Processing of tachistoscopic displays with controlled order of characters and spaces

The task used was designed to force Ss consistently to process the letters of a tachistoscopic display in the same spatial order, if Ss are able to process the letters in a brief display serially and if Ss have enough voluntary control over the selection of a processing order to use the order chosen by the E. In the main series of experiments the set of slides shown in each session included slides having a blank space in some position in the linear array of letters. For control, no-blank slides, a sharp, monotonic decrease in the percentage of correct detections of a signal letter with distance of the signal letter from the focusing dot was obtained. An unexpected result from the slides having a blank space was that detection of the signal letter was considerably more accurate on the slides having a blank space immediately following the signal letter than on the control slides having no blank space or the slides having a blank space immediately before the signal letter in the processing order. In one experiment blank spaces were replaced by black rectangles with no substantial change in the pattern of results. The results from the slides having a blank space or a black rectangle were interpreted as indicating that the onset of processing the image of a letter was determined by the distance in the display from the focusing dot to the letter and that the duration of processing an image of a letter was determined by the distance in the display from the letter to the next letter in the processing order.     

Eye movements when reading: The importance of the word to the left of fixation

In reading, it is well established that word processing can begin in the parafovea while the eyes are fixating the previous word. However, much less is known about the processing of information to the left of fixation. In two experiments, this issue was explored by combining a gaze-contingent display procedure preventing parafoveal preview and a letter detection task. All words were displayed as a series of xs until the reader fixated them, thereby preventing forward parafoveal processing, yet enabling backward parafoveal or postview processing. Results from both experiments revealed that readers were able to detect a target letter embedded in a word that was skipped. In those cases, the letter could only have been identified in postview (to the left of fixation), and detection rate decreased as the distance between the target letter and the eyes' landing position increased. Most importantly, for those skipped words, the typical missing-letter effect was observed with more omissions for target letters embedded in function than in content words. This can be taken as evidence that readers can extract basic prelexical information, such as the presence of a letter, in the parafoveal area to the left of fixation. Implications of these results are discussed in relation to models of eye movement control in reading and also in relation to models of the missing-letter effect.     

Confusability and interference between members of parafoveal letter pairs

In each of three experiments, confusability between members of a parafoveally exposed pair of letters affected accuracy of identifying the peripheral, but not the central, letter. Confusability was determined from a confusion matrix developed for each subject. In Experiment 1, only one letter in each pair was identified on each exposure, and the position of pair members was varied over trials while the absolute position of the pair was held at a constant distance from fixation. In Experiment 2, both letters were identified on each exposure. In Experiment 3, the criterion letter was presented at a constant distance from fixation, and both letters were identified on each exposure. Since results in Experiment 3 were the same as in Experiments 1 and 2, the effect cannot be explained with reference to an interaction between confusability and acuity. The implications of the findings for various models of visual information processing are discussed.     

Detection and identification of words and letters in simulated visual search of word lists

Ss were shown a rapid sequence of words and had to (a) make a speeded response to the presentation of a predefined target and (b) report a "response word" which they thought immediately followed the target in the sequence. In Experiment I presentation rate was varied orthogonally with the number of alternative targets. Detection errors and latency increased with target set size, as did the distance of the response word from the target in the list sequence. Increases in presentation rate produced greater target-response distance without affecting detection time. In Experiment II Ss were in some conditions given only the initial letter of the targets; the response could be either the whole word following the target or only its initial letter. The results indicated that Ss could, within limits, concurrently detect initial letters and identify words. Alternatives to hierarchical-type models of stimulus processing in visual search were discussed.     

Adult age differences in letter-level and word-level processing

Older and young adults' letter detection and lexical decision performance were examined as word frequency varied to determine whether there were age differences in word recognition. Allen and Madden (1989) found that older adults' pattern of reaction time (RT) across word frequency categories was different from young adults' pattern for a letter detection task. In this study, for both letter detection and lexical decision tasks, older adults exhibited a monotonically decreasing RT function as word frequency increased. However, young adults exhibited a nonmonotonic RT function across word frequency for the letter detection task but a monotonically decreasing RT function as word frequency increased for the lexical decision task. An expanded parallel input serial analysis model of word processing was hypothesized.     

