Chapter 6 Flashcards
What is a photon?
The smallest possible unit of light energy
What is the electromagnetic spectrum?
the continuum of energy produced by electric charges and is radiated as waves.
How does light travel through the eye?
cornea → pupils → lens → retina → optic nerve
What is the point of central focus on the retina?
The fovea. this is where the image should be concentrated.
If they don’t send a signal, nothing is seen. what are they?
Retinal cells (rods, cones, retinal ganglion cells)
Where are most of our cones located?
On the fovea.
Photoreceptors (rods+cones) convert light into _________.
nerve impulses (transduction)
What does isomerization do?
triggers transformation of light into electricity in receptors. occurs when retina changes shape, sticking out from the opsin.
What is it called when the retina becomes lighter in colour, when light is constant and all the photoreceptors are bleached. + Retinal separates from the opsin. ?
Visual pigment bleaching
What is visual pigment regeneration?
As light remains on, more of retinal detaches, but more are regenerated at the same time. Opsin and retinal are rejoined. When sleeping (no light) all visual pigment molecules regenerated. That’s why light seems brighter in the morning.
What is the duplexity theory of vision?
Rods and cones are both used for vision, but they are specialized for different tasks.
Which cell is better for grayscale, and which for colour?
Rods = grayscale. Cones = colour.
What are some characteristics of cones?
- found mostly in fovea
- better for seeing detail (high acuity)
- colour vision
- daytime (photopic) vision
- need lots of light
- 6 million
- no convergence
What are some characteristics of rods?
- night (scotopic) vision
- low detail (acuity)
- gray scale vision
- need little light
- more sensitive
- 120 million
- more convergence (ganglion cells receive input from over 120 rod receptors)
What are “M and P channels”?
Magnocellular ganglion cells and Parvocellular ganglion cells
What are some characteristics of Magnocellular ganglion cells (M channel)?
input largely from rods.
Fast moving channel.
Low acuity, high contrast sensitivity, faster conduction
Motion and grayscale processed
Layers 1-2 carries lighter info like motion
What are some characteristics of Parvocellular ganglion cells (P channel)?
input largely from cones.
Slow moving channel.
High acuity
slower conduction
Colour processed
Layers 3-6, carries heavy info like details
What is the Mach Band Illusion and what does it show?
optical illusion where same colour rectangle looks darker next to the lighter rectangle and vice versa. Shows how the brain adds contrast & emphasizes borders.
What is selective reflection?
some wavelengths are reflected more than others
What is selective transmission?
Only some wavelengths pass through the object or substance
What is spectral sensitivity?
Our sensitivity to light at each wavelength.
How can we measure spectral sensitivity?
To test, would present a monochromatic beam of light to peripheral; vision of participants who would turn it down until they could just barely see it. Much easier for human to detect red, yellow, green. This is a test of both rods and cones together. When rods are tested alone, it was much easier to see short/medium waves of blue and green.
What is the Purkinje effect?
Johannes Purkinje noticed he liked red + yellow flowers better during the day and blue ones better at night. This is bc blue appears brighter at night with rods mostly working.
What are the 3 kinds of cones?
short (blue), medium (green), and long (red) wavelength cone receptors. Remember most technology uses RGB values for colour.
