chapter 7 sensation zthe raw experience of a sensory stimulus, such as a light or sound zperception:...
TRANSCRIPT
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Chapter 7
Sensation
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Sensation
The raw experience of a sensory stimulus, such as a light or sound
Perception: The interpretation of sensory information according to expectations and prior learning
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The Senses as Evolved Adaptations
Sensing Tastes and Smells sensitivity to chemicals important for feeding
and reproduction chemical receptors became more
sophisticated Smell vs. Taste receptors evolved
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The Senses as Evolved Adaptations
Sensing Light responsiveness to the sun’s energy provides “remote guidance” for sensing things
at a distance eyes allow us to process form, color,
movement and visual acuity
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The Senses as Evolved Adaptations
Sensing Sounds sensing sound increases range of sensation
beyond that of smellallows localization and identification
sound can be used as a form of communication
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The Senses as Evolved Adaptations
Sensing Touch, Warmth and Pain skin senses allow location of nearby objects touch enables skilled movements pain motivates behavior
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Psychophysics
The study of how humans and animals respond to sensory stimuli The mathematical relationship of sensory
intensity to the magnitude of a physical stimulus
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Just Noticeable Difference (JND)
The minimal amount of sensory change in a stimulus that can be detected e.g. how much more weight do you need to
perceive a difference in weights?
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Just Noticeable Difference
Weber’s Law:
jnd = kI Just Noticeable Difference = Constant x Intensity
The size of the just noticeable difference is equal to some some proportion of the standard
Constant varies depending on sensory modality
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Just Noticeable Difference
Fechner: JND is a measure of the “psyche” similar to inches on a ruler
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The Absolute ThresholdMinimum amount of stimulation that can be detected
on half the trialsCount up number of “yes” responses (Frequency of
“seeing”)
P(yes)
0
50
100
Stimulus Intensity
Threshold =
50% response point
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Psychophysical Methods: How to Measure Thresholds
Method of Limits Start with a low intensity stimulus, gradually
increase until observer reports a sensation (ascending)
Start with a high intensity, gradually decrease until observer no longer reports a sensation (descending)Problems:
• observer may not pay attention on low intensity trials• observer may anticipate stimulus on descending series
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Psychophysical Methods: How to Measure Thresholds
Method of Constant Stimuli Present stimuli in a random order
observer cannot predict whether stimulus is above or below threshold
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Method of Magnitude Estimation
Stevens: Observers use numbers to describe the
perceived intensity of a stimulus Relationship between stimulus intensity
and magnitude estimates follows a power function
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Signal Detection Theory
The detection of a stimulus involves decision processes as well as sensory processes Observers responses will change with
motivatione.g. paid $1 for each detection of stimulus results
in a greater number of detections
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Signal Detection MatrixJudgment
Stimulus
Present
Absent
“Yes” “No”
Hit Miss
CorrectRejection
FalseAlarm
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Signal Detection MatrixJudgment
Stimulus
Present
Absent
“Yes” “No”
Hit Miss
CorrectRejection
FalseAlarm
Pay $1 for each detection
Hit
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Signal Detection MatrixJudgment
Stimulus
Present
Absent
“Yes” “No”
Hit Miss
CorrectRejection
FalseAlarm
Deduct $2 for each False Alarm
Miss
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Two-Point Limen
A measure of tactile sensitivity
Sensitivity differs for different body areas Sensitivity
corresponds with Sensory Homunculus
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Subliminal Perception
Perception of stimuli below the absolute threshold e.g. very briefly flashing messages no evidence for effectiveness in advertising However, flashed words can “prime”
awareness of other stimuli e.g. “bread” - “butter”
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A Five-Stage Modelof Sensory Systems
Each sensory system must have:
1. An adequate stimulus
2. Receptors adapted to the stimulus
3. Nerve pathways
4. Destination points in the brain
5. The psychological experience
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Seeing
The Stimulus: The Visible Spectrum The portion of the electromagnetic spectrum
between 400 to 700 nanometers
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The Eye
The eye focuses light on the retinaRetina: multilayered structure on the inner
surface of the eye
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Transduction
The conversion of energy from one type to another The eye transduces light energy into neural
energy at the retina
Transduction occurs at the photoreceptors: Rods: dim-light receptors Cones: bright-light receptors
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The Retina
Photoreceptors receive lightNeural signal sent to Bipolar Cells.Signal then sent to Retinal Ganglion CellsGanglion cells send signal out the eye to
the brain exit point is a “blind spot
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The Retina
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The Retina
Cones: Located in the center of the retina Often see a single cone connecting to a
single ganglion cell
Rods: Located in the periphery of the retina Often see many rods connecting to a single
ganglion cell
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Visual Nerve Pathways
Axons of ganglion cells for the optic nerve pathway
Optic nerve sends signals to the lateral geniculate nucleus (LGN) of the thalamus
Signals are then sent to the primary visual cortex in the occipital lobe primary visual cortex = striate cortex
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Conscious vs. Non-conscious Visual Pathways
Retina - LGN - Striate cortex: “conscious visual pathway”
“Non-conscious pathways”: Retina - Superior Colliculus: Responsible for
perception of peripheral movement Retina - Pretectum: Responsible for changing pupil
size when presented with bright light.
