The effect of repetition on the perception of single letters

Single letters were presented for from one to five flashes, with S required to report what he saw after each flash. The clarity of the letter increased sharply with repetition. Since the letters were no larger than one-third of a degree in size, clarity could not have been increased by S making different fixations from flash to flash and combining them into a total percept. Nor was S guessing, since this could be ruled out by other indicators. Thus, it was concluded that repetition of the stimulus can have a direct effect on the clarity of a S’s percept of that stimulus.     

How much help do repeated presentations give to recognition processes?

A recent experiment by Haber and Hershenson (1965) had shown that in a recognition task one long look at a stimulus was always superior to two or more shorter looks summing to the same total presentation time. In order to explore this more fully and to account for opposite results in a different type of recognition task, as well as in a serial learning task, an improved replication of the earlier study was carried out using very short durations and single letters as stimuli. The same non-reciprocity was found, again strongly favoring duration over repetition as a determinant of clarity of a percept, even though repetition alone was also shown to be a significant independent variable. As a subsidiary finding, an error analysis showed that when a letter was misnamed it was nearly always confused with one that looked like it rather than one that sounded like it. Some discussion was offered as to the role of an auditory information storage in low memory load tasks such as this one, as well as some general implications for information processing analyses of the non-reciprocity of duration and repetition.     

Repetition benefit in mental rotation is independent of stimulus repetition

In this study, we investigated whether there is a repetition benefit in mental rotation that is independent of stimulus repetition (i.e., due to increased efficiency in postencoding processing). Three experiments were conducted, in which different conditions of stimulus repetition (different letters on consecutive trials in Experiment 1, letters of different orientations on consecutive trials in Experiment 2, and priming of rotation direction in Experiment 3) were used, and the extent of repetition of rotation direction between two consecutive trials was manipulated. The results of all three experiments showed clear evidence of a repetition benefit without repeating the stimulus, suggesting that this effect is independent of stimulus repetition and lending support to the notion of increased efficiency in mental rotation as a result of repeated rotation direction per se.     

Temporal separation of two part-letter arrays and size changes in a nonmasking work-superiority effect

In two experiments subjects were asked to report the identity of a position-cued critical letter in an array of four letters. Four types of arrays were used: (i) unpronounceable nonwords; (ii) pronounceable nonwords ('pseudowords'); (iii) words in which the critical letter was minimally constrained by the context letters; and (iv) words in which the critical letter was maximally constrained by the context letters. All four-letter stimuli were presented in two parts. A leading array in which the information from two quadrants of a vertical by horizontal division of each letter was presented, and, after intervals of 0, 20, 40, 80, 100, 120, 160, 320, and 480 ms and infinity (ie, no trailing array), a trailing array of the complementary letter parts. In experiment 1 a single group of eight subjects responded to the one hundred and sixty combinations of the four types of letter strings, the four serial positions, and the ten stimulus onset asynchrony values. In experiment 2 the stimulus onset asynchrony values were varied among subjects, with twelve subjects responding at each value. The results from these two studies were generally similar. Performance in the word conditions was consistently superior to performance in the nonword conditions, and the magnitude of this difference (ie, the word-superiority effect) increased with increasing stimulus onset asynchrony up to 120 ms, and then gradually declined. The fact that the magnitude of the word-superiority effect initially increased with the separation of leading and trailing arrays was interpreted as support for Johnston's suggestion that letters in words are represented during visual encoding both in the form of individual letter percepts and in a decay-resistant word percept, as opposed to letters in nonwords, which are represented only as decay-susceptible letter percepts. The experimental findings are discussed in relation to the 'interactive activation' model of word perception.     

A different look at perceptual defense for taboo words

Hober has concluded from previous work that meaningfulness, frequency, and related stimulus variables directly affect the clarity of letters of words. To examine whether the letters of taboo words would be harder to see, 12 taboo words were matched in length to 12 very frequent and 12 very rare neutral words. Each word was shown an unpredictable number of times. Three groups of 8 Ss each were required, respectively, either to name the letters they saw on each flash, name the letters and then guess the word, or guess the word only. While no differences were found among the three groups, the clarity of the letters of the frequent words exceeded that for the rare words, which in tum was higher than that of the taboo words. This difference was apparent on even the first flash, supporting the interpretation of a perceptual defense effect.     

