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Chapter 4

PSY100Y5 Chapter Notes - Chapter 4: Synesthesia, Sensory System, Psychophysics

Course Code
Dax Urbszat

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Chapter 4 Textbook Notes – Sensation and Perception
Synesthesia – condition where perceptual/cognitive activities trigger
exceptional experiences. (many forms). Experiences from dierent
senses become paired
oGrapheme-colour – words, letters, digits associate with speci#c
oTaste-touch – taste leads to feelings
oWord-taste – words/names lead to taste sensations
oSound-colour – notes lead to colour sensations
Sensation – stimulation of sense organs (absorption of energy by ears
or eyes)
Perception – selection, organization, interpretation of sensory input
(into something meaningful)
Psychophysics – study of how physical stimuli are translated into
psychological experience
(130) Thresholds (dividing point between energy levels that do/don’t have a
detectable eect)
Absolute Threshold – minimum amount of stimulation that an organism
can detect. De#ne boundaries of an organism’s sensory capabilities
oAbsolute thresholds are anything but absolute
oAs stimulus intensity increases, subject’s probability of
responding increases
oRede#ned as - Stimulus intensity detected 50% of the time.
oJust Noticeable Dierence (JND) – smallest dierence in the
amount of stimulation that a speci#c sense can detect (vary by
oWeber’s law – size of a JND is a constant proportion of the size of
the initial stimulus (WEBER FRACTION)
Signal-Detection Theory
^ the detection of stimuli involves decision processes as well as
sensory processes, both in8uenced by many factors
Perceptions can’t be measured on absolute scales
Your performance depends on the level of noise (irrelevant stimuli in
env) in the system
This theory replaces fetcher’s sharp threshold with detectability
(measured in probability)
Perception without Awareness

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Subliminal perception - registration of sensory input without conscious
oMoney, sex, religion, rock music
1957, Vicary started controversy w/ hidden messages
Perception without awareness can take place
Subliminal stimulation - weak eects
Sensory Adaption
^ gradual decline in sensitivity bc of prolonged stimulation
Automatic process keeps ppl tuned in to the changes in the env
Behavioural adaption sculpted by natural selection
The Stimulus: Light
Light is a form of electromagnetic radiation that travels as a wave,
moving @ the speed of light.
Vary in amplitude (aects brightness), wave length (aects perception
of colour), purity (aects saturation
Incoming visual input must be converted into neural impulses that are
sent to the brain
The Eye
Eyes: channel light to neural tissue that receives it (retina) and house
that tissue.
Light enters the eye through the cornea that and the crystalline lens
form an upside-down image of objects in the retina
Lens - focuses on light rays falling on the retina
oAccommodation - curvature of lens adjusts to alter visual focus
oNearsightedness - clear objects seen clearly, and distant are
Pupil - opening in iris that regulates the light passing into the rear of
the eye
Eye movements = saccades
(135) The retina
Lines back surface of eye, absorbs light, processes images and sends
visual info to brain
Part of CNS located at the eyeball
Axons from the retina to the brain converge @ optic disk (hold in retina
where optic nerve #bres exit the eye[blind spot])

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(137) Visual Receptors: Rods & Cones
Light must pass through layers of cells before getting to detecting
receptors (10% reach)
2 receptors
1. Cones - visual receptors - key role in daylight and colour vision
i. Bright light dazzles rods, cones more sensitive
ii. Centre of retina
iii. Fovea - spot in retina center that only has cones; visual
acuity is greatest here
2. Rods - visual receptors key role in night vison and peripheral vision
i. More sensitive to dim light
ii. Outnumber cones in periphery
iii. Density greatest outside fovea
Dark and light Adaption
Adjustment to dark light = dark adaption (eye becomes more sensitive
to light in low illumination)
Declining thresholds = less light to see
Complete in 30 mins, progress in 10 mins
Light adaption - process where eyes become less sensitive to light in
high illumination
Information Processing in Retina
Receptive #eld - visual cell is the retinal area that when stimulated
aects the #ring of a cell
oMany shapes/sizes - common circular
When #eld stimulated retina cells send signals to the brain and lateral
(sideways) toward visual cells
Visual Pathways to the Brain
Axons leaving back of eyes form optic nerves, which travel to optic
chiasm (point at which optic nerves from the inside half of each eye
cross over and project to the opposite half to the brain)
Then the optic nerve #bres diverge 2 pathways.
1. Main one goes to thalamus.
90 % axons in LGN. Visual signals processed here and
distributed to occipital lobe
2. Goes to midbrain called superior colliculus before going to
Function here is coordination of visual input with other
sensory input
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