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| features play a central role in object recognition |
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neurons in the retina or brain that repsond to specific features of the stimulus (movement, orientation)
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| What do we use to organize our perception of visual stimuli? |
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| Interpretation: features, interpretation, organization |
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| school of pshychology that emphasized organization as an essential feature of all mental activity; emphasizes the role of organized wholes in perception |
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| separate a scene into individual objects, linking together the parts of each object that go together |
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| Principles of parsing: list |
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| similarity, proximity, good continuation, subjective contours |
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principle of parsing
* principle in perception by which we tend to group together figures that resemble each other (blue dots w blue dots) |
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| principle in perception by which we tend to group together figures that are closer together; the closer the figures are to each other, the more we tend to group them together perceptually ( we tend to see kids playing together in groups rather than individual) |
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| principle in perception by which we tend to prefer organization in which contours continue smoothly along their original course (leash tangled still looks like one long continuous one rather than many) |
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| perceived contours that do not exist physically; we tend to complete figures that have gaps in them by perceiving a contour as continuing along its original path; special case of good continuation |
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| separation of the visual field into a part (figure) that stands out against the rest (ground)/ allows you to focus on the figure/ usually the figure is perceived as being closer to the viewer than the background |
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| visual patterns that easily allow more than one interpretation, including figures that allow parsing such that what is initially perceived as figure becomes ground and vice versa |
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| Exampels of reversible figures |
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| Necker cube, demonstrates that the visual organizaton of the stimulus is not specified by the stimulus itself, but is instead up to the perceiver |
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| model of object recognition in which there is a hierarchy of detectors with detectors in each layer serving as the triggers for detection in the next layer/ activation of feature nets can flow from bottom up and top down simultaneously |
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| Bottom up activation of feature nets |
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| processes move from detection of basic features through more complex detectors; data driven processes |
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| Top down activation of feature nets |
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| knowledge driven processes guided by the ideas and expectations that the receiver brings to the situation |
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| primitive 3D geometric figures (cubes, cylinders, pyramids) from which all other shapes are created through combinations. (30 geons) |
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| some brain lesions can lead to this disorder, which impairs people's ability to recognize the objects they see; they can describe the object's structures and form, but can't name it or tell its function |
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| In object recognition, the perceiver must first identify its features and then use these features to determine which geons are present. then we use our visual memory to see if there's an object that matches up with what we've detected to determine what the objects are |
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| Problem in object recognition |
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| signals travel from the rods and cones to bipolar cells to the ganglion cellss which form the opic nerve, leaves the eyeball and travels to the brain |
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| Ganglion cells can be classified into 2 categ: |
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| smaller cells that blanket the entire retina; outnumber the magno cells; senstitive to hue and brightness differences; play a crucial role in perception of pattern and form |
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| larger cells found primarly in the retina's periphery; insensitive to hue differences but respond strongly to changes in brightness; play a central role in detection of motion and perception of depth |
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| Single cell recording technique |
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| evidence for neural specializatio comes from single cell recording techniques - determine which specoific stimuli elicit a response from a cell and which don't |
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| Parallel processing in the Visual Cortex |
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=different cells and areas of the brain specialize in a particular kind of analysis, and these different analyses go on in parallel - some cells are analyzing form, other motion, color, etc
a) allow for greater speed
b) allows each system to draw info from the others and to help and influence each other
c) explains how feature detection depends on interpretation, and vice versa; ensures that our perception makes sense at both the larger scale and fine grained levels |
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| The "what" and "where" systems |
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| in the inferotemporal cortex and parietal cortex |
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-occipital temporal pathway
- system of visual circuits and pathways leading from the visual cortex to inferotemporal cortex (temporal lobe); especially involved in object identification (i see a pen)
- damage leads to visual agnosia- unable to recognize visual objects and faces |
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- occipital parietal pathway
- system of visual circuits and pathways leading from viaul cortex to parietal lobe
involved in spacial localization of objects and coordination of movement (pencil's lying to my right and i moved my hand to reach it)
- damage leads to having difficulty with visual orientation and reaching for objects but no problem identifying them |
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| how the nervous system manages to bind together elements that were initially detected by separate systems |
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= different groups of neurons firing in synchrony with each other; brain uses these patterns to identify which sensory elements belong with witch
