During a I-sec tachistoscopic exposure, Ss responded with a right or left leverpress to a single target letter from the sets Hand K or Sand C. The target always appeared directly above the fixation cross. Experimentally varied were the types of noise letters (response compatible or incompatible) flanking the target and the spacing between the letters in the display. In all noise conditions, reaction time (RT) decreased as between-letter spacing increased. However, noise letters of the opposite response set were found to impair RT significantly more than same response set noise, while mixed noise letters belonging to neither set but having set-related features produced intermediate impairment. Differences between two target-alone control conditions, one presented intermixed with noise-condition trials and one presented separately in blocks, gave evidence of a preparatory set on the part of Ss to inhibit responses to the noise letters. It was concluded that S cannot prevent processing of noise letters occurring within about 1 deg of the target due to the nature of processing channel capacity and must inhibit his response until he is able to discriminate exactly which letter is in the target position. This discrimination is more difficult and time consuming at closer spacings, and inhibition is more difficult when noise letters indicate the opposite response from the target.

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...

No abstract

In two experiments, using memory sets of up to 10 letters, the response competition paradigm was employed to investigate the extent to which extraneous visual stimuli interfere with or affect the process of memory search. It was assumed that if selective attention could exclude the effect of noise letters from a Sternberg-type memory comparison process, then there would be an increase in intercept for the reaction time-set size functions but no increase in slope. This result was obtained. However, a large difference in response times to both positive and negative set targets was found when the accompanying noise letters indicated a competing response, as opposed to when they indicated the same response as the target. This implies rapid identification of the nature of both target and noise, independent of a serial comparison process. A modification of a dual process model (Juola, Fischler, Wood, & Atkinson, 1971) in which stimuli activate a familiarity value independent of memory search was suggested to account for these results.

Three studies investigated the effect on the response time for voicing a four-letter word of delaying one of the letters or the entire word for intervals of up to 500 msec. Experiment I found delay of the first letter most detrimental, while delay of the second, third, or fourth letter facilitated performance. Experiment II confirmed these findings and indicated that delay of the entire word produced response times similar to delay of the first letter. Experiment III investigated the possibility that knowledge of the pronunciation of the first letter was the essential factor in facilitating performance when later letters were delayed. It was concluded that when pronunciation of the first letter was known, Ss were able to begin processing the word immediately.The purpose of the present experiments was to analyze the processes involved in the recognition of a single word by skilled readers. It is generally acknowledged that a skilled adult reader uses "higher order units" than words (Gibson, 1967) in reading the printed page. But it is also a rather obvious fact that the child, in learning to read, must at first proceed one word at a time. Although linguists continue to argue about whether the "word" is the "natural perceptual unit of spoken language [Jones, 1965, p.44]," it is apparent that our graphic representations are organized around words.Since the studies of Cattell in the latter part of the 19th century (Huey, 1908), it has been apparent that words are perceived somehow differently from single letters. Cattell reported that whole words could be recognized as quickly as single letters and that the response to a word could occur at a shorter latency than the response to a single letter. Cattell concluded that reading was done by whole-word units. This same conclusion has been reached by Reicher (1969) and Wheeler (1970). The question arises as to what cues are available in words which enable Ss to make these rapid judgments. Studies have concentrated on two lines of inquiry: cues related to letters as visual cues and cues related to sound-spelling correspondences. Visual CuesThe shape of the word, which depends on the pattern of letters, was proposed as the main means of recognition by Erdman and Dodge (Huey, 1908). Goldsheider and Muller (Huey, 1908) found that certain "determining" letters seemed to be more important to *This research was supported by Public Health Service Research Grant MH-1206 and United States Public Health Service Research Career Program Award K6-MH-22014 to the second author. The paper is based on a thesis submitted by the first author to the University of Illinois in partial fulfillment of the requirements for her master's degree. 66word recognition than others. By presenting word skeletons for identification, they found that the first letter was nearly always necessary for recognition and that other determining letters were those which supplied clues to the word sound.Using words with deliberate transpositional spelling errors, Bruner and O'Dowd (1958) found that errors at the beg...