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COGNITIVE CH 3
Terms in this set (71)
The inability to see motion, also known as motion blindness.
-you can detect the object is now in a position different from its position a moment ago but seeing "nothing in between"
How does vision operate?
process begins with light
process of the human eye seeing something
-Light enters the eye through the cornea, and
-the cornea and lens refract the light rays to produce a sharply focused image on the retina.
-The iris can open or close to control the amount of light that reaches the retina.
-The retina is made up of three main layers: the rods and cones, which are the photoreceptors; the bipolar cells; and the ganglion cells, whose axons make up the optic nerve.
The clear tissue that covers the front of the eye
the transparent structure behind the pupil that changes shape to help focus images on the retina
the light sensitive tissue that lines the back of the eyeball
respond to light
on the retina there are two types of photoreceptors
-sensitive to very low levels of light
-play an essential role when youre moving around in semi-darkness
-less sensitive to rods and needs more incoming light to operate
-3 types of cones and they each have their own pattern of sensitivity to different wavelengths
ability to see fine details of objects
very center of the retina
rods and cones do not report directly to the cortex, instead the photoreceptors stimulate bipolar cells
Bipolar cells excite ganglion cells
Ganglionic axons converge to form optic nerve
nerve tract that leaves the eyeball and carries info to various sites in the brain
Optic nerve first passes through lateral geniculate nucleus then the info travels to the primary visual cortex of the occipital lobe. Cells that link retina to the brain process info while sending the signal to the visual cortex
a pattern in which cells, when stimulated, inhibit the activity of neighboring cells
a process by which the visual system makes edges as visible as possible, facilitating perception of where one object or surface ends in the retinal image and another begins (picture of the grayscale picture, if u cover the lines it will be the same shade of grey)
Perception of a thin dark band on the dark side of a light-dark border and a thin light band on the light side of the border. These bands are an illusion because they occur even though corresponding intensity changes do not exist. (grey scale)
single cell recording
a procedure through which investigators can record, moment by moment, the pattern of electrical changes within a single neuron
when a neuron fires, each response is the same size which is called
the all or none law
the size and shape of the area in the visual world to which that cell responds (EX: when the neurons would only fire when the light was straight)
-when light is presented to the central region of the receptive field of these cells causes these cells to fire
-when light is presented to the surrounding regions of the receptive field, it causes these cells to stop firing
-strong uniform stimulus is equivalent to no stimulus at all
Orientation specific cells
-only fire for their respective stimulus
-horizontal or vertical line
the site on the occipital lobe where axons from the LGN first reach the cortex
-a system in which many different steps are going on simultaneously.
a system in which steps are carried out one at a time (EX: in a series)
Advantages of parallel processing
1) no wait time for multiple levels of analyses
2) The possibility of mutual influence among multiple systems (no one system has priority over another). This is important because:
- Sometimes our interpretation of an object's motion depends on our understanding of the object's 3-dimensional shaped. This suggests that it might be best if the perception of shape happened first
P cells and M cells
-p cells provide the main input for the LGN parvocellular cells; spatial & form analysis
-m cells provide the input for the LGN's magnocellular; motion and depth perception
The temporal lobe has the "what system" which plays a major role in the identification of visual objects, telling you whether the object is a cat, an apple or etc
if damaged leads to visual agnosia ( inability to recognize visually presented objects like a cup or pencil)
the parietal lobe has the "where system" which guides your actions based on your perception of where an object is located, above or below you, to your right or left
if damaged it leads to difficulty in reaching for objects
the task of reuniting the various elements of a scene, elements that are initially addressed by different systems in different parts of the brain
3 elements contribute to solving the binding problem
The areas processing features like shape, color, and motion each know the spatial position of the object, keeping track of where the target is
-identify which sensory elements belong with which (vertical line neuron, downward motion neuron)
-when both neurons are firing together it is neuron synchrony, the brain encodes the fact that these attributes are bound together
how do neurons become synchronized in the first place?
when we overload someones attention, they are likely to make
occur when attention is overloaded
-impaired feature conjunction
-info is reflected in which cells are firing, how often they are firing, whether the cells are firing in synchrony with other cells and the rhythm in which they are firing
stimulus attributes are picked up by visual system, attributes then must be assembled together into recognizable wholes
A visual pattern that easily allows more than one interpretation, people perceive it first one way and then another.
