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Chapter 4

PSYC 1001 Chapter Notes - Chapter 4: Parallel Computing, Prosopagnosia, Thalamus


Department
Psychology
Course Code
PSYC 1001
Professor
Jennifer Pettalia
Chapter
4

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Chapter 4 – Sensation and Perception
Sensation – the stimulation of sense organs;
Objective
Involves the absorption of energy, such as light or sound waves, by sensory organs
(ears and eyes)
Perception – the selection, organization, and interpretation of sensory input
Involves organizing and translating sensory input into something meaningful, such as
your best friend’s face or other environmental stimuli
Subjective
Stimulus – any detectable input from the environment
Psychophysics – the study of how physical stimuli are translate into psychological experience
Threshold - a dividing point between energy levels that do and do not have a detectable effect.
Hardware stores sell a gadget with a photocell that automatically turns a lamp on
when a room gets dark
Absolute Threshold - for a specific type of sensory input is the minimum amount of stimulation that
an organism can detect
Defines the boundaries of an organism’s sensory capabilities
The stimulus intensity detected 50% of the time
Examples on table 4.1
oVision – a candle flame seen at 50km on a dark clear night
oTaste – 5mm of sugar in 7.5L of water
oHearing – tick of a watch under quiet conditions at 6m
Just Noticeable Difference (JND) - the smallest difference in the amount of stimulation that a
specific sense can detect
Determination of the difference between 2 stimuli
Vary by sense, and the smallest detectable difference is a fairly stable proportion of
the size of the original stimulus
Webers Law – states that the size of a JND is a constant proportion of the size of the initial
stimulus.
Concerned with the amount of “difference” that is required in order for us to
notice it
Biggest loser -120lbs. loses 10lbs compared to 300lb losing 10lbs.
Turning the volume up by 1 click
Fechners Law – the magnitude of a sensory experience is a proportional to the number of
JNDs that the stimulus causing the experience is above the absolute threshold
As we increase the intensity of a stimulus, our sensory experiences increases
rapidly at first and then slows
Ex: imagine you are in a dark room with a single lamp that has 3 bulbs of the
same wattage. Turn on the switch and one bulb lights up, and do it one at a
time for the other 2 bulbs. It adds just as much light but does not make a
difference.
Thus, 3 equal increases in stimulus intensity (amount of light) produce
progressively smaller differences in the magnitude of sensation.
Signal-detection theory – proposes that the detection of stimuli involves decision processes as well as

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sensory processes, which are both influences by a variety of factors besides stimulus intensity.
Actual Stimulus
Condition
Present Absent
Participant’s
Response
“Present” Hit False Alarm
“Absent Miss Correct
Rejection
Subliminal Perceptions – the registration of sensory input without conscious awareness.
Things can be perceived without consciousness
Advertisers can influence your product preference
Ex: alcohol advertisement word “sex” is embedded into ice cubes
oSelf-help: facilitates weight loss, sleep, memory, self-esteem
oMusic and religion – messages encouraging devil worship played backwards
in rock music
Sensory adaptation – a gradual decline in sensitivity due to prolonged stimulation
Perspective aspect of life, adapting
Keeps people tuned into the changes. It allows people to ignore the obvious and focus
on changes in their environment that may signal threats to safety.
Ex: garbage in the kitchen smells but you do not remove it. The smell will soon start
to fade. In reality, the stimulus intensity of the odour is stable, but with continued
exposure, the sensitivity decreases.
- Jumping into a pool of cold water
–Hearing a baby cry in public, even if the parents don’t
Dark Adaptation – the process in which the yes become more sensitive to light in low
illumination
Light Adaptation – the process whereby the eyes become less sensitive to light to high
illumination
The Visual System
Cornea – the “window”, surface
Lens – the transparent eye structure that focuses the light rays falling on the retina.
“Accommodation” – occurs when the curvature of the lens adjusts to alter visual focus.
When you focus on a close object, your lens gets fatter (rounder) to give you a clear
image. When you focus on distant objects, the lens flattens out to give you a better image.
Nearsighted – close objects are seen clearly but distant objects appear blurry.
Farsighted – distant objects are seen clearly, but close objects appear blurry
Iris – coloured ring of muscles surrounding the pupil
Pupil – black centre of the eye
Regulates light, the opening in the centre of the iris that helps regulate the amount of light
passing into the rear chamber
The opening in the centre of the iris that helps regulate the amount of light passing into
the rear chamber of the eye
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Constricted – less light sharper images
Opens (dilates) – more light, less sharp (ex: intoxicated)
Saccades – eye movements made when your eyes are scanning the visual environment
and making brief fixations at various parts of the stimuli.
Retina – the neural tissue lining the inside back surface of the eye; it absorb light, processes
images, and sends visual information to the brain
Brain’s envoy of the eye
Optic disk – “blind spot”, a hole in the retina where the optic nerve fibres exit the eye
Optic Nerve – “connection”; a collection of axons that connect the eye with the brain
Receptors
Light must pass through several layers of cells before it gets to the receptors that
actually detect it. Only 10% of light actually reaches the receptors
2 types of receptors:
oRods are elongated and Cones are stubbier.
oRods – 100-125 million, Cones – 5-6.4 million
Cones – specialized visual receptors that play a key role in daylight vision and
colour vision
oDo not respond well to dim light, which is why we don’t see colour well in
low illumination.
oProvides better visual acuity (sharpness and precise detail)
oFovea – tiny spot in the centre of the retina that contains only cones; visual
acuity is greatest at this spot
oConcentrated heavily in the centre of the retina and quickly fall off in in
density towards its periphery.
Rods – specialized visual receptors that play a key role in night vision and
peripheral vision
oHandle the lion’s share of peripheral vision because they outnumber cones
in the periphery of the retina.
oDensity of the rods is greatest just outside the fovea and gradually
decreases toward the periphery of the retina
oAvert your gaze when trying to focus on an object that is dimly lit in the
dark.
Information Processing
Light striking the retina’s receptors triggers neural signals that pass into the
intricate network of cells in the retina, which in turn send impulses along the
optic nerve
The axons depart from the eye through the optic disk, carrying visual
information, encoded as a stream of neural impulses to the brain
Receptive field of a visual cell – the retinal area that, when stimulated, affects
the firing of that cell.
oCome in a variety of shapes and sizes; commonly circular fields with a
centre-surround arrangement.
Lateral Antagonism (lateral inhibition)- occurs when neural activity in a cell
opposes activity in surrounding cells
oResponsible for the opposite effects that occur when light falls on the
inner versus outer portions of centre-surround receptive fields
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