Two bs or not two Bs? A signal detection theory analysis of repetition blindness in a counting task

Stimulus repetition usually benefits performance. A notable exception is repetition blindness (RB), in which subjects fail to report a repeated stimulus in a rapid serial visual presentation. Theories differ in attributing RB to either perceptual encoding or memory retrieval and to impaired discrimination versus response bias. In the present study, subjects judged whether one or two letters were imbedded in sequences of digits. Unlike previous studies, false guesses of two unrepeated letters were distinguished from false guesses of two repeated letters. When repeated- and unrepeated-letter trials were randomly intermixed (Experiment 1), RB was entirely attributable to response bias. However, when they were separately blocked (Experiments 2 and 3), RB was manifested in discriminability (d'). The results support perceptual-encoding accounts of RB but indicate that effects on discriminability depend on subjects' processing strategies.     

Inhibition of return and repetition priming effects in localization and discrimination tasks.

Inhibition of return (IOR) refers to slower responding to a stimulus that is presented at the same, rather than a different location as a preceding, spatially nonpredictive, stimulus. Repetition priming refers to speeded responding to a stimulus that duplicates the visual characteristics of a stimulus that precedes it. IOR and repetition priming effects interact in nonspatial discrimination tasks but not in localization tasks; three experiments examined whether this is due to processing differences or due to response differences between tasks. Two stimuli, S1 and S2, occurred on each trial. In Experiment 1, S1 and S2 were both peripheral arrows; in Experiment 2, S1 was a central arrow and S2 was a peripheral nondirectional rectangle; in Experiment 3, S1 was a peripheral nondirectional rectangle and S2 was a peripheral arrow. S1 never required a response; S2 required a localization or a discrimination response. Despite evidence that form information was likely extracted from the arrow stimuli, the localization task revealed no repetition priming: IOR occurred regardless of shared visual identity of the S1 and S2 arrows. The discrimination task revealed IOR only when the visual identity changed from S1 to S2; otherwise, facilitation occurred. These results suggest that IOR is masked by repetition priming only when the response depends on the explicit processing of form information; repetition priming does not occur when such information is extracted automatically but is task (and response) irrelevant.     

Using ambiguous plaid stimuli to investigate the influence of immediate prior experience on perception

In a series of three experiments, we used an ambiguous plaid motion stimulus to explore the behavioral and electrophysiological effects of prior stimulus exposures and perceptual states on current awareness. The results showed that prior exposure to a stimulus biased toward one percept led to subsequent suppression of that percept. In contrast, in the absence of stimulus bias, prior perceptual experience can have a facilitative influence. The suppressive effects caused by the prior stimulus were found to transfer to an ambiguous plaid test stimulus rotated 180º relative to the adaptation stimulus, but were abolished if (1) the ambiguous test stimulus was only rotated 90º relative to the adaptation stimulus or (2) the adaptation stimulus was heavily biased toward the component grating percept. Event-related potential recordings were consistent with the involvement of visual cortical areas and suggested that the influence of recent stimulus exposure may involve recruitment of additional brain processes beyond those responsible for initial stimulus encoding. In contrast, the effects of prior and current perceptual experience appeared to depend on similar brain processes. Although the data presented here focus on vision, the work is discussed within the context of data from a parallel series of experiments in audition.     

Sensory features and the reduction of imaginal interference

Interference generated among the sensory features of PA stimulus words is not eliminated by processing at the imaginal level. This experiment was planned to test the reverse possibility. Will interference generated by similar imaginal referents be eliminated by sensory overlap between the stimuli and their responses? Thus, stimulus words did or did not evoke similar images, pairs did or did not share initial letters, and lists were acquired either under an instructional set t o form interacting images or to repeat the items aloud. The results indicated that the imagery strategy was superior to the repetition strategy in all conditions, and that stimulus interference was statistically eliminated when pairs shared the same initial letters. The findings were interpreted as consistent with a levels of processing conceptualization.     

Being confident without seeing: What subjective measures of visual consciousness are about

Can observers be confident about the accuracy of a discrimination response without a visual experience of the stimulus? In a series of five experiments, observers performed a masked orientation discrimination task, a masked shape discrimination task, or a random-dot motion discrimination task, followed by two subjective ratings after each trial, in which participants reported either their visual experience of the stimulus or their confidence in being correct. We observed that the threshold for ratings of the perception of the stimulus was above the threshold for ratings of a decision, that decision ratings outperformed stimulus ratings in predicting trial accuracy, and that different decision-related scales were more strongly associated with other decision-related scales than with ratings of stimulus clarity. We propose a taxonomy of subjective measures of consciousness that differentiates between subjective measures relating to the percept of the stimulus and measures relating to a discrimination decision and discuss the relation to type II blindsight.     

