The role of lateral masking and orthographic structure in letter and word recognition.

The present experiments evaluated the contribution of orthographic structure and lateral masking in the perception of letter, word, and nonword test displays. Performance was tested in a backward recognition masking experiment in which a masking stimulus followed the test display after a variable blank interstimulus interval. In agreement with previous findings across different experiments, words were recognized better than single letterd at short interstimulus intervals, but the opposite was the case at long intervals. Performance on the nonwords resembled performance on letters at short masking intervals and performance on words at long masking intervals. The quantitative results were described by a processing model that incorporates the effects of lateral masking and orthographic structure in the dynamic processing of letter strings. Lateral masking tends to lower the potential perceptibility of letters whereas orthographic structure can reduce the uncertainty of the candidate letters in the letter sequence. The present model predicts that the quantitative contribution of each of these processes to performance is critically dependent upon the processing time available before the onset of the masking stimulus.     

Hemispheric differences in stimulus identification

Subjects were presented with either verbal (letters) or nonverbal (outline forms) stimuli to their left or right cerebral hemispheres. Verbal items presented with a lateral masking stimulus were identified more quickly and accurately when presented to the right hemisphere rather than to the left. When the letters were presented without a masking stimulus, weak hemispheric effects were obtained. Nonverbal forms demonstrated faster reaction time and fewer errors for right-hemisphere presentations under both masked and unmasked conditions. Retinal locus of the display item was also varied and produced faster responding with fewer errors when the stimulus was presented foveally rather than peripherally under all display conditions. These effects were attributed to the use of a manual response procedure that effectively reduced the ability of subjects to employ names for the stimulus objects.     

Working memory, perceptual priming, and the perception of hierarchical forms: Opposite effects of priming and working memory without memory refreshing

Previous research has shown that stimuli held in working memory (WM) can influence spatial attention. Using Navon stimuli, we explored whether and how items in WM affect the perception of visual targets at local and global levels in compound letters. Participants looked for a target letter presented at a local or global level while holding a regular block letter as a memory item. An effect of holding the target’s identity in WM was found. When memory items and targets were the same, performance was better than in a neutral condition when the memory item did not appear in the hierarchical letter (a benefit from valid cuing). When the memory item matched the distractor in the hierarchical stimulus, performance was worse than in the neutral baseline (a cost on invalid trials). These effects were greatest when the WM cue matched the global level of the hierarchical stimulus, suggesting that WM biases attention to the global level of form. Interestingly, in a no-memory priming condition, target perception was faster in the invalid condition than in the neutral baseline, reversing the effect in the WM condition. A further control experiment ruled out the effects of WM being due to participants’ refreshing their memory from the hierarchical stimulus display. The data show that information in WM biases the selection of hierarchical forms, whereas priming does not. Priming alters the perceptual processing of repeated stimuli without biasing attention.     

Application of geometric models to letter recognition: distance and density

This article reviews studies in which a single letter is visually presented under adverse conditions and the subject's task is to identify the letter. The typical results for such studies are (a) certain pairs of letters are more often confused than other pairs of letters; (b) certain letters are more easily recognized than others; and (c) confusion errors for a letter pair are often asymmetric, the number of errors differing depending on which letter of the pair is presented as the stimulus. A geometric model incorporating the properties of distance and spatial density (after Krumhansl) is presented to account for these results. The present application of the distance-density model assumes that each letter is constructed in a typical 5 X 7 dot matrix. Each letter is represented in 35-dimensional space based on its constituent dots. A central idea behind the model, embodied in the property of spatial density, is that an explanation of typical results must take into account the relationship of the entire stimulus set to both the presented letter and the responded letter. Specifically, according to the model, (a) pairs of letters that are close in geometric space are more often confused than pairs of letters that are distant; (b) letters that are in less spatially dense regions are more easily recognized than letters that are in more spatially dense regions; and (c) asymmetric confusion errors result when one member of a letter pair is in a denser region than the other member of the letter pair. The distance-density model is applied to published and unpublished results of the authors as well as published results from two other laboratories. Alternative explanations of the three typical letter recognition results are also considered. The most successful alternative explanations are (a) confusions are an increasing function of the number of dots that two letters share; (b) letters constructed from fewer dots are easier to recognize; and (c) asymmetries arise when one member of a letter pair is more easily recognized, since that letter then has fewer confusion errors to give to the other letter of the pair. The model is discussed in terms of the distinction between template matching and feature analysis. An alternative classification of letter recognition models is proposed based on the global versus local qualities of features and the spatial information associated with each feature. The model is extended to explain reaction time study results. It is suggested that the distance-density model can be used to create optimal letter fonts by minimizing interletter confusions and maximizing letter recognizability.     

