Sensation and Perception: Audition and Touch
Draw a simple sound wave on axes of pressure and time and indicate the following labels: compression, rarefaction, wavelength, and amplitude. What do compression and rarefaction represent? What is a Hertz and what is 1 Hertz equal to? [10]
COMPRESSION: air molecules are forced together; increase atmospheric pressure. RAREFACTION: air molecules spread apart and atmospheric pressure HERTZ: frequency; number of cycles of compression/rarefaction 1 Hertz = count cycles per second [draw graph]
How is the dynamic range of hearing calculated, and how does it vary with frequency? [5]
Dynamic range is the difference between the absolute threshold and pain threshold which is measured in decibels. The ear is most sensitive to sounds with frequencies between 1,000 and 5,000 Hz. The dynamic range in this zone of maximum sensitivity is 150 dB. This represents a 7.5 million fold increase in the sound pressure from the weakest sound detectable to the most intense sound tolerable.
Define monaural and binaural and explain why lower threshold are associated with binaural presentation in comparison with monaural presentation. [5]
Monaural is hearing from one ear and Binaural is hearing from both ears. The minimum threshold varies in monaural and binaural presentation of auditory stimulus. Binaural presentation results in lower thresholds. The threshold for two ear detection is about half of that for one ear detection. Binaural sound interaction does not need to take place simultaneously. Two sub-threshold monaural tones will be heard if they occur within 200 milliseconds.
Describe how a mechanical event is transduced into electrical activity by and auditory hair cell: [8]
The organ of corti has three rows of sensory hair cells and stereocilia, about 3,500 inner hair cells and 12,000 outer hair cells. The "hairs" or stereocilia are in the cochlear duct which is full of endolymph which is rich in positively charged potassium ions. [draw diagram]
How is the action of a vibratory stimulus frequency on the skin similar to that of the sound on the ear? List 3 other similarities between the auditory and somatosensory systems. [7]
VIBRATORY STIMULUS: is a slow touch adaption process; action of vibratory stimuli on skin is greatest for certain stimulus frequencies; this is similar to auditory stimuli because it depends on different frequencies to reach threshold PACINIAN RECEPTOR SYSTEM: most sensitive to higher frequency vibrations (>250 Hz) NON-PACINIAN RECEPTOR SYSTEM: more sensitive to lower frequency vibrations (below 200 Hz)
Give a brief description of the evolution of the anatomy of the ear: [8]
1. LATERAL LINE ORGAN: horizontal linear array of nerve endings in skin of fish in which sensory hairs are embedded [fish and amphibians] 2. LABYRINTH: lateral line evolves looping passages filled with fluid and lined with hairs [fish] 3. COCHLEA: complex form of labyrinth; contains long membrane covered with sensory cells with hairs [mammals, birds, reptiles]
Name and define the four perceptual dimensions of sound: [8]
1. LOUDNESS: related to amplitude of a tone 2. PITCH: how high or low something sounds measured in frequencies 3. LOCALIZATION: location of the sounds which is perceived by the left and right ears 4. TIMRE: two tones with same loudness are presented in same way but sound different
Describe the mechanism of transduction in the Pacinian corpuscle. [5]
1. Mechanical stimulation deforms the corpuscle 2. This leads to mechanical stretch of the tip of the dendrite 3. Mechanical effects physically opens pores in the dendritic membrane that allows influx of Na+ 4. When generator potential reaches threshold, a nerve impulse is sent to the Dorsal root ganglion of the spinal cord 5. Where it becomes either a reflex or is relayed to the brain
Name the different types of receptors found in the skin. Indicate which of these are "corpuscular" and which are "non-corpuscular." What is the difference between glabrous and hairy skin? [10]
1. Meissner's Corpuscles: glabrous; touch, vibration (FAST) cor. 2. Merkel's Disk: touch, pressure (SLOW) cor. 3. Ruffini's Ending: heat (SLOW) nc 4. Pacinian Corpuscle: pressure (VERY FAST) cor. 5. Hair Follicle Receptor: light touch, vibration (VERY FAST) cor. 6. Free Nerve Endings: pain/cool, and warm (VERY SLOW) nc GLABROUS SKIN: smooth an free from hair