注意捕获效应受知觉负载及目标与干扰项距离的共同影响

研究考察了无关干扰项引发的注意捕获效应如何受到任务知觉负载以及目标与干扰项距离的共同影响。被试在视觉搜索集中搜索目标并做辨别反应。通过控制搜索集的大小来控制任务知觉负载, 同时在搜索集中存在一个用颜色标定的无关干扰项(奇异项), 该奇异项与当前的搜索目标存在一致、中性或不一致的关系, 该奇异项的位置与当前目标相邻或相距较远。结果发现, 被试在低负载条件下出现显著的干扰效应(不一致条件的反应时减中性条件的反应时), 而在高负载条件下干扰效应减小。此外, 在高负载条件下, 当目标与干扰项相距较近时没有出现干扰效应, 而当目标与干扰项相距较远时存在显著的干扰效应。干扰效应受到任务知觉负载和目标与无关干扰项距离的共同影响。这些结果说明, 与任务无关的刺激是否捕获注意取决于当前任务总体上是否存在可用的剩余注意资源, 也受到其周围临近区域的局部注意资源是否充足的影响。     

Flexible mental processes in numerical size judgments: The case of hebrew letters that are used to convey numbers

In addition to its primary linguistic function, the Hebrew alphabet is sometimes used as a means of number notation (i.e., the system of gematria). Hebrew letters, Arabic numerals, Hebrew number names, and Hebrew letter names were used in a numerical size comparison task, in which two visually presented symbols were compared for numerical value while irrelevant variations in their physical size had to be ignored. A size congruity effect, indicated by faster responses when differences in physical and numerical size were consistent, was larger for Arabic numerals than for number names. The effect for Hebrew letters was similar to that for Arabic numerals and was stronger than that observed for letter names. These results suggest flexible processing of Hebrew letters, so that they function as ideographic symbols in an arithmetic context. A distance effect, indicated by an inverse relationship between reaction time and numerical distance, was found for all notations but was particularly strong for Hebrew letters.     

Processing of sequentially presented letters

The effect on the number of letters S can report of the duration of each sequentially presented letter was compared with that of processing time, defined as the time from the onset of a letter to the onset of the next letter. Four Ss were each shown 1250 common English words, from four to eight letters long, one letter at a time. Each letter acted as a visual noise field for the preceding letter. The duration of each letter and the interval between letters was varied independently. The S reported the letters he saw after each word was displayed. It was found that the processing time (onset to onset) predicted the number of letters correctly reported, regardless of the partition between on time and off time. A calculation was made of the number of milliseconds of on plus off time that are needed to ensure correct report of each letter. This time was independent of the duration of the processing time, but was positively correlated with the number of letters in the word. This correlation is probably in part artifactual, so that no claim can be made that it takes longer to process a letter of a long as compared to a short word.     

Word recognition with forced serial processing: Effects of segment size and temporal order variation

Serial processing was forced by displaying words one letter or letter cluster at a time. Letters or clusters appeared in adjacent spatial positions and in rapid sequence, followed immediately by a mask. Under these conditions, there was a sharp increase in the percentage of words correctly identified as the size of the letter clusters presented in series increased. In a control condition without masking, designed to permit parallel processing across clusters, words were identified near-perfectly, regardless of the size of the clusters displayed. Words displayed one letter at a time without masking were identified fairly well even when letters were presented in random order. The results are interpreted as evidence that skilled readers tend to process letters within words in parallel.     

The extent of processing of noise elements during selective encoding from visual displays

Circular visual displays of 12 elements, consisting of A, H, M, and U, were presented to S. She responded with a lever movement in one direction if a given letter designated by a bar indicator was a member of the set A-U and in the opposite direction if it was from the other set. The principal experimental variables were the SOA by which the indicator preceded the display and whether the target letter was flanked by letters of the same or opposite set. The results indicated that the interference produced by noise letters is primarily on the response as opposed to the processing side. Also, there is a limit to the precision of selective attention in the visual field. The interference of opposite-set letters was inversely proportional to their distance from the target.     

