How to test for two point discrimination
- subject is seated with eyes closed
- experimenter will separate points if a two point compass by 4cm
- gently touch the two points of the compass to the palm
- if subject reports being touched by two points,decrease distance of two points until subject believes they’re only being touched by one point
- now increase the distance and continue testing to determine the smallest possible distance the subject can perceive as two distinct points.
Describe the relative size of the receptive field in diff regions
-fingers = receptors are less than a millimeter in diameter
-palm 3-8 mm
-side of nose 7mm
-back of hand 9mm
-back of neck are about about 36-75 mm
In areas like the palm and and fingers you can be very precise about the location of a stimulus
The larger the receptive field the poorer your ability to recognize a stimulus
Why does density matter in tactile receptors
Because the ability to distinguish between one point or two points depend on how dense tactile receptors are in the area being touched.
-fingertips/palm have a higher density of tactile receptors than your back does
Describe what is meant by receptor adaptation
The continuous stimulation of sensory receptors
Receptors that are fast adapting are called
Phasic receptors
Receptors that are slowly adapting are called
Tonic receptors
How did we test phasic and tonic receptors in lab
With the subjects eyes closed we placed a coin on the anterior surface of the subjects forearm and determine how long the sensation persists
Are the cutaneous receptors stimulates here phasic or tonic receptors explain your choice
They are phasic receptors because the response of the cell diminishes very quickly and then stops.
Describe the Snellen eye chart is used to test visual activity
- Visual acuity refers to the ability to perceive a clear image.
- letters of different sizes and thickness are arranged on a chart
- our ability to recognize the letters from a distance tests our visual acuity.
Describe how to test peripheral vision
- the subject places places the vision disk to their forehead and stares directly at the point in front of them.
- the subject moves the arm of the vision disk behind the subjects ear and selects a card to place in the arm of the vision disk
- slowly move the arm containing the card while ensuring your test subject keeps their eyes pointed straight ahead
- have your subject report when they can determine the shape and colour of an object
Location of cones on retina and their function
- cones are located at the central fovea
- responsible for visual acuity and colour vision in bright light
Location of rods on the retina and their function
- Rods are found in the outer edges of the retina and are used in the peripheral vision
- responsible for vision in dim light or at night
Describe what is meant by the “blind spot” and how you observed it in lab ?
light striking the optic disc goes unnoticed because there are no photoreceptors in this area is commonly (the blind spot.)
- an area where the person is missing a visual image but an individuals brain uses that missing information to fill it.
- we observed our blind spots in class when holding a card that had an “x “and an “o” on it at arms length.
- we aligned the “x” on the card directly I front of our right eye and the “o” to the right
- covered our left eye and moved the card slowly towards our eye while concentrating on the “x”
- eventually the “o” disappears and becomes a continues straight line
Describe what is meant by eye dominance
Eye dominance is the tendency to prefer visual input from one eye compared to the other
What is stereopsis(depth perception)
-allows us to perceive the relative distance of objects from us.
How do stereopsis and eye dominance relate to normal binocular vision
In order to have normal binocular vision we must be able to bias one input from one of the eyes(the dominant eye) aswell as be able to identify how far an object is from us (stereopsis)
Describe how to test for colour blindness
- have an experimenter hold a book of test plates approximately 1m from the test subject
- start with plate #1 and proceed in the sequence to plate #17
- compare the responses of the test subject to information on the documents that accompany the set of test plates
- determine whether your test subject has normal vision or colour blindness
What is protanopia, why can it be a hazard when driving?
A lack of red sensitive cones causing confusion of greens reds and yellows. Impacts a persons driving because they can’t accurately distinguish what colour each light is
Describe how balance changes with age
Older people often have poor balance due to loss of muscle strength and reduced vision and reaction time.
What is nerve deafness
Deafness resulting from damage to cochlea or cochlear nerve.
Ex(cochlear implants offer some hope to restoring some hearing to individuals with nerve deafness)
What is conduction deafness
Deafness resulting from damage to the tympanic membrane
Ex(hearing aids can provide help to individuals with conduction deafness)
Emmetropia
(normal vision) In the healthy eye, when the ciliary muscle is relaxed and the lens is flattened.
Hyperopia
(Farsightedness)
Occurs if the eyeball is too shallow or the lens is too flat.resulting in objects nearby to look blurry
Myopia
(nearsightedness) If the eyeball is too deep or the resting curvature of the lens is too great. The person will see distant objects as blurry and out of focus.
