Five experiments investigated the influence of the differences in stimulus familiarity among a dot-matrix letter, word, and nonword upon the relative judged duration of 30-msec flashes. Figure-ground contrast was manipulated by varying the number of dots comprising each display letter. With 30-msec presentations, judgments ranked subjective durations of the displays nonword > word> letter. Differences in judged duration among stimulus fortns were greater when both forward and backward masking reduced recognition probability to chance level than when no mask was employed, and discriminations among masked presentations were easier for subjects. Figure-ground contrast influenced apparent duration judgments only as increases in figure-ground contrast contributed to clarity of familiarity differences among displays. The data were interpreted to indicate that differences in stimulus familiarity operate as early in visual processing as do differences in figure-ground contrast, with greater familiarity facilitating an automatic contact between a stimulus and its memory representation and therein reducing experienced duration.Several writers have recently proposed cognitive theories of time perception.For example, Frankenhaeuser (1959) has suggested that subjectively experienced duration is related to the total amount of experience or "mental content" occurring within a clock-time interval. Michon (1965) emphasized the amount of information "actively coped with" in determining the experience of duration. Ornstein (1969) claimed that subjective duration is determined by the "cognitive storage size" of the processed information and " ... as storage size increases, the experience of duration lengthens" (p,41).The studies offered by these investigators in support of their theories employed stimulus presentations of clock-time durations well above the tachistoscopic range. Ornstein, for example, suggests that the experience of duration does not accompany stimulus inputs briefer than 3 or 4 sec. However, several recent findings have indicated that, while the real-time duration of the processing of a single perceptual unit may be no briefer than 130 msec (Efron, 1973), the apparent or subjective duration of shorter presentations is not constant. Further, the differences in apparent duration of tachistoscopic presentations may index the operations of perceptual or preperceptual processing. When Liss (1968) presented 1-, 2-, or -l-Ietter arrays for real-time durations ranging from 7 to 100 msec, his subjects volunteered

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12 independent groups were used to examine the relationship between response latency and regularity of signal occurrence. In each of 6 groups 20 simple visual signals were presented sequentially at one of 6 constant intervals. Interval durations were 10, 20, 40, 80, 160, or 320 sec. For each constant-interval group tested, there was also a variable-interval group with intervals of the same average duration. For all intervals except one (40 sec.), the variable-interval groups had longer response latencies than the constant-interval groups, the difference in response latency between the constant- and variable-interval groups increasing as a function of the duration of the interval, up to intervals of 160 sec. For both constant- and variable-interval groups, response latency varied directly with interval duration.

Four experiments were designed to investigate automatic processing of letter case and lexical/semantic information under forward and backward masking conditions that disallowed a visible image. Stimulus displays were letter string pairs; the letter case for each pair matched or mismatched, and the relationship between the two strings within pairs varied. Experiment 1 required direct Same-Different responses to stimulus pairs, and the results indicate that tasks requiring direct responses to stimulus inputs cannot distinguish between conscious response biases and unconscious use of information. Experiments 2 and 3 employed an indirect index of automatic prerecognition analyses of verbal-linguistic parameters and showed that, with 30-msec pre-and postmasked presentations, letter case, orthographic regularity, and lexical/semantic information are all analyzed in unconscious operations. Experiment 4 demonstrated that, under the viewing conditions of Experiments 2 and 3, subjects had no awareness of the stimulus input.Results of several recent studies indicate that subjects access the meaning of words under central masking conditions that deny a visible image of letters in a display (e.g., Balota, 1983;Fowler, Wolford, Slade, & Tassinary, 1981;Friedman, 1980;Huber & Johnson, 1980;Marcel, 1980 Marcel, , 1983bMarcel & Patterson, 1978). Unless these results can be shown to be artifactual and/or fail to gain converging support from other methods for studying the earliest operations of visual processing, they have important implications for theoretical accounts of (1) the means by which semantic access occurs, (2) the function performed by central pattern masking, and (3) the distinction between visual, but not visible, operations and the outcomes of those operations that constitute current perceptual awareness.Direct and indirect measures of processing have provided at least partial converging evidence of prerecognition semantic access. Fowler et al. (1981), Friedman (1980, Huber andJohnson (1980), and Marcel (1983b;Marcel & Patterson, 1978) used procedures that required direct responses to stimulus inputs. Marcel's (1983b;Marcel & Patterson, 1978) data are the most surprising and counterintuitive. When he determined the longest onset asynchrony between a stimulus and a following pattern mask (SOA) at which subjects made chance-level judgments (defined as .60 probability of correct response), Portions of these data were reported at the meeting of the Midwestern Psychological Association, Chicago, May, 1983. The authors express appreciation to Paul Koch, Chris Conzemius, and Angela Hemmer for assistance in conducting the experiments, and to Roberta Klatzky, David Balota, and three anonymous reviewers for critical comments on an earlier draft of this paper. Address reprint requests to L L Avant, Department of Psychology, Iowa State University, Ames, IA 50011.Marcel found that the SOA for judgments of semantic similarity between a masked word and two unmasked words was lower than that for judgments of form similarity betw...

Three experiments further explored the Avant, Lyman, and Antes finding that, during prerecognition processing, differences in subjects' familiarity with letters, words, and nonwords generate differences in the apparent duration of tachistoscopic flashes. The results replicate and extend the earlier findings, showing apparent duration differences with a variety of verbal stimuli over a range of tachistoscopic exposure intervals. The results also suggest that exposures of stimuli on early trials of an experiment reduce differences in preexperimental stimulus familiarity such that unfamiliar stimuli come to be processed more nearly like familiar stimuli. Familiarity acquired on early trials appears to accumulate at prerecognition levels of processing and to reduce apparent duration differences among stimuli on later trials.