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PSY 280 L10.10

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Matthias Niemeier

PSY 280 – P ERCEPTION M. N EIMEIER 10/10/12 Q. What are formants? What are they good for? A resonance of the vocal tract. Formants are specified by their center frequency. Formants are peaks in the speech (harmonic sound) spectrum, labeled by number, from lowest frequency to highest. These concentrations of energy occur at different frequencies, depending on the length of the vocal tract. Listeners use the relationships between formant peaks to perceive speech sounds. The first three (lowest) formants are important because one can distinguish almost all speech sounds on the basis of energy in the region of these three. TOUCH - Touch: Mechanical displacements and other physical impacts on the skin - Proprioception: perception mediated by kinesthethic and vestibular receptors - Somatosensation: a collective term for sensory signals from the body - Action plays a special role: haptics - Hand-pen demo o Close eyes, hold pen and asked what is felt o Instead of saying, “the pen,” the person describes what the pen is ‘touching,’ e.g., “something hard/soft”  Subtracting (less interesting) sensation of the pen; focus directed on what the pen ‘feels’ - Cutaneous rabbit demo o 2 separate locations stimulated multiple times in quick succession feels like a rabbit, hopping across the skin between the 2 locations  Pen tapped on the crook of the elbow and on the wrist very fast – didn’t exactly worked in class o Investigated with fMRI  Middle location equally activated as stimulated locations - Touch receptors: embedded in outer layer (epidermis) and underlying layer (dermis) o Multiple types of touch receptors o Touch receptors (and other somatosensory receptors) have three attributes: 1. Type of stimulation the receptor responds to 2. Size of the receptive field 3. Rate of adaptation - Tactile receptors (four): mechanoreceptors respond to mechanical stimulation or pressure o Meissner corpuscles o Merkel cell neurite complexes o Pacinian corpuscles o Ruffini endings - Response characteristics of the mechanoreceptor populations o FA I: skin slip; low-frequency vibration (3-40 Hz) - Meissner o FA II: first contact with objects; hig frequency vibration (50-700 Hz) – Pacinian o SA I: fine spatial details, textures, patterns, Braille; sustained pressure, spatial deformations (<5 Hz) - Merkel o SA II: lateral stretch (e.g., grasping), hand shape; low sensitivity to vibration – Ruffini - Other types of mechanoreceptors within muscles, tendons and joints: o Proprioceptive/kinesthetic receptors: • Necessary to sense posture and what kinds of movements are made - Spindles: convey the rate at which the muscle fibers are changing in length - Receptors in tendons provide signals about tension in muscles attached to tendons - Receptors in joints react when joint is bent to an extreme angle - Proprioceptive illusions – stimulation of certain muscles feels like muscles are stretching and lengthening when they are not - Thermoreceptors o Sensory receptors that signal information about changes in skin temperature o Warmth fibers, cold fibers o Body is consistently regulating internal temperature o Thermoreceptors kick into gear when you make contact with object warmer or colder than your skin o Gap in nerve fiber temperature around 37° because it’s body temperature – neutral – receptors not interested in almost same temperature produced by body o Shiver to warm up, sweat to cool down - Nociceptors: o Sensory receptors that transmit information about noxious stimulation that causes damage or potential damage to the skin o A-delta fibers: strong pressure, heat; myelinated  fast signal transmission o C fibers: pressure, heat, cold, chemicals; unmyelinated  slow signal transmission (because it works with reflex – lesser pain, damage) o 2 phases of pain - Benefit of pain reception o Sensing dangerous objects o Hansen’s disease – loss of pain sensation – seriously debilitating and can lead to death - Pathways: up to 2m long o Information must pass through spinal cord o Axons of various tactile receptors combine into single nerve trunks o Several nerve trunks from different areas of body o Once in spinal cord (via dorsal root ganglion) – two major pathways: • Spinothalamic (slower) • Dorsal colum-medial lemniscal (faster) - Spinothalamic pathway synapses multiple times within spinal cord – slow, nociception, thermal information o Why is pain slow? Shouldn’t it be fast? • Pathway provides a mechanism for inhibiting pain reception when necessary - Dorsal-column-medial-lemniscal (DCML) pathway: fast o Synapse in medulla, near base of the brain, then ventral posterior nucleus of thalamus, then somatosensory area 1 (S1), somatosensory 2 (S2) o Patient with selective lesion in DCML pathway felt passive hand movements over surface – why? This is because spinothalamic pathway is stimulated – change in skin temp as hand swept over surface - Touch sensations are represented somatotopically: analogous to retinotopy found in vision o Adjacent areas on skin – connected to adjacent areas in brain, called homunculus - Sensory homunculus o Distorted representation reflects receptor density o Brain contains several sensory maps of the body, several homunculi, i.e., different sub-areas of S1, secondary areas as well - Phantom limb o Perceived sensation from a physically amputated limb of the body o Parts of the brain listening to missing limb(s) not fully ‘aware’ of altered connections, so they attribute activity in these areas to stimulation from missing limb(s) • I.e., brain areas that used to communicate with the lost limb has been relocated to another assignment (area) but are still listening to their old location • E.g., finger brain areas might be relocated to facial areas so stimulation in the face might make it feel like amputee has fingers o Phantom pain - Pain: o Pain sensations triggered by nociceptors o Responses to noxious stimuli can be moderated by cognitive, emotional and social factors o Bottom-up sensation + top-down modulation – feeling from body and -modulation from external factors • E.g., men would pretend something painful is not that painful in front of a (beautiful) woman • E.g., injury during sports o Analgesia • Decreasing pain sensation during conscious experience • Sports injury: endogenous opiates releas
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