Sensation, Perception & Vision - Psychology Lecture

Chapter 4: Sensation, Perception & Vision i. Sensing and Perceiving Sensation- awareness resulting from the stimulation of a sense organ Perception- the organization and interpretation of sensations Transduction- the conversion of stimuli detected by receptor cells to electrical impulses that are then transported to the brain 4.1 We Experience Our World Through Sensation ii. iii. iv. Sensory Thresholds: What Can We Experience? a. There is much that we sense, but there is even more that we do not Measuring Sensation Psychophysics- the branch of psychology that studies the effects of physical stimuli on sensory perceptions and mental states Absolute threshold- the intensity of a stimulus that allows an organism to just barely detect it Signal detection analysis- a technique used to determine the ability of the perceiver to separate true signals from background noise a. A measure, sensitivity, refers to the true ability of an individual to detect the presence or absence of signals Difference threshold- the change in a stimulus that can just barely be detected by the organism Weber’s law- just noticeable difference of a stimulus is a constant proportion of the original intensity of the stimulus Blindsight- a condition in which people are unable to consciously report on visual stimuli but nevertheless can accurately answer questions about what they are seeing b. People with blindsight can correctly determine an object’s location and direction of movement, as well as identify simple geometrical forms and patterns Key Takeaways a. Sensation is the process of receiving information from the environment through our sensory organs. Perception is the process of interpreting and organizing the incoming information in order that we can understand it and react accordingly b. Transduction is the conversion of stimuli detected by receptor cells to electrical impulses that are transported to the brain c. Although our experiences of the world are rich and complex, humans- like all specieshave their own adapted sensory strengths and sensory limitations d. Sensation and perception work together in a fluid, continuous process e. Our judgements in detection tasks are influenced by both the absolute threshold of the signal as well as our current motivations and experiences. Signal detection analysis is used to differentiate sensitivity from response biases f. The difference threshold, or just noticeable difference, is the ability to detect the smallest change in stimulus about 50% of the time. According to Weber’s law, the just noticeable difference increases in proportion to the total intensity of the stimulus g. Research has found that stimuli can influence behavior even when they are presented below the absolute threshold (i.e., subliminally). The effectiveness of subliminal advertising, however, has not been shown to be of large magnitude 4.2 Seeing i. The Sensing Eye and the Perceiving Visual Cortex Cornea- a clear covering that protects the eye and begins to focus the incoming light Pupil- a small opening in the center of the eye Iris- the colored part of the eye that controls the size of the pupil by constricting or dilating in response to light intensity Lens- a structure that focuses the incoming light on the retina Retina- the layer of tissue at the back of the eye that contains photoreceptor cells Visual accommodation- the process of changing the curvature of the lens to keep the light entering the eye focused on the retina a. For people who are nearsighted images from far objects focus too far in front of the retina whereas people who are farsighted, images from near objects focus too far behind the retina Optic Nerve- a collection of millions of ganglion neurons that sends vast amounts of visual information, via the thalamus, to the brain Rods- visual neurons that specialize in detecting black, white, and gray colors b. 120 million rods in each eye, highly sensitive to shorter-waved and weak light Cones- visual neurons that are specialized in detecting fine detail and colors Fovea- the central point of the retina ii. iii. c. Even if only one eye is functional, both hemispheres will still receive input from it d. Because there are no photoreceptor cells at the place where the optic nerve leaves the retina, a hole or blind spot in our vision is created Feature Detector Neurons- specialized neurons located in the visual cortex that respond to the strength, angels, shapes, edges, and movements of a visual stimulus Perceiving Color a. The shade of a color Is conveyed by the wavelength of the light that enters the eye Opponent-Process Color Theory- proposes that we analyze sensory information not in terms of three colors but rather in three sets of “opponent colors”: red-green, yellowblue, and white-black b. When light rays enter the eye the red, blue, and green cones on the retina respond in different degrees and send different strength signals of red, blue, and green through the optic nerve Perceiving Form a. Summary of Gestalt Principles of Form Perception i. Figure and ground 1. We structure input such that we always see a figure (image) against a ground (background) iv. ii. Similarity 1. Stimuli that are similar to each other tend to be grouped together iii. Proximity 