Transcript Sensation
Sensation Sensation a process by which our sensory receptors and nervous system receive and represent stimulus energy Perception a process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events Sensation Bottom-Up Processing analysis that begins with the sense receptors and works up to the brain’s integration of sensory information Top-Down Processing information processing guided by higherlevel mental processes as when we construct perceptions drawing on our experience and expectations Sensation- Basic Principles Psychophysics study of the relationship between physical characteristics of stimuli and our psychological experience of them Light- brightness Sound- volume Pressure- weight Taste- sweetness Sensation- Thresholds Absolute Threshold minimum stimulation needed to detect a particular stimulus usually defined as the stimulus needed for detection 50% of the time Difference Threshold minimum difference between two stimuli that a subject can detect 50% of the time just noticeable difference (JND) increases with magnitude Sensation- Thresholds 100 Percentage of correct detections 75 50 Subliminal stimuli 25 0 Low Absolute threshold Intensity of stimulus Medium When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”. Sensation- Thresholds Weber’s Law- to perceive a difference between two stimuli, they must differ by a constant proportion a constant for each sense: light intensity- 8%, weight- 2% tone frequency- 0.3% Just noticable difference has a proportion to be met in order to sense difference Weber’s Law Classic and still identified today but it did not account for extreme values….175 watt and a 200 watt… Ability to recognize difference diminishes….so in 1860s Sensation- Thresholds Fechner’s Law- “upgrade” of Weber’s law includes increase of jnd with extreme measures/magnitude Adding the relationship of the perceived magnitude to physical intensity of a stimuli Same basic idea: ½ pound book in 2lb vs. 60lb backpack 1 voice in chorus of 10 versus 2 in 20 Sensation- Thresholds Steven’s Power Law - upgrade to Fechner (Fechner’s law didn’t work for pain*, other stimuli) Strength of a sensation related to the intensity of the stimuli raised to some power So pain like electric shock you will sense a a small change at higher intensities than at the lower intensities when more may be needed to recognize difference Stevens Fechner Sensation - Thresholds Note that one of the implications of Steven’s law is that with higher levels of pain you get MORE sensitive! Sensory adaptation- diminished sensitivity with constant stimulation Sensation- Thresholds Signal Detection Theory predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise) assumes that there is no single absolute threshold detection depends partly on person’s experience expectations motivation level of fatigue Sensation- Thresholds Signal Detection Theory Assumes TWO things going on: 1. sensitivity to stimulus (physical) 2. response bias – also called decision criterion (psychological) Can measure & plot these in a Receiver Operating Characteristic curve (ROC curve) Vision Transduction- conversion of one form of energy to another (for us, it’s specifically: converting physical energy to neural impulses) Properties of light and vision Physical Psychological intensity brightness wavelength hue (color) wave purity saturation Vision Wavelength- the distance from the peak of one wave to the peak of the next Amplitude - the height (strength) of a wave Hue- perceived “color” of the light Intensity- amount of energy in a wave determined by amplitude Saturation - perceived “purity” of a color (e.g. pastels have low saturation) Vision- Spectrum of Electromagnetic Energy (quantum particle/waves) Vision- Physical Properties of Waves Short wavelength=high frequency (bluish colors, high-pitched sounds) Great amplitude (bright colors, loud sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Small amplitude (dull colors, soft sounds) Vision Pupil- adjustable opening in the center of the eye Iris- a ring of muscle the forms the colored portion of the eye around the pupil and controls the size of the pupil opening Lens- transparent structure behind pupil that changes shape to focus images on the retina Vision Vision Accommodation change in shape of lens focus near objects Retina inner surface of eye light sensitive contains rods and cones layers of neurons beginning of visual information processing Vision Acuity- the sharpness of vision Nearsightedness nearby objects seen more clearly lens focuses image of distant objects in front of retina Farsightedness faraway objects seen more clearly lens focuses near objects behind retina Retina’s Reaction to Light- Receptors Cones near center of retina (fovea) fine detail and color vision daylight or well-lit conditions Rods peripheral retina detect black, white and gray twilight or low light Saccades - quick eye movements Retina’s Reaction to Light Bipolar cells- neurons that combine info from multiple receptors Ganglion cells – neurons that combine info from multiple bipolar cells. Optic nerve – bundle of axons of the ganglion cells that carry info from retina to brain. Vision- Receptors Receptors in the Human Eye Cones Rods Number 6 million 120 million Location