Psych Perception - Perception Perception • • • •...

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Unformatted text preview: Perception Perception • • • • What is perception? Bottom-up and top-down processing influences on perception Face perception Perception and action What is perception? • most studies are based off visual and auditory The process of organizing, interpreting, and recognizing information from senses – Experiences (such as seeing or hearing) that start by stimulating sensory receptors • Everything we perceive is represented in the brain Feature detectors • Neurons that respond to features that make up objects • Physiological evidence – Hubel & Wiesel (1959, 1965) • Each neuron fired only to a specific stimulation (orientation, length, movement) 1 Perception Feature detectors • Behavioral evidence – Gibson (1969) Results: Quicker to discriminate between letters with unique features • G vs. W: RT = 458 ms • M vs. W: RT = 571 ms Conclusion: Detection of individual features is important for perception What information influences our perceptions? • Perception is determined by three sources of information: – Info originating from stimulation of the receptors • Bottom-up processing – Knowledge or expectations of the perceiver • Top-down processing – Additional information Prior k nowledge Additional information Top-down Perception Bottom-up Sensory receptors • e.g., nearby objects Bottom-up vs. top-down processing example • What does each sign say? Top-down- more complex because it incorporates memory, if you expect to see something somewhere nd you see it, that is top-down <---- Bottom up: colors, shape, letters (features), not enough info to tell you what it is; Top-down: using colors, shapes, and letters plus your memory tells you what the signs say 2 Perception Bottom-up processing • Recognition-by-Components (RBC) Theory (Biederman, 1987) – We perceive objects by decomposing them into geons – Objects are recognized when enough information is available to identify an object’s geons GEONS geons- geometric ions, shapes -3 geons- you can figure out object -3 stages: 1) identify edges of object so you can tell orientation 2)edges intersection 3) identify geons (3 geons= object recognition) OBJECTS RBC Theory • Biederman & Blickle (1985) – Recognition of fragmented objects: intersections vs. continuous edges 3 Perception Biederman & Blickle (1985) • less than; you need continuous edges to perceive objects Results: – Pictures with intersections removed were recognized _________________ than pictures with continuous edges deleted • Conclusion: – Recognition depends on ___________________________ Top-down processing • Helmholtz’s theory of unconscious inference – Some of our perceptions result from unconscious assumptions we make about the environment – We use our prior knowledge to inform our perceptions • Gestalt laws of perceptual organization – These laws specify how our brains combine and organize individual pieces into a meaningful perception – Example: Law of closure Illusory Contours http://www.iknow.net/phys_eye_education.html • • What do you perceive? Gestalt law of closure – We see complete figures even when information is missing. 4 Perception Other examples of top-down processing • How come we don’t confuse two objects with the same geons? • Top-down processing can result in misperceptions • Visual illusions Perceiving size • We perceive size by taking distance into account ̶ -Top down: how far you actually are based on experience -Bottom up- Initial size of object object’s distance is inversely related to the size of the retinal image Terror Subterranea 5 Perception Terror Subterranea • • Two monsters cast same size image on retina Background gives us information about distance Tunnel gives us perspective making monster in back look bigger; other aspects we see influence our perception: what we see is not what we get – Monster in back is farther away Additional information influences perception Face perception • Faces are processed differently from other objects Houses were more easy to identify parts whereas faces are processed holistically -happens in temporal lobe: feusiform face area – Evidence that they are processed holistically – Tanaka & Farah (1993) 6 Perception Face perception • Tanaka & Farah (1993) – Learned names that were paired with faces or houses – Tested on recognition with whole or parts. Tanaka & Farah (1993) holistically • Results: Percent correct 90 Isolated-part condition Whole-object condition 80 70 60 50 Faces Houses • Conclusion: − Faces are processed _________. Tanaka & Farah (1993) inverted • Another experiment used upright vs. inverted faces during learning. – Results: Percent correct 90 Isolated-part condition Whole-object condition 80 70 60 50 Upright Faces Inverted Faces – Conclusion: _______ faces disrupts holistic processing. 7 Perception Face perception • How is a face represented in the brain? Experience-dependent plasticity- mechanism through which the structure of the brain is changed by experience – Distributed coding: representation by a pattern of firing across a number of neurons – Experience-dependent plasticity Experience-dependent plasticity • • Some neurons respond best to faces that occur regularly in the environment – and can be taught to do this. Gauthier et al. (1999) – Measured activity in the FFA in response to faces and to “Greebles” Gauthier et al. (1999) • Results: – Activation of the FFA in recognizing novel objects __________________________ 8 Perception Gauthier et al. (1999) • established by experience with the objects Conclusion: – The particular objects to which neurons respond best are ____________________ Own-race bias • Golby et al. (2001) – Participants studied faces that were either the same or different race as themselves. – Behavioral results: • In a face recognition test, participants were better able to recognize same-race faces than other-race faces. – Physiological results: • Greater activation in the FFA for same-race faces than for other-race faces. Own-race bias • Golby et al. (2001) – Correlational results: • Differences in face recognition performance correlated with activation in FFA. – Conclusions: • Attention to race occurred spontaneously, in very early stages of face processing. • Experience versus racial categorization? • Cross-race faces are perceived less holistically than own-race faces? 9 Perception Perception and action • Perception and action are processed in two separate pathways in the brain: – “What” pathway for perceiving objects – “Where/how” pathway for locating and taking action toward these objects • Evidence for separate pathways – Dissociations in neuropsychology – Brain ablation studies Physiological methods • Dissociations in neuropsychology – Milner and Goodale (1995) • D.F.: damage to temporal lobe • Dissociation between judging orientation (impaired) and coordinating vision and action (intact) – People with parietal lobe damage can ____________________ but cannot accomplish a task that ________________ 10 Perception Physiological methods • Brain ablation -identify objects(object discrimination) -difficulty solving Landmark discrimination problem- cannot tell location of object – Ungerleider & Mishkin (1982) • Removing a monkey’s temporal lobe made it difficult to __________________ • Removing a monkey’s parietal lobe made it difficult to ___________________ 11 ...
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This note was uploaded on 12/04/2011 for the course EXP 3604 taught by Professor Fasig during the Fall '08 term at University of Florida.

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