Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 4 Sensation and Perception Sensation and Perception: The Distinction • Sensation : stimulation of sensory receptors and produces neural impulses • Perception: selection, organization, and interpretation of sensory input • Psychophysics = the study of how physical stimuli are translated into psychological experience Psychophysics: Basic Concepts • Sensation begins with a detectable stimulus – Psychological versus physical • Fechner: the concept of the threshold – Absolute threshold: detected 50% of the time. – Just noticeable difference (JND): smallest difference detectable • Weber’s law: size of JND proportional to size of initial stimulus Examples of Absolute Thresholds • Vision: a candle flame at 30 miles on a dark, clear night • Hearing: the tick of a watch under quiet conditions at 20 feet. • Taste: one teaspoon of sugar in 2 gallons of water • Smell: one drop of perfume diffused into the entire volume of a six room apartment • Touch: the wing of a fly falling on your cheek from a distance of 1 centimeter Psychophysics: Concepts and Issues • Signal-Detection Theory: Sensory processes + decision processes = detection – applications • Sensory Adaptation: Decline in sensitivity • Transduction: Where (in vision, it is in the retina) does the energy (in vision it is electromagnetic energy) of the stimulus become converted to electrical/chemical energy and the signal is sent to the brain. Subliminal Perception • Subliminal Perception: registration of input without conscious awareness. – 1957 study in a movie “Eat Popcorn” – Objective evaluation – studies have not confirmed the influence of subliminal messages: – Subliminal Perception: What our unconscious perceives (4 min) Vision: The Stimulus • Light = electromagnetic radiation – Amplitude: perception of brightness – Wavelength: perception of color – purity: mix of wavelengths • perception of saturation, or richness of colors. The Eye: Converting Light into Neural Impulses • The eye: housing and channeling • Components: – Cornea: where light enters the eye – Lens: focuses the light rays on the retina – Iris: colored ring of muscle, constricts or dilates via amount of light – Pupil: regulates amount of light The Retina: An Extension of the CNS • Retina: absorbs light, processes images, and sends information to the brain • Optic disk: where the optic nerve leaves the eye (The blind spot) • Receptor cells: – Rods: black and white/ low light vision – Cones: color and daylight vision • Adaptation: becoming more or less sensitive to light as needed – F 4.10 Optic Nerve, Blind Spot & Fovea Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where optic nerve leaves the eye, because there are no receptor cells located here, it creates a blind spot. Fovea: Central point in the retina, around which the eye’s cones cluster. http://www.bergen.org 10 The Retina and the Brain: Visual Information Processing • Light -> rods and cones -> neural signals > bipolar cells -> ganglion cells -> optic nerve -> optic chiasm ->thalamus> opposite half brain -> primary visual cortex. Figure 4.15 The what and where pathways from the primary visual cortex Shape Detection Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses. 14 Feature Detectors in the Visual Cortex Principles of Perception • Gestalt principles of form perception: – figure-ground, proximity, similarity, continuity, closure, and simplicity – Point of view effects • Recent research: – Distal (stimuli outside the body) vs. proximal (stimulus energies impinging on sensory receptors) stimuli. – Perceptual hypotheses • Context – Object recognition – object background consistency – Perceptual Learning • Change in the brain that alters how we process sensory information • Perceptual Habits: Ingrained patterns of organization and attention – Other-Race Effect: Tendency to be better at recognizing faces from one’s own racial group than faces from other racial or ethnic groups – Active Movement: Self-generated action; accelerates perceptual adaptation – Context: Information surrounding a stimulus; affects perception – Frames of Reference: Internal standards for judging stimuli Hearing: The Auditory System • Stimulus = sound waves (vibrations of molecules traveling in air) – Amplitude (loudness) – Wavelength (pitch) – Purity (timbre) • Wavelength described in terms of frequency: measured in cycles