Chs. 3 & 4 Perception PDF

Chs.3 & 4 Perception Energy from the environment Top-down Processing converted into neural impulses Sensation vs Perception The interpretation of Bottom-up Processing sensory information  Sensation...

Chs.3 & 4 Perception Energy from the environment Top-down Processing converted into neural impulses Sensation vs Perception The interpretation of Bottom-up Processing sensory information  Sensation What is it? Information from the environment via receptor cells E.g. Info from the senses Bottom-up (or stimuli/data-driven) processing Sensations are sent to the brain via Transduction Energy from the environment converted into neural impulses  Sensory Receptor Cells Specialized cells that transduce sensory information Sensory Receptor cells tell the brain about stimuli Quality = What the stimulus is like Specific receptors for quality of stimulus E.g. Taste : sweet, sour, bitter, salty, etc.? Intensity = How strong the stimulus is. Neural firing frequency + number of neurons firing. E.g. brightness, loudness, amount of sweetness Sensory Receptors Summary Each sense has dedicated cells that are unique in location and function These cells tell the brain about the intensity and quality of the sensation  But how does information from the environment become coded in a language that the brain can understand? Transduction From Sensation to Perception Environment to Meaning From environment to meaning Sensations Neuron Receptor to in Transduction Brain Perception cells Neuron Environment Communication Energy from the environment Top-down Processing converted into neural impulses Sensation vs Perception The interpretation of Bottom-up Processing sensory information Perception What is it? It is the interpretation of sensory information Top-down (or concept-driven) processing Influenced by Experience Prior knowledge Expectations Context  Implications of Perception Individual differences lead to differences in perceptions background, knowledge, context, and experience All influence expectations and interpretations -> Perception  The word superiority effect and top-down processing We are faster and more accurate at identifying letters when they’re in the context of a word.  Top-down processing and the word superiority effect We are faster and more accurate at identifying letters when they’re in the context of a word. Word Recognition: The Good News Word reading made easier! Why does word superiority happen? Probability How likely is it that letter combinations appear in English? CONTEXT Word Recognition: The Bad News Errors also driven by probability! Likely to misread words predictably  Depth Cues More ways that experience influences perception.  How do we see interpret the world? Perceptions are experience based Depth cues (a specific type of contextual info) Tell us the distance and relative size of objects in our environment.  How do we see interpret the world? Perceptual constancy perceiving objects as unchanging in color, shape, or size despite illumination and retinal images changes. Example of size constancy Size perception depends on depth perception Illusion –a perception of something that differs systematically from reality. Ponzo Illusion ZAPS Ponzo Illusion  Ponzo Illusion Depth Cues The top line looks farther and longer But it is the same size In reality, a farther object would have to be longer than a nearer one for it to produce retinal images of the same size. Muller-Lyer Illusion How do the Ponzo and Muller Lyer Illusions Occur? Size Constancy! Special note: Muller Lyer Illusion is Cultural! It is mainly an illusion for Western, Educated, Industrialized, Rich, and Democratic societies! Sensations and Perceptions are Multimodal Sensory Integration creates a single percept The McGurk Effect (Illusion) Your Experience “GA” Video Stimulus “DA” “BA” Auditory Stimulus Sensory Integration creates a single percept The McGurk Effect Implications Multiple sensations from the environment can be combined to create meaning  Perception goes “beyond the information given.” Gestalt psychology –“organized whole” : The whole is greater than the sum of its parts Gestalt Principles: Proximity & Similarity Proximity = the closer two figures are to each other, the more likely they will be grouped together. Similarity = figures that resemble each other (shape, color, orientation) tend to be grouped together. Gestalt principles –continuation Continuation = the tendency to perceive smooth, continuous patterns rather than discontinuous ones. Gestalt principles –closure Closure = we tend to fill in gaps to create a complete, whole object. Gestalt principles –simplicity Simplicity: We tend to interpret a form in the simplest way possible.  Gestalt principles –figure and ground Figure-ground = our perceptual system divides scenes into figure and ground. Figure - contains the objects of interest. Ground - is the rest of the scene behind the figure.  Pattern Recognition The whole is greater than the sum of its parts, but what are the parts? Through recognition, we determine what objects are The brain uses the form (shape) of an object as a cue to identify it. How do we know what the parts are? Biederman (1987): Recognition by components (RBC) The components/ elementary part = “geons” An idea borrowed from linguistics (phonemes). Geons are identified by regions of concavity Detection of features is automatic Putting features together is NOT automatic. Relies on context and memory  Bottom-up recognition Geon recognition leads to object recognition Viewpoint invariant (Viewpoint Independent) Feature Integration Now that we know about features/parts, how do we put them together? Face recognition –the Thatcher illusion Thatcher illusion –illustrates the perceptual difficulties with inverted faces. Inverting faces interferes with the configuration and orientation information Different Objects, Different Recognition Systems? Viewpoint dependence appears when Interpreting faces Expertise is high (e.g., dog judges) Specific individuals have to be recognized Configurations of component parts are important Recognition by components Geons don’t need rotation to be identified viewpoint independent Whole objects need to be rotated to be identified viewpoint dependent Object Recognition Difficulty in judging how more than one feature is bound together in objects Integrative agnosia, parietal cortex damage E.g. prosopagnosia Visual Search ZAPS Visual Search A. Serial Search (aka conjunctive search) 1. Requires Attention 2. Search Time Increases with Set Size 3. Controlled Process B. Parallel Search (aka feature search) 1. Requires Little Attention 2. Search Time DOES NOT Increase with Set Size 3. Automatic Process Why is perception important?  Perception relies on multiple processes that work together to construct our experience. Our senses gather information from relatively limited sources of physical energy. Context and experience contribute to the perceptual process. Bottom line –perception involves: Focusing attention Brain interpreting sensory information, integrating information, resolving ambiguities. Your interpretation of sensations (e.g. perceptions) have far reaching effects on: Memory What you expect affects what you experience and remember Thoughts Are you thinking more about oranges and basketballs than before Behaviors Are you more likely to eat or engage in physical activity? Are you likely to be nice or aggressive? Implications of Perception Confirmation bias - the tendency to search for, interpret, or prioritize information in a way that confirms one's beliefs or expectations Politics Police investigation Some Take Home Points Sensation: Receptor cells transduce information in the environment to neural impulses Perception: Interprets the sensations. Interpretation influenced by: Experience Prior knowledge Expectations Context