ABSTRACT
A procedure, based on the method of adjustment, for estimating perceptual noise is presented. The resulting estimates can be used to obtain a better understanding of categorization behavior, to answer questions about the distributional form of perceptual noise, and to test for perceptual independence. All three applications are demonstrated in a categorization task involving two categories.
Subject(s)
Discrimination Learning , Pattern Recognition, Visual , Psychometrics , Adult , Bias , Female , Humans , Male , Orientation , Psychomotor Performance , Psychophysics , Size PerceptionABSTRACT
Observers were tested in a perceptual category-learning experiment in which they were instructed to make classification decisions as rapidly as possible without making errors. Nosofsky and Palmeri's (1997b) exemplar-based random walk (EBRW) model of speeded classification was tested for its ability to fit the classification response times and accuracies. The authors demonstrated that the EBRW model provided good quantitative fits to the mean response times and accuracies associated with individual objects as a function of their locations in a multidimensional similarity space and as a function of practice in the task. Preliminary evidence was also obtained that stimulus-specific adjustments in the random walk response criteria may have occurred during the course of learning.
Subject(s)
Attention , Decision Making , Mental Recall , Reaction Time , Adult , Association Learning , Color Perception , Discrimination Learning , Female , Humans , Male , Orientation , Pattern Recognition, VisualABSTRACT
A neuropsychological theory is proposed that assumes category learning is a competition between separate verbal and implicit (i.e., procedural-learning-based) categorization systems. The theory assumes that the caudate nucleus is an important component of the implicit system and that the anterior cingulate and prefrontal cortices are critical to the verbal system. In addition to making predictions for normal human adults, the theory makes specific predictions for children, elderly people, and patients suffering from Parkinson's disease, Huntington's disease, major depression, amnesia, or lesions of the prefrontal cortex. Two separate formal descriptions of the theory are also provided. One describes trial-by-trial learning, and the other describes global dynamics. The theory is tested on published neuropsychological data and on category learning data with normal adults.
Subject(s)
Caudate Nucleus/physiopathology , Gyrus Cinguli/physiopathology , Learning Disabilities/diagnosis , Learning Disabilities/physiopathology , Prefrontal Cortex/physiopathology , Adult , Aged , Amnesia/physiopathology , Child, Preschool , Depressive Disorder/physiopathology , Humans , Huntington Disease/physiopathology , Neuropsychological Tests , Parkinson Disease/physiopathologyABSTRACT
A congenital abnormality of the urachus is extremely rare in pregnancy. We reviewed the English literature since 1877 and found only 12 case reports of urachal complications during pregnancy. Eight patients developed complications from a urachal cyst or sinus, and four patients had a patent urachus with urinary fistula. We report an additional case of a patent urachus which uniquely presented for the first time during pregnancy with urinary drainage from the umbilicus. Urodynamic changes in pregnancy which may have produced this complication are discussed. Abdominal wall ultrasonography is extremely helpful in the diagnostic evaluation of suspected urachal tract complications during pregnancy.
