Midterm 1: Chapter 3 Flashcards
What is vision based on?
Visible light; a band of energy within the electromagnetic spectrum.
The distance between the peaks of the electromagnetic waves.
Wavelength
The energy within the electromagnetic spectrum that humans can perceive has wavelengths ranging from about 400-700 nm.
Visible light
Light reflected from objects in the environment enters the eye through the _________.
Pupil
The clear, dome-shaped outer layer of the eye that covers the iris and pupil, and lets light in/ focuses the light reflected.
Cornea
From sharp images of the objects/focuses light onto the retina
Lens
The network of neurons that covers the back of the eye and that contains the receptors from vision.
Retina
Receptors for vision; function by converting light into electrical signals; has cones, and rods.
Photoreceptors
Reacts to light and triggers electrical signals; in the outer segments
Visual Pigments
The part of the receptor that contains light-sensitive chemicals is called visual pigments.
Outer Segment
Contains a million optic nerve fibers that conduct signals toward the brain.
Optic Nerve
When we look directly at an object, the object’s image falls on the __________, contains only cones
Fovea
Includes all of the retina outside of the fovea, contains both rods and cones.
Peripheral Retina
Destroys the cone-rich fovea and a small area that surrounds it. This creates a blind region in central vision.
Macular Degeneration
Degeneration of the retina that is passed from one generation to the next. First attacks the peripheral rod receptors and results in poor vision in the peripheral visual field.
Retinitis Pigmentosa
Area in the retina where there are no photoreceptors.
Blind Spot
What don’t we see our blind spot?
A mechanism in the brain fills in the place where the image disappears.
What two parts of the eye focuses light reflected from an object into the eye onto the retina?
Cornea and lens
Can change its shape to adjust the eye’s focus for objects located at different distances
Lens
What is important about lens being able to adjust?
It controls a process called accommodation; comes to the rescue to help prevent blurring.
The change in the lens’ shape that occurs when the ciliary muscles at the front of the eye tighten and increase the curvature of the lens so that it gets thicker.
Accommodation
Age-related loss of ability to accommodate
Presbyopia
An inability to see distant objects clearly; occurs when the optical system brings parallel rays of light into focus at a point in front of the retina, so the image that reaches the retina is blurred.
Myopia/Nearsightedness
The cornea and/or the lens bends the light too much
Refractive Myopia
Eyeball is too long
Axial Myopia
Can see distant objects clearly but have trouble seeing nearby objects because the focus point for parallel rays of light is located behind the retina.
Hypertonia/Farsightedness
The transformation of one form of energy into another form of energy.
Transduction
What are the two parts of visual pigments?
a long protein called opsin and a much smaller light-sensitive component called retinal.
How is the first step of transduction initiated?
When the incoming light hits the retina.
What happens during the first step of transduction?
The visual pigment molecule absorbs the light. This causes the retinal within that molecule to change its shape from bent to straight.
Creates a chemical chain reaction that activates thousands of charged molecules to create electrical signals in receptors.
Isomerization
The process of increasing sensitivity in the dark and is measured by determining a dark adaption curve.
Dark Adaption
a dark adaptometer is used to measure the brightness of light needed to achieve a threshold response after bleaching the retina with an intense light
Dark Adaption Curve
the least intensity of light visible to the eye
Threshold
1/threshold=
Sensitivity
High threshold corresponds to _______ ___________.
low sensitivity
What does the dark adaption curve show?
As adaption proceeds, the participant becomes more sensitive to light.
On a dark adaption curve, since higher sensitivity is at the bottom of the graph, what does the downward movement of the curve mean?
The participant’s sensitivity is increasing.
At how many minutes does the participant sensitivity increase? (dark adaption curve)
The first 3-4 minutes and at about 7-10 minutes.
How do we measure cone adaption?
Have the participant look directly at the test light so its image falls on the all-fovea, and by making the test light small enough so that its entire image falls within the fovea.
How do we measure rod adaption?
We use people who have a rare genetic defect called rod monochromats. These individuals have no cones.
When do rods reach their final dark-adapted level?
25 minutes.
What happens as soon as the light is extinguished?
the sensitivity of both the cones and the rods begins increasing
When do cones reach their maximum sensitivity?
3-5 minutes
How long does it take for rods’ sensitivity to catch up to cones?
7 minutes
The place where the rods begin to determine the dark-adaption curve instead of the cones
rod-cone break
How long does it take rods to reach their maximum sensitivity?
20-30 minutes
The change in shape and separation from the opsin causes the molecule to become lighter in color
Visual pigment bleaching.
Cone pigment takes ________ minutes to regenerate completely.
6
Rod pigment takes more than _________ minutes to regenerate completely.
30
What does our sensitivity depend on?
the concentration of the visual pigment
What does the speed at which our sensitivity increases in the dark depends on what?
the regeneration of the visual pigment
The eye’s sensitivity to light as a function of the light’s wavelength.
Spectral sensitivity
the relationship between wavelength and sensitivity
Spectral Sensitivity Curve
How to determine one’s spectral sensitivity?
We determine the person’s threshold for seeing monochromatic lights across the spectrum using one of the psychophysical methods for measuring threshold.
Threshold is higher at _________ and __________ wavelengths.
short, long
Threshold is lower at _________ wavelengths.
middle
________ are more sensitive to short-wavelength light.
rods
________ are most sensitive to light of 500 nm.
rods
________ are most sensitive to light of 560 nm.
cones
A plot of the amount of light absorbed versus the wavelength of the light
Absorption spectrum
Short-wavelength pigment absorbs light best at about _______ nm.
419
Medium-wavelength pigment absorbs light best at about _______ nm.
531
long-wavelength pigment absorbs light best at about _______ nm.
558
