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Title:The P300 and Stages of Human Information Processing: An Additive Factors Study
Author(s):Mccarthy, Gregory
Department / Program:Psychology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Psychology, Psychobiology
Abstract:The P300 is an event-related brain potential (ERP) recorded at the scalp following the presentation of a task-relevant stimulus. Several investigators have found that the latency of P300 covaries with reaction time (RT) in discrimination and categorization tasks. However, other investigators have reported that P300 and RT are or can be dissociated. These latter findings suggest the hypothesis that P300 latency is associated with the time required to evaluate or categorize a stimulus, and is relatively independent of response selection and execution processes. This hypothesis was directly tested in the present study. Two experimental variables, stimulus discriminability and stimulus-response (S-R) compatibility, were manipulated in an factorial design. In previous studies using Sternberg's additive factors method these variables were found to have additive effects upon RT. The conclusion from these findings is that stimulus discriminability and S-R compatibility affect different stages of information processing, with stimulus discriminability affecting early stages associated with stimulus encoding and S-R compatibility affecting later stages associated with response selection. In the present study, subjects viewed matrices composed of 4 rows and 6 columns of characters which were briefly exposed on a cathode ray tube. The word RIGHT or LEFT was present in each matrix, written horizontally, and appearing with equal probability in each row. The remaining background positions of the matrix were filled with the character '#' for the high discriminability or 'no noise' condition, or with randomly chosen alphabetic characters in the low discriminability or 'noise' conditions. The target words were presented with equal probability. The subjects were required to identify which target word was present in each matrix and to indicate this decision as quickly as possible by pressing a button. There were two response buttons, one for the left thumb and one for the right thumb. For each matrix, the appropriate response mapping was determined by a response cue which preceded the presentation of the matrix. For the cue SAME the right thumb was the appropriate response for the target stimulus RIGHT and the left thumb was correct for LEFT. This was the compatible S-R mapping. For the cue OPPOSITE the right thumb was the correct response for the target LEFT and the left thumb was correct for RIGHT. This was the incompatible S-R mapping. Each cue was presented with equal probability. The cue, matrix background, target word, and matrix row of the target were randomly and independently chosen for each trial. The first experiment confirmed that the discriminability and S-R compatibility manipulations had additive effects upon mean RT, as well as upon the percentage of correct responses. The variance of RT was significantly affected by target discriminability. In the second experiment, ERPs were recorded simultaneously with RTs. An estimate of the latency of P300 was made for each single ERP epoch. P300 latency was sensitive only to manipulation of target discriminability, while reaction time was again affected by both discriminability and S-R compatibility in an additive manner. The variance of P300 latency was not significantly affected by either manipulation. These data were interpreted as supporting the hypothesis that P300 latency reflects the durations of a subset of the mental processes which compose RT. More specifically, those processes which affect the time required to categorize a stimulus affect P300 latency while those affecting the time required to choose a response have little or no affect upon P300 latency.
Issue Date:1980
Description:157 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
Other Identifier(s):(UMI)AAI8108602
Date Available in IDEALS:2014-12-13
Date Deposited:1980

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