Modules 18-24 Flashcards
Light waves
Light (electromagnetic radiation) travels in waves
Can travel through air, empty space–and even some liquids and solids
Often diagramed as single wave, but actually two waves at 90 degrees from each other, one electrical and one magnetic
Amplitude (Light)
Intensity of energy (determines the brightness of light)
Wavelength (Light)
Length in space of each cycle of the wave (determines the hue of light)
Frequency (Light)
How fast the wave cycles (hz = cycles per second)
longer wavelength = lower frequency
shorter wavelength = higher frequency
Wavelength and frequency describe same thing that determines hue of light
Electromagnetic spectrum
Radio waves
Infrared waves
Visible spectrum
Ultra-violet
X-rays
Gamma rays
Scale goes up by frequency/wavelength
Cornea
Outer protective layer
Pupil
Hole for light to get in
Iris
Muscle around pupil allows hole to expand or retract
Lens
Curved structure behind helps filter light
Retina
Layer of photoreceptor cells in eye
Fovea
Point of central focus
Optic nerve
Goes to brain’s visual cortex
Blind spot
Where there are no photoreceptors where optic nerve connects
Visual Pathway
If something is on the left, goes to right side of both eyes, sent to the right side of thalamus, right primary visual cortex
If object on left, light bouncing off object will hit left side of retina in both eyes, down axons sending information to left thalamus and into left primary visual cortex
Retina
Has two types of photoreceptors rods and cones
Rods
Night vision, motion, more in periphery
Cones
Allow color perception more in fovea
Three cone types for short, medium, long wavelengths
No single cone type on its own gives us color information
The ratiosof firing rates between different cone types tell
us the hue of the light
Color vision deficiency “colorblindness”
Occurs when one cone type is absent, not fully functional, or has a tuning curve that is not sufficiently different from another cone size
Helmholtz’s trichromatic theory of color perception
Any color can be represented as position on three continua
Red vs. green
Yellow vs. blue
White vs. black
Can be demonstrated using negative afterimages (desensitization to color increases sensitivity to opposite color)
Opponent processing of motion
Waterfall illusion
Desensitization to unchanging direction of motion causes aftereffect of perceived motion in opposite direction
(if you stare at a waterfall for a while you desensitize yourself to downward motion, thus increased your sensitivity to upward motion, so when you look at a motionless rock it seems to float upwards)
Can occur with multiple directions in different parts of the visual field at the same time
Depth perception
Monocular and binocular depth cues
Monocular depth cues
Only need one eye
Size and height (closeness to horizon) in the visual field
Linear perspective: parallel lines converge in the visual field as they get farther away
Texture gradient: textures appear more densely packed, less spread out and detailed when they are farther away
Interposition/occlusion: if an object is partly blocking another, it must be closer
Atmospheric/aerial perspective (haze): light especially higher frequency light gets increasingly scattered as it travels through the air so more distant objects look fainter, blurrier, and bluer
Relative motion: when you’re moving, closer objects move across your visual field faster than distant objects
Binocular depth cues
Binocular/retinal disparity: the farther away an object is, the more similar its position on the two retinas (because it’s hitting the two retinas at a similar angle)
Binocular depth cues: convergence (how much you have to cross your eyes to focus on the object)
Feature detectors
Neurons that respond to specific features such as shape, angle, movement
Color constancy and lightness constancy
The brain adjusts our perception of color to keep colors constant under different lighting conditions
In the real world, that simplifies perception (objects don’t appear to change color just because lighting changes)
But we can exploit that to create optical illusions by manipulating images to imply different lighting conditions
Top-down process influences perception: we have expectations about what colors things should be
Color constancy and lightness constancy (cube)
In the image, the top-middle
square is made using the
same color as the side-middle
square. But the side-middle
square is implied to be in
shadow, so we perceive it as
a brighter color (because in
the real world, it actually
would need to be a brighter
color in order for It to reflect
the same amount of light as
the top-middle square even
when in shadow).
Color constancy and lightness constancy
We perceive the B square as lighter than the A square because:
It is implied to be in shadow, so in the real world it would have to
be lighter to reflect the same amount of light as the A square
It’s light compared to surrounding squares,
whereas the A square is dark compared to surrounding squares.
We are familiar with checkerboard patterns,
so we expect the squares to alternate
between light and dark.
Sound waves
Sound waves are mechanical waves (they need a medium such as air to travel through)
Oscillation between compression (bunching together) and rarefaction (spreading apart) of molecules
Basically vibration
Sound waves are longitudinal, meaning the oscillation is in the same dimension (in this case the left–right dimension) that the wave is traveling.
But sound waves are typically diagrammed like this, with the vertical dimension representing the amount of compression/rarefaction
The air molecules aren’t actually traveling from left to right. What’s traveling is the energy. Although the regions where the air molecules are compressed are continuously moving from left to right, the Individual air molecules themselves are vibrating back and forth (watch the red ones)
When we diagram a wave like this the horizontal dimension can be thought of either distance or time (because a wave takes a certain amount of time to travel a certain distance through space)
Sound waves don’t actually travel in single straight line
Emanate from sound source in all directions
Amplitude (sound)
Intensity of energy (overall amplitude determines the loudness of sound)
Great amplitude = loud sounds
Small amplitude = soft sounds
Wavelength (sound)
Length in space of each cycle of the wave (determines the pitch of sound)
Frequency (sound)
How fast the wave cycles
Frequency is measured in Hertz (hz) meaning cycles per second
Humans can hear from 20 hz to 20 kHz but gradually lose sensitivity to high frequencies with age so adults can’t typically hear above 16-18 kHz and older adults can’t hear anywhere near that high
Long wavelength = lower frequency = low-pitched sounds
Shorter wavelength = higher frequency = high-pitched sounds
Complex sound waves
Most sounds are complex not simple sine waves without single consistent frequency
We can think of those complex sounds as made up of multiple component sine waves with different frequencies, amplitudes, and phases (starting positions in the cycle), added together
Frequency components
When you turn up the bass or turn down the treble on your stereo, you aren’t making the pitch of the sound lower, but your bringing out more of the lower frequency components within the sound
Fundamental frequency
Frequencies of the component sine waves are multiples of a single frequency (e.g. 100, 200, 300, 400, and 500 hz are all multiples of 100 hz), the lowest frequency is what typically determines the pitch that we perceive
Harmonics
Multiples of the component sine waves of a single frequency
Pinna
Like a cup to catch sound
Ear drum/tympanic membrane
Sound waves enter the ear canal and vibrate the tympanic membrane (ear drum)
Ossicles
Tiny bones that vibrations of tympanic membrane vibrate and that connects the tympanic membrane to the cochlea