07. Important Information Flashcards
What percentage of the human brain is devoted to the analysis of input from the eyes?
25- 40%
What are photoreceptors?
Specialized light-detecting cells connected to the nervous system in many multicellular animals. In humans and other vertebrates, the photoreceptors are rods and cones.
What is one theory of the early evolution of photoreceptors?
They initially enabled circadian rhythms
What is the retina?
A thin membrane of cells that lines the rear interior of the eyeball; it contains the receptor cells for vision (rods and cones).
What is the cornea?
he curved, transparent tissue at the front of the eyeball that helps to focus light rays as they first enter the eye.
What is the iris?
The coloured (usually brown or blue), doughnut-shaped, muscular structure in the eye, located behind the cornea and in front of the lens, that controls the size of the pupil and in that way controls the amount of light that can enter the eye’s interior.
What is the pupil?
The hole in the center of the iris of the eye through which light passes
What is the lens?
In the eye, the transparent structure behind the iris that helps focus light that passes through the pupil.
How is the brain wired to interpret images on the retina?
Input from lower on the retina is interpreted as up and input from higher is interpreted as down
Which cells are responsible for transduction in the eye?
photoreceptor cells
What are the two types of photoreceptor cells?
rods and cones
what are cones?
The class of receptor cells for vision that are located in and near the fovea of the retina, operate in moderate to bright light, and are most important for the perception of colour and fine detail
What are rods?
The class of receptor cells for vision that are located in the peripheral portions of the retina (away from the fovea) and are most important for seeing in very dim light.
What is the fovea?
The pinhead-size area of the retina of the eye in which the cones are concentrated and that is specialised for high visual acuity.
How many rods and cones does the human eye contain?
about 6 million cones and 120 million rods
What is the photochemical for rods called?
rhodopsin
What is rhodopsin?
The photochemical in rods that undergoes structural changes in response to light and thereby initiates the transduction process for rod vision
How many varieties of cones exhist?
3, each with their own photochemical
What is the optic nerve?
The cranial nerve that contains the sensory neurons for vision, which run from the eye’s retina into the brain.
What is the blind spot?
The place in the retina of the eye where the axons of visual sensory neurons come together to form the optic nerve. Because the blind spot lacks receptor cells, light that strikes it is not seen.
Define cone vision
The high-acuity color vision that occurs in moderate to bright light and is mediated by cones in the retina; also called photopic or bright-light vision.
Define rod vision
The low-acuity, high-sensitivity, noncolor vision that occurs in dim light and is mediated by rods in the retina of the eye. Also called scotopic vision
Why is it easier to see objects in dim light if you don’t look directly at them?
Because the fovea doesn’t contain any rods
Define dark adaptation
The increased visual sensitivity that occurs when the eyes are exposed for a period of time to dimmer light than was present before the adaptation period.
Define light adaptation
The decreased visual sensitivity that occurs when the eyes are exposed for a period of time to brighter light than was present before the adaptation period.
Describe rhodopsin’s role in dark adaptation
Rhodopsin is more sensitive to light than the cone photochemicals. Bright light causes it to break down thus making rods nonfunctional. It takes about 25 minutes for rhodopsin to regenerate and only 5 minutes to break down. Which is why it takes longer to adapt to darkness than brightness
What wavelengths of light are visible to humans?
400- 700 (nm) nanometers
Which shorter waves fall below human visible range?
ultraviolet rays, x-rays, and gamma rays
Which longer waves fall above human visible range?
infrared rays, radar rays and radio waves
What is the three-primaries law?
Three different wavelengths of light (called primaries) can be used to match any colour that the eye can see if they are mixed in the appropriate proportions.
What is the law of complementarity?
The observation that certain pairs of limited-wavelength lights that produce different colours (such as red and green) alone will produce the perception of white (no colour) when mixed.
What kind of colour mixing does light use as opposed to pigments (art)?
Light uses additive colour mixing (add all colours together and you get white) while pigment uses subtractive colour mixing (add all colours together and you get black)
What is trichromatic theory?
Theory proposed independently by Young and Helmholtz that holds that the human ability to perceive colour is mediated by three different types of receptors, each of which is most sensitive to a different range of wavelengths. (3 types of cones exist in the eye)
What are dichromats?
persons born with only 2 of the 3 cone photochemicals
How many photochemicals do most birds have and what are they?
- red, green, blue and a set which are sensitive to wavelengths in the ultraviolet range
What is the opponent process theory?
A theory of colour vision designed by Hering to explain the law of complementarity, it holds that units (neurons) that mediate the perception of colour are excited by one range of wavelengths and inhibited by another (complementary) range of wavelengths. According to the theory, such units cancel out the perception of colour when two complementary wavelength ranges are superimposed.
When does vision in human children reach adult (20/20) levels?
By about 6 years of age
What is experience-expectant processes (or experience-expectant synaptogenesis)?
Processes whereby synapses are formed and maintained when an organism has species-typical experiences; as a result, functions (such as vision) will develop for all members of a species, given a species-typical environment.
What is the primary visual area?