Perceptual reports vs recognition responses: A reply to Parks

Parks (1968) objects to the interpretation offered by Haber and Nathanson (1968), especially with respect to the following condition: S responds to a figure seen oscillating behind a narrow slit that it is foreshortened and also reports that he has a percept only of what is visible in the slit at any instance. Parks argues from these two responses that S must actually have a percept of most or all of the figure, a conclusion denied by the authors. This reply goes to some length to reiterate a distinction between knowledge of a stimulus gained from a percept and that gained from recognizing or constructing what the figure must be, based upon memory of previous percepts and past experience. Parks fails to make this distinction in his reply, and thus equates what S says he knows with what S actually sees. Therefore, this experiment still provides little support for any postretinal storage of the type Parks proposes.     

Wholistic and analytic stimulus processing: The development of selective perceptual strategies

This experiment reports an investigation of the development of selective processing strategies as subjects become increasingly more practised at a serial self-paced RT task. It demonstrates the effect a preceding stimulus can have on the analysis of a current signal and the development of active analytic strategies in favour of passive wholistic processing, with practice. The stimuli used were letters with irrelevant visual noise dot patterns superimposed on them. The letter, or the dot pattern, or both, could be repeated on successive trials. Early in practice repetition of both stimulus components simultaneously produced short reponse latencies relative to repetition of the letter alone. The number of noise dots markedly affected RT. Late in practice, however, letter repetition RTs were small, irrespective of whether or not the noise dot pattern was repeated. Furthermore, the number of noise dots no longer had an effect on the RT to these stimulus transitions. The results suggest that subjects appear to be able to select relevant information to process as they become progressively more practised, even though there is evidence that they compare the current stimulus with an iconic representation of the immediately preceding one.     

Letters in time and retinotopic space

Various phenomena in tachistoscopic word identification and priming (WRODS and LTRS are confused with and prime WORDS and LETTERS) suggest that position-specific channels are not used in the processing of letters in words. Previous approaches to this issue have sought alternative matching rules because they have assumed that these phenomena reveal which stimuli are good but imperfect matches to a particular word-such imperfect matches being taken by the word recognition system as partial evidence for that word. The new Letters in Time and Retinotopic Space model (LTRS) makes the alternative assumption that these phenomena reveal the rates at which different features of the stimulus are extracted, because the stimulus is ambiguous when some features are missing from the percept. LTRS is successfully applied to tachistoscopic identification and form priming data with manipulations of duration and target-foil and prime-target relationships.     

Inhibition of return for target discriminations: the effect of repeating discriminated and irrelevant stimulus dimensions

Inhibition of return (IOR) refers to slowed reaction times when a target repeats in the same location as a preceding stimulus. In four experiments, the participants were presented with two successive stimuli, S1 and S2. In Experiments 1 and 2, the participants made a speeded discrimination of the identity or orientation of both S1 and S2 (Experiment 1) or of S2 only (Experiment 2). An IOR effect occurred for the repetition of stimulus location, but a facilitatory effect occurred if the stimulus remained unchanged or if an overt response was repeated. In Experiments 3 and 4, the participants localized S1 and S2 (Experiment 3) or S2 only (Experiment 4) to the left or right of center. In this case, repeating the same stimulus had no effect: IOR occurred any time stimulus location repeated. These results demonstrate that the expression of IOR is modulated by the repetition of a target object, but only when the task requires the discrimination of that object; when no discrimination is required, IOR is unaffected.     

Location and shape in inhibition of return

Inhibition of return (IOR) is characterized by a delay in responding to a target preceded by an irrelevant stimulus (cue) at the same location, or, in other words, by a response delay when the same location is stimulated twice. It is not clear, however, if the same phenomenon is present when there is a repetition of a simple nonspatial attribute of the stimulus. The present study examines the repetition of shape. Six experiments were conducted. In Experiments 1, 2, 3, and 6 the stimuli were geometrical shapes, whereas in Experiments 4 and 5 letters were used. In Experiment 1 all the stimuli were presented at fixation, whereas in Experiments 2 to 6 they were presented in the periphery. In Experiments 2 and 3, location and shape of the cue and the target were independently manipulated in order to test independently inhibitory effects (IOR?) attributable to location repetition and shape repetition. Results showed an inhibitory effect for location and a much smaller inhibitory effect for shape. The latter was restricted to the cued location. Experiments 4 and 5 tested the possibility that inhibition caused by shape repetition is due to repetition blindness. Experiment 6 contrasted the presence or absence of a central neutral attractor in the delay interval between presentation of the cue and the target. Taken together the results seem to favor IOR as the basis for the inhibition caused by shape repetition.     

