Sensation: Principles and Processes PDF

SENSATION SENSATION Sensation How do we construct our representations of the external world? To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation. When we select, organ...

SENSATION SENSATION Sensation How do we construct our representations of the external world? To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation. When we select, organize, and interpret our sensations, the process is called perception. 5 - 22  5-3 SENSATION Sensory Processing  Transduction SENSATION  Sensory coding  Psychophysics  Transduction Location of Sense Organ Environmental Stimuli Energy Transduced T 5.1 Eye Light Radiant energy Ear Sound Mechanical energy Vestibular system Tilt and rotation of head Mechanical energy SENSATION Tongue Taste Recognition of molecular shape Nose Odour Recognition of molecular shape Skin, Internal Organs Touch Mechanical energy Temperature Thermal energy Vibration Mechanical energy Muscle Pain Chemical reaction Stretch Mechanical energy Anatomical coding: interprets the location SENSATION and type of sensory stimulus according to which incoming nerve fibers are active Psychophysics The systematic study of the relation between the physical characteristics of stimuli and the sensations they produce Physics of the mind How do we measure these sensations 7 5-7 Psychophysics A study of the relationship between physical characteristics of stimuli and our psychological experience with them. Psychological Physical World World Light Brightness Sound Volume Pressure Weight Sugar Sweet 5-8 8 Just Noticeable Difference The smallest difference between two similar stimuli that can be distinguished Also called the difference threshold The minimum difference between two stimuli required for detection 50% of the time 5-9 Psychophysics F 5.1 SENSATION Just Noticeable Difference The smallest difference between two similar stimuli that can be distinguished, also called the difference threshold The detectable difference increases with the strength of the stimulus 5 - 11 Weber’s Law Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Stimulus Constant (k) Light 8% Weight 2% Tone 3% 12 5 - 12 Absolute threshold Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. 13 5 - 13 Subliminal Threshold Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness. Kurt Scholz/ Superstock 14 5 - 14 Signal Detection Theory F 5.3 SENSATION  Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.” 5 -16 16 Top-Down Processing Information processing guided by higher- level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT 17 5 - 17 Making Sense of Complexity Our sensory and perceptual processes work together to help us sort out complex images. “The Forest Has Eyes,” Bev Doolittle 18 5 - 18  Sensing the World Senses are nature’s gift that suit an organism’s needs. A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice. 19 5 - 19 Sensory Adaptation Diminished sensitivity as a consequence of constant stimulation. Put a band aid on your arm and after awhile you don’t sense it. 20 5 - 20 The Stimulus Input: Light Energy Visible Both Photos: Thomas Eisner Spectrum 21 5 - 21  Wavelength (Hue) Hue (color) is the dimension of color determined by the wavelength of the light. Wavelength is the distance from the peak of one wave to the peak of the next. 22 5 - 22 Wavelength (Hue) Violet Indigo Blue Green Yellow Orange Red 400 nm 700 nm Short wavelengths Long wavelengths Different wavelengths of light result in different colors. 23 5 - 23  Intensity (Brightness) Intensity: Amount of energy in a wave determined by the amplitude. It is related to perceived brightness. 24 5 - 24  Intensity (Brightness) Blue color with varying levels of intensity. As intensity increases or decreases, blue color looks more “washed out” or “darkened.” 25 5 - 25 The Eye and Its Functions F 5.7 SENSATION Parts of the eye 1. Cornea: Transparent tissue where light enters the eye. 2. Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light. 3. Lens: Focuses the light rays on the retina. 4. Retina: Contains sensory receptors that process visual information and sends it to the brain. 5. Sclera: the tough white coating on the eye 27 5 - 27 The Eye and Its Functions F 5.8 SENSATION  Transduction of Light by Photoreceptors F 5.12 SENSATION  Photoreceptors E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969 30 5 - 30 SENSATION SENSATION Visual Information Processing Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex. 33 5 - 33  Visual Information Processing Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc. 34 5 - 34 Shape Detection Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses. Ishai, Ungerleider, Martin and Haxby/ NIMH 35 5 - 35  Eye Movements  Vergence Movements: Cooperative movements of the eyes  Saccadic Movements: Rapid movements of SENSATION the eyes, used for scanning a visual scene  Pursuit Movements: Movements made to keep a moving image on the foveas SENSATION SENSATION  Colour Vision Perceptual Physical Dimension Physical Characteristics T 5.2 Dimension Hue Wavelength Length of oscillation of light radiation SENSATION Brightness Intensity Amount of energy of light radiation Saturation Purity Intensity of dominant wavelength relative to total radiant energy  Hue, Brightness, and Saturation F 5.14 SENSATION Colour Mixing F 5.15 SENSATION Colour and Paint Mixing F 5.16 SENSATION SENSATION Color Blindness Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory. Ishihara Test 44 5 - 44  Opponent Colors Gaze at the middle of the flag for about 30 Seconds. When it disappears, stare at the dot and report what you see. 5 -45 45  Defects in Colour Vision  Protanopia: Red cones filled with green photopigment SENSATION  Deuteranopia: Green cones filled with red photopigment  Tritanopia: Lack of blue cones