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Perception. What you want to remember. Perception is more than photons and pressure. Perception is divided from cognition/emotion but they are often intertwined. Perception follows laws and heuristics. Sensation. Sensation - the registration of physical stimuli
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What you want to remember • Perception is more than photons and pressure. • Perception is divided from cognition/emotion but they are often intertwined. • Perception follows laws and heuristics.
Sensation • Sensation - the registration of physical stimuli • Hearing - anatomy and function of the ear • Vision - anatomy and function of the eye
Sensation • What is the purpose of sensory processing? • To transform physical stimuli in the environment into neural signals in the brain • Example (Hearing): Sound waves are transformed into vibrations in the ear, and the strength of those vibrations are coded by sensory neurons
Some Questions of Interest • How can we perceive an object like a chair as having a stable form, given that the image of the chair on our retina changes as we look at it from different directions?
Some Questions of Interest • What are two fundamental approaches to explaining perception? • What happens when people with normal visual sensations cannot perceive visual stimuli?
Perception Is… • The process of recognizing, organizing, and interpreting information • How do you recognize these items?
Basic Concepts (Gibson) • Distal object • Grandma’s face • Informational medium • Reflected light from Grandma’s face • Proximal stimulation • Photon absorption in the rod and cone cells of the retina • Perceptual object • Grandma’s face
Perceptual Basics • Sensory adaptation • Occurs when sensory receptors change their sensitivity to the stimulus • Constant stimulation leads to lower sensitivity • Our senses respond to change • Perceptual training
Perceptual Illusions • Sometimes we cannot perceive what does exist • Sometimes we perceive things that do not exist
Perceptual Illusions • Sometimes we perceive what cannot be there
http://www.vimm.it/cochlea/cochleapages/overview/history.htm
Figure 7.4 Figure 7.4 The basilar membrane of the human cochlea. High-frequency sounds produce their maximum displacement near the base. Low-frequency sounds produce their maximum displacement near the apex.
Corresponds to apex of cochlea Corresponds to base of cochlea Primary auditory cortex Secondary auditory cortex Auditory Cortex • Tonotopic organization in superior temporal lobe
Typical human range about 20 - 20 kHz Audiograms for various species
Our Visual System • Light travels through the eye and focuses on the retina • Electromagnetic light energy is converted into neural electrochemical impulses
Our Visual System • Three main layers of neural tissue in retina • Ganglion cells • Amacrine cells, horizontal cells, bipolar cells • Photoreceptors • Rods and cones
Visual Pathways in the Brain • What/where hypothesis • One path for identifying • Temporal lobe lesions in monkeys • Can indicate where but not what • Another for spatially locating • Parietal lobe lesions in monkeys • Can indicate what but not where
Theories of Perception • Bottom-up theories • Parts are identified, put together, and then recognition occurs • Top-down theories • People actively construct perceptions using information based on expectations
0 Bottom-Up Processing Theories • Direct perception • Template theories • Feature-matching theories • Recognition-by-components theory
0 Template Theories • Basics of template theories • Multiple templates are held in memory • To recognize the incoming stimuli, you compare to templates in memory until a match is found Search memory for a match See stimuli
0 Template Theories • Weakness of theory • Problem of imperfect matches • Cannot account for the flexibility of pattern recognition system Search for match in memory See stimuli No perfect match in memory
0 Feature-Matching Theories • Recognize objects on the basis of a small number of characteristics (features) • Detect specific elements and assemble them into more complex forms • Brain cells that respond to specific features such as lines and angles are referred to as “feature detectors”
Pandemonium Model • Four kinds of demons • Image demons • Feature demons • Cognitive demons • Decision demons
0 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, exact location abstracted • Hypercomplex cells detect particular colors (simple and complex cells), bars, or edges of particular length or moving in a particular direction
0 Recognition-by-Components (RBC) Theory • Biederman (1987) • Describes how 3D images are identified • Breaks objects down into geons • Objects are identified by geons, relationship between them
Gibson’s Theory of Direct Perception (Ecological psych) • The information in our sensory receptors is all we need to perceive anything • Do not need the aid of complex thought processes to explain perception
Gibson’s Theory of Direct Perception (Ecological psych) • Use texture gradients as cues for depth and distance • Allows us to perceive directly the relative proximity or distance of objects
0 Top-Down Processing (Constructive Approach) • Perception is not automatic from raw stimuli • Processing is needed to build perception • Top-down processing occurs quickly and involves making inferences, guessing from experience, and basing one perception on another
0 Evidence for Top-Down Processing • Context effects
Configural-Superiority Effect • Objects presented in context are easier to recognize than objects presented alone • Task: Spot the different stimuli, press button
Configural-Superiority Effect Target Composite Measure reaction time Target alone = 1884 Composite = 749 Target spotted faster in a context!
Which Approach Is Right? • Top-down or bottom-up • Perhaps a bit of both
Beginning of Gestalt psychology • 1910 – Max Wertheimer on vacation noticed that distal objects seemed to move with the train; nearby objects went past. Why? • Study of apparent motion – why stationary objects appear to move 34
Apparent motion • Phi phenomenon – flashing a vertical light that is followed 50-60 msec later by a horizontal light produces the appearance of movement. The light appears to move from vertical to horizontal • Movement only perceived if delay was 50 – 60 msec • The perceptual experience had properties the individual components did not • 1st Gestalt paper presented in 1912 35
Basic premise of Gestalt psychology • Humans are not passive receivers of sensory information. Our perceptions are active, lively, and organized • We actively organize perceptions into coherent wholes – today the process is referred to as top-down or conceptually driven processing 36
Scientific Method • Gestalt perspectives on scientific method reflect their acceptance of field physics as a model for psychology. • They emphasized the physical environment. • They used experience to guide analysis in psychology. • They started research with phenomenological investigation. • They accepted a broad range of methods in psychology.
Mind and Brain • Gestalt perspectives on mind and brain reject reductionistic and linear models of mind. • Köhler argued for models of mind based in natural systems. • He used models of mind based in the brain. • He described models in terms of free dynamics. • Köhler advocated isomorphism (ex. psychophysical isomorphism). • There is a structural correspondence between experience and underlying brain processes.
Key terms in gestalt psychology: Geographical versus behavioral environment • Geographical environment – the physical world • Behavioral environment – our interpretation of the physical world • Our interpretation or organization can produce a behavioral world that is very different from the physical world • Illusions, dreaming, fantasies 39
Gestalt’s View of Perception • Basic tenet • “The whole is more than a sum of its parts” • Law of Prägnanz • Individuals organize their experience in as simple, concise, symmetrical, and complete manner as possible
Perception is not just detection • Perception is not just about detecting color or shape. • Perception is about organizing visual information. • How do we organize visual information?
Gestalt’s Principles of Visual Perception • Figure-ground • Organize perceptions by distinguishing between a figure and a background • Proximity • Elements tend to be grouped together according to their nearness • Similarity • Items similar in some respect tend to be grouped together
The figure represents “some thing.” The contours belong to the figure rather than to the ground.
Which one if the figure and which is the ground? This is easy. The figure tends to have solid and continuous surface.