Why is it difficult to classify pain as a sensory or emotional response? Give evidence for and against both definitions. Describe gate-control theory of pain. Describe measurement of pain and why the distribution of pain sensitivity varies over the body surface. [15]
1. Pain prevents damage to compromise organisms (protection) 2. Pain forces the organism to cope with injury (promotes healing) PSYCHOLOGICAL FACTORS: within: fatigue, fear, anxiety; between: different thresholds for different people BEECHER (1968) PLACEBO STUDY: 35% of patients were given a placebo rather than an analgesic reported on alleviation of pain GATE-CONTROL THEORY: involves the interaction of all three types of nerve fibers (cutaneous, pain, and kinesthetic) which either enhance or inhibit pain signals. FOR A NORMAL TOUCH: stimulates low threshold, fast Alpha-beta fibers go to the substantia gelatinosa (SG), which inhibits the T-cell and cancels the excitation of fast fiber connection FOR A NOXIOUS TOUCH: stimulates high threshold, slow pain fibers and fast fibers. Slow fibers inhibit the SG and thus fails to inhibit the T-cell input PAIN THRESHOLDS: measured in therms of the intensity of a stimulus that will just barely give a sensation of pain -differences in pain sensitivity are due to the variability distribution of pain receptors over the body HARDY (1943): -measured pain using a DOLORIMETER -focused intense beam of light on blackened forehead -found pain thresholds are affected by the neurological, pharmacological, and psychological state of the individual -created "dol scale" based on JND's of pain intensity -PAIN ADAPTATION: the more noxious the stimulus, the less adaption occurs
Name two ways that receptor nerve fibers may be classified and differentiate between the three fiber types found in human skin using these criteria. [12]
1. Types of stimulus that elicits response (touch, propioreception, pain) 2. The speed at which they respond 3. Size of the receptive field Classified as either: CORPUSCULAR RECEPTORS: touch stimuli NON-CORPUSCULAR RECEPTORS: pain and temperature stimuli Two types of skin: HAIRY: type of skin that covers most of the body GLABROUS: "hairless" skin found on palms of hands, soles of feet, lips and other places
What is auditory scene analysis? Describe the processing streams and their organizational characteristics differentiate the elements that are "conscious" and "unconscious" [7]
AUDITORY SCENE ANALYSIS is the process of building separate mental representations of sound producing events in the auditory scene based on the mixture of sound received from those events UNCONSCIOUS MECHANISMS: auditory grouping breaks "streams" of sound into chunks based on time and frequency. CONSCIOUS MECHANISMS: uses schemas to guide listening processes and to tap knowledge of familiar sounds. This requires attention. The brain groups like sounds together and is then able to conclude what is happening.
Describe the process of sound transduction in relation to the anatomy of the outer, middle, and inner ear and the pathway of auditory info in the brain. [17]
EXTERNAL EAR: collects, focuses, and filters sound. Pinna focuses sound; auditory canal; Eustachian Tube: establishes communication between middle ear and nasopharynx. MIDDLE EAR: focuses and amplifies effects of sound waves; Tympanic Membrane: eardrum; Ossicles: smallest bones focus sound pressure onto oval window, malleus, incus, stapes; Oval Window: takes amplified signal and stimulates inner ear INNER EAR: transduces mechanical energy into neural activity; Cochlea: fluid-filled snail, membranes move out oval and round window, three parallel canals: tympanic, vestibular, cochlear. Basilar Membrane: flexible structure that separates the tympanic canal from the cochlear duct - vibrates in response to sound; Cochlear Duct: filled with endolymph, fluid is more viscous than perilymph and is rich in K+ ions; Tectorial Membrane: rigid extension from Reissner's membrane
Describe how sound frequencies are coded by their position on the basilar membrane and represented tonotopically throughout the auditory system: [8]
Georg von Bekesy found frequency dependent vibratory qualities of the basilar membrane. The envelope of a traveling wave has two important properties: 1. It peaks at one point on the basilar membrane. Hair cells at the peak will send info to their neighbors. 2. The position of the peak is a function of the frequency. There is also a timing code for frequencies. different frequencies are signaled by the timing of nerve impulses in nerve fibers or groups of nerve fibers.
