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Sensation
This document provides an overview of sensation and perception. It discusses how sensation is the conduction of a stimulus to consciousness through our sensory nerves, with different nerves perceiving the same stimulus as different modalities like light, sound, or pain. It then covers topics like sensory transduction through labeled lines; spatial encoding of stimulus location; intensity encoding through action potential frequency; common plans across sensory systems; somatic sensory processing through receptors, pathways, and cortex; two point discrimination; shape and size sensation; vibration sense; pain signal processing through nociceptors and dual pathways; theories of pain modulation; and phenomena like phantom limbs and pain.
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Sensation
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- 3. Scientific (Objective) realism7/11/2010Perception3
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- 6. Attributes of aStimulusModalityLocationTimingIntensity
- 7. Sensory Modality IsDetermined by the Stimulus EnergyThe same cause, such as electricity, can simultaneously affect all sensory organs, since they are all sensitive to it; and yet, every sensory nerve reacts to it differently; one nerve perceives it as light, another hears its sound, another one smells it; another tastes the electricity, and another one feels it as pain and shock. One nerve perceives a luminous picture through mechanical irritation, another one hears it as buzzing, another one senses it as pain. . .. . . Sensation is not the conduction of a quality or state of external bodies to consciousness, but the conduction of a quality or state of our nerves to consciousness, excited by an external cause. Johannes Müller 1826 Handbuch der Physiologie des Menschen für Vorlesungen, 2nd Ed., translated by Edwin Clarke and Charles Donald O'Malley:
- 8. Modality Is Encodedby a Labeled Line Code – Stimulus transduction
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- 10. Stimulus thresholdThe SpatialDistribution of Sensory Neurons Activated by a Stimulus Conveys Information About the Stimulus Location
- 11. Weber’s Law of“Just Noticeable Difference”
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- 13. Stimulus intensity isencoded by frequency of AP
- 14. Sensory Systems Havea Common Plan
- 15. Somatic Sensory SignalProcessing
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- 18. Types of nervefiber - Principle of Connectional Specificity
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- 25. Integration of tactileinformation by Cortex
- 26. The columnar organizationof cortical neurons
- 27. Each region ofthe somatic sensory cortex receives inputs from primarily one type of receptor.
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- 30. Shape and SizeSensation
- 31. Spatial and TemporalSummation
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- 37. Dual Pathways forTransmission of Pain Signals into the Central Nervous System
- 38. Nociceptive Components ofthe Thalamus and Cortex
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- 44. Phantom Limbs andPhantom Pain
Editor's Notes
- #4 Scientific realism states The universe really contains just those properties which feature in a scientificdescription of it, and so does not contain properties like colour per se, but merely objects that reflect certain wavelengths owing to their microscopic surface texture. The naïve realist, on the other hand, would say that objects really do possess the colours we perceive them to have. An example of a scientific realist is John Locke, who held the world only contains the primary qualities that feature in a corpuscularian scientific account of the world (see corpuscular theory), and that other properties were entirely subjective, depending for their existence upon some perceiver who can observe the objects.The argument from the scientific account of perception"The main aspects of that account that are cited in this connection are: (i) the fact that the character of the resulting experience and of the physical object that it seems to present can be altered in major ways by changes in the conditions of perception or the condition of the relevant sense-organs and the resulting neurophysiological processes, with no change in the external physical object (if any) that initiates this process and that may seem to be depicted by the experience that results; (ii) the related fact that any process that terminates with the same sensory and neural results will yield the same perceptual experience, no matter what the physical object (if any) that initiated the process may have been like; and (iii) the fact that the causal process that intervenes between the external object and the perceptual experience takes at least a small amount of time, so that the character of the experience reflects (at most) an earlier stage of that object rather than the one actually existing at that moment. In extreme cases, as in observations of astronomical objects, the external object may have ceased to exist long before the experience occurs. These facts are claimed to point inexorably to the conclusion that the direct or immediate object of such an experience, the object that is given, is an entity produced at the end of this causal process and is thus distinct from the physical object, if any, that initiates the process."[8]
- #5 C) Psychophysics can be defined as,the study of how physical stimuli are translated into psychological experience.In order to measure these events, psychologists use THRESHOLDS.1) Threshold - a dividing line between what has detectable energy and what does not.For example - many classrooms have automatic light sensors. When people have not been in a room for a while, the lights go out. However, once someone walks into the room, the lights go back on. For this to happen, the sensor has a threshold for motion that must be crossed before it turns the lights back on. So, dust floating in the room should not make the lights go on, but a person walking in should.2) Difference Threshold - the minimum amount of stimulus intensity change needed to produce a noticeable change.the greater the intensity (ex., weight) of a stimulus, the greater the change needed to produce a noticeable change.For example, when you pick up a 5 lb weight, and then a 10 pound weight, you can feel a big difference between the two. However, when you pick up 100 lbs, and then 105 lbs, it is much more difficult to feel the difference.
