Lesson 1: Introduction to Perception Flashcards
What is transduction?
Turning light perception into electrical perceptions
Where are the cones and rods found?
The retina, which is in the back of the eye.
Proximal stimulus?
The image on the retina (representation of the tree, named this way because it is in proximity of the receptors)
Distal Stimulus
The object observed at a distance in the environment
Top-down processing/ knowledge-based processing
Our knowledge of how things usually appear in the environment can play an important role in determining what we perceive
Bottom-up processing/ data-based processing
Processing based on the stimuli reaching the receptors
How many layers are there in the retina?
5
Levels of analysis (3)
1.behaviour
2.stimulus
3.physiology
Behaviour
-perception
-recognition
-action
Stimulus
-proximal
-distal
Physiology
-processing
-receptors
What are the seven steps of the perceptual process?
- Stimulus in the environment
- Light is reflected and focused
- Receptor processes
- Neural processing
- Perception
- Recognition
- Action
Principle of transformation
States that stimuli and responses created by stimuli are transformed, or changed, between the distal stimulus and perception.
Retina
0.4 mm thick network of nerve cells that covers the back of the eye and that contains the receptors for vision.
the image on the retina is the…
proximal stimulus (so called because it is in proximity to the receptors)
Principle of Representation
States that everything a person perceives is based not on direct contact with stimuli but on representations of stimuli that are formed on the receptors and the resulting activity in the person’s nervous system
Sensory receptors
cells specialized to respond to environmental energy, with each sensory system’s receptors specialized to respond to a specific type of energy.
what happens when the visual receptors that line the back of the eye receive the light reflected from the tree?
- Transform environmental energy into electrical energy
- they shape perception by the way they respond to different properties of stimuli.
why do visual receptors transform light energy into electrical energy?
Because they contain a light-sensitive chemical called visual pigment, which reacts to light
Transduction
transformation of one form of energy (e.g., light energy) to another form (e.g., electrical energy).
Visual form Agnosia
inability to recognize objects
What Stimulus part of the electromagnetic spectrum can we see?
The visible spectrum. (We do not have receptors to perceive other ones.)
What are the optics?
-cornea (transparent, fixed, 80% of the focusing, light goes through) iris is behind (coloured part of the eye) pupil is the hole in the eye (aperture)
-lens (20% of focusing, moves/change (ciliary muscles contract) its shape)
What does the optic nerve do?
It takes the light outside of the eye (chemical signal) and into the brain.
What do cones and rodes differ in? (3)
-Distribution across the retina
-Number
(6mil cones, 120 mil rods)
-shape
Blind spot?
No receptors to receive light stimulus in those areas. Brain fills up the area not seen with background visuals.
Retinal diseases (2)
- macular degeneration (center of the eye visuals are not seen because the cones are not wired up) destruction of phobia +
-retinitis pigmentosa
(Rods affected, if cones are affected they are blind) tunnel vision
Presbyopia
-distance of near point changes with age, lens harden, ciliary muscles (accommodation) weaken.
What is isomerization?
When the retinal absorbs the light and straightens out and detaches. Changes light energy to electrical energy.
Rod monocromates
People with rods only. Can only see one colour.
which colors are rods and cones sensitive to?
Rod see blues and greens
Cones see red and yellows
Which are more sensitive? Rods or cones and why?
Rods because they converge (additive) upon 1 ganglion cell to fire an action potential. Rod are more sensitive to light. Whereas, in the cone it is a 1-1 relationship = not enough stimulation to activate an action potential.
Can cones and rods perceive multiple sources of light?
Rods cannot because of their additive nature. Are good at detecting low levels of light. Periphery
Cones can! Because of the lack of convergence. Can see fine details. Straight on.
Visual receptors transform light energy into electrical
energy because they contain a light-sensitive chemical called___, which reacts to light.
Visual Pigment
How do the visual pigments shape perception? (2)
- Ability to see dim light depends on a high concentration of light-sensitive pigments in the receptors
- Different types of pigments, respond best to light in different parts of the visible spectrum.
Stimulus-perception relationship
relates stimuli to behavioral responses.
This is confirmed by: presenting white and black striped stimuli called gratings and measuring grating acuity
grating acuity
The smallest width of lines at which subjects can indicate the correct orientation.
stimulus-physiology relationship
the relationship between stimuli and physiological responses.
Confirmed by: optimal brain imaging on ferrets –>
physiology-perception relationship
Relates physiological responses and behavioral responses.
-Subjects were able to detect the horizontal (908)
and vertical (08) orientations at smaller light–dark differences than for the oblique orientations (458 and 1358).
knowledge, memories, and expectations
cognitive influences on perception
Thresholds
measure the limits of sensory systems; they are measures of
minimums—the smallest line-width that can be detected,
the smallest amount of light energy we can see, the smallest
amount of sound energy we can hear, the smallest concentration of a chemical we can taste or smell.
psychophysics
the study of the relation between mental (psycho) and physical (physics)
method of limits (measuring thresholds)
presents stimuli in ascending or descending order to indicate the threshold for hearing a tone. the threshold from the average of the crossover values of this experiment is 98.5
Fechner’s classical psychophysical methods (3 methods for measuring thresholds )
- methods of limits
- adjustment
- constant stimuli
what are the two types of thresholds? explain
- absolute threshold (the smallest stimulus level that can just be detected or the smallest amount of energy needed to detect a stimulus)
- difference threshold (the smallest difference between two
stimuli that enable us to tell the difference between them)
What does the improvement in perception after spending some time in the dark reflect?
a decrease in the threshold for seeing light
Q1: What is the perceptual magnitude of a stimulus?
Technique: magnitude estimation
- Presents “standard stimulus” (ex: moderate light with a value of 10) light of different intensities must be assigned to numbers that are proportional to the “brightness” of the original light. That “brightness” is the perceived magnitude of the stimulus.
Q2: What is the identity of the stimulus?
Technique: Recognition testing (categorization)
- What is that called?
Q3: How quickly can I react to it?
Technique: Reaction Time
- the time between the presentation of a stimulus and the
person’s reaction to it. - Experiment: (a) A reaction time experiment in which the subject is told to look at the + sign, but pay attention to the location at A, and to push a button as quickly as possible when a dark target flashes anywhere on the display. (b) Reaction times in milliseconds, which indicates that reaction time was faster when the target was flashed at A, where the subject was attending, than when it was flashed at B, where the subject was not attending
Q4: How can I describe what is out there?
what does the vase-face stimulus demonstrate?
how people perceive objects in front of a background
What is the Hermann grid?
A phenomenological report in which people often report that there are dark spots in the white
areas at the intersections, but when they look directly at an
intersection, the spot vanishes.
Q5: How can I interact with it?
Technique: Physical Tasks and judgments
- concerned not with perception but with actions that follow perception
- Experiment: people judge a box to be heavier if they think they will be lifting it than when they think someone will be helping them.