a) uses the timing of the firing by these groups of neurons if the neurons are firing at the same time, seems to indicate that the messages from the neurons are bound together
b) for ex, if neurons detecting a vertical line are firing at the same time as the neurons signaling movement, then these attributes are registered as belonging to the same object
- if the neurons aren't firing together, the features are registered as belonging to separate objects
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| the constant attributes of a distal object (size shape) that we are able to perceive despite differences in the proximal stimulus; we perceive the constant properties of objects, even though the sensory information we receive about these attributes changes whenever our viewing circumstances change |
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| the tendency to perceive objects as retaining their shapes, despite the increase or decrease in the size of the image projected on the retina by moving closer to or farther from the objects |
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| the tendency we perceive objects as retaining their shapes, despite changes in our viewing angle that produce changes in the image projected on the retina |
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| the capacity to perceive an object as having an unchanging brightness, despite the fact that changes in illumination cause a change in how much light refelcts off the object and reaches the eye |
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these perceptual constancies seem to be achieved by making inferences unconsciously, taking our viewing circumstances into account in a way that allows us to perceive the constant properties of the visual world
* process proposed by Helmholtz to explain how we accomplish size constancy by using distance calculation w/o consciously doing so |
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| How is size constancy achieved? |
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a) unchaging relationships: relationships between size within retinal image stay the same as we move closer or farther away
b) distance info - Helmholtz inverse relat b/in distance and retinal image size: size of image * distance
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= features of the stimulus that indicate an object's position; sources of info that signal the distance from the observer to the distal stimulus
- binocular and monocular cues |
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cues for distance that involve using both eyes
- binocular disparity (3D movies) |
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cues for distance that only involve using one eye
- pictorial cues - used by artists to create an impression of depth on a flat surface
- interposition and linear perspective |
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| Monocular distance cue in which an object that is blocked by another object is viewed as farther away than the object that's blocking our view of it |
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| a monocular cue for distance in which parallel lines seem to converge as they get farther and farther away from the viewer; this cue is based on the fact about optics that distant objects produce a smaller retinal image than do nearby objects of the same size |
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| depth cue provided by the fact that as an observer moves, the images cast by nearby objects move more rapidly on the retina than images cast by objects that are farther away |
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| a depth cue provided by the fact that, as an observer approaces an object, the object's retinal images enlarges, whereas when an observer retereats from the objects, the retinal image of the object shrinks; this cue gives us crucial info about depth and plays a large role in coordination of our movements |
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different distance cues become important in different circumstances, for example:
a) binocular disparity is used when objects are relatively close (closer than 30ft)
b) motion parallax and optic flow are used only when we're moving
c) texture gradients are used only if there's an uniform texture in view |
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| cells in the visual cortex that are sensitive to an image moving across the retina; these cells are direction specific |
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| motion detectors in the visual cortex fire if a stimulus moves across their receptive field from a particular direction only; other motion detector cells fire if the motion is from another direction |
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| perception of movement by stimuli that are stationary but flash on and off at apropriate positions and at appropriate time intervals; can be indistinguishable from real movement (movies) |
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| we perceive an object as having an unchanging position in space, despite the fact that changes in the viewer's position cause a change in the spatial position of the retinal image cast by the object |
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| the theory that explains the position constancy-it states that we take our own movements into account by computing the shift in the retinal image that our own motion will produce and cancelling out the amount of movement in interpreting the visual input; we can compare the anticipated shit due to our movements with the shift that actually occurs- if they match, then all movement is due to our movement and there's no movement in the environment |
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| movement is perceived in a stationary stimulus that's enclosed by a moving framework |
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| in a moving display, a pattern in which surrounding objects are in fact moving but are perceived as stationary, and in which the self (not moving) is perceived as moving |
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| How do we pay attention to some inputs but not to others? |
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| orienting, conjunction search, priming |
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| tendency of an organism to shift its attention and sensory machinery (turn heads, etc) to inspect a novel, unexpected, or otherwise interesting stimulus; there are physical adjustments in selecting what we pay attention to, which includes moving parts of our body to better perceive the stimulus |
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| search in which the target is defined by a combination of features, such as looking for a red circle among a display of red verticals and yellow circles; involves mental adjustments in selecting what we pay attention to |
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| a warming up of certain detectors so they're better prepared to respond than they otherwise would be; helps to focus our attention and avoid distracters, but may hinder our perception of anything else; seems to influence how we allocate our rpcessomg resources affecting our internal selection process |
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