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Chapter 4

PSY100H1 Chapter Notes - Chapter 4: Semicircular Canals, Astrocyte, Stirrup

Course Code
Dax Urbszat

of 9
Chapter 4 – Perception and Sensation
Canadian Space Psychology is rapidly developing; includes the examination
of such matters as the effects of isolated and extreme environments and the
nature and effects of multicultural interactions
Study was done to show that there is a reduction in hand-eye co-ordination
when up in space
oWhile on earth, gravity gives us a cue for our judgment of up and
down; however in space, there is spatial disorientation in which these
judgments are much harder to make and can lead to discontinuity
between sensory information derived from the vestibular system
(organs in ear)
oResearch was done to examine the role of vision in determining the
body’s position and sensory adaptation to microgravity
People rely on 3 cues: visual, gravity and body direction to establish
direction of up and down
Sensation and perception:
oSensation: stimulation of sense organs; involves the absorption of
energy such as light or sound waves by sensory organs (ears and eyes)
oPerception: the selection, organization and interpretation of sensory
input; involves organizing and translating sensory input into something
meaningful such as a familiar face or other environmental stimuli
Thresholds: Looking for limits
Sensations begin with a stimulus; but at what point can a stimulus be
detectable to an organism? (ex. what is the minimum amount of light that a
human can detect?)
A threshold is a dividing point between energy levels that do and do not
have a detectable effect
an absolute threshold is the minimum amount of stimulation that an
organism can detect; they define the boundaries of an organisms sensory
capacity; but it does not really exist
odoes not really exist – ex. when a light is flashed at us at varying
intensity, we do not just detect one certain intensity of light; rather as
the intensity of the light increases, there’s an increase the stimulation
otherefore, the absolute threshold is the stimulus intensity at detected
50% of the time
Just noticeable difference (JND) is the smallest difference in the amount of
stimuli that an organism’s senses can detect
They vary by sense
Weber’s Law states that the size of the jnd is a constant proportion
of the size of the initial stimulus (weber’s fraction)
oAs the stimuli increases in magnitude, the JND becomes larger
Signal-detection theory
Signal detection theory proposes that the detection of stimuli involves
decision processes as well as sensory processes, which are both influence by
a variety of factors besides stimulus intensity
oex. when you are given a task to watch the radar screen, you need to
use your ability to a) decide what you think is a strong stimulation
(creating criterion) and b) respond to how you feel about certain
intensities of a stimulaton
Perception without awareness
Can sensory stimuli that fall beneath the threshold of awareness still
influence behavior?
Subliminal perception: the registration of sensory input without conscious
We are consciously unaware of certain messages or hidden that we see
everyday, but our subconscious can pick up these messages and it can affect
our actions and decisions without us knowing why
People are defenseless against appeals operating below our threshold of
Subliminal inputs can produce measurable although small effects in
subjects who subsequently report that they did not consciously register that
Subliminal stimulation generally produces weak effects and usually can
only be detected by very precise measurements in laboratory conditions (ex.
during experiments conducted specifically to find these effects)
Sensory adaptation
Sensory adaptation is a gradual decline in sensitivity due to prolonged
Ex. if you stay in the kitchen without removing the garbage, you realize the
stench starts to fade
Sensory adaptation is an automatic, built-in process that keeps people tuned
in to the changes rather than the constants in their sensory input. It allows
people to ignore the obvious and focus on changes in the environment that
may signal threats to safety
Our sense of sight: Our Visual System
The stimulus: Light
Lights that humans normally see are mixtures of several wavelengths; it
varies in purity: how varied the mix of light is; it influences perception of the
saturation, or richness of colours
Vision is a filter that permits people to sense but a fraction of the real world
and animals have different capabilities and live in a different world
The eye: A living Optical Instrument
The eye serves two purposes: they channel light to the retina, and they
house that tissue
Light enters through the cornea and with the crystalline lens, they form
upside-down images of objects to the retina – the brain knows the rule for
relating positions on the retina in correspondence to the positions in the
The lens is the transparent eye structure that focuses the light rays falling
on the retina; facilitates accommodation
Accommodation occurs when the curvature of the lens adjusts to alter your
focus; focus on close objects, lens gets fatter; focus on far objects, lens
flattens out for a better image
oNearsightedness – when close objects can be seen but far objects
cant because the focus of the light falls short of the retina
oFar-sightedness – when you can see far distance but not close
objects because the focus of light falls behind the retina
the pupil is the opening in the center of the iris that helps regulate the
amount of light passing into the rear chamber of the eye; constricts – less
light to retina, sharpens image; dilates – lets more light night, but not as
sharp of an image
Saccades is the movement of the eye as it scans the visual environment;
tiny movements are essential to good vision
The Retina: the brain’s envoy in the eye
The retina is the neural tissue lining the inside back surface of the eye; it
absorbs light, processes the image and sends visual information to the brain
The axons that run from the retina to the brain converge at the optic disk, a
hole in the retina where the optic nerve fibres exit the eye – at this spot in
the retina, you have a blind spot; but not in the same spot in both eyes so
your one eye accounts for the blind spot in the other
Visual Receptors
Retina contains millions of receptor cells that are sensitive to light; but only
10% of the light arriving at the cornea reaches the receptors
Cones are specialized visual receptors that play a key role in daylight and
colour vision; better at visual acuity - sharpness and precision in detail
oConcentrated heavily in the fovea: tiny spot in the center of the retina
that contains only cones; visual acuity is greatest at this spot
Rods are specialized visual receptors that play a key role in night and
peripheral vision; located just outside the fovea
Dark adaptation is the process in which the eyes become more sensitive to
light in low illumination – declining absolute thresholds
Light adaptation is the process where the eyes become less sensitive to
light at high illumination
oThese adaptations are caused by chemical changes in the rods
and cones
Information processing in the Retina
Light that triggers the receptors triggers neural signals that send impulses
along the optic nerve, which is a collection of axons that connect the eye with
the brain; impulses carry the visual information to the brain