The thick, transparent outer covering of the eye. It focuses incoming light in a process called refraction. It is not adjustable.
Light rays that pass through the cornea enter this and are bent further inward, and are focused to form an image on the retina. It is adjustable by muscles behind the iris which flatten it to focus on distant objects or thicken it to focus on closer objects.
The inner surface of the back of the eyeball. It contains photoreceptors that transduce light into neural signals.
The small opening in the front of the lens which lets in light waves. It contracts or dilates to control how much light enters the eye. It enlarges in dim light, but also when we see something that we like.
The colored, opaque muscular circle on the surface of the eye, which changes shape to let in more or less light.
The name for the process in which the muscles behind the iris flatten the lens to focus on farther objects or thicken it to focus on closer objects.
The two types of receptor cells in the retina.
Retinal cells that respond to low levels of illumination and result in black-and-white perception; responsible primarily for night vision; resolve fine detail poorly. There are about 120 million of them in each retina.
Retinal cells that respond to higher levels of illumination and result in color perception and greater resolution of detail. There are about 6 million in each retina.
These light-sensitive chemicals in the rods and cones initiate the transduction of light waves into electrical neural impulses.
The center of the retina, where cones are densely packed; rods are more prevalent near the edges of the retina.
bipolar, amacrine, horizontal
Terms for the three other types of cells in the retina besides rods and cones which perform on visual impulses a series of sophisticated computations that help the visual system process the incoming information. Their outputs converge on the ganglion cells.
The first cells in the visual pathway to generate action potentials; they receive outputs from the computations of the bipolar, amacrine, and horizontal cells in the retina. They send their signals along axons from inside the eye to the thalamus; these axons gather in a bundle called the optic nerve.
Bundle of axons which exits the eye from the back of the retina and carries the signals of the action potentials produced by the ganglion cells. The point at which it exits the retina has no rods or cones, resulting in a blind spot that exists in the middle of your vision.
The point where half of the axons in the optic nerves cross (those that project from the portion of the retina nearest the nose).
primary visual cortex
Cortical areas in the occipital lobe at the back of the head to which visual information is transmitted from the thalamus (which itself receives information from most of the ganglion cells). This pathway carries all the information that we consciously experience as seeing.
A given visual neuron's tuning specifies its this; the region of visual space to which neurons in the primary visual cortex are sensitive.
A visual process in which adjacent photoreceptor tend to inhibit one another; this emphasizes changes in visual stimuli and helps detect edges of objects.
hue, brightness, saturation
The three dimensions used to categorize color.
The distinctive characteristics that place a particular color in the spectrum, which depends primarily on the light's dominant wavelength when it reaches the eye
A color's perceived intensity or luminance, determined chiefly by the toltal amount of light reaching the eye.
A psychological dimension of color perception; it is determined by an objects brightness relative to its surroundings. Perception can be altered but the effect of simultaneous contrast. More useful than brightness for describing appearance.
A color's purity, or intensity; the vividness of the hue. Varies according to the mixture of the wavelength in a stimulus. Pure spectral colors have only one wavelength, whereas pastels have a mixture of many wavelengths.
subtractive color mixing
A way to produce a given spectral pattern in which the mixture occurs within the stimulus itself and is actually a physical, not psychological, process. When colors are mixed, they absorb each other's wavelengths.
additive color mixing
A way to produce a given spectral pattern in which different wavelengths of lights are mixed. The perception is determined by the interaction of these wavelengths with receptors in the eye and is a psychological process.
red, yellow, blue
The subtractive primary colors, which, when mixed together, make black because they absorb all of each other's wavelengths.
three primaries law of color
Through this law, almost any color can be created by combining just three wavelengths, so long as one is from the long-wave end of the spectrum (red), one is from the middle (green-yellow), and one is from the short (blue-violet).
red, green, blue
The additive primary colors. When their wavelengths are mixed they yield white light.
This short-wavelength light stimulates "S" cones
This medium-wavelength light stimulates "M" cones
This long-wavelength light stimulates "L" cones
An optical illusion in which identical stimuli appear different when presented against different backgrounds. Though we know they're identical, we can't make ourselves see them as the same. Lateral inhibition may explain this.
The sense that is our perception of our limbs in space.
The sense that is our perception of balance, which uses data from receptors in the semicircular canals of the inner ear, bending hair cells at the ends of the canal. The bending generates nerve impulses that inform us of the head's rotation.
primary auditory cortex (A1)
Located in the temporal lobe, neurons in this region code the frequency (pitch) of auditory stimuli. Neurons towards its rear respond best to lower frequencies, whereas those toward the front respond best to higher frequencies.
primary somatosensory cortex
Located in the parietal lobe, touch information from the thalamus is projected here.
primary visual cortex
Located in the occipital lobe, the main area of visual processing.
The lower visual pathway beyond V1; specialized for the perception and recognition of objects such as determining their colors or shapes.
The upper visual pathway beyond V1; specialized for spacial perception--determining where an object is and relating it to other objects in a scene.
The inability to recognize objects.
Term which in the context of psychology means "organized whole;" this psychological approach holds that our brains use innate principles to organize sensory information.
principle of proximity
Gestalt law that states that the closer two figures are to each other, the more likely we are to group them and see them as part of the same object.
principle of similarity
Gestalt law that states that we tend to group figures according to how closely they resemble each other, whether in shape, color, or orientation.
Gestalt law; tendency to interpret intersecting lines as continuous rather than as changing direction radically
Gestalt law; tendency to complete figures that have gaps.
Gestalt law; the fact that we perceive contours even though they do not exist. Illusory contours appear when stimulus configurations suggest that contours ought to be present.
A hierarchical model of pattern recognition in which data are relayed from one processing level to the next, always moving to a higher level of processing
A hierarchical model of pattern recognition in which information at higher levels of processing can also influence lower, "earlier" levels in the processing hierarchy.
Selected deficits in the ability to recognize faces
A region of this structure in the right hemisphere may be specialized for perceiving faces.
A face's emotional significance appears to activate this, which is involved in calculating potential danger.
binocular depth cues
Cues of depth perception that arise from the fact that people have two eyes.
monocular depth cues (pictorial depth cues)
Cues of depth perception that are available to each eye alone.
binocular disparity (retinal disparity)
A cue of depth perception that is caused by the distance between a person's eyes, which provides each eye with a slightly different image
The ability to determine an object's depth based on that object's projections to each eye
A pictorial depth cue in which a near object blocks an object that is farther away.
A pictorial depth cue that causes far-off objects to project a smaller retinal image than close objects do
A pictorial depth cue; we know how large familiar objects are, so we can tell how far away they are by the size of their retinal images
A pictorial depth cue; Parallel lines appear to converge in the distance.
A pictorial depth cue; As a uniformly textured surface recedes, its texture continuously becomes smaller
position relative to horizon
A pictorial depth cue; All else being equal, objects below the horizon that appear higher in the visual field are perceived as being farther away. Objects above the horizon that appear lower in the visual field are perceived as being farther away.
The relative movements of objects that are at various distances from the observer.
These are strong evidence for motion-sensitive neurons in the brain. When you stare at movement in a particular direction, the neurons associated with its detection become fatigued and less sensitive, so when you look away, the motion detectors for all other directions are much more active.
When the brain correctly perceives objects as constant despite sensory data that could lead it to think otherwise.