The forest revisited: More on global precedence

Summary Several issues pertaining to the notion of global precedence, its testing, and its ecological validity are discussed. Global precedence is presented as a claim that, other things being equal, global structure is available in the percept earlier than local features are. It does not state that local processing starts only after global processing is terminated. Since global precedence is a hypothesis about temporal development of percepts, a natural way to test it is to limit exposure duration. Global precedence predicts that local features will be more sensitive to stimulus duration than global ones.An experiment is reported in which subjects were presented with 150 ms exposures of large letters made up of small ones, and had to discriminate either just the large letters or just the small ones. In addition, they had to respond to the presence of a concurrent tone. Local letters were responded to more slowly than global ones, and were associated with more tone errors. The variation of the global level as well as the consistency between the identities of the levels affected the latency to the local letter, but not vice versa. A single small-letter control-condition was used to rule out an explanation in terms of relative size. The effects, albeit weaker than some previous results, are compatible with the hypothesis tested.The results of this experiment are interpreted in the context of an extensive discussion of findings in the paradigm and the generality of the phenomenon assumed to underly them. Possible mechanisms which may mediate global precedence are evaluated. Among them are relative size, lateral masking, diffuse attention, and spatial uncertainty. The magnitude, or even the presence, of global precedence depends on some factors, most prominent of which are visual angle and retinal position. Ecological considerations suggest that proximal sizes and eccentricities which favor global features may be very frequent. Some further subtleties of, as well as problems with, the logic of compound letters are discussed.     

Temporal integration of vibrotactile patterns

Three experiments were conducted to measure the temporal integration of vibrotactile patterns presented to the fingertip. In Experiment 1, letters were divided in half and the time between the onsets of the first half of the letter and second half of the letter, stimulus onset asynchrony (SOA), was varied. The recognizability of the letters declined as the SOA was increased from 9 to 100 msec. In Experiment 2, the time between two patterns constituting a masking stimulus was varied and the stimulus effectiveness in interfering with letter recognition was determined. The amount of masking increased as the SOA increased from 9 to 50 msec. In Experiment 3, the SOA between a letter and its complement (the portions of the tactile array not activated by the letter) was varied. Increasing SOA from 9 to approximately 50 msec led to increasingly accurate letter recognition. The results of the three experiments suggest that the skin is capable of complete temporal integration over a time period of less than 10 msec, and that the temporal integration function becomes asymptotic in 50 to 100 msec. The results also suggest that the onset of a vibrotactile pattern is critical for generating contours. The implications of the results for modes of generating tactile patterns and for temporal masking functions are discussed.     

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.     

Processing of global and local information in memory

The experiments reported in this paper were designed to test how global and local information are processed by the memory system. When subjects are required to match a given letter with either a previously presented large capital letter or the small capital letters comprising it, (1) responses to the global level (i.e. the big letter) are faster than responses to the local level (i.e. the small letters), and (2) responses to the latter level only are affected by the consistency between the large and the small letters (Experiment 2), a pattern similar to that obtained in perception (Experiment 1). Such results obtain when subjects are required to attend to only one level with a short ISI between the first and second stimulus, but not when a longer ISI is used (Experiment 5) or when subjects are required to attend to both levels at the same time (Experiments 3 and 4). The results are discussed in the light of a model that postulates a temporal precedence of the global information over the local one at the perceptual level.     

Revisiting the global-dominance phenomenon outside the focus of attention

Previous research has demonstrated global dominance for attended and unattended stimuli. In this paper, this phenomenon is shown to be restricted to small compound stimuli. As a first step, local dominance was obtained with large (8 deg in height) attended stimuli when a single stimulus was displayed. Next, dominance in attended and unattended stimuli was investigated by displaying two large compound stimuli, one surrounded by a square (attended compound stimulus), the other one enclosed in a circle (unattended compound stimulus). The way attention was directed to the attended stimulus was varied. No dominance was observed when subjects were instructed to process the stimulus appearing in the square (experiment 2). However, when a rapid-onset cue pre-directed attention to the attended stimulus, local dominance emerged for attended, but not for unattended stimuli (experiment 3). This latter result was obtained whether or not subjects were more experienced at local than global processing (experiment 4). The implications of the results for the locus of processing dominance are discussed.     