-not an illusion
-single reality being perceived differently (cube)
determination of what is the figure and what is the ground
-you shape the perception
-perception flips back & forth
-stimulus isnt changing
EX: CANADIAN FLAG
Describe the top-down processing that organizes sensory information into distinct forms. Six principles: similarity, simplicity, closure, proximity, and good continuation
info about the stimulus (corners or angles) or curves that are in view
Many aspects of the brain's functioning depend on ______ ______, with different brain areas all doing their work at the same time.
we perceive the constant properties of objects in the world (their sizes, shapes, and so on) even though the sensory info we receive about these attributes changes whenever our viewing circumstances change. (being close or far away from an object)
if you are far away from an object youre viewing, then the image cast onto you retinas by that object will be relatively small, but if you approach the object, then the image size will increase.
correctly perceiving the sizes of objects despite the changes in retinal-image size created by changes in viewing distance
-objects far away seem smaller in size but we are not fooled by this
correctly perceiving the brightness of objects whether they're illuminated by dim light or strong sun
if an object doubles its distance from the viewer, the size of its image is reduced by half.
if an object triples its distance, the size of its image is reduced to a third of its initial size.
-in real life we see objects against some background
-provides comparison cues
-the relationship btwn objects contribute to size constancy
-misperception of the world
-misperception of depth
-misperception of depth relationships
the perception of depth
-to know the distance we need info regarding the viewing angle and illumination.
-knowing distance is important so we know which objects are nearby and which are further away.
features of the stimulus that indicate an object's position
-each eye looks out on the world from slightly different positions, resulting in slightly different view
difference between the two eyes
monocular distance cues
cues about depth from just one eye
-shape of lens adjusting to focus the image on the retina
-degree of adjustment by ocular muscles to achieve the visual acuity is used to calculate the distance
cues to depth perception that are used to convey depth in drawings and paintings
-rely on straightforward priciple of physics
--the blocking of one object by some other object
-the object blocking is perceived to be closer than the object being blocked
the tendency for parallel lines to appear to converge on each other as they get farther and farther from the viewer
when we move our head, the images projected by objects in our view more across the retina
another type of info about depth and plays a large role in the coordination of bodily movements
binocular disparity is a powerful cue, but its informative only when objects are relatively close by
motion parallax tells you a great deal about the spatial layout of your world, but only if youre moving
One brain area that has been mapped in considerable detail is the visual system. This system takes its main input from the rods and cones on the retina. Then, information is sent via the optic nerve to the brain. An important point is that cells in the optic nerve do much more than transmit information; they also begin the analysis of the visual input. This is reflected in the phenomenon of lateral inhibition, which leads to edge enhancement
Part of what we know about the brain comes from single-cell recording, which can record the electrical activity of an individual neuron. In the visual system, this recording has allowed research- ers to map the receptive fields for many cells. The mapping has provided evidence for a high degree of specialization among the various parts of the visual system, with some parts specialized for the perception of motion, others for the perception of color, and so on. The various areas function in parallel, and this parallel processing allows great speed. It also allows mutual influence among multiple systems
Parallel processing begins in the optic nerve and continues throughout the visual system. For example, the what system (in the temporal lobe) appears to be specialized for the identification of visual objects; the where system (in the parietal lobe) seems to identify where an object is located
The reliance on parallel processing creates a problem of reuniting the various elements of a scene so that these elements are perceived in an integrated way. This is the binding problem. One key in solving this problem lies in the fact that different brain systems are organized in terms of maps, so that spatial position can be used as a framework for reuniting the separately analyzed aspects of the visual scene.
Visual perception requires more than the "pick- up" of features. Those features must be organized into wholes — a process apparently governed by the so-called Gestalt principles. The visual system also must interpret the input, a point that is especially evident with reversible figures. Crucially, though, these interpretive steps aren't separate from, and occurring after, the pickup of elementary features, because the features themselves are shaped by the perceiver's organization of the input.
The active nature of perception is also evident in perceptual constancy. We achieve constancy through a process of unconscious inference, taking one aspect of the input (e.g., the distance to the target) into account in interpreting another aspect (e.g., the target's size). This process is usually quite accurate, but it can produce illusions
The perception of distance relies on many cues — some dependent on binocular vision, and some on monocular vision. The diversity of cues lets us perceive distance in a wide range of circumstances
Recommended textbook explanations
Katherine Minter, Mary Spilis, William Elmhorst
C. Nathan DeWall, David G Myers
Richard A. Kasschau
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