PSY 341 Chapter 3Perception- Sensationo Absorbing raw energy (ex, light waves, sound waves) through our sensory organs - Transductiono Conversion of this energy to neural signals - Attention o Concentration of mental energy to process incoming information - Perceptiono Recognizing, selecting, organizing, and interpreting these signals  Not an exact copy of the world  Partially based on our past experience and expectations From Sensation to Representation - Energy contains information about the world (usually incomplete, full of noise, and distorted)- Sensory receptor transduces energy into a neural response o Equal playing field, what matters is which nerves are excited o Stimulation of a specific nerve provides codes for that one sense - Sensory nerve transmits the coded activity to the central nervous system - Thalamus processes and relays the neural response o For all senses but olfaction (which projects to the olfactory bulb)- Relayed to specialized areas of the cortexBottom-Up Processing Feature Matching Theories - Recognize objects on the basis of a small number of characteristics (features)o Detect specific elements and assemble them into more complex forms o Brain cells that respond to specific features such as lines and angles are referred toas feature detectors Physiological Evidence For Features Hubel & Wiesel (1979)- Simple cells detect bars or edges of particular orientation in particular location - Complex cells detect bars or edges of particular orientation, motion, direction Feature Searches - Simple features seem to “pop out”o Fast processing o But sometimes need to engage in serial search for simple features o Occurs when distractors share simple feature as target- Serial search o If feature doesn’t pop out, must rely on serial search - Combined features don’t “pop out”o Don’t have conjoined feature detectors o Requires serial search  Processing speed depends on number of distractors - More distractors=longer processing o Hierarchical processingFeature Analysis Bottom up processing - Perception may start with the senses - Incoming raw data - Energy registering on receptors Top down processing - Perception may start with the brain - Persons knowledge, experience, expectations - The use of preexisting knowledge to organize individual features into unified whole o Guided by higher level cognitive processes such as knowledge and expectations - Top down processes influence how we perceive objects o Example: the multiple personalities of a blob Object Perception- Four concepts o Helmholtz’s unconscious inference o Regularities Approach o Bayesian inference o Gestalt laws Unconscious inference - The problem: Stimulus on receptors can be ambiguous - The solution: Helmholtz’s Theory of Unconscious Inference (1860)o We perceive the object that would most likely cause the pattern of stimulation o Termed the likelihood principle - Perceptions are the result of unconscious assumptions we make about the environment o We use our knowledge to inform our perceptions o Top down processes help us interpret the signal Regularities in the environment - Similar to Helmholtz’s idea of unconscious inference - This approach suggests that perception is influenced by our knowledge of regularities in the environment - Semantic Regularities: characteristics associated with the functions carried out in different scenes o Scene Schemas - Physical regularities: regularly occurring physical properties of the environment o Oblique effect: we are biased to perceive vertical and horizontal orientations because those are more frequent than other orientations - Light from above assumption - Good continuation: perceive covered object as continuous in form Object Recognition - Perceptual set (perceptual expectancy)o The tendency to perceive things a certain way because previous experiences or expectations influence those perceptions o Our experiences create schemas Schemas can bias our perceptions Bayesian Inference - Unconscious inference and regularities in the environment lead to a third approach, basedon probabilities - Based on:o Prior probability: initial belief regarding probability of an outcome o Likelihood of the outcome: extent to which available evidence is consistent with the outcomeGestalt Psychology - A perspective proposed around the time of Helmholtz’s theory of unconscious inference o A shift away from structuralism - Whole is greater than the sum of its parts - Principles of perceptual organization: explains how we group objects - Law of Pragnanz o Individuals organize their experience in as simple, concise, symmetrical, and complete manner as possible Gestalt and regularities in the environment - The Gestalt principle of good continuation is likely related to the fact that object continuations occurs in the environmentPerception and action - Action facilitates perception (Gibson)o Movement helps us perceive objects in the environment more accurately - What and where streams o What (Ventral) stream  Identifying an object  AKA Perception Pathway o Where/How (Dorsal) stream  Identifying the objects location AKA Action Pathway Neurons and the environment - Neurons becomes tuned to respond best to what we commonly experience o Horizontals and verticals Change Detection - Flicker paradigmo Blank intermediate image o Distrupts attention  Draws attention away from scene  Serial Search  Increased reaction time - Uninterrupted image o Pop out effecto Decreased reaction time - Importance of attention in perception o Interactive processes - Change