Effects of generative processes on probe identification time

Studies of character classification have shown that reaction time is reduced when the probe is the same as the last-rehearsed target item. If rehearsal functions as a generative process to reduce response time by stimulus activation, comparable results should be obtained if the task is changed from probe classification to probe naming. A letter identification baseline was obtained in Session 1 where subjects named single probe letters as quickly as possible. In Sessions 2 and 3, each probe letter was preceded by a target of three to five letters, which were rehearsed individually prior to the probe, and subjects reported their last rehearsal after naming the probe. The results showed that (1) naming latencies were longer in Sessions 2 and 3 than in Session 1, suggesting that rehearsal requires conscious attention; (2) letter probes that matched the last-rehearsed target item were named faster than those that were different; (3) when performance was examined in terms of the rehearsal distance between the target items and probe, target set size had no effect on probe identification time. Generative processes were suggested to influence probe encoding time through stimulus preprocessing.     

Selective attention and target search with brief visual displays

In a series of four experiments, subjects were presented with eight item arrays tachistoscopically. In two tasks, the subject was required to recall a digit presented among seven letters or a letter among seven digits. The remaining tasks required the subject to detect the presence of a specific letter either in the context of seven random letters or seven digits. An examination of the effects of a masking stimulus for various target positions suggested that subjects could attend selectively when the target was a different category than its context but had to process the entire array when the target was the same category as the context. The effects of selective attention and masking are explained in terms of parallel and sequential identification processes.     

注意和非注意条件下的整体和局部性质加工

以往关于整体和局部知觉的研究通常要求被试直接对出现在复合刺激整体或局部水平上的靶目标做反应,因此复合刺激与任务相关并被注意。该研究通过测量复合字母的整体和局部性质对随后出现的探测刺激的启动效应来研究在非注意条件下整体和局部性质加工的差异。实验一发现复合刺激的整体和局部性质对探测刺激产生负启动效应,但二者没有显著差异。实验二缩短了启动刺激与探测刺激之间的时间间隔,复合刺激的整体和局部性质对探测刺激都不再产生启动效应。在实验一、二中,当要求被试直接对复合刺激做反应时,其分辨局部性质的错误率都比分辨整体性质的错误率高。根据这些结果,讨论了在注意和非注意下的整体和局部性质加工的差异。     

Processing order in visual perception

Initial increases in the availability of items for report following tachistoscopic presentation of centrally-fixated rows of seven random letters were directly evaluated by measuring report accuracy following exposure durations of 10, 20, 40, 80 and 160 ms. A partial-report technique was used, and each presentation of a letter row was immediately followed by the presentation of a masking stimulus. Each of 10 subjects received 840 trials which reflected 24 trials for each exposure-duration by position-probed combination. The letters at both ends of a row became available for report prior to the centre letters. In addition, report of the left-most letter was consistently better than report of the right-most letter, and report of the centre item at fixation improved at a more rapid rate with increased exposure duration than report of the other centre letters. This pattern of results provides support for certain components of several different previous proposals concerning the order in which individual items from multi-element displays become available for report.     

Self-construal priming modulates the scope of visual attention

Although it is well documented that cultures influence basic cognitive processes such as attention, the underlying mechanisms remain unclear. We tested the hypothesis that self-concepts that characterize people from different cultures mediate the variation of visual attention. After being primed with self-construals that emphasize the Eastern interdependent self or the Western independent self, Chinese participants were asked to discriminate a central target letter flanked by compatible or incompatible stimuli (Experiment 1) or global/local letters in a compound stimulus (Experiment 2). Experiment 1 showed that, while responses were slower to the incompatible than to the compatible stimuli, this flanker compatibility effect was increased by the interdependent relative to the independent self-construal priming. Experiment 2 showed that the interdependent-self priming resulted in faster responses to the global than to the local targets in compound letters whereas a reverse pattern was observed in the independent-self priming condition. The results provide evidence for dynamics of the scope of visual attention as a function of self-construal priming that switches self-concept toward the interdependent or independent styles in Chinese.     

Sources of interference in the attentional blink: target-distractor similarity revisited

Observers monitored streams of words or letters (10 items/sec) for one or two targets. An attentional blink (AB) effect was observed in which identification of the first target temporarily impaired identification of the second target. Target identification was impaired when the distractors were composed of either letters or false-font characters (cf. Maki, Couture, Frigen, & Lien, 1997). An asymmetrical AB effect was observed with letters and mathematical symbols; the AB effect was largest for symbol targets and letter distractors. The characters used in these experiments were rated on their meaningfulness, familiarity, and other stimulus properties. The rating data showed that pixel density best accounted for the asymmetrical target-distractor similarity effects. Modulation of the AB effect by target-distractor similarity appears to result partly from low-level masking. But masking effects may be reduced by attentional capture by target features.     

