Sensation and Perception
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Sensation and Perception
Psychophysics
Vision Audition Touch Chemical Senses KinestheticSystem
VestibularSystem
Our Senses Attention
Sensation and Perception
Psychophysics
the study of how physical stimuli are translated into psychological experience
Sensation vs PerceptionOliver Sak’s “Dr. P”
Psychophysics
Sensation the stimulation of sense organs
Perception the selection, organization and interpretation
of sensory input“Dr. P”
visual sensation was intact visual perception was severely impaired “visual agnosia”
Basic Concepts of Psychophysics
stimulus any detectable input from the environment
threshold dividing point between energy levels that do
and do not have a detectable effect absolute threshold
minimum amount of stimulation that an organism can detect
defined as the level where the stimulus intensity is detected 50% of the time
Basic Concepts of Psychophysics
JND (Just Noticeable Difference)smallest difference in amount of stimulation
that a specific sense can detectWeber’s Law
• the size of a JND is in proportion to the size of the initial stimulus
• as stimuli increase in magnitude, the JND becomes larger
Fechner’s Law• constant increments in stimulus intensity produce
smaller and smaller increases in the perceived magnitude of sensation
Subliminal Perception
registration of sensory input without conscious awareness “Eat popcorn” rock music “backward masking” self-help tapes priming
altering participants’ attitude towards target person depending on type of subliminal photos seen
visual priming/semantic priming
Basic Concepts of Psychophysics
Signal Detection Theorydetection of a stimulus involves sensory processes
but also emotional and cognitive processes“noise” from irrelevant stimuli in the environment
Sensory Adaptationgradual decline in sensitivity to prolonged
stimulationautomatic, built-in process designed to keep people
tuned in to changes rather than constants in their sensory input
• Shouldn’t need constant confirmation that your clothes are still on!
W. W. Norton
Psychophysics
Vision Audition Touch Chemical Senses KinestheticSystem
VestibularSystem
Our Senses Attention
Sensation and Perception
Vision: The Stimulus
Light electromagnetic waves amplitude brightness wavelength colour purity “richness” or “saturation”
incoming visual input must be converted into neural impulses
Nature of the stimulus:
-one small band of electromagnetic radiation.
W. W. Norton
Optic Disk: point where the ganglion cell axons converge and exit the retina.
-creates a blind spot in the visual field.
Retina
-contains: Photoreceptor cellsInterneurons.Retinal ganglion cells.
1. Outer Nuclear Layer:
-contains the photoreceptor cells.
}Outer Nuclear Layer
2. Inner Nuclear Layer:
-contains the interneurons:bipolar, amacrine & horizontal cells.
-transmit signals from the photoreceptor cells toganglion cells.
}Outer Nuclear Layer
}Inner Nuclear Layer
3. Ganglion Cell Layer:-contains ganglion cells.
-output cells of the retina.
-axons form the optic nerve.
}Outer Nuclear Layer
}Inner Nuclear Layer
}Ganglion Cell Layer
Photoreceptor CellsTwo types:
RodsCones
Rods:-very sensitive to light.
-used in dim light.
-dense in periphery of retina
Fovea:
-center of the retina.
-densely packed with cones.
Cone vs Rod Vision
Perception of an item and the perception of color are separate.
A volunteer please!
Trichromatic Theory of Color Vision-three types.
-each sensitive to a particular wavelength of light
-red, blue, green
Trichromatic Theory of Color Vision
Opponent Process Theory of Color Vision
Ganglion cells (and neurons) depend on receptors that respond best to pairs of colours.
Yellow onBlue off
Blue onYellow off
Red onGreen off
Green onRed off
Theory of Color Vision
Cones appear to follow trichromatic theory
Lateral Geniculate Nucleus and Visual Cortex appear to follow opponent process theory
so … takes both theories to explain color vision
Colour Blindness
2 - 8% of males..03% of females.
due to a loss or mutation of pigment gene.Red/Green is most common.
First Stage of Visual Processing
Information Processing in the Retina
Info from about 130 million rods and cones converge upon 1 million axons in the optic nerve
bipolar and ganglion cells in the intermediate layers integrate and compress signals from many receptors.
Axons from the ganglion cells form the optic nerve
Information Processing in the Cortex
Feature Detectors (Hubel & Wiesel) neurons respond selectively to very specific
features of more complex stimulisimple cells
respond best to line of correct width, oriented at the correct angle and located in correct position in receptive field
complex cells respond best to specific width and orientation but
any position in receptive field
Information Processing in the Cortex
Parallel processing simultaneously extracting different
kinds of info from same input Parvocellular channel Magnocellular channel
Information Processing in the Cortex
Parallel processing Parvocellular channel
process details about the objects“what” channelhandles perception of color, form and texture__________ lobeprosopagnosia
Magnocellular channelprocesses “where” the ojbects areperception of motion and depth__________ lobe
Review
1. Physical Shapeelongated stubby
2. number 125 million 6.4 million
3. area of retinawhere dominant
Periphery Center/fovea
4. critical to colorvision?