1. We tend to group nearby figures together iv. Continuity 1. We tend to perceive stimuli in smooth, continuous ways rather than in more discontinuous ways v. Closure 1. We tend to fill in gaps in an incomplete image to create a complete whole object Perceiving Depth Depth Perception- the ability to perceive three-dimensional space and to accurately judge distance Visual Cliff- a mechanism that gives the perception of a dangerous drop-off, in which infants can be safely tested for their perception of depth Depth Cues- messages from our bodies and the external environment that supply as with information about space and distance Binocular Depth- depth cues that are created by retinal image disparity- that is, the space between our eyes, and thus which require the coordination of both eyes Convergence- the inward turning of our eyes that is required to focus on objects that are less than about 50 feet away from us Monocular Depth Cues- depth cues that help us perceive depth using only one eye v. a. Monocular Depth Cues That Help Us Judge Depth at a Distance i. Position 1. We tend to see objects higher up in our field of vision as farther away ii. Relative size 1. Assuming that the objects in a scene are the same size, smaller objects are perceived as farther away iii. Linear perspective 1. Parallel lines appear to convergence at a distance iv. Light and shadow 1. The eye receives more reflected light from objects that are closer to us. Normally, light comes from above, so darker images are in shadow v. Interposition 1. When one object overlaps another object, we view it as closer vi. Aerial perspective 1. Objects that appear hazy, or that are covered with smog or dust, appear farther away Perceiving Motion a. The brain detects motion partly from the changing size of an image on the retina and in part from the relative brightness of object Beta Effect- the perception of motion that occurs when different images are presented next to each other in succession Phi Phenomenon- we perceive a sensation of motion caused by the appearance and disappearance of objects that are near each other vi. Key Takeaways a. Vision is the process of detecting the electromagnetic energy that surrounds us. Only a small fraction of the electromagnetic spectrum is visible to humans b. The visual receptor cells on the retina detect shape, color, motion, and depth c. Light enters the eye through the transparent cornea and passes through the pupil at the center of the iris. The lens adjusts to focus the light on the retina, where it appears upside down and backward. Receptor cells on the retina are excited or inhibited by the light and send information to the visual cortex through the optic nerve d. The retina has two types of photoreceptor cells: rods, which detect brightness and respond to black and white, and cones, which respond to red, green, and blue. Color blindness occurs when people lack function in the red- or green- sensitive cones e. Feature detector neurons in the visual cortex help us recognize objects, and some neurons respond selectively to faces and other body parts f. The Young-Helmholtz trichromatic color theory proposes that color perception is the result of the signals sent by the three types of cones, whereas the opponent-process color theory proposes that we perceive color as three sets of opponent colors: redgreen, yellow-blue, and white-black g. The ability to perceive depth occurs through the result of binocular and monocular depth cues h. Motion is perceived as a function of the size and brightness of objects. The beta effect and the phi phenomenon are examples of perceived motion 4.3 Accuracy and Inaccuracy in Perception vii. viii. ix. x. Perceiving Form a. (same as above) Perceiving Depth a. (same as above) How the Perceptual System Interprets the Environment Sensory Interaction- the working together of different senses to create experience a. An experience in which one sensation creates experiences in another is called synesthesia Selective Attention- the ability to focus on some sensory inputs while turning out others Sensory Adaptation- a decreased sensitivity to a stimulus after prolonged and constant exposure Perceptual Constancy- the ability to perceive a stimulus as constant despite changes in sensation Illusions Illusions- occur when the perceptual processes that normally help us correctly perceive the world around us are fooled by a particular situation so that we see something that does not exist or that is incorrect xi. xii. The Important Role of Expectations in Perception a. Our perceptions are influenced by our desires and motivations Key Takeaways a. Sensory interaction occurs when different senses work together, for instance, when taste, smell, and touch together produce the flavor of food b. Selective attention allows us to focus on some sensory experiences while tuning out others c. Sensory adaptation occurs when we become less sensitive to some aspects of our environment, freeing us to focus on more important changes d. Perceptual constancy allows us to perceive an object the same, despite changes in sensation e. Cognitive illusions are examples of how our expectations can influence our perceptions f. Our emotions, motivations, desires, and even our culture can influence perceptions