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Psychology 1000
Ross Esson

Psych 1000 December Exam 1 Chapter 5: Sensation and Perception Sensation: stimulus-detection process, sense organs respond to and translate environmental stimuli into nerve impulses receptors are the first link o Receptors take a stimulus and turn it into an electrical signal Perception: making sense of the impulses an active process of organizing this stimulus input and giving it meaning. This is influenced by ideas and memories Psychophysics: studies relations between the physical characteristics of stimuli and sensory capabilities relationship between the world and the way it is perceived o Two kinds of sensitivity: 1. Detection: absolute limits of sensitivity that we can detect (dimmest light, softest sound) 2. Discrimination: sensitivity for the differences between stimuli that we can discriminate Detection Absolute threshold: the lowest intensity at which a stimulus can be detected correctly 50% of the time the lower the absolute threshold, the greater the sensitivity o Usually a gradual, not abrupt function Signal detection theory: concerned with the factors that influence sensory judgments o A persons apparent sensitivity can fluctuate quite a bit o There is a range of uncertainty, people set their own decision criterion (standard of how certain they are, before they say they detect it) o Ask participants to indicate if they perceive a stimulus: 2 conditions (stimulus present, stimulus absent) and 2 responses (yes or no) o Outcomes if a stimulus is present: hit or miss o Outcomes if a stimulus is not present: false alarm or correct rejection At low stimulus intensities, the participants and situations characteristics influence the decision criterion Subliminal stimulus: a stimulus so weak or brief that it cannot be perceived consciously. Found to influence thoughts, feelings Discrimination Just Noticeable Difference threshold (jnd): the smallest difference between two stimuli that people can perceive 50% of the time Webers law: difference threshold (jnd) is directly proportional to the magnitude of the stimulus with which the comparison is being made our senses are predictable o Represented by a Weber fraction o Law breaks down at extremely high and low intensities Sensory adaptation: diminishing sensitivity to an unchanging stimulus (receptors reduce and eventually stop firing signals to the brain occurs in all sensory modalities) o Frees senses from the unchanging to be more sensitive to changes in environment The Skin and Body Senses Touch: somatosensation o Allows to explore and manipulate, avoid dangers, alert to disorders o A lack of touch retards physical, social and emotional development Humans are sensitive to four tactile sensations: pressure, pain, warmth, cold Primary receptors for pain and temperature are free nerve endings, simple nerve cells beneath the skins surface Pressure receptors are nerve fibres at the base of hair follicles Psych 1000 December Exam 2 Phantom limb: irritation of the nerves that used to originate in the limb fools the brain into interpreting the resulting nerve impulses as real sensations o Cortical reorganization o Mirror therapy so amputees can see and move their missing limbs to relieve discomfort (use of imagination/illusion Kinesthesis: provides us with feedback about our muscles and joints positions and movements receptors are never endings in muscles, tendons, joints Vestibular sense: sense of body orientation. Receptors are located in the vestibular apparatus of the inner ear. There are three semicircular canals that contain fluid and hair cells, contain receptors for head movements (lie in left/right, up/down and back/forward planes) o Vestibular sacs respond to position of body, indicate upright or at an angle Taste and Smell Smell/olfaction: receptors are long, project through the lining of the upper part of the nasal cavity and into the mucous membrane o About 40 million receptors o Hypersomia: genetic, physiological state can affect reaction o Anosmia: complete inability, often temporary, loss of appetite and libido Olfactory process: 1. Olfactory receptor cells: transduce odour molecules into neural signal (constantly die and are replaced) 2. Olfactory nerve: transmits electrical signals to olfactory bulb 3. Olfactory bulb receives input from olfactory nerve 4. Olfactory cortex and limbic system: from bulb to limbic system (including amygdala and hippocampus), emotion and memory Pheromones: chemical signals found in natural body scents o McClintock effect: women who live together menstruate in synchrony Taste: closely related to smell o Flavour: complex sensation, based on taste + smell Tongue has chemical receptors located inside taste buds o Messages from the limbic system (emotions and memories) and the frontal cortex (conscious thought) may be at odds with each other Like odour, the pattern of responses across all the different receptors are unique o Can you taste PTC? Supertasters, non-tasters, tasters Adaptation: dislike bitterness, avoid toxins Audition Frequency: cycles/s, Hz (humans can hear 20-20 000 Hz) Amplitude: vertical size of waves, loudness, decibels (dB) Auditory transduction: o Pinna funnels sound waves through auditory canal to eardrum o Beyond eardrum to middle ear (stirrup, hammer, anvil) where the three bones vibrate to amplify the sound waves more than 30x o Inner ear contains the cochlea (filled with fluid, contains basilar membrane) o Resting on the basilar membrane is the organ of Corti o The organ of corti contains thousands of hair cells that are the actual sound receptors Psych 1000 December Exam 3 o The hair cells synapse with the neurons of the auditory nerve, which then sends impulses to the auditory cortex in the temporal lobe o When sound waves strike the eardrum, pressure at the oval window increases, so the fluid in the cochlea is in motion. Fluid vibrates the basilar membrane, causing a bending of hair cells in the organ of corti, causing a release of NT Sound Localization: arrival of the sound earlier at the ear lets us know where the sound is coming from head acts as a sound barrier. Use differences in time and intensity to locate Coding for: o Loudness: high-amplitude waves cause more bending and release more NT (higher rate of firing). Different receptors have different thresholds, so a specific cell pattern. Coded in terms of rate of firing in the axons of the auditory nerve, and which hair cells are sending messages o Pitch: Frequency theory of pitch perception: nerve impulses to the brain match frequency of the sound wave. BUT neurons can only fire to match 1000Hz, how do we hear anything above that? Place theory of pitch perception: specific point where sound wave hits in the cochlea and most strongly bends hair cells is where frequency is coded. The
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