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Elizabeth Olds

PS262 October 6, 2012 Chapter 5: Object Perception Introduction Perceptual Organization  Grouping: gestalt approach o Strucutalism  Add up perception of each bit of scene to get perception of while scene o Gestalt  The whole is more than the sum of its parts  Perception of one part of stimulus depends on the nature of other parts of stimulus  Not purely bottom-up  Whole vs. sum of parts  Laws of perceptual organization o Grouping of elements in an image to create larger objects o Good continuation  Points that when connected result in straight or smooth curving lines are seen as belonging together, lines tend to be seen a way as to follow the smoothest path o Proximity  Things that are near each other appear to be grouped together o Common Region o Uniform Connectedness o Synchrony o Common Fate o Meaningfulness  Perceptual Segregation o Problem of figure-ground segregation  When we see a separate object, it is usually seems a and figure that stands out from its background which is called the ground o Reverse figure ground  Perceiving image as two different ways o Regions in the lower part of a display are more likely to be seen as figures that in the upper  Recognition-by- Components theory o How do we recognize objects ? o Our recognition of objects is based on features called geons o NAPs (non-accidental properties)  Properties of edges in the retinal image that correspond to the properties of edges in the three-dimensional environment  Edges that are only seen from certain viewpoints o Principle of Componential Recovery  Identify objects even when parts of the objects are hidden by other objects  Based on small number of geons  Gists o Naturalness o Openness o Roughness o Expansion o Colour  Regularities of the Environment o Physical regularities  Regularly occurring physical properties of the environment o Semantic  Meaning of a scene  Characteristics associated with the functions carried out in different types of scenes  Theory of Unconscious Inference o Some of our perception are the result of unconscious assumptions we make about the environment o Account for our ability to create perceptions from stimulus information that can be seen in more than one way  Likelihood Principle o We perceive the object that is most likely to have caused the pattern of stimuli we have received  Contextual Modulation o The effect of stimuli that fall outside of the neuron`s receptive fields bg  Rules o Similarity o Meaningfulness  Problems with gestalt o Laws describe, don’t predict  What happens when two conflict o Simplicity o Similarity  Overall contribution o Pay attention to overall stimulus pattern o Doesn’t explain mechanisms of how visual system groups portions  Perceptual Figure-ground segregation o Transition from perceptual grouping to perceptual segregation o Depends on object recognition  Neurons and o Perceptual groping  Neural response to grouping by  Similarity of orientation  Good continuation  Response is affected by stimuli outside of its RF o Figure-ground segregation  Early neural representation = affected by overall context Identifying the Object  What object has produced this portion of the retinal image  Recognition by Components o Recognize 3-D object by decomposing image of object into its basic Components  Experience o Binocular rivalry  Perception alternating between 2 images o Report of perceptual experience and activity in the brain are correlated  Apparent Movement o No movement, just two stationary stimuli flashing on and off Chapter 6:Attention Intro  Fixation o Places where the eyes pause to take in information about specific parts of the scene o Lines connecting the dots are eye movements called saccades o About 3 per second o People fixate on few objects that were irrelevant to the task and that eye movements and fixations were closely linked to the actions they were about to take  Stimulus Salience o Characteristics of the environment that stand out because of physical properties such as as colour, brightness, contrast, or orientation  Parkhurst o Initial fixations were closely associated with the saliency map, with fixations being more likely on high saliency o Dual task condition, performance also high o It is possible to take in information about faces when attention is not focused on the faces  Perception can occur without focused attention o When observers only had to do one task at a time they performed well  Is attention necessary for perception? o Inattentional blindness o Failure to perceive stimulus that isn`t attended to fully o Gorilla video  Neisser  Attention is directed towards objects and events o Change blindness  Gradual changes a difficult for us to detect o Attention improves perception, not guaranteed  Effects of Attention on Information Processing o Posner o Observers react more rapidly on valid trials than on invalid trials o Information processing is more effective at the place where attention is directed o Evidence that attention is directed at one place on object and then spread  Help with perceiving obscured objects  Why? o Visual system has a limited capacity  Themes o Overt: ( visible) orienting (selects for in depth processing  Acuity = best at fovea  Vs covert (secret)= moving attention o Selection  Spatial  Selection (1)  Object  Selection  Feature/property selection (same location/object) o Control of selection  Bottom up  Stimulus driven, peripheral cues  Top down  Goal driven, central cues 2 o 4 categories of experiment  Detection  Judge if stimulus present  Filtering  Concentrate on one of many inputs, exclude others  Search  Look for target among others  Resource Allocation  For executing two tasks jointly Detection  Threshold of sensitivity o Weakest stimulus necessary for obs. to detect  Spatial attention o Posner  Does attention enhance perception?  Knowing in advance the correct spatial location of a T helps you react faster to that to  Effects of Attention on Perception o When two gratings were actually the same, the one that received attention appeared to have more contrast o Attention enhances the appearance of an object  Binding o Features such as colour, form, motion, and location are combined to create our perception of a coherent objects o Binding problem  How do we combine all of these physically separated neural signals to achieve a unified perception of the ball?  Feature Integration Theory o Processing an object by the visual system as occurring in two stages  Preattentive stage  Because it does not depend on attention  Object broken down into features such as colour, orientation, location  What stream  Focused Attention  Features are recombined so we perceive the whole object, not individual features  Where stream o Illusory Conjunctions  Features associated with one object can become incorrectly associated with another object o Visual search  Something we do anytime we look for an object among a number of others objects, su
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