The area in the rearmost part of the occipital lobe that receives input from the optic nerves (by way of the thalamus) and sends output to other visual-processing areas of the brain.
What are feature detectors?
In vision, any neuron in the brain that responds to a specific property of a visual stimulus, such as its color, orientation, movement, or shape of its contour. More generally, any neuron in the brain that responds to a particular property (feature) of any sensory stimulus.
Treisman’s two-stage feature-integration theory invovles which 2 types of processing?
parallel processing and serial processing
What is parallel processing?
In perception, the early (unconscious) steps in the analysis of sensory information that act simultaneously on all (or at least many) of the stimulus elements that are available at any given moment.
What is serial processing?
The steps in the processing of sensory information that operate sequentially, an item at a time, on the available sensory information.
What is Gestalt psychology?
A school of psychological thought, founded in Germany, which emphasises the idea that the mind must be understood in terms of organised wholes, not elementary parts.
List the 6 Gestalt principles of grouping
- Proximity
- Similarity
- Closure
- Good continuation
- Common movement
6.Good form
Briefly describe the 6 Gestalt principles of grouping
The rules, proposed by Gestalt psychologists, concerning the manner by which the perceptual system groups sensory elements together to produce organized perceptions of whole objects and scenes. They include the principles of (a) proximity (nearby elements are grouped together), (b) similarity (elements that resemble one another are grouped together), (c) closure (gaps in what would otherwise be a continuous border are ignored), (d) good continuation (when lines intersect, those segments that would form a continuous line with minimal change in direction are grouped together), (e) common movement (elements moving in the same direction and velocity are grouped together), and (f) good form (elements are grouped in such a way as to form percepts that are simple and symmetrical)
Gestaltists called attention to our automatic tendancy to divide any visual scene into two elements. They are..
Figure and ground. We tend to see the circumscribing form as the ground ad the circumscribed form as the figure
Define figure (in perception)
In perception, the portion of a visual scene that draws the perceiver’s attention and is interpreted as an object rather than as the background.
Define ground (in perception)
In perception, the portion of a visual scene that is interpreted as the background rather than as the object of attention.
What is top-down control?
In theories of perception, mental processes that bring preexisting knowledge or expectations about an object or scene to bear upon the perception of that object or scene.
What is bottom-up control?
n theories of perception, mental processes that bring the individual stimulus features recorded by the senses together to form a perception of the larger object or scene
Define the condition called visual agnosia
A condition caused by damage to specific portions of the occipital and temporal lobes of the cortex, in which people cannot make sense of what they see.
What is visual form agnosia?
A variety of agnosia in which people can identify some elements of what they see but cannot perceive an object’s shape.
What is visual object agnosia
A variety of agnosia in which people can identify and draw the shapes of objects but cannot identify the objects.
What are the two streams of visual processing in the brain?
The what pathway (lower temporal stream, identifying objects, conscious vision)
The where pathway (Upper parietal stream, map of 3d space, unconscious visual control of movement)
What is the own-race bias?
The tendency to more easily recognise and remember members of one’s own race than members of other races (also known as cross-race bias, other-race effect, and same-race effect).
What is the fusiform face area?
Part of the human temporal cortex that is specialized for recognizing familiar faces.
What is the condition called prosopagnosia?
An inability to recognize the faces of familiar people (also known as face blindness)
What is binocular dispartity?
The cue for depth perception that stems from the separate (disparate) views that the two eyes have of any given visual object or scene. The farther away the object is, the more similar are the two views of it.
What is the motion parallax?
The cue for depth perception that stems from the changed view one has of a scene or object when one’s head moves sideways to the scene or object; the farther away an object is, the smaller is the change in view.
What are pictorial cues for depth? List 6 of them
The depth cues that operate not only when viewing real scenes but also when viewing pictures. They include occlusion, relative image size for familiar objects, linear perspective, texture gradient, differential lighting of surfaces, and (for outdoor scenes) position relative to the horizon.
What is size constancy?
The perceptual ability to see an object as the same size despite change in image size as it moves farther away or closer.
What is the Ponzo illusion?
A visual size illusion in which two converging lines cause objects between the two lines to look larger near the converging ends of the lines and smaller near the diverging ends.
What is the Müller-Lyer illusion?
A visual size illusion in which a horizontal line looks longer if attached at each end to an outward-extending, V-shaped object, and looks shorter if attached at each end to an inward-extending, V-shaped object.
What theory did Richard Gregory offer for the Ponzo and Müller-Lyer illusions?
One object in each illusion appears larger because of distance cues that lead it to be judged as farther away
Explain the moon illusion
The illusion by which the moon appears larger when seen near the horizon and smaller when seen near the zenith, even though it is objectively the same size and distance from the viewer in either location.
What is multisensory integration?
The integration of information from different senses by the nervous system
What is the visual dominance effect?
The phenomenon in which visual stimuli, when presented simultaneously with stimuli from other senses, tend to dominate awareness.
What is the McGurk effect?
In the ba/ga example most people hear da
What is synesthesia?
A condition in which sensory stimulation in one modality induces a sensation in a different modality.