Mental rotation of compound stimuli: The effects of task demands,practice, and figural goodness

Four experiments examined whether or not mental rotation of compound stimuli is a holistic process. Large letters (global aspect) composed of small letters (local aspect) were presented, and the format (normal vs. reflected) of each aspect was manipulated independently. In Experiment 1, the rate of mental rotation was compared under divided- and focused-attention instructions. The overall rate of mental rotation was faster under focused-attention instructions than under divided-attention instructions. Also, contrary to previous findings, in the divided-attention task, the slope of the rotation function was smaller when the stimulus configurations contained aspects with congruent formats (both aspects were normal or mirror-reversed letters) than when they contained aspects with incongruent formats (one normal and one mirror-reversed letter). This pattern of results is unlikely to be caused by the subjects' level of familiarity with the divided-attention task (Experiment 2), by postrotation processes (Experiment 3), or by stimulus attributes (figural goodness) confounded with the format-congruency variable (Experiment 4). The implications of these results for models of mental rotation of compound stimuli are discussed.     

Vibrotactile letter recognition: The effects of a ma king stimulus

A series of experiments examined the effect of masking stimuli on the ability of observers to recognize letters of the alphabet through their fingertips. The letters were generated on the 6 × 24 vibrotactile array of the Optacon, a reading aid for the blind. Letter recognition was interfered with by the presence of masking stimuli occurring at the same site on the skin either before (forward masking) or after (backward masking) the target letter had been presented. In general, backward masking interfered with letter recognition more than did forward masking. Backward masking was particularly effective for letters in which the information critical for identification is located on the right side of the letter. Presenting the letters reversed resulted in more forward masking for those letters with critical information now located on the left side. Increasing the time between the target letter and the masking stimuli resulted in improved letter recognition. The implications of the results for tactile reading are discussed.     

Self-construal priming modulates the scope of visual attention

Although it is well documented that cultures influence basic cognitive processes such as attention, the underlying mechanisms remain unclear. We tested the hypothesis that self-concepts that characterize people from different cultures mediate the variation of visual attention. After being primed with self-construals that emphasize the Eastern interdependent self or the Western independent self, Chinese participants were asked to discriminate a central target letter flanked by compatible or incompatible stimuli (Experiment 1) or global/local letters in a compound stimulus (Experiment 2). Experiment 1 showed that, while responses were slower to the incompatible than to the compatible stimuli, this flanker compatibility effect was increased by the interdependent relative to the independent self-construal priming. Experiment 2 showed that the interdependent-self priming resulted in faster responses to the global than to the local targets in compound letters whereas a reverse pattern was observed in the independent-self priming condition. The results provide evidence for dynamics of the scope of visual attention as a function of self-construal priming that switches self-concept toward the interdependent or independent styles in Chinese.     

Parallel scanning of auditory and visual information

Two experiments involving memory retrieval of auditorilv and visually presented materials were performed. In Experiment I, subjects were presented with memory sets of 1, 2, or 4 stimuli and then with a test item to be classified as belonging or not belonging to the memory set. In Condition 1, each memory stimulus was a single, auditorily presented letter. In Condition 2, each memory stimulus was a visually presented letter. In Conditions 3 and 4, each memory stimulus was a pair of letters, one presented visually and the other auditorily. Mean reaction time (RT) for the classification task increased as a function of number of memory stimuli at equal rates for all four conditions. This was interpreted as evidence for a parallel scanning process in Conditions 3 and 4 where the auditory item and visual item of each memory stimulus pair can be scanned simultaneously. Experiment II compared memory retrieval for a simultaneous condition in which auditory and visual memory items were presented as pairs with a sequential condition in which mixed auditory-visual memory sets were presented one item at a time. RTs were shorter for the simultaneous condition. This was interpreted as evidence that parallel scanning may depend upon memory input parameters.     

The effects of forced serial processing on identification of words and random letter strings

Skilled readers identified words and random letter strings displayed one letter at a time on the screen of a computer-controlled oscilloscope. Letters were either displayed in a single position, or painted left-to-right in adjacent positions. Adjacent displays were either unmasked, masked by a letter-like pattern following each letter (backward masking) or masked by a pattern preceding each letter (forward masking). Unmasked words were identified with a high degree of accuracy, and accuracy was independent of the exposure duration of the letters over the range 50–200 msec. Masked adjacent word displays and one-position word displays were identified much less accurately, and accuracy was highly dependent on letter exposure duration. In contrast to these results, identification of random strings, or of letters within random strings, was almost unaffected by the presence of the mask and was dependent on letter exposure duration under all display conditions. The results are interpreted as evidence that (a) masking forces subjects to process serial displays one letter at a time, and (b) words, or large segments of words, are habitually processed in parallel, while random strings are processed as a series of individual letters or small chunks.