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

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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 • • 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 ...
View Full Document

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.

Ask a homework question - tutors are online