- #6 detection of a stimulus involves some decision making process as well as a sensory process. Additionally, both sensory and decision making processes are influenced by many more factors than just intensity.For example - at a party, you order a pizza...you need to pay attention so that you will be able to detect the appropriate signal (doorbell), especially since there is a lot of noise at the party. But when you first order the pizza, you know it won't be there in 2 minutes, so you don't really pay attention for the doorbell. As the time for the pizza to arrive approaches, however, your criterion changes...you become more focused on the doorbell and less on extraneous noise.
- #8 Here is Müller's statement of the law, from HandbuchderPhysiologie des MenschenfürVorlesungen, 2nd Ed., translated by Edwin Clarke and Charles Donald O'Malley:The same cause, such as electricity, can simultaneously affect all sensory organs, since they are all sensitive to it; and yet, every sensory nerve reacts to it differently; one nerve perceives it as light, another hears its sound, another one smells it; another tastes the electricity, and another one feels it as pain and shock. One nerve perceives a luminous picture through mechanical irritation, another one hears it as buzzing, another one senses it as pain. . . He who feels compelled to consider the consequences of these facts cannot but realize that the specific sensibility of nerves for certain impressions is not enough, since all nerves are sensitive to the same cause but react to the same cause in different ways. . . (S)ensation is not the conduction of a quality or state of external bodies to consciousness, but the conduction of a quality or state of our nerves to consciousness, excited by an external cause.[edit] ClarificationAs the above quotation shows, Müller's law seems to differ from the modern statement of the law in one key way. Müller attributed the quality of an experience to some specific quality of the energy in the nerves. For example, the visual experience from light shining into the eye, or from a poke in the eye, arises from some special quality of the energy carried by optic nerve, and the auditory experience from sound coming into the ear, or from electrical stimulation of the cochlea, arises from some different, special quality of the energy carried by the auditory nerve. In 1912, Lord Edgar Douglas Adrian showed that all neurons carry the same energy, electrical energy in the form of action potentials. That means that the quality of an experience depends on the part of the brain to which nerves deliver their action potentials (e.g., light from nerves arriving at the visual cortex and sound from nerves arriving at the auditory cortex).In 1945, Roger Sperry showed that it is the location in the brain to which nerves attach that determines experience. He studied amphibians whose optic nerves cross completely, so that the left eye connects to the right side of the brain and the right eye connects to the left side of the brain. He was able to cut the optic nerves and cause them to regrow on the opposite side of the brain so that the left eye now connected to the left side of the brain and the right eye connected to the right side of the brain. He then showed that these animals made the opposite movements from the ones they would have made before the operation. For example, before the operation, the animal would move to the left to get away from a large object approaching from the right. After the operation, the animal would move to the right in response to the same large object approaching from the right. Sperry showed similar results in other animals including mammals (rats), this work contributing to his Nobel Prize in 1981.