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Chapter 4

Chapter 4 notes - Sensation.docx

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St. Thomas University
Brad Mc Kay

SENSATION o Sense: Biological system that transforms information from outside the nervous system into neural activity o Sensations are messages from the sense o Points to remember:  Information from different senses interacts  What we experience can change our sensations  Sensory information does not necessarily reflect “objective” reality (i.e: reality is subjective) SENSORY SYSTEMS o The basic process of sensation  Incoming energy is modified by an accessory structure  Incoming energy is transduced into neural activity  Transduction occurs at sensory receptors (cells designed to detect certain forms of energy; similar to neurons in that they fire action potentials & release neurotransmitters)  Sensory receptors can adapt to stimulation & become less responsive over time  Sensory nerves carry information from receptors to the CNS  Sensory information (except olfactory) first undergoes preliminary analysis by the thalamus before continuing to the cerebral cortex CODING: TRANSLATING THE PHYSICAL PROPERTIES OF A STIMULUS INTO A PATTERN OF NEURAL ACTIVITY o Doctrine of Specific Nerve Energies  Stimulation of a particular sensory nerve provides codes for that one sense no matter how the stimulation takes place o Temporal Code  Coding attributes of a stimulus by altering the timing of the neurons firing o Spatial Code  Coding attributes of a stimulus by altering the positional pattern of neurons firing HEARING o Sound  Fluctuations in pressure that occur when objects vibrate  Repeated fluctuations in pressure radiate out from their source as waves  Physically sound waves differ in terms of amplitude, wavelength and frequency o Psychological experience of sound  Loudness (amplitude)  Greater amplitude = louder sound  Pitch (frequency; no# of complete waves/sec)  how high or low a tone sounds  Humans can hear sounds ranging from about 20 hertz to about 20 000 hertz  Timbre (wave form)  Mixture of frequencies & amplitudes; allows us to distinguish the same sorts of sounds as coming from different sources HEARING: THE EAR o Accessory Structures: outer ear (pinna; ear canal), middle ear (tympanic membrane, malleus, incus, stapes, oval window), inner ear (cochlea) o Transduction  Cochlea  floor of the cochlea is the basilar membrane; sound passing into the cochlea causes movement of the membrane  Movement of the basilar membrane causes hair cells on the Organ of Corti to bend  Bending of hair cells stimulate the neurons of the auditory nerve HEARING: THE CNS o After preliminary processing in the thalamus, auditory information is sent to the primary auditory cortex in the temporal lobe  Information travels to the contralateral hemisphere  Cortical cells respond maximally to sounds of particular frequencies  Temporal coding is used to localize sounds o Coding Intensity (loudness) & Frequency (tones)  The firing rate of auditory nerves increases as sound intensity increases  Frequen
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