What is haptic perception? What are some of the stimulus dimensions that this dynamic modality can provide us with? Also describe the use of haptic perception in Tadoma: [7]
HAPTIC PERCEPTION: experience of world is based on a combination of cutaneous and kinesthetic sensations (touch and movement); can use haptic abilities to discriminate length, texture, and shape VISUO-HAPTIC CROSS-MODAL TRANSFER: -VISUALLY: line xyz appears "bent" -TACTILEY: plane xyz feels "bent" if explored tactiley wiht no sight TADOMA: method of assisting speech perception in people who are blind and hearing impaired -haptically monitor speech movement in teacher and self -Helen Keller and Anne Sullivan
What is a homunculus and what determines the extent of cortical representation of a particular body part? [5]
HOMUNCULUS: representation of physical stimuli and how much reception is available in that area Four Homunculi of S1: -Area 3a: muscle length -Area 3b: slowly adapting receptors in skin -Area 1: rapidly adapting skin receptors -Area 2: joint and pressure
What is kinesthesis and what kind of stimuli and receptors play a role in this ability? [10]
KINESTHESIS: physical stimulus is movement -provides sensations of force, weight, limb position and movement -this system is always active because it monitors body position and adjusts posture against gravity; info comes from receptors on and around muscles SKIN RECEPTORS: -free nerve endings: pain -Pacinian corpuscle: pressure MUSCLE/JOINT RECEPTORS: -Flower spray endings -Muscle spindles: stretch receptors -Golgi tendon organ: stretch and contraction
According to Locke, why is temperature a secondary sensory quality? Is this an appropriate classification or would there be a better explanation for two different perception of the same stimulus? [8]
PRIMARY QUALITIES: properties objects have that are independent of any observer like solidity, extension, motion, number, and figure SECONDARY QUALITIES: properties that produce sensations in observers such as color, taste, smell, and sound THERMAL THRESHOLDS AND ADAPTATIONS: -secondary qualities are subjective -we feel cold when the skin temperature has dropped below physiological zero -reference skin temperature has a "floating" neutral point based on the temperature the skin receptors have adapted -we are more sensitive to temperature changes that are life-threatening
Describe the pathways of somatosensory info for each fiber system: [12]
RAPIDLY ADAPTING RECEPTOR: body sensory receptor that responds briefly to the beginning and end of a stimulus onthe body SLOWLY ADAPTING RECEPTOR: body sensory receptor that responds as long as a sensory stimulus is on the body RAPID VS SLOW ADAPTING AFFERENTS: -slow adapting afferent with early peak and lowered response to sustained skin deformation -rapid adapting afferent responds to onset and termination of skin deformation -slow adapting response to sustained skin deformation RECEPTIVE FIELD SIZE VARIES BETWEEN PATCHES OF SKIN AND AS A FUNCTION OF RECEPTOR TYPE: -the receptive field of a higher-order neuron in a sensory pathway has a characteristic pattern of excitation that increases spatial resolution -the receptive field of a central sensory neuron typically has a central excitatory receptive field surrounded by an inhibitory region
What is touch adaption and why is adaption an important feature of sensory systems in general? How does static and vibratory stimulation differ in rate of adaption as a function of body region stimulated? [10]
TOUCH ADAPTION: after stimulus is applied to skin and if the stimulus remains unchanged will gradually disappear -RATE OF ADAPTATION: slow = heavier/smaller; fast = lighter/larger -you are not aware of the sensation of wearing a shirt except right after you put it on -different parts of the dermatome have different rates of adaptation TOUCH INTENSITY: -vibratory stimuli slow touch adaptation processes -action of vibratory stimuli on skin is greatest for certain stimulus frequency -Common Evolutionary Origin for Mechanosenses: for a given amount of pressure, some vibration frequencies give more intense touch sensations than others
Describe 3 methods for deriving touch thresholds. Also describe the 2-point discrimination task developed by Weber that is a means for mapping the dermatome. Describe how inhibitory interactions on the skin help contribute to the sensation of a single stimulus. [10]
TOUCH THRESHOLD: determined by touching a hair of varying thickness (tension) to different areas of the skin -by varying the thickness of the hair you manipulate the amount of the force/unit area TOUCH THRESHOLDS ARE MEASURED IN 3 WAYS: -ESTHESIOMETER: area under hair remains constant but force to hair is varied to derive threshold -TWO-POINT THRESHOLD: points close together are perceived as one; receptive field size can be implied by the distance points must be separated to be felt as two; lower thresholds on hands and feet reflect manipulatory function and larger S1 representation -VIBROTACTILE STIMULATION: gives lower thresholds that are frequency dependent; skin is sensitive to a limited range of vibratory stim: 40-2500 Hz; absolute thresholds also depend on temperature; high skin temp = low threshold
What is a threshold response curve and what does it illustrate? [4]
The threshold response curve shows that the auditory threshold varies based on the frequency. We also have different perceptions of loudness based on the frequency of sound. In the graph of human audition, we have less intensity for higher frequencies. This also shows that there is more auditory space for high frequencies rather than low. [draw graph]
Describe how sounds are localized in extra personal space using direction cues, distance cues, and physiological mechanisms. [15]
There are two basic cues for localization of sound: 1. INTERAURAL TIME DIFFERENCE: the difference in time it takes for sound to get to ears 2. INTERAURAL INTENSITY DIFFERENCES: occur because the head casts a "shadow" that decreases the intensity of sound reaching the far ear The direction and distance cues in localization include: PRECEDENCE EFFECT: phenomenon where the first of a group of sounds to arrive at the ear is the major determinant of where the sound source is located; something like an ECHO is usually not perceived, but when it is, we know it's an echo SOUND INTENSITY: changes in sound distance are related to sound intensity REVERBERATION: reflected sound waves are a cue to distance because greater distance means less direct and more "reverberated" sounds reach the ear The physiological mechanisms include: TIME DIFFERENCES: neurons in the superior olives, inferior colliculi and auditory cortex respond best to binaural stimuli that reach the ears at two different times INTENSITY DIFFERENCES: there are also neurons in the same structures that respond best to binaural intensity cues
