Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 07 table of contents.
Just as visual images can be imagined, so can motor productions. Vivid motor imagination exists during dreams. It is accompanied by signals from motor neurons (neurons specialized for movement), and those neural impulses must be dampened by a special physiological mechanism so that we do not act out our dreams.
What is evidence that dream movements are partly transmitted to muscles? What did Hebb point out? How might this help humans learn?
Motor imagination can also be stimulated by observation. Hebb (1960) noted that we naturally put ourselves in another person's place when watching body activity. Hebb reported that when he was in a back brace after an injury and had to stand up very carefully, he winced when he saw somebody stand up quickly. Similarly, many people wince when they see somebody do a difficult gymnastic move such as the splits, not because it hurts the person who does the splits, but because it would hurt the observer. Such motor empathy probably helps humans learn by observation. When we closely observe an activity, part of our brain is acting it out in imagination. Hebb's speculation is now anchored in physiological reality, with the discovery in the 1990s of mirror neurons that fire patterns in the motor cortex of observing animals, identical to neural activity in the motor cortex of animals actually producing a movement.
What did Carpenter's experiment show about motor imagination?
Carpenter (1985) described an experiment that showed subjects could not remember whether they had actually traced a design or just imagined tracing it. They could, however, remember whether they had done one of those acts or only seen the design. So they remembered whether the motor system or visual system was involved, but they could not remember whether activity was imagined or actually carried out.
What did Cacioppo and Petty demonstrate, using EMG measurements?
Cacioppo and Petty did studies in the early 1980s using the electromyogram (EMG): a measure of electrical activity in muscles. They concluded that imagined activity is often accompanied by EMG activity at appropriate sites around the body. For example, happy and sad mental states (or imagined events) produced activity in muscles used to form happy or sad facial expressions. Messages designed to be controversial and provocative led to activity in speech muscles, even when subjects were not allowed to reply. Dimberg, Thunberg, and Elmehed (2000) found that people looking at emotional facial expressions responded with EMG activity in relevant facial muscles, as if they were imitating the expressions. This response was unconscious; subjects did not realize they were doing it.
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