* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download View Presentation
Biological neuron model wikipedia , lookup
Animal echolocation wikipedia , lookup
Metastability in the brain wikipedia , lookup
Embodied cognitive science wikipedia , lookup
Surface wave detection by animals wikipedia , lookup
Development of the nervous system wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Sound localization wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
C1 and P1 (neuroscience) wikipedia , lookup
Sensory substitution wikipedia , lookup
Neural correlates of consciousness wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Signal transduction wikipedia , lookup
Sensory cue wikipedia , lookup
Time perception wikipedia , lookup
Evoked potential wikipedia , lookup
Perception of infrasound wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Chapter 7 Sensation Sensation The raw experience of a sensory stimulus, such as a light or sound Perception: The interpretation of sensory information according to expectations and prior learning The Senses as Evolved Adaptations Sensing Tastes and Smells sensitivity to chemicals important for feeding and reproduction chemical receptors became more sophisticated Smell vs. Taste receptors evolved The Senses as Evolved Adaptations Sensing Light responsiveness to the sun’s energy provides “remote guidance” for sensing things at a distance eyes allow us to process form, color, movement and visual acuity The Senses as Evolved Adaptations Sensing Sounds sensing sound increases range of sensation beyond that of smell allows localization and identification sound can be used as a form of communication The Senses as Evolved Adaptations Sensing Touch, Warmth and Pain skin senses allow location of nearby objects touch enables skilled movements pain motivates behavior Psychophysics The study of how humans and animals respond to sensory stimuli The mathematical relationship of sensory intensity to the magnitude of a physical stimulus Just Noticeable Difference (JND) The minimal amount of sensory change in a stimulus that can be detected e.g. how much more weight do you need to perceive a difference in weights? Just Noticeable Difference Weber’s Law: jnd = kI Just Noticeable Difference = Constant x Intensity The size of the just noticeable difference is equal to some some proportion of the standard Constant varies depending on sensory modality Just Noticeable Difference Fechner: JND is a measure of the “psyche” similar to inches on a ruler The Absolute Threshold Minimum amount of stimulation that can be detected on half the trials Count up number of “yes” responses (Frequency of “seeing”) 100 Threshold = P(yes) 50 50% response point 0 Stimulus Intensity Psychophysical Methods: How to Measure Thresholds Method of Limits Start with a low intensity stimulus, gradually increase until observer reports a sensation (ascending) Start with a high intensity, gradually decrease until observer no longer reports a sensation (descending) Problems: • observer may not pay attention on low intensity trials • observer may anticipate stimulus on descending series Psychophysical Methods: How to Measure Thresholds Method of Constant Stimuli Present stimuli in a random order observer cannot predict whether stimulus is above or below threshold Method of Magnitude Estimation Stevens: Observers use numbers to describe the perceived intensity of a stimulus Relationship between stimulus intensity and magnitude estimates follows a power function Signal Detection Theory The detection of a stimulus involves decision processes as well as sensory processes Observers responses will change with motivation e.g. paid $1 for each detection of stimulus results in a greater number of detections Signal Detection Matrix Judgment “Yes” Present Hit Absent False Alarm “No” Miss Stimulus Correct Rejection Signal Detection Matrix Pay $1 for each detection Judgment “Yes” Present Hit Absent False Alarm “No” Miss Stimulus Correct Rejection Signal Detection Matrix Judgment “Yes” Present Hit Absent False Alarm “No” Miss Stimulus Correct Rejection Deduct $2 for each False Alarm Two-Point Limen A measure of tactile sensitivity Sensitivity differs for different body areas Sensitivity corresponds with Sensory Homunculus Subliminal Perception Perception of stimuli below the absolute threshold e.g. very briefly flashing messages no evidence for effectiveness in advertising However, flashed words can “prime” awareness of other stimuli e.g. “bread” - “butter” A Five-Stage Model of Sensory Systems Each sensory system must have: 1. An adequate stimulus 2. Receptors adapted to the stimulus 3. Nerve pathways 4. Destination points in the brain 5. The psychological experience Seeing The Stimulus: The Visible Spectrum The portion of the electromagnetic spectrum between 400 to 700 nanometers The Eye The eye focuses light on the retina Retina: multilayered structure on the inner surface of the eye Transduction The conversion of energy from one type to another The eye transduces light energy into neural energy at the retina Transduction occurs at the photoreceptors: Rods: dim-light receptors Cones: bright-light receptors The Retina Photoreceptors receive light Neural signal sent to Bipolar Cells. Signal then sent to Retinal Ganglion Cells Ganglion cells send signal out