Application of the diffusion model to two-choice tasks for adults 75-90 years old

The effects of aging on simple 2-choice decision making was investigated with the diffusion model (R. Ratcliff, 1978). Data for 75- to 90-year-olds were collected and compared with previous data from 60- to 75-year-olds and college students for 5 tasks: a signal detection-like task, letter and brightness discrimination with masking, recognition memory, and lexical decision. The model fit the data well and therefore allows components of processing to be examined as a function of age. Compared with decision-making processes in college students, decision criteria and nondecision components of processing increased with participants' age. However, the quality of the evidence on which decisions were based decreased with age only for letter and brightness discrimination.     

Letter recognition at low contrast levels: effects of letter size

Contrast variation was used to measure recognition thresholds for lowercase letters, with the aim of obtaining a better understanding of the role that early stages of visual processing play in letter recognition. Frequency-of-recognition curves were measured for alphabets of different letter size. Since variation of the adaptational state of the eye changes the characteristics of primary visual processing in a quantifiable way, recognition thresholds were measured both at a high (150 cd m-2) and at a low (0.9 cd m-2) adaptation level. Thresholds decreased as letter size increased, in a way comparable with data on visual acuity. At the lower adaptation level, recognition thresholds became higher, which is also in accordance with visual acuity data. Furthermore, the slopes of the frequency-of-recognition curves for alphabets as a function of log contrast decreased with decreasing letter size. It is argued that this is mainly caused by an increasing dispersion of internal representations of individual letters on the internal psychological scale as letter size decreases.     

The symbolic distance effect for alphabetic order judgements: A subjective report and reaction time analysis

The time needed to decide whether a pair of letters is in the correct alphabetic order varies inversely with alphabetic separation. This is an example of a phenomenon generally found with the comparison of ordered symbols or concepts, called the symbolic distance effect (Moyer and Bayer, 1976). It is argued that when letters are compared, an important determinant of this effect is the degree to which subjects subvocally run-through parts of the alphabet to determine the correctness of the order of a stimulus pair. A trial-by-trial introspection procedure coupled with reaction time measurements is used in the present experiment, in which letter order judgements were made over a range of separations. RTs increased with increasing number of letters in the reported run-through. At small letter separations, run-through occurred more frequently, and this was found to be the basis of the symbolic distance effect. For trials on which no run-through was reported the symbolic distance effect was absent. The data are summarized as a model in which comparisons are made from directly available order information from memory, or with an additional run-through process. The details of the run-through process suggest that groupings learned in childhood are probably involved in the selection of the starting letter for run-through.     

The involvement of letter names in the silent processing of isolated letters: A developmental perspective

This study was designed to clarify the nature of the mental representations underlying the processing of letters. A total of 96 Hebrew readers randomly recruited from three levels of education were asked to make rapid same/different judgments for Hebrew letter dyads with monosyllabic and bisyllabic names. The results obtained from the performance of participants under perceptual and conceptual processing conditions suggest that Hebrew readers access nominal letter representations in order to mediate letter processing in tasks that cannot be resolved on the basis of a sheer perceptual analysis of the letters?? visual properties. The finding that the retrieval of nominal letter representations was evident for participants who differed rather markedly in their letter-processing speeds highlights the central role of letter names in the processing of isolated letters.     

Reaction time in reading a tachistoscopic display for a memory set item

Reaction times were measured in a task which requires the subject to search a brief visual array for a critical letter embedded in a row of background letters. In Experiment 1, the position of a critical letter in an instructed reading order and the size of a set of memorized letters were varied. Mean reaction time increased monotonically with distance of the critical letter from the beginning of the instructed reading path in the display. The variables reading position and memory set size were additive in their effect on mean reaction time. Data from a second experiment in which the retinal location of the critical letter and its reading position were varied showed that both reading position and retinal location influenced mean reaction time, but the effect of reading position on reaction time was greater. These variables interacted.     

