Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.1 Touch Three types of two part sensations Research –skin mapping –two-point threshold Ascending pathways –lemniscal –Spinothalamic Perceptual experiences –temperature –pain –touch

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.2 Three Types of Sensations Pressure –light –deep Temperature –cold –warm (not hot) Pain –sharp –dull

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.3 Research Skin mapping –many different types of receptors are found in the skin –test differential sensitivity of different spots on the skin –findings: sensations are not continuous across skin - localized in discrete points number of pain spots > number of pressure > number for temperature over time the localization shifts the specific sensations do not always correspond directly with the type of receptor found at that location in the skin

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.4 Examples of Receptors

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.5 Examples of Mapping Results

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.6 Research Two - point threshold - measure of pressure acuity - varies greatly over different areas of the body

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.7 Ascending Pathways Lemniscal system –pressure information –small receptive fields –rapid transmission in long axons –travels up the back of the spinal chord –travels to somatosensory I in the Parietal lobe (front part of parietal lobe) –SSI is organized into the sensory humunculus the greater the sensitivity of a body part the greater the area of the brain devoted to it Spinothalamic (Extralemniscal) system –pain & temperature information –large receptive fields (dermatomes) –small axons and slower transmission –travels up sides of spinal chord –travels to somatosensory II in the parietal lobe (back part of parietal lobe) –SSII does not have a neat organization many overlapping representations

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.8 Sensory Humunculus

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.9 Sensory Humunculus What a person would look like if their sensory humunculus represented size rather than sensitivity

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.10 Dermatomes

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.11 Perceptual Experiences Temperature –cold is independent of warm, not a two way system but two independent systems –hot is not the extreme of warm - both warm and cold spots respond to “hot” stimuli - science museum demonstrations touching something that is both warm and cold produces a “hot” perception –“paradoxical cold” -can not distinguish extreme hot from extreme cold –physiological zero adapt to current temperature and all other temperatures are judged relative to that demonstration of each hand getting a different perception of tepid water based on their previous adaptation

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.12 Perceptual Experiences Pain –sharp and dull pain are independent systems travel in different areas of spinal chord treatment for one is usually not effective for the othe –cognitive factors influence pain socialization cultural differences attention (Lamaze child birth) Adaptation –all tactile senses except pain adapt very quickly survival function of pain

Sensation and Perception - touch.ppt © 2001 Laura Snodgrass, Ph.D.13 Perceptual Experiences Anesthesia –tactile sensations drop out and return in order temperature, pressure, pain e.g. Novocain for a dental procedure Touch –the difference between active and passive touch touch nose and touch knee - which “feels touched”? –Haptic perception active touch - the use of kinesthetic and tactile information to do object identification (blind people and babies) –healing touch Harlow monkey studies premature babies and “failure to thrive”