When a target stimulus in a predesignated location is identified by a keypress response, responses are slightly faster if noise stimuli in adjacent locations are identical to the target than if they are a different stimulus assigned to the same response (a repeated-stimulus superiority effect). An exception to this result has been found in experiments that used randomly intermixed letter and digit stimuli. These experiments showed slower responding for identical noise than for nonidentical, response-compatible noise (a repeated-stimulus inferiority effect). The present study investigated these phenomena in three experiments. Experiments 1 and 2 established that both the superiority and inferiority effects can be obtained in the same experiment. They also provided evidence that the repeated-stimulus inferiority effect is a function of the intermixing of letters and digits and not of the larger target-set size that has been used for mixed lists. Experiment 3 demonstrated that, with unmixed presentation, the repeated-stimulus superiority effect is enhanced by an increase in the number of stimuli assigned to each response. The experiments are consistent with accounts that attribute the repeated-stimulus superiority effect to competition that occurs when different internal recognition responses are activated. Moreover, the experiments suggest that the repeated-stimulus inferiority effect has its basis in processes that occur subsequent to feature extraction.
When subjects identify a target stimulus with an assigned keypress response, flanking noise stimuli produce interference if they signal an alternative response and slight facilitation if they are identical to the target. However, when the possible stimuli come from two distinct categories Getters and digits), interference also occurs if the noise letters are identical to the target. Four experiments were conducted to determine whether this mixed-category, repeated-stimulus inferiority effect is due to stimulus-identification or response-selection processes. The inferiority effect was (1) absent when letters were assigned to one response and digits to another; (2) absent when the target stimulus was named, rather than identified by a keypress response; and (3) eliminated when subjects practiced with mixed assignments of letters and digits. These findings converge on a response-selection basis for the inferiority effect.
In previous studies subjects who have learned a positioning response with kinesthetic feedback tended to make greater errors when visual feedback was provided during later trials. These subjects have always performed with both kinesthetic and visual feedback available. This study determined whether subjects with only visual feedback would produce errors similar to those who received kinesthetic plus visual feedback. Blindfolded subjects learned to move a handle to a criterion location with knowledge of results following each trial. Subjects then were assigned to one of three experimental groups, with only kinesthetic feedback, with kinesthetic plus visual feedback, or with only visual feedback. Subjects had 9 trials without knowledge of results in these feedback conditions. When visual feedback was available, subjects tended to make longer response errors. This finding replicates previous studies. Also, the similarity of performances from the conditions with visual feedback indicated the dominance of visual information in the condition with kinesthetic plus visual feedback.
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