Absolute identification with simple and complex stimuli

It is well known that people can perfectly identify only a handful of distinct unidimensional stimuli, such as line lengths, but can identify thousands of complex stimuli, such as letters and words. This result is consistent with capacity limits in identifying unidimensional stimuli but not complex stimuli. The experiments reported here tested this theoretical dissociation using Luce's (1963) Similarity Choice Model to measure the psychological distance between stimuli in line-length-identification and letter-identification tasks. The psychological distance between line-length stimuli decreased with the number of to-be-identified stimuli; this result is concordant with capacity limits in unidimensional absolute identification. Surprisingly, the opposite result held in letter identification. Psychological distance between letters increased with an increased number of to-be-identified stimuli. This result indicates an opposite type of processing deficit: People process letters more efficiently with more choices.     

Global-local orientation congruency effects in visual search

In a visual search task, subjects had to decide which of 2 possible target letters was presented among 12 distractor letters. The 13 characters were arranged to form a global Navon-type letter. The global letter and the local letters (target and distractors) were independently presented in four different viewer-related orientations. When the global letter and the target were frequently congruently oriented, the response times increased with growing orientation disparity between them. This global-target congruency effect was independent from target identity (Experiment 1), and it diminished when global and target orientations were not correlated (Experiment 2). The results indicate that the orientation of the global letter can be deliberately used in order to facilitate the processing of congruently oriented local targets. The alignment of a spatial frame of reference is discussed as the most probable process underlying this facilitation.     

Measuring the size of mental images

Mental images seem to have a size; the experimental problem was to map that image size onto a scale of physical measurement. To this end, two experiments were conducted to measure the size of mental images in degrees of visual angle. In Experiment 1, college students employed light pointers to indicate the horizontal extent of projected mental images of words (the letter string, not the referent). Imagined words covered about 1.0 degress of visual angle per letter. In Experiment 2, a more objective eye-movement response was used to measure the visual angle size of imagined letter strings. Visual angle of eye movement was found to increase regularly as the letter distance between the fixation point and a probed letter position increased. Each letter occupied about 2.5 degrees of visual angle for the four-letter strings in the control/default size condition. Possible relations between eye movements and images are discussed.     

Letter and word code interactions elicited by normally displayed words

The dependence of visual word recognition on letter processing was investigated by measuring the effect of a cue word on subsequent target word processing for various degrees of cue/ target similarity. Using a simultaneous matching task (Experiments 1 and 2), modest facilitation was found for identical cue/target items only, whereas items that differed by a single letter led to substantial interference. Targets that shared internal or external letters with cues yielded latencies comparable to those for neutral or different cue conditions. The identical facilitation and high-similarity interference was also found in a lexical decision task under normal display conditions (Experiment 3). However, when direct letter processing was measured using spatially transformed targets (Experiment 4), large facilitatory effects were found for similar as well as for identical cue/target conditions. Although both letter and word codes appear to be activated by normally displayed words, such word code activity may not routinely depend upon letter code outputs.     

Are letter codes always activated?

This investigation assesses whether a word’s constituent-letter codes are activated when whole-word processing is encouraged, as well as when letter processing is encouraged. In Experiments 1 and 2, word primes were followed by a target item that had to be named. The target was a word, a constituent letter that had appeared in the prime, or a nonconstituent letter that had not appeared in the prime. The measure of constituent-letter activation was the difference in letter-naming latency between constituent and nonconstituent letters. Presumably, if constituent letters are named faster, letters are being activated by the words in which they appear. To encourage either whole-word or letter analysis during the processing of the priming word, the proportion of word versus letter targets was systematically varied. When the proportion heavily favored letter targets, constituent letters were named faster than their nonconstituent controls. However, a constituent-letter (vs. a nonconstituent-letter) advantage was not obtained when the proportion favored word targets. Experiment 3 replicated the effect with a priming task that required a discrimination response, instead of a naming response. Thus the results suggested that the activation of constituent-letter codes need not take place during the processing of words, but occurs only when letter analysis is stressed by the task.