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Chapter 6

Chapter 6 Non-Associative Learning

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Daniela Palombo

Chapter 6 – Non-Associative Learning  Habituation involves a decrease in the strength or frequency of a behavior after repeated exposure to the stimulus that produces the behavior. If the stimulus is preseeted again after a delay, the behavior may reappear at its original level, a process called spontaneous recovert. A behavior decreased through habituation can also be renewed (dishabituated) by a novel stimulus. Habituation is stimulus- specific.  Whereas habituation decreases the response to a repeated stimulus, sensitization can increase the response to a stimulus. In sensitization, exposure to a threatening or a highly attractive stimulus causes a heightened response to any stimulus that follow. Sensitization is not stimulus-specific.  Priming is a phenomenon in which prior exposure to a stimulus improves the organism’s ability to recognize that stimulus later.  In perceptual learning, experience with a set of stimuli improves that organism’s ability to distinguish that stimuli. In mere exposure learning, simply being exposed to the stimuli results in perceptual learning. (A related term is latent learning: learning that takes place without corresponding changes in performance.) Perceptual learning can also occur through discrimination training, in which an organism explicitly learns to distinguish stimuli through feedback about the class to which each stimulus belongs.  Many kinds of spatial learning take the form of perceptual learning Often, this is latent learning about the environment that results from mere exposure as the organisms explores its world.  Comparator models suggest that habituation is a special case of perceptual learning whereas dual process theory proposes that changes in behavioral response after repeated exposure to a stimulus reflect the combined effects of habituation and sensitization, with habituation decreasing responses and sensitization increasing responses. Differentiation theory explains perceptual learning as resulting from new details being added to existing stimulus representations.  In marine invertebrates such as Aplysia, habituation can be explained as a form of synaptic deression (any change that reduces synaptic transmission) in circuts that link a stimulus (sensory neuron) to a particular reflexive response (motor neuron), as proposed by dual process theory. Habituation in Aplysia is homosynaptic, meaning that changes in one sensory neuron do not affect other sensory neurons. In contrast, sensitization in Aplysia is heterosynaptic and reflects increases in synaptic transmission.  The capacity of cortical networks to adapt to internal or environmental changes is called cortical plasticity. During perceptual learning, cortical changes occur that parallel improvements in discrimination abilities. These changes include refinement o receptive fields of neurons that response to sensory inputs, which can lead to widespread changes on the cortical map. In extreme cases such as when a form of sensory input is absent from birth, the cortical map may reorganize so that active inputs take over the areas normally devoted to processing the missing inputs.  One mechanism for cortical plasticity is Hebbian learning, based on the principle that neurons that fire together, wire together. In other words, repeated exposure can strengthen associations within particular subsets of cortical neurons, and these subsets can then provide an increasingly reliable basis for discriminating the stimuli that activate them.  Place cells are neurons in the hippocampus that become most active when an animal is at particular location (the place field for that neuron). However, it is not clear how the information from different place cells is linked together to form a useful spatial map to guide navigation through an environment.  Place fields change with learning, and if place cells are disrupted, spatial navigation is disrupted. As an environment becomes more familiar, the corresponding place cells become more selective, responding to increasingly precise locations in that environment.  People with landmark agnosia have lost the ability to identify familiar buildings and landscapes. This condition often results from damage to the parahippocampal region of the cortex.  Immediately after a stroke, many patients experience large losses in perceptual and motor function. The patients may suffer from learned non-use, which occurs when a functional limb takes over the role of a limb that still has motor function but has lost sensation. Learned non-use can be overcome by restraint therapy, forcing the individual to use the desensitized limb. Recovery of function in stroke patients is thought to result from cortical plasticity.  Sensory prostheses, electronic devices that interface directly with neurons or sensory receptors, are designed to provide individuals with sensory processing capabilities they would not otherwise have. The most extensively developed sensory prosthesis is the cochlear implant, which is used to treat profound deafness. Training with a cochlear implant leads to perceptual learning that improves the users ability to discriminate simulated speech sounds. Non-associative Learning: Learning that involves only one, relatively isolated stimulus at a time. Associative Learning: learning to associate one stimulus with another or to associate a stimulus with a new response. Learning about repeated stimuli Habituation: a decrease in the strength or occurrence of a behavior after repeated exposure to the stimulus that produces that behavior. The Process of Habituation Acoustic Startle reflex: a defensive response to a startling stimulus. Orienting Response: an organism’s innate reaction to a novel stimulus. Factors Influencing Rate and Duration of Habituation As exposure to stimuli increases, its responsiveness gradually decreases. Spontaneous Recovery: reappearance of a previously habituated response after a short period of no stimulus presentation. A rat is exposed to a startling stimulus. After an hour, the rat is likely to startle anew when the stimulus is presented again. Dishabituation Dishabituation is stimulus sp
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