Sensation and Perception Lecture Notes PDF

Sensation and Perception  Sensation and Perception Sensation: The detection of physical energy emitted or reflected by physical objects; it occurs when energy in the external environment or the body stimulates receptors in the sense organs. Perception: The process by which...

Sensation and Perception  Sensation and Perception Sensation: The detection of physical energy emitted or reflected by physical objects; it occurs when energy in the external environment or the body stimulates receptors in the sense organs. Perception: The process by which individuals organize and interpret sensory information in order to give meaning to their environment.  MEANING….. Perceptions differ from person to person. Each individual perceives the same situation differently. Group perceptions can influence and individual’s perception. Individuals organize and interpret things based on their past experiences and the important values they consider important.  Video (with notes) Sensation V Perception https://www.youtube.com/watch?v=feT1O dI6Htg Sensation  Psychophysics Psychophysics Psychophysics is the branch of psychology that studies the effects of physical stimuli on sensory perceptions and mental states. The field of psychophysics was founded by the German psychologist Gustav Fechner (1801–1887), who was the first to study the relationship between the strength of a stimulus and a person’s ability to detect the stimulus. The Absolute threshold of sensation: The smallest amount of the stimulus we can detect The difference threshold (or just noticeable difference [JND]), refers to the change in a stimulus that can just barely be detected by the organism. The German physiologist Ernst Weber (1795– 1878) made an important discovery about the JND—namely, that the ability to detect differences depends not so much on the size of the difference but on the size of the difference in relationship to the absolute size of the stimulus. Weber’s law maintains that the just noticeable difference of a stimulus is a constant proportion of the original intensity of the stimulus https://www.youtube.com/watch?v=-1e0uIS5j2Q (Weber’s Law)  Absolute Threshold (we can accurately report on its existence (or its nonexistence) better than 50% of the time) The human eye can detect the equivalent of a single candle flame burning 30 miles away and can distinguish among more than 300,000 different colors. The ear can detect sounds as low as 20 hertz (vibrations per second) and as high as 20,000 hertz, and it can hear the tick of a clock about 20 feet away in a quiet room. We can taste a teaspoon of sugar dissolved in 2 gallons of water, and we are able to smell one drop of perfume diffused in a three-room apartment. We can feel the wing of a bee on our cheek dropped from 1 centimeter above (Galanter, 1962).  Transduction is the conversion of stimuli detected by receptor cells to electrical impulses that are transported to the brain. Coding is when the brain converts particular stimuli into specific sensations To Summarize …. Perception  Perception The study of perception deals with the question of how organisms process and organize incoming raw sensory information in order to (1) form a coherent representation or model of the world within which the organism dwells and (2) use that representation to solve naturally occurring problems, such as navigating, grasping, and planning.  Perception Minute 4:11 – 6:30 https://www.youtube.com/watch?v=9tWUUBkNk fQ The distal stimulus is the external object which is sensed. proximal stimulus. Is representation of that distal stimulus on the sensory apparatus (e.g. retina) Functions of Perception  Five functions of perception Five major functions of the perceptual system are: (1) Attention: determining which part of the sensory environment to attend to, (2) Localization: or determining where objects are, (3) Recognizing, or determining what objects are, (4) Abstracting the critical information from objects, and (5) Perceptual constancy keeping the appearance of objects constant, even though their retinal images are changing. Another area of study is how our perceptual capacities develop.  1. Attention We have three anatomically distinct sets of processes in our brain enabling us to selectively attend to only a small part of all the information around us, one: is responsible for keeping us alert, is responsible for focussing on task relevant information only and decides whether we want to continue attending to the information or switch our attention to other information.  2. Localisation To localize objects, we must first separate them and then organize them into groups. Localization involves determining an object’s position in the up–down and left–right dimensions. This is relatively easy because the required information is part of our retinal image. Localizing an object also requires that we know its distance from us. This form of perception, known as depth perception, is not so easy because it’ not available in the retinal image. We have a variety of depth cues, both monocular and binocular, that allow us to do this. Localizing an object sometimes requires that we know the direction in which an object is moving.  Perceptual Groupings The Gestalt Laws of Perceptual Grouping. Objects in a scene appear to group pre-attentively according to certain laws or principles and based on distinctive features or their mutual positions https://www.youtube.com/watch?v=RWJSC1HU32c Some factors underlying grouping are: Continuity Closure Proximity Similarity  A. Continuity/connectednes s B. Proximity C. Similarity D. CLOSURE  E. Figure Ground Distinction (Determining where objects are) In order to localize objects, we have to separate them from their surrounding background. Usually, large things are perceived as the background of small things  IN GROUPS DRAW EXAMPLES OF PERCEPTUAL GROUPINGS EXAMPLE More elaborate examples Gestalt’s principles of perceptual groupings  3. Recognition (Determining what kind of object it is) Recognizing an object requires that the various features associated with the object (such as shapes and colors) be correctly bound together, a process that requires attention. Recognition of a particular object is aided by first acquiring ‘global’ aspects of the scene; for example quickly understanding that you are looking at a kitchen helps recognizing an ambiguous object as a loaf of bread rather than a mailbox.  3. Recognition cont. (Determining what kind of object it is) Recognizing an object entails binding together various features of an object such as its shape and its color. The features themselves are acquired via pre-attentive processes, while ‘gluing’ them together require attention.  4. Abstraction (critical features) Abstraction is the process of converting the raw sensory information acquired by the sense organs (for example, patterns of straight and curved lines) into abstract categories that are pre-stored in memory (for example letters or words). Abstracted information takes less space and is therefore faster to work with than raw information. A useful analogy is between a bitmapped computer image of a face versus an abstracted image of the same face that is made up of preformed structures such as ovals and lines. Advantages of Abstraction: Takes less space Faster to work with (e.g faster processing of images) Retention of the critical information Figure 5.23 Verbal Labels and Abstraction. Carmichael, Hogan, and Walter (1932) showed people the kind of ambiguous stimuli shown in the middle panel. Observers were given one of the two verbal labels shown in the second and fourth columns. The subjects’ later reconstructions of what they had seen conformed to the verbal label, as shown in the first and fifth columns. This experiment indicates that subjects remember not what they literally saw but rather abstract the fundamental information from it. 5. Perceptual constancy, Constancy- brain’s ability to maintain a perception of the underlying physical characteristics of an object, such as shape, size or colour, even when the sensory manifestations of these objects change drastically. https://study.com/academy/lesson/perceptual-constancy-in-psychology-definition-examples.html  Perceptual constancy Another major function of the perceptual system is to achieve perceptual constancy – to keep the appearance of objects the same in spite of large variations in the initial representations of the stimuli received by the sense organs that are engendered by various environmental factors. Color and brightness constancy entail perceiving the actual color and brightness of a stimulus even when the actual information arriving at the eye varies in color makeup (because of the color makeup of the ambient lighting) and in brightness (because of the level of ambient illumination)  Perceptual constancy Size constancy entails perceiving the actual size of a stimulus even when the actual size of the object’s image on the retina varies because of the object’s distance. Intrinsically, constancies entail ‘illusion’ in the sense that by a constancy’s very nature, perception differs systematically from the physical nature of the stimulus. It logically follows, and is empirically true that many visual illusions may be explained by the various constancies. Constancies occur in all sensory modalities. Various kinds of perceptual illusions can be explained by the perceptual system’s insistence on maintaining constancies. Although visual constancies are the most salient, constancies exist in all sensory modalities.