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Bio-Psych: General Sensory Processing.doc

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PSYC 280
Neil Watson

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Biological Psychology 7edition Website-sourced Study Questions Chapter 8: General Principles of Sensory Processing… Sensory Processing Sensory Receptor Organs Detect Energy or Substances • Sensory systems of particular animals have restricted ranges of responsiveness Study questions: 1) Specialized body components, collectively called sensory receptor organs, are sensitive to energies of various sorts that come into contact with the body. The job of these organs is to convert environmental energy into electrical signals. 2) Here is great diversity in receptor organs across species, reflecting the particular ecology of each species. For example, some migratory animals can sense magnetic fields, some snakes have detectors adapted to perceiving infrared radiation, and some species of fish are sensitive to electricity. 3) Humans do not hear sounds above 20,000 Hz. The type of sound above this range is ultrasonic. 4) Complete the following statements about hearing in different classes of animals (based on Figure 8.2). a. Fish hearing is adapted to much lower frequencies than that of humans, with best detection typically below 1000 Hz and little sensitivity above 1100 Hz. b. Birds and humans have similar auditory sensitivity, with peak detection in the range of about 500 to 4000 Hz. c. Humans are least sensitive to low-frequency sounds. What Type of Stimulus Was That? Study questions: 1) The idea that each sense has its own unique receptors and independent neural channels is called the doctrine of specific nerve energies. If you press on your eye, you will experience various whorls of color and shapes; this phenomenon is consistent with this doctrine. 2) The notion of a labeled line refers to the idea that the sensory qualities of any particular sensory afferent are predetermined. For instance, activity in the touch receptor pathway can be perceived as touch only. Sensory Processing Begins in Receptor Cells • The initial stage of sensory processing is a change in electrical potential in receptor cells Study questions: 1) A receptor cell is a specialized device for detecting particular energies or chemicals. Such cells produce a change in their membrane potential when exposed to an adequate stimulus, a process formally known as sensory transduction. 1 2) The change in the membrane potential of the receptor cell when it is stimulated is called a generator potential, which in many ways is similar to an EPSP. Since these changes are the sole means of transducing environmental signals into a neural code, they are said to be necessary and sufficient for generating nerve impulses. Sensory Information Processing Is Selective and Analytical • Coding: Sensory events are represented by action potentials o Stimulus Intensity o Stimulus Location • Adaptation: Receptor response can decline even if the stimulus is maintained • Suppression: Sometimes we need receptors to be quiet • Pathways: Successive levels of the nervous system process sensory information • Receptive fields: What turns on this particular receptor cell? o Receptive Fields in the Cerebral Cortex • Attention: How do we notice some stimuli but not others? • Sensory systems influence one another Study questions: 1) Mechanical stimulation causes the Pacinian corpuscle to deform, which stretches the tip of the axon embedded within it. This causes mechanically gated Na+ channels in the cell membrane to open, leading to a depolarization. 2) Whereas early investigators thought that sensory nerves transmit accurate information to brain centers, we now know that a good deal of processing and transforming of sensory information occurs in the peripheral nervous system. The first step in the processing of sensory information is the conversion of stimuli into patterns of impulses, a process called coding. 3) The maximal rate of firing for an individual neuron is about 1200 per second. Once a cell reaches its maximum firing rate, it is no longer able to convey any new information. Therefore, either the range of stimulus intensities that the cell can encode is limited to a small subset of all the possible intensities, or else the sensory cell may encode the whole range, but only in large steps. One solution is to “recruit” additional cells as stimulus intensity increases, allowing more cells to fire. A different solution is to use an array of receptors, each of which is sensitive only to
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