per second (Hz) – Frequency increase = pitch increase • Sound pressure (SPL) – decibels Loudness ratings and potential hearing damage. The Ear: Three Divisions • External ear (pinna): collects sound. • Middle ear: the ossicles (hammer, anvil, stirrup) • Inner ear: the cochlea – a fluid-filled, coiled tunnel – contains the hair cells, the auditory receptors – lined up on the basilar membrane Figure 4.49 The human ear Figure 4.50 The basilar membrane The Auditory Pathway • • • • Sound waves vibrate bones of the middle ear Stirrup hits against the oval window of cochlea Sets the fluid inside in motion Hair cells are stimulated with the movement of the basilar membrane • Physical stimulation converted into neural impulses • Sent through the thalamus to the auditory cortex (temporal lobes) Theories of Hearing: Place or Frequency? • Hermann von Helmholtz (1863) – Place theory: different portions (or places) along the basilar membrane are activated by a specific frequency • Other researchers (Rutherford, 1886) – Frequency theory: suggests that the entire basilar membrane is activated to differing degrees by different frequencies • Georg von Bekesy (1947) – Traveling wave theory suggests that a combination of both the Place and Frequency theories explain hearing. Auditory Localization: Where Did that Sound Come From? • Two cues critical: • Intensity (loudness) • Timing of sounds arriving at each ear – F 4.51 – Head as “shadow” or partial sound barrier • Timing differences as small as 1/100,000 of a second Hearing Deficits Older people tend to hear low frequencies well but suffer hearing loss for high frequencies. 27 The Chemical Senses: Taste • Taste (gustation) • Physical stimulus: soluble chemical substances – Receptor cells found in taste buds – 25% of people have a very large number of taste buds. They are “supertasters”. • Pathway: taste buds -> neural impulse -> thalamus -> cortex – Four primary tastes: sweet, sour, bitter, and salty (maybe a 5th “umami”, a savory taste) – Taste: learned and social processes • Culture and taste – – May explain why some people enjoy hot peppers The Chemical Senses: Smell • Smell (Olfaction) – Studies show women’s smell sensitivity is better than men’s. • Physical stimuli: substances carried in the air – dissolved in fluid, the mucus in the nose – Olfactory receptors = olfactory cilia • Pathway: Olfactory cilia -> neural impulse > olfactory nerve -> olfactory bulb (brain) – The only sensory information that does not go through thalamus © Richard Costano, Discover Magazine, 1993 Fig. 5.25 Receptors for the sense of smell (olfaction). Olfactory nerve fibers respond to gaseous molecules. Receptor cells are shown in cross section at the left of part (a). (c) On the right, an extreme close-up of an olfactory receptor cell shows the fibers that project into the airflow inside the nose. Receptor proteins on the surface of the fibers are sensitive to different airborne molecules. Smell and Memories Brain region (red) for smell is closely connected with brain regions (limbic system) involved with memory, that is why strong memories are made through the sense of smell. Skin Senses: Touch • Physical stimuli = mechanical, thermal, and chemical energy impinging on the skin. receptors/detector – • Pathway: Sensory receptors -> the spinal column -> brainstem -> cross to opposite side of brain -> thalamus -> somatosensory (parietal lobe) • Temperature: free nerve endings in the skin • Pain receptors: also free nerve endings – Two pain pathways: fast vs. slow Gate Control Theory of Pain • Gate Control Theory: Pain messages from different nerve fibers pass through the same “neural” gate in the spinal cord. – If gate is closed by one pain message, other messages may not be able to pass through Other Senses: Kinesthetic and Vestibular • Kinesthesis - knowing the position of the various parts of the body – Receptors in joints/muscles • Vestibular - equilibrium/balance – Semicircular canals Fig. 5.30 The vestibular system. Vestibular System and Motion Sickness • Motion sickness is directly related to vestibular system • Sensory Conflict Theory: Motion sickness occurs because vestibular system sensations do not match sensations from the eyes and body – After spinning and stopping, fluid in semicircular canals is still spinning, but head is not – Mismatch leads to sickness • Medications, relaxation, and lying down might help