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Dark Adaptation
An increase in visual sensitivity as a result of time spent in the dark Sensitivity appears to plateau at 10 minutes,
but then starts to increase again at 15 minutesRod-Cone Break
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Dark Adaptation
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Color Vision: Trichromatic Theory (Young-Helmholtz)
Color vision results from the activity of three cone pigments, each maximally sensitive to on of three wavelengths Trichromatic Theory explains additive color
mixing - the mixing of colored lights to create other colorsDichromatism: color blindness resulting from
missing one of three color receptors
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Color Vision: Opponent Process Theory (Hering)
Colors are sensed by “opponent pairs” Red-Green Blue-Yellow White-Black
Can be used to explain negative afterimages
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Color-Opponent Cells
Ganglion cells are connected to photoreceptors such that they respond in an opponent process fashion to color e.g. inhibited by green and excited by red
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Hearing
The Stimulus: Sound Waves a wave of compressed air resulting from
vibration
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Sound Waves
Waves of air that can vary in amplitude and frequency
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Sound as a Wave
Amplitude (intensity): related to psychological dimension of loudness
Frequency: related to psychological dimension of pitch
Complexity: related to psychological dimension of timbre
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Amplitude
Determined by size of wave Measured in decibels (dB)
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Frequency Determined by number of waves per second Measured in Hertz (Hz)
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The Ear
Three Parts: The Outer Ear The Middle Ear The Inner Ear
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The Ear
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The Outer Ear
Consists of Pinna Auditory Canal Tympanic Membrane (Eardrum)
Main Function: Gather sounds to send to middle and inner
ear
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The Middle Ear
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The Middle Ear
Ossicles: Transfer and amplify sound to inner ear Malleus (Hammer) Incus (Anvil) Stapes (Stirrup)
Oval Window To inner ear
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Inner Ear (Cochlea)
Sound vibrations enter at oval windowTravel through fluid, vibrating basilar
membrane
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Organ of Corti
Where sound is transduced into a neural signal
Sound is transduced by Hair CellsCilia on hair cells contact tectorial
membraneAs basilar membrane vibrates, hair cells
are pulled and neural signal is generated
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Flowchart of the Ear and Other Things
Airborne Vibrations
Mechanical Vibrations (Eardrum & ossicles amplify)
Pressure Waves (Cochlear Fluid)
Bending (Cilia)
Electrical Charges (Hair cells)
Ripples (Basilar Membrane)
Neuro-transmitter (Auditory Nerve Fibers)
Brain
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Place Theory: How we perceive pitch
Sound waves generate vibration in cochlear fluid and basilar membrane - travelling wave
Frequency of sound is encoded by the stimulation of specific place on basilar membrane High frequencies cause vibrations at thin part
of basilar membrane near oval window Low frequencies cause vibrations at thicker
part
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Place Theory: How we perceive pitch
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Loudness Perception
Increased amplitude of sound wave leads to greater displacement of basilar membrane
Increase displacement of basilar membrane leads to increased activity of hair cells
Increased activity of hair cells leads to greater number of EPSPs
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Conductive Hearing Loss
Hearing loss due to reduced functioning of outer or middle ear e.g. damage to ear drum or damage to
ossicles otitis media: middle ear infection
reduces movement of ossicles
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Sensorineural Hearing Loss
Hearing loss due to damage to the cochlea
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Central Hearing Loss
Hearing loss due to damage to brain areas e.g. Wernicke’s aphasia - an inability to attach
meaning to language
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Central Auditory Processes
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Taste
The Stimulus: Chemicals in solution Four basic tastes:
sweetsaltsourbitter
Taste is also a product of what we smell
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How we Taste
Taste receptors are found in taste buds on the tongue
Membranes of receptor cells bathed in solution of chemicals in saliva
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How we Taste
Receptor cells generate action potentials in taste nerves
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Smell
The Stimulus: Airborne chemicals (olfactants)
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How we Smell (just terrible)
Olfactants are dissolved in olfactory mucosa at top of nasal passageway
EPSPs are generated in olfactory neuronsSignals sent to the olfactory bulb then to
brain
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How we Smell
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Touch
The Stimulus: Mechanical Pressure
The receptor: Receptors found in skin
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Touch Receptors
Free Nerve Endings Process touch, temperature and pain
Pacinian Corpuscles: Process “deep pressure”
Meissner Corpuscles and Organ of Ruffini Process gradual changes in skin pressure
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Pain
The Stimulus: Typically, damaging stimuli - mechanical, heat,
chemical
Pain can be influenced by non-sensory factors e.g. rubbing a hurt area
Phantom Limb Pain Pain associated in a “limb” even though it has
been amputated