waves are vibrations of molecules
       • Sound waves are generated by vibrating objects or by forcing air past a chamber(pipe organ) or by suddenly releasing a burst of air (clapping)
         • Sound waves are characterized by amplitude, wavelength, and purity
           • are described in terms of their FREQUENCY, measured in hertz(Hz) cycles per second
             • Greater the amplitude of sound waves, the louder the sound is perceived.Amplitude is measured in decibels (dB) which measure a physical property of sound
               • The purest sound is one that has only a single frequency of vibration.
   • Sensory Processing in the Ear
     • Human ear is divided into 3 sections
       • External ear
         • depends on the vibration of air molecules
           • consists mainly of the PINNA, a sound collecting cone
             • Sound waves are funnelled along the AUDITORY CANAL to the EARDRUM
               • eardrum is a taut membrane that vibrates in response.
       • Middle ear
         • depends on the vibration of moveable bones
           • Vibrations of the eardrum are transmitted by a mechanical chain of the 3 tiniest bones in your body, the OSSICLES (hammer,anvil and stirrup)
             • Ossicles amplify tiny changes in air pressure
       • Inner ear
         • Depends on waves in a fluid
           • Consists largely of the COCHLEA
             • Cochlea is a fluid filled, coiled tunnel that contains the receptors for hearing. term comes from Greek meaning spiral-shelled snail
             • Sound enters the cochlea through the oval window, which is vibrated by the ossicles
               • Basilar membrane, runs the length of the cochlea, holds the auditory receptors
                 • Auditory receptors are called hair cells.
                   • Waves in the fluid of the inner ear stimulate them.
                     • Signals are routed through the thalamus to the auditory cortex, located in the temporal lobes
   • Theories of Hearing
     • Place Theory
       • holds that perception of pitch corresponds to the vibration of different portions, or places along the basilar membrane
       • Specific frequencies vibrate specific portions of the basilar membrane
     • Frequency Theory
       • holds that perception of pitch corresponds to the rate  or frequency at which the entire basilar membrane vibrates
       • whole membrane vibrates in unison to sound
     • both theories are valid in part
   • pg 159 ear diagram

5. Our Chemical Senses: Taste and Smell

   • Gustatory System
     • Physical stimuli are chemical substances that are soluble
       • receptors are taste buds, they live about 10 days
         • 4 primary tastes; sweet, sour, bitter, salty
           • UMAMI is Japanese for savoury the 5th taste
             • we can be nontasters, super tasters, or medium tasters. Supertasters tend to be female.
               • non tasters have a sensitivity to PTC or PROP
               • flavor is a combination of taste, smell,and tactile sensation of food in one's mouth.
   • Smell:The Olfactory System
     • physical stimuli are chemical substances- carried on air
       • receptors are OLFACTORY CILIA, hairlike structures in the upper portion of the nasal passages
         • Smell is the only sensory system in which incoming information is not routed through the thalamus before it projects to the cortex

6. Our Sense of Touch:Sensory Systems in the Skin

   • Touch can be fooled
     • Physical stimuli are mechanical, thermal, and chemical energy
       • human skin has at least 6 types of sensory receptors
         • nerve fibres that carry incoming info about tactile stimulation are routed through the spinal cord to the brainstem.
           • then projects through the thalamus and onto the somatosensory cortex in the parietal lobe
             • pain sensation is crucial to survival and is a warning system.
               • receptors for pain are mostly free nerve endings in the skin
                 • fast pathway uses thicker, myelinated neurons called A delta fibres
                   • slow pathway use thin unmyelinated neurons called C fibres
                     • Gate control theory
                       • holds that incoming pain sensations must pass through a "gate'in the spinal cord that can be closed, thus blocking ascending pain signals

7. Our Other Senses

   • Kinesthetic System
     • monitors the positions of the various parts of the body
       • receptors found in joints and muscles
         • transmitted to the brain along the same pathway as tactile stimulation, but kept seperate
   • Vestibular System
     • response to gravity
       • keeps you informed of your body's location in space; provides sense of balance
         • shares space in the inner ear with the auditory system
           • semicircular canals make up the largest part of the vestibular sytem

8. pg 172-173 diagram of major senses