in retina Center Periphery Sensitivity in dim light Low High* Color sensitive? Yes No *Why pirates wore eyepatches? Arrrr… Retina’s Reaction to Light Optic nerve- nerve that carries neural impulses from the eye to the brain Blind Spot- point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there Fovea- central point in the retina, around which the eye’s cones cluster Pathways from the Eyes to the Visual Cortex Vision- Stabilized Images on the Retina Retina’s Reaction to Light Receptive fields – regions in which receptors respond to light Lateral inhibition – receptor (or neuron) making it’s neighbors less sensitive Helps in things like edge detection Visual Information Processing Feature Detectors neurons in the visual cortex respond to specific features shape angle movement Cell’s responses Stimulus Visual Information Processing Parallel Processing simultaneous processing of several dimensions through multiple pathways color motion form depth Visual Information Processing Abstraction: Brain’s higher-level cells respond to combined information from feature-detector cells Feature detection: Brain’s detector cells respond to elementary features-bars, edges, or gradients of light Retinal processing: Receptor rods and conesbipolar cells ganglion cells Recognition: Brain matches the constructed image with stored images Scene Visual Information Processing Neural pathways (multiple!) Optic nerve through optic chiasm (crossover), becomes the optic “tract” then… Primary visual cortex (striate cortex) then splits into… The “what” path (thru temporal lobes) The “where” path (up into parietal lobes) Visual Information Processing – Color vision Trichromatic (three color) Theory The Young–Helmholtz theory three different retinal color receptors sensitive to red green Blue Visual Information Processing – Color vision But Tri-chromatic didn’t explain afterimages or colorblindness! So… Opponent Process Theory Black-white receptors (for brightness & saturation) Red-green receptors (for hue) Blue-yellow receptors (for hue) Opponent ProcessAfterimage Effect Color-Deficient Vision People who suffer red-green blindness have trouble perceiving the number within the design Visual Information Processing Opponent-Process Theory- opposing retinal processes enable color vision “ON” “OFF” red green green red blue yellow yellow blue black white white black Visual Information Processing – Color vision So who’s right??? Turns out they’re both right: Tri-chromatic theory works in the retina Opponent process works in the higher visual processing parts of the brain Together they explain what we know about color vision quite well. Audition Audition the sense of hearing Properties of sound and hearing Physical Psychological intensity loudness wavelength pitch wave purity timbre (tone) Audition Frequency the number of complete wavelengths that pass a point in a given time Pitch a tone’s highness or lowness depends on frequency Timbre - tonal quality; “richness” The Intensity of Some Common Sounds Audition- The Ear Outer Ear Auditory Canal Eardrum Middle Ear hammer anvil stirrup Inner Ear oval window cochlea basilar membrane hair cells Audition Place Theory the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated Frequency Theory the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch Audition So who’s right? They’re both probably right: At low frequencies: frequency theory At high frequencies: place theory At middle frequencies: both How We Locate Sounds How we locate sounds Two cues: Differences between the two ears in loudness Differences in the arrival time at the ears Audition Conduction Hearing Loss hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea Nerve Hearing Loss hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve Audition Older people tend to hear low frequencies well but suffer hearing los for high frequencies Amplitude required for perception relative to 20-29 year-old group 1 time 10 times 100 times 1000 times 32 64 128 256 512 1024 2048 4096 8192 16384 Frequency of tone in waves per second Low Pitch High Touch Skin Sensations pressure only skin sensation with identifiable receptors warmth cold pain Pain Gate-Control Theory theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain “gate” opened by the activity of pain signals traveling up small nerve fibers “gate” closed by activity in larger fibers or by information coming from the brain Taste Taste Sensations sweet sour salty bitter Sensory Interaction the principle that one sense may influence another as when the smell of food influences its taste Smell Olfactory nerve Olfactory bulb Nasal passage Receptor cells in olfactory membrane Age, Sex and Sense of Smell Number of correct answers Women and young adults have best sense of smell 4 Women 3 Men 2 0 10-19 20-29 30-39 40-49 50-59 60-69 Age Group 70-79 80-89 90-99 Smell Less important in humans than animals but we still can detect: Pheromones Smell-communicated chemicals secreted by organisms People can often identify gender by smell of sweaty hands or articles of clothing! Body Position and Movement Kinesthesis the system for sensing the position and movement of individual body parts Vestibular Sense the sense of body movement and position including the sense of balance