chaptor 5 Flashcards
what is sensation?
the stimulus-detection process by which our organs translate stimuli into nerve impulses
What is perception?
it is making sense of what our senses tell us; the active process of organization of input and giving it meaning
What is the absolute threshold?
the lowest intensity at which a stimulus can be detected correctly 50% of the time
the lower it is the greater the sensitivity
what is signal detection theory concerned with?
with the factors that influence sensory judgements
Explain how a signal detection experiment might be designed.
say after a flashing light there may or not be a beep
there are 4 possible outcomes
stimulus
present absent yes detected hit false alarm
not
detected miss correct
rejection
this demonstrates that stimuli are a perception
what is the difference threshold?
the smallest difference between two stimuli that people can perceive 50% of the time
also called just noticeable difference
What is Weber’s law?
states that “the difference threshold is proportional to the magnitude of stimulus for which comparison is being made
what is the cornea?
a transparent protective structure at the front of the eye
What is the pupil?
adjustable opening that controls amount of light that can enter
What is the lens?
Elastic structure for focusing.
becomes thinner to focus on distant objects, thicker for near
what is the retina?
site where photoreceptors transduce light energy into electrical impulses
what is myopia?
nearsightedness; difficulty seeing far away objects
eyeball is longer, lens focuses light in front of retina
What is hyperopia?
farsightedness, difficulty seeing close up objects
what are cones for?
colour and detail
what type of light do cones function best in?
high illumination
Where are cones concentrated and what is this area called?
in the center of the retina
called the FOVEA
What are rods for?
light sensitivity (night vision)
500 x more sensitive than cones
where are rods found?
periphery off retina
explain how rods and cones synapse to the optic nerve
rods and cones have a synaptic connection to bipolar cells
bipolar cells synapse to ganglion cells
axions of ganglion cells form optic nerve
optic nerve creates a blindspot
What does dual vision refer to?
some animals see in daylight, some at night
humans visual system is adapted for both
What does dark adaptation mean?
progressive improvement in brightness sensitivity in low illumination
how long does it take for a rod and cone to adapt to its maximum?
cone: 10 minutes
rod: 30 minutes
what type of wavelengths are red not sensitive to?
red light
what is trichromatic theory?
three types of colour receptors in retina
cones must be sensitive to blue green and red
visual system combines activity from these cells
colours are perceived by an additive mixture of impulses
What does trichromatic theory (young-helmoltz) not account for?
red green colour individuals should not be able to perceive yellow (red+green = yellow)
afterimages; stare at red look away and you’ll see green
What is opponent process theory (hering)
three cone types:
red or green
blue or yellow
black or white
explains afterimages; neural processes become fatigued and have a rebound effect responding to its opposite reaction
What is dual process theory?
combines trichromatic and opponent process
3 types of cones sensitive to blue, green, and red wavelengths stimulate opponent process reactions
current view
what is a trichromat?
someone with regular colour vision
what is a dichromat?
deficient in one system, red-green colour blind
what is a monochromat?
sensitive to black and white only
what is a feature detector?
a group of neurons that fire selectively in response to stimuli that have specific characteristics such as bars, slits, edges
others respond to colour, depth, and movement
What is parallel processing?
separate modules of the brain simultaneously analyzing different aspects of the information and constructing a unified image of its properties
Explain the process of constructing a visual scene
stimulus travels to thalamus (the switchboard) then to the primary visual cortex in the occipital lobe
then FEATURE DETECTORS fire and analyze the data using PARALLEL PROCESSING to create a unified image
information is then rerouted from visual cortex to VISSUAL ASSOCIATION CORTEX to integrate memories and knowledge to recognize and respond
what are the 2 kinds of processing functions
BOTTOM UP:
stimulus -> breakdown/analysis -> recombining into a whole
TOP DOWN:
concept, expectation -> guides analysis -> interpretation of incoming stimuli
top-down shows that our higher brain processes (experiences, beliefs, expectations) can affect our perception
What are the two processes of attention?
focusing on certain stimuli
filtering out other incoming information
What are shadowing experiments and what do they show us?
experiments where there are two stimuli and ppl are told to focus on one. can recall details about the one they focused on but not the other
shows that we can’t attend completely to more than one thing at a time, but we can shift are attention rapidly back and forth between two messages
explain what the gestalt principle of perceptual organization is.
suggests perception is governed by how things are grouped together
What are the 4 laws of gestalt laws of organization?
SIMILARITY: similar items belong together
PROXIMITY: elements that are close together belong together
CLOSURE: close open edges; perceive boundaries
CONTINUITY: elements linked to form a continuous line (rather than a series of individual items)
explain perception in terms of a hypothesis.
perception is essentially a hypothesis about the meaning/nature of stimuli based on knowledge and experience
What is the perceptual set?
it is our set of expectations that influence our perception
“readiness to perceive stimuli in a particular way”
creates context in top down processing
What is a perceptual constancy?
being able to recognize stimuli under varying conditions
Give some examples of perceptual constancy
SHAPE constancy: when a door opens the shape changes, but we still recognize it as the same object
SIZE constancy: as we walk away from a car, it decreases in size but remains the same object
BRIGHTNESS constancy: colours become brighter or darker in different light but we still perceive the same object
what are the two cues that the brain uses to translate 2D images into a 3 dimensional world?
MONOCULAR cues:
- light and shadow
- linear perspective (parallel lines converge in distance
- interposition (closer objects in front of others)
- height in horizontal plane (further objects are higher in the plain)
- texture (less detailed with distance)
- clarity (hazier with distance)
- relative size
- motion parallax (nearby objects move faster
BINOCULAR cues:
- binocular disparity (two images being compared)
- convergence (eye muscle provides feedback signals to the brain based on position)
What is an illusion?
an incorrect perception
What is the primary and secondary cue for movement?
the movement of stimulus across the retina
also the relative movement of an object against a background
What is the phy phenomenon and what is its application?
when a light is flashed and then a few milliseconds later it flashes again nearby
this is used in motion pictures
What is the ponzo illusion?
an illusion that uses convergence of an object to make parallel lines of the same size appear to be different lengths
example: two lines parallel and equal set on a train track as it runs to the horizon
What is the Muller-Lyer illusion?
> —–<
which line is longer?
note actually need the point where the two arrow lines converge to touch the horizontal lines
What are the two factors that interplay in perceptual development?
BIOLOGY: genes that determine our development
EXPERIENCE: ex can adapt to an upside down environment
What is a critical period in perceptual development?
a time period during which certain experiences must occur in order for perception to develop normally
if normal development doesn’t occur, permanent perceptual problems will exist
eg: kittens reared in a striped environment show no response to certain orientations as a normal cat would
eg: people who have restored vision late in life can’t perceive there environment