the eye to the brain exit point is a “blind spot The Retina The Retina Cones: Located in the center of the retina Often see a single cone connecting to a single ganglion cell Rods: Located in the periphery of the retina Often see many rods connecting to a single ganglion cell Visual Nerve Pathways Axons of ganglion cells for the optic nerve pathway Optic nerve sends signals to the lateral geniculate nucleus (LGN) of the thalamus Signals are then sent to the primary visual cortex in the occipital lobe primary visual cortex = striate cortex Conscious vs. Non-conscious Visual Pathways Retina - LGN - Striate cortex: “conscious visual pathway” “Non-conscious pathways”: Retina - Superior Colliculus: Responsible for perception of peripheral movement Retina - Pretectum: Responsible for changing pupil size when presented with bright light. Dark Adaptation An increase in visual sensitivity as a result of time spent in the dark Sensitivity appears to plateau at 10 minutes, but then starts to increase again at 15 minutes Rod-Cone Break Dark Adaptation Color Vision: Trichromatic Theory (Young-Helmholtz) Color vision results from the activity of three cone pigments, each maximally sensitive to on of three wavelengths Trichromatic Theory explains additive color mixing - the mixing of colored lights to create other colors Dichromatism: color blindness resulting from missing one of three color receptors Color Vision: Opponent Process Theory (Hering) Colors are sensed by “opponent pairs” Red-Green Blue-Yellow White-Black Can be used to explain negative afterimages Color-Opponent Cells Ganglion cells are connected to photoreceptors such that they respond in an opponent process fashion to color e.g. inhibited by green and excited by red Hearing The Stimulus: Sound Waves a wave of compressed air resulting from vibration Sound Waves Waves of air that can vary in amplitude and frequency Sound as a Wave Amplitude (intensity): related to psychological dimension of loudness Frequency: related to psychological dimension of pitch Complexity: related to psychological dimension of timbre Amplitude Determined by size of wave Measured in decibels (dB) Frequency Determined by number of waves per second Measured in Hertz (Hz) The Ear Three Parts: The Outer Ear The Middle Ear The Inner Ear The Ear The Outer Ear Consists of Pinna Auditory Canal Tympanic Membrane (Eardrum) Main Function: Gather sounds to send to middle and inner ear The Middle Ear The Middle Ear Ossicles: Transfer and amplify sound to inner ear Malleus (Hammer) Incus (Anvil) Stapes (Stirrup) Oval Window To inner ear Inner Ear (Cochlea) Sound vibrations enter at oval window Travel through fluid, vibrating basilar membrane Organ of Corti Where sound is transduced into a neural signal Sound is transduced by Hair Cells Cilia on hair cells contact tectorial membrane As basilar membrane vibrates, hair cells are pulled and neural signal is generated Flowchart of the Ear and Other Things Airborne Vibrations Bending (Cilia) Mechanical Vibrations (Eardrum & ossicles amplify) Electrical Charges (Hair cells) Pressure Waves Ripples (Cochlear Fluid) (Basilar Membrane) Neurotransmitter Brain (Auditory Nerve Fibers) Place Theory: How we perceive pitch Sound waves generate vibration in cochlear fluid and basilar membrane travelling wave Frequency of sound is encoded by the stimulation of specific place on basilar membrane High frequencies cause vibrations at thin part of basilar membrane near oval window Low frequencies cause vibrations at thicker part Place Theory: How we perceive pitch Loudness Perception Increased amplitude of sound wave leads to greater displacement of basilar membrane Increase displacement of basilar membrane leads to increased activity of hair cells Increased activity of hair cells leads to greater number of EPSPs Conductive Hearing Loss Hearing loss due to reduced functioning of outer or middle ear e.g. damage to ear drum or damage to ossicles otitis media: middle ear infection reduces movement of ossicles Sensorineural Hearing Loss Hearing loss due to damage to the cochlea Central Hearing Loss Hearing loss due to damage to brain areas e.g. Wernicke’s aphasia - an inability to attach meaning to language Central Auditory Processes Taste The Stimulus: Chemicals in solution Four basic tastes: sweet salt sour bitter Taste is also a product of what we smell How we Taste Taste receptors are found in taste buds on the tongue Membranes of receptor cells bathed in solution of chemicals in saliva How we Taste Receptor cells generate action potentials in taste nerves Smell The Stimulus: Airborne chemicals (olfactants) How we Smell (just terrible) Olfactants are dissolved in olfactory mucosa at top of nasal passageway EPSPs are generated in olfactory neurons Signals sent to the olfactory bulb then to brain How we Smell Touch The Stimulus: Mechanical Pressure The receptor: Receptors found in skin Touch Receptors Free Nerve Endings Process touch, temperature and pain Pacinian Corpuscles: Process “deep pressure” Meissner Corpuscles and Organ of Ruffini Process gradual changes in skin pressure Pain The Stimulus: Typically, damaging stimuli - mechanical, heat, chemical Pain can be influenced by non-sensory factors e.g. rubbing a hurt area Phantom Limb Pain Pain associated in a “limb” even though it has been amputated