No Yes
5. critical toperipheralvision?
Yes No
6. sensitivity todim light
Strong Weak
Dimension Rods Cones
CENTRAL VISUAL PATHWAYS
Optic nerve: fibres from retina to the optic chiasm.
Optic chiasm: optic nerves from both eyesconverge and partially cross over.
Optic tract: optic fibres beyond the chiasm.
W. W. Norton
Visual Perception
The same visual input can result in radically different perceptions.
W. W. Norton
Perceptual Set
How we perceive the stimulus depends on our expectations.
Perceptual Theories
Bottom-up processingTop-down processing
Bottom-up Processing
Feature Analysis process of detecting specific elements
in visual input and assembling them into a more complex form
progression from individual elements to the whole
supported by work of Hubel and Wiesel
Top-Down Processing
Gestalt psychologyStep 1: formulate perceptual
hypothesis about the nature of the stimulus as a whole
Step 2: select and examine features to check hypothesis
Step 3: recognize stimulus
Top-Down Processing
Whole can be greater than the sum of its parts visual illusions take advantage of this most common visual illusion is
televisionsee smooth motion but actually objects just
moving from slightly different positions in successive frames
Gestalt Principles of Top-Down Processing
figure-ground divide visual displays into figure and
ground
Gestalt Principles of Top-Down Processing
figure-groundproximity
things that are near one another seem to belong together
similaritycontinuity
tend to follow in whatever direction they’ve been lead
Gestalt Principles of Top-Down Processing
figure-groundproximitysimilaritycontinuitysimplicityclosure
you may “complete” figures that actually have gaps in them
Visual Perception
Need both top-down bottom-up
Perception of Depth
Monocular depth perceptionBinocular depth perception
Monocular Depth Perception
Van Gogh
1889
The Garden of St. Paul’s Hospital
Monocular Depth Perception
Occlusion (near objects block distant ones)
Relative SizeFamiliar SizeLinear Perspective
W. W. Norton
Monocular Depth Perception
Occlusion (near objects block distant ones)
Relative SizeFamiliar SizeLinear PerspectiveTexture GradientPosition Relative to Horizon
Binocular Depth Perception
Clues about the distance based on the differing views of the two eyes “retinal disparity”
convergence sensing the eyes converging towards each
other as they focus on closer objects
Perceptual Constancy
Tendency to experience a stable perception in the face of continually changing sensory input
table looks like a table no matter what angle
door looks like a door even if partly openfriend does not shrink before your eyes if
walking away
Psychophysics
Vision Audition Touch Chemical Senses KinestheticSystem
VestibularSystem
Our Senses Attention
Sensation and Perception
The Stimulus: Sound
-waves of changing air pressure-generated by vibrating objects
Frequency: Pitch.
Low
High
Frequency = cycles per second (hertz)
20 Hz up to 20,000 Hz
Amplitude: loudness (decibels)
Quiet
Loud:
Sensory Processing in the Ear
External ear - vibration of air moleculesMiddle ear - vibration of moveable bonesInner ear - waves in a fluid
converted to stream of neural signals sent to brain
system designed to convert relatively large movements with little force into smaller motions with greater force
W. W
. No r
ton
Inner Ear:
Cochlea:
-circular structure filled with fluid.
-regions of the basilar membrane preferentiallyvibrate in response to sound waves of specific frequencies
33 mm
100 m 500 m
Low FreqHigh Freq
18,000 Hz
50 Hz
-connected to bipolar ganglion cells of the spiralganglion (auditory nerve).
Theories of Auditory Perception
Place theory perception of pitch/frequency
corresponds to vibration of different portions, or places along basilar membrane
Theories of Auditory Perception
Place theoryFrequency Theory
frequency/pitch corresponds to the rate, or frequency, at which the entire basilar membrane vibrates
Theories of Auditory Perception
Place theoryFrequency Theory both are valid in part
sounds under 1000 Hz - frequency theory (entire membrane vibrates)
sounds between 1000 and 5000 Hz - combination
sounds above 5000 Hz - place coding only
Auditory Pathway
1. Cochlear Nuclei:
3. Inferior Colliculus (IC)
4. Medial Geniculate Nucleus (MGN)
5. Auditory Cortex
Auditory Localization
Intensity loss of sound intensity with distance “shadow” effect of head
Timing sound takes longer to reach ear that is
farther away
Primary Auditory Cortex (A1):
-lies along the transverse temporal gyrus.
Tonotopically organized:
-high frequency sounds caudal.-low frequency sounds rostral.
33 mm
100 m 500 m
Organization is not fixed:
2K3K
4K5K
6K2K
3K4K
5K6K
Trained to recognize 4K sound
Association Areas:Planum temporale.
-contains Wernicke’s area.-speech comprehension.
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