Two experiments indicate that reaction time and accuracy are not always equivalent measures of the underlying processes involved in the recognition of visually presented letters. In conjunction with the results of previous work, our research suggests the following generalizations: (a) Under data-limited viewing conditions (the short exposure durations of the typical tachistoscopic task), response accuracy is sensitive to early perceptual interference between target and noise items, whereas reaction time is more sensitive to later processes involved in response interference. (b) Under resource-limited viewing conditions (the long exposure durations of the typical reaction time task), both accuracy and reaction time appear to be sensitive to processes occurring in the later rather than the earlier stages of processing. Since the two dependent measures do not always reflect the same perceptual processes, we suggest that the convergence of reaction time and accuracy within the context of a specific information processing model should be demonstrated empirically rather than assumed a priori.

The effects of target-noise similarity on the ability to discriminate between two target letters were investigated in two paradigms. In both paradigms pairs of letters were presented briefly. In one, subjects had to report which of two target letters (e.g., A or E) had appeared in a location specified by a poststimulus cue. In the other, subjects simply had to indicate whether either target was presented, without regard to location. The results indicate that performance is poorer when the noise letter is the same as the target letter (e.g., AA) than when it is the other target (e.g., AE) or a nontarget (e.g., AK). More important, performance was also low when the noise letter shared only the same name as the target (e.g., Aa). This latter finding indicates that interletter interference effects cannot be entirely explained in terms of inhibition between visual features. We discuss the results in relation to a hypothesis of "cognitive masking." In addition, we discuss the relations between these findings of inhibition due to stimulus repetition and the findings of facilitation due to stimulus repetition that have been observed in other paradigms.

The role of perceptual interference in letter identification was investigated in three experiments designed to test the feature-specific inhibition model proposed by Bjork and Murray (1977). According to their extension of Estes ' (1972, 1974) interactive channels model, input channels leading to the same feature detector inhibit one another more than do channels leading to different detectors. The model therefore predicts perceptual interference between two letters to be a function of the degree of their feature overlap. Experiment 1 confirmed the feature-specific inhibition model and Bjork and Murray's finding that the accuracy of report is lower when a briefly presented target letter is flanked by an identical letter than when flanked by another target letter or by a nontarget letter. Results from Experiment 2 indicated that single-target performance is a function of the degree of feature similarity between the target letter and background characters in a stimulus display. Experiment 3 ruled out a spatial-uncertainty explanation of feature-specific inhibition in a new paradigm that does not require subjects to process a poststimulus cue. The results of these experiments are discussed in relation to recent studies exhibiting strong effects of noise letters at the response stage of processing. It is suggested that discrepancies between feature-specific interference and response-interference studies may be a function of the particular mode of stimulus presentation and of the dependent measures that are used. Bjork and Murray (1977) have recently proposed a model of visual processing that emphasizes featurespecific inhibition among visual input channels. The model is based upon their finding that the accuracy of report is lower when a briefly presented target letter (e.g., B) is flanked by an identical letter than when flanked by another target letter (e.g., R) or by a nontarget letter (e.g., P or K). For instance, they found that if a poststimulus cue indicated that the left-hand member of a letter pair was to be reported, then report of B from the pair BB was less accurate than report of B from the pair BR or from the pair BK.The feature-specific inhibition model, as proposed by Bjork and Murray, assumes that alphanumeric characters are represented in memory as hierarchical lists of features (e.g., Estes, 1972;Rumelhart, 1970;Wolford, 1975). Information about the features contained within visually presented stimuli is extracted over parallel, but interactive, input channels that lead to feature detectors. According to the model, the excitation of a particular input channel caused by the presence of a particular feature contained within a letter results in both feature-specific inhibition of other This research was supported in part by a grant from the National ScienceFoundation (BNS-76-{)1227) to Howard Egeth and James Pomerantz. The authors would like to thank Alfonso Caramazza, Charles W. Eriksen, Michael McCloskey, James Pomerantz, Lawrence Sager, and Edward E. Smith for their helpful advice. Requests for r...

It is widely assumed, based on Chocholle's (1940) research, that stimuli that appear equal in loudness will generate the same reaction times. In Experiment 1, we first obtained equal-loudness functions for five stimulus frequencies at four different intensity levels. It was found that equal loudness produced equal RT a~80 phons and 60 phons, but not at 40 phons and 20 phons. It is likely that Chocholle obtained equivalence between loudness and RT at all intensity levels because of relay-click transients in his RT signals. One main conclusion drawn from Experiment 1 is that signal detection (in reaction time) and stimulus discrimination (in loudness estimation) require different perceptual processes. In the second phase of this investigation, the RT-intensity functions from six different experiments were used to generate scales of auditory intensity. Our analyses indicate that when the nonsensory or "residual" component is removed from auditory RT measures, the remaining sensory-detection component is inversely related to sound pressure according to a power function whose exponent is about -.3. The absolute value of this exponent is the same as the .3 exponent for loudness when interval-scaling procedures are used, and is one-half the size of the .6 exponent which is commonly assumed for loudness scaling.The historic traditions that underlie the present research are formidable. Psychophysicists have consistently found a direct relation between auditory stimulus intensity and loudness. Specifically, Stevens and his colleagues have established that perceived loudness grows as a power function of stimulus intensity (Marks, 1974(Marks, , 1979. Equally impressive is the evidence in support of an inverse relation between stimulus intensity and simple auditory reaction time (RT). Classic experiments by Cattell (1886), Chocholle (1940), Pieron (1920), and Wundt (1874) have convincingly shown that RT decreases monotonically with corresponding increases in auditory stimulus intensity.Based on the fact that stimulus frequency, along with stimulus intensity, are the primary determinants of both loudness and RT, the present paper comprises two major sections in which these two stimulus attributes are evaluated. First, we evaluated the relation between equal loudness (across frequencies) and RT, using Chocholle's (1940) attempted to synthesize the data from several RT experiments in order to construct a uniform scale of sensory intensity that is based on RT measures. PHASE 1: EQUAL LOUDNESS AND REACTION TIMEIt is remarkable how many investigators have cited Chocholle's research, conducted over 40 years ago at the Sorbonne Laboratory, as the definitive study of the relation between auditory RT and signal intensity and frequency. His experiments were extensive but simple in design. Three experienced subjects generated RT-intensity functions over a wide range of intensity levels for frequencies of 20, 50, 250, 500, 1,000, 2,000, 4,000, 6,000, and 10,000 Hz. From these initial results, he drew "equal-RT" contours; that is, stimul...

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