Chapter 4Sensation and Perception Sensation Experience associated with a sound, light, etc., and the initial steps by which the sense organs and neural pathways take in stimulus information. Not consciously aware of it Perception The organization of the information brought in by sensation and its meaningful interpretation Physical stimulus The matter or energy that contacts our sense organs Physiological response Patter of electrical activity that occurs in sense organs as a result of a physicalstimulus Sensory experience Subjective sensation of sight, sound, touch, ect. How many senses are there Elementary = 5 Barnes = 16+ Pain, temp, balance Receptor cells A specialized cell that responds to physical stimulus by producing electrical changes that can initiate neural impulses Transduction Process in which a receptor cell produces a response to a physical stimulus Sometimes neurons do this Sensory neurons They carry neural impulses from receptor cells to CNS Receptor Potential An electrical charge caused by transduction (lots of partial depolarization caused by neurons releasing neurotransmitters can activate another neuron. Receptor potentials can also activate a neuron and cause an action potential) Coding The action potentials sent to the brain carry information about the strength andtype of stimulus Examples Type (red or green light) Strength (dim or bright) Type (salt or pepper) Strength (lot or little) Qualitative information Type or kind of energy or matter present Determined by which neurons are firing Quantitative information Amount or strength of stimulus Determined by rate of firing Sensory adaptation Change of sensitivity Less stimulus results in more sensitivity More stimulus results in less sensitivityAudition What the heck is “sound” anyway One answer is that it is a physical stimulus. For our purposes it is a vibration of air caused by some object (vocal cords, speaker on stereo, ect.) Aspects of sound Amplitude Corresponds to perceived loudness Frequency Corresponds to perceived pitch 20 Hz is 20 alternation of compressed/uncompressed air per second How the ear works Sound waves travel through the auditory canal and make the tympanic membrane (ear drum) vibrate The ear drum makes the hammer, anvil, & stirrup vibrate The stirrup makes the oval window vibrate which makes the fluid in the cochlea vibrate The fluid in the cochlea triggers movement sensitive hairs in the cochlea This finally triggers an electrical potential and message is sent to the brain. Two types of deafness Conduction deafness Hammer, anvil, stirrup becomes rigid Solution? It takes more to move them so hearing aid will do the trick sensorineural deafness Problem is between the stirrup and the brain (the cochlea or auditory neurons) Normal hearing aids won’t work How do we perceive loudness More hairs move = louder How do we perceive pitch Lower frequency of sound, the father along the basilar membrane ( the membrane with the hair cells on it) the sound will travel Under 4 kHz the timing of the bursts of action potentials corresponds with the frequency of the sound and codes for pitchVision Light Amplitude Think intensity Wavelength (frequency) Think perceived color 400-700 nm is visible Parts of the Eye Cornea Clear tissue that helps to focus light Iris Opaque film that keeps out light and changes size to affect pupil size Pupil Hole in iris Lens Behind the pupil It focuses light It is adjustable but gets less so over time Retina Membrane in rear interior eye Contains millions of receptor cells Sensation/ eye/ retina Rods Black and white Works in dim light All over retina 120 million Low acuity High sensitivity Rhodopsin Cones Color Work in bright light Most in fovea 6 million High acuity Low sensitivity 3 different photo pigments Photochemical When hit by light they cause an electrical change across cell membrane This is known as receptor potential This leads to action potential in other cells. In this way a signal reaches thebrain Why do we see colors we see Subtractive color mixing Different substances absorb and reflect different wavelengths of light “blue” objects are those that reflect a lot of short wavelength light but absorb long and medium wavelength light Red + green + blue finger paint results in muddy color Additive color mixing This occurs when mixing lights not pigments Put lights of all colors together and get white light, not darkness 3 primaries law Using different intensities of 3 wavelengths of light one can create every color imaginable Law of complementarity For any color, you find another such that the two put together will yield white light Trichromatic theory Cells in retina have 3 pigments that absorb different wavelengths of light Short wavelength cones - peak absorption wavelength is 425 nm Medium wavelength cones - peak absorption wavelength is 525 Long wavelength cones - peak absorption wavelength is 560 nm Why propose such a theory in the first place In subtractive color mixing, you can make all the colors of the rainbowusing only 3 In additive color mixing you can get all color using only 3 wavelengths of light THEORY IS CORRECT There are three types of cones Each cone type has one of the 3 types of pigments Not everyone has three cones, however Colorblindness Condition where people only have 2 types of pigments Often either long wavelength or medium wavelength cones don’t exist You can be color blind and still function and not even know you are color blind Problem is genetic ( on X chromosome) Therefore, more common in men Opponent-process theory Blue-yellow opponent cells Excited by blue and inhibited by the yellow or vice versa Red-green opponent cells Excited by red and inhibited by green or vice versa Why propose it Law of complementarity Two colors in additive color mixing can yield white light Complementarity of afterimage Color and brightness constancy are not accounted for by either tri-c or o-p theories Ever been in a room illuminated with red light bulb? Do bananas still seem yellow, blued eyed