Variations in intensity and frequency moderate the facilitative effects of a complex rhythm stimulus on long-term memory consolidation in the day-old chick (Callus gallus)

The authors have previously shown that exposure to 1 min of a complex, but not an isochronous, rhythm stimulus facilitates long-term memory consolidation in chicks (Gallus gallus) trained on a passive-avoidance task (S. R. Toukhsati & N. S. Rickard, 2001). The acoustic parameters of this stimulus were explored further in the current study. Retention was found to be best facilitated when the complex rhythm stimulus was presented at intensities between 5 and 15 dBA above background laboratory noise levels and at a frequency of 1 kHz. Removal of an accent from the stimulus did not moderate the effect. These findings provide confirmation that memory in an avian species can be facilitated by exposure to a complex rhythm stimulus and suggest that pattern repetition may be an important feature of this effect.     

Interactions among levels of processing

This article examines associations among representations of physical, name, and category information by determining effects of category repetition on and following physical, name, and category match trials. Subjects decided whether two letters were from the same half of the alphabet. Category repetition effects were evidenced by faster ~nd more accurate responses when letters from the same half of the alphabet were used on successive trials. Although physical matches showed no effect of category repetition, name and category matches did. Trials following physical matches were less affected by category repetition than were trials following name or category matches. The results suggested that these category repetition effects were mediated by interletter associations: Reaction time increased with the alphabetic distance between preceding and current letters. However, these distance effects held only for forward (A → B) and not backward (B → A) alphabetic sequences, suggesting that the alphabetic representation is ordinal and unidirectional.     

The role of attention in temporal integration

When two visual patterns are presented in rapid succession, their contours may be combined into a single unified percept. This temporal integration is known to be influenced by such low-level visual factors as stimulus intensity, contour proximity, and stimulus duration. In this study we asked whether temporal integration is modulated by an attentional-blink procedure. The results from a localisation task in experiment 1 and a detection task in experiment 2 pointed to two separate effects. First, greater attentional availability increased the accuracy of spatial localisation. Second, it increased the duration over which successive stimuli could be integrated. These results imply that theories of visible persistence and visual masking must account for attentional influences in addition to lower-level effects. They also have practical implications for use of the temporal-integration task in the assessment of group and individual differences.     

Response repetition benefits and costs

In a wide variety of tasks, choice reaction time (RT) is reduced for repetitions of the previous response. However, when the task itself or a relevant physical feature that successive trials have in common changes, costs for response repetitions can be observed. In a series of three experiments it was investigated whether the repetition of a response results in costs if the stimulus category changes. Furthermore, it was asked whether there need to be informative physical task features that successive trials have in common to produce response repetition costs. In alternating runs, participants had to respond to either one of four symbols or one of the letters with a binary choice reaction: Results suggest that a change of stimulus category is a sufficient condition to produce response repetition costs. It is hypothesized that any change of a task feature that is part of the task representation participants adopt leads to a disruption of repetition-based facilitation and tends to facilitate a response alternation.     

Hemispheric differences for the integration of stimulus levels and their contents: evidence from bilateral presentations

Several studies have demonstrated that hemispheric differences for the processing of hierarchical letter stimuli are more likely to occur when the letters at the levels are associated with conflicting responses. Typically, a single stimulus is presented, so that the conflict occurs between the global and the local levels of the same stimulus. Our hypothesis is that in this situation, conflict resolution requires integration of the letters and their respective levels and that the hemispheres differ in this integration process. According to this integration theory, the favorable effect of response conflict on hemispheric differences should vanish if other features, such as location, can also serve for conflict resolution. This prediction was tested in the present study by simultaneously presenting an individual hierarchical stimulus to each visual field. Conflicting letters either were arranged within one stimulus or were placed in different stimuli. In the latter case, a response conflict could also be resolved by integrating letters and locations. As was expected, there were no visual field effects in these conditions. On the other hand, visual field effects showed up when the conflicting letters were located within the same stimulus. These results support the idea that the hemispheres differ in their capacity for integrating level and form.