Cognitive Psychology: 414 Thursday, February 18, 2010 What is a mental code? First, we must define: What is a code? A format for representing information A representational structure consisting of a limited ?vocabulary? (e.g. ?dits? and ?dahs? in telegraphy, the alphabet in language), syntax (rules how to put elements of the code together), and processes that can operate on the structure in specified ways. Be readily encoded (i.e., created from some other form of information Be amendable to storage, and to manipulation and/or transformation (e.g., mathematical operations) Be amendable to decoding back into original form or some new form What is a mental code? It is a hypothetical code used by the mind to encode, represent, and transform information (Representation and transformation of information includes the processes that we call ?thinking?) A mental code is different from a neural code how patterns of neural activity represent information Examples: Rate encoding Biased competition as a mechanism of selective attention How many mental codes operate in a cognitive system? We don?t know, but a general rule of thumb of theorizing in cognitive psychology is, strive for parsimony (the use of the simplest or most frugal route of explanation available) first, and only add complexity to a model if important theoretical or empirical considerations require it. Criteria for positing two distinct mental codes: Associated with clearly different sense or organs Different neuroanatomical sites Inability to use one part of the brain, produces the inability to do some cognitive tasks, but leaves in tact the ability to use another part of the task? ect, dorsal stream vs. ventral stream example Less interference between two codes than within the same code Different dynamic properties (e.g., latency for arousal by a stimulus, or persistence in memory) Associated with clearly different sense or organs Dual-code theory (Paivio, 1971) ?There are separate representations for verbal and visual information? Preliminary suggestive evidence: Memory is much better if we encode verbal information visually as well as verbally. Roger Shepard's study of Mental Rotation: Question: do the movements of mental images have characteristics similar to movements of real objects? i.e. what is the nature of mental imagery? In humans, the greater the angle the letter had to be rotated to get back to upright? the longer it took subjects to judge whether they were mirror reversed or not. Key question regarding the format or nature of mental images: Are mental images propositional or analog? Propositional: represented like any other kind of information. Sentence-like descriptions of the properties of the ?image? people believe they are experiencing Analog: a representation that maintains the properties of or otherwise functions in a manner functionally similar to a real visual image For example? consider the representation of a square. Propositional code: Four straight lines At right angles to each other Each line segment connected at the end to two other Analog code: Shepard Task Are the two shapes the same but viewed different? Kosslyn 1983 Elephant, mouse and paper clip experiment Different neuroanatomical sites Brain Activation During Imagery of Small and Large Letters Patient with epilepsy example Less interference between two coeds than within the same code Crossover interaction ? Visual signal Auditory signal Concurrent visual imagery 53.2% 63.3% Concurrent auditory imagery 59.4% 54.3%
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