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An account of same-different discriminations that is based upon a continuous-flow model of visual information processing (C. W. Eriksen & Schultz, 1979) and response competition and inhibition between the responses by which the subject signifies his judgment is presented. We show that a response signifying same will on the average be executed faster due to less priming or incipient activation of the competing response, different. In the experiment, the subjects matched letters on the basis of physical identity. The degree of priming of different responses on same trials and of same responses on different trials was manipulated by an extraneous noise letter placed in the display. Latency for judgments on same trials increased as the feature overlap of noise and target letters decreased. Latencies were shorter on different trials when the noise letter was dissimilar to either target letter than when the noise letter was the same as one of the targets. These results were consistent with the response-competition interpretation. 261Tasks in which a subject is presented two stimuli and asked to determine whether they are the same or different have been employed to study a variety of human behaviors ranging from psychophysical functions to semantic processing. When employed in psychophysics, the primary dependent variable has been the accuracy of the subject's judgments, whereas, in the investigation of cognitive processes, the task has typically been used to measure the speed with which the subject could arrive at his judgment. Recently, the judgmental act itself has become a subject of increasing interest. Within the past few years, two major attempts have been made to provide a model of the processing steps involved in the subject's same-different discrimination (Krueger, 1978;Proctor, 1981).One of the critical tests of such models has been their ability to account for the counterintuitive finding that same judgments often are made more rapidly than different judgments. As Nickerson (1975) has pointed out, the subject needs only one aspect or feature of difference between two stimuli for a correct different judgment but a correct same judgment requires the comparison of the stimuli on every possible feature. The latter operation would appear to require more processing and greater time.Krueger (1978) has proposed a "noisy operator" theory that assumes that, on a certain proportion of trials, a high difference count between two identical stimuli can be obtained due to random noise in the perceptual system. Due to erroneous different counts that can arise on same trials, the subject is required to recheck on true different trials. The time required for the recheck operation leads to longer reaction times for different judgments, since a large proportion of the same trials are not affected by the sensory perceptual noise.Proctor's (1981) model attributes the longer latencies required for judging different stimuli to inhibition in the naming responses. Identical stimuli activate only one naming response, but different st...

Several studies in the recent literature have shown that subjects' ability to control their attention to specific objects in the visual field is limited in the sense that they are unable to completely gate out the processing of irrelevant and unwanted material. In the present study, the paradigm used by Posner and Mitchell was utilized to investigate levels of noise processing. Three experiments are reported in which subjects had to judge whether two letters were the same or different. Each experiment had different instructions for defining same responses-physical match, name-identity match, and category match for Experiments 1, 2, and 3, respectively. The two target letters were separated by 2.2° of visual angle, and two noise elements were inserted between them. The nature of the noise elements and their relation to the targets were experimentally varied and constituted the main focus of the present study. The results of all experiments were in complete agreement with those obtained by Posner and Mitchell, thus extending their conclusions to situations where noise is present. More important, the results suggest that noise elements are processed to the same level as targets. It was proposed that subjects are tuned by the nature of instructions to a certain level of processing (or by analogy, to a specific "program") and are unable to gate out-or process to a lower level-unwanted or irrelevant information near the targets. A final experiment demonstrated this conclusion is robust and holds even under situations where there is complete certainty with regard to the spatial position of the attended object.

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In each of five experiments, the subjects viewed tachistoscopically presented pairs of letters and made speeded comparison judgments on the basis of name identity. On most trials, a noise letter string (word or anagram) was placed directly between the target letters. The results indicated that correct "same" RTs were a function of noise item type and its relation to target letters. Anagrams increased RTs more than their counterpart words, except when the noise word was either unmeaningful or response incompatible with respect to the target letters (e.g., B Tea b). The interference effects were also found to be independent of sequence length. It was posited that the subjects were unable to completely ignore the irrelevant attributes of the displays and that under certain conditions, the subjects were able to identify the noise items in a holistic fashion. The data were interpreted in terms of a unitization hypothesis of word recognition, response competition, and a continuous-flow conception of information processing.In a recent paper, O'Hara and Eriksen (1979) demonstrated the paradigmatic value of a characterclassification task with interference as a means of examining and supporting a unitization hypothesis of word recognition. Their subjects viewed tachistoscopically presented pairs of letters which were physically identical, name identical, or different, and made speeded comparison judgments on the basis of name identity. On some of the trials, noise trigrams composing either nonwords or familiar words appeared between the target letters (e.g., B ODG b or B DOG b). As expected, correct "same" responses were faster for PI than for NI letter pairs. Surprisingly, however, correct "same" reaction times (RTs) were also a function of noise type. Anagrams increased RTs significantly more than their counterpart words. Word noise, on the other hand, failed to appreciably affect RTs compared to the no-noise condition.Since the word and anagram items were composed of the same letters, O'Hara and Eriksen attributed the differential noise effects to the subjects' ability to perceptually unitize the word noise. They posited that a unitized word's featural or memorial representation would not interfere with the comparison task. The anagrams, however, were likely perceived as a group of free-floating letters and processed along with the target letters to the point of incipient response activation. At this juncture, response compe-