Effect of level of confusability on reporting letters from briefly presented visual displays

In a report paradigm, two letters are presented on a trial which are either confusable(e.g., P and R) or nonconfusable (e.g., P and M) in terms of visual features. Across trials, interletter distance, retinal location, duration, and visual field are varied. Identification accuracy on confusable trials was generally lower than on nonconfusable trials, and this effect of level of confusability increased with distance from the fixation point, decreased with duration, and was smaller on the central letter than on the more peripheral letter. A quantitative model, incorporating aspects of the interactive channels model (Estes, 1972) and feature perturbation model (Wolford, 1975), is developed and tested. One parameter of the model measures the effective similarity between two letters after lateral inhibition has occurred, and other parameters measure the probability of feature perturbation in foveal and peripheral directions.     

Interocular non-independence

Binocular interaction was studied by presenting a different letter form to each eye via a dichopic tachistoscope. The two dissimilar letters were presented simultaneously or at short delay internals of 0–200 msec and were either presented on corresponding or non-corresponding retinal areas. At delay internals of less than 100 msec stimulation of corresponding areas resulted in identification performance below that to be expected on the basis of independent chances to perceive. Stimulation on non-corresponding areas resulted in both presented letters being identified at the accuracy level predicted by an independence assumption.     

Extracting identity and location information from briefly presented letter arrays

The effect on identification and location of briefly presented targets (letters and blanks) of number of targets, retinal location, and direction and distance of simultaneously presented targets is investigated. In three different conditions, one, two, or three targets are presented on a trial with the location of targets varying from trial to trial. A model is proposed to describe identification and location performance in the one-letter condition. This model distinguishes between two sets of parameters, perceptual parameters and decision parameters, and assumes that in terms of these parameters, identification and location are independent processes. The perceptual and decision parameters of the model, estimated by assuming that these parameters are linearly related to retinal location, indicate that retinal location has a different effect on the decision parameters for both identification and location than on the perceptual parameters. Variables affecting the performance decrements found when multiple letters are presented are evaluated in terms of models stated for the multiple letter conditions. Estimates of the effects of distance from the fixation point and inter-letter distance indicate that, as both of these variables increase, performance decreases. In the three-letter condition, a serial position effect is found, with performance on center letters being relatively poor. A peripherally presented letter is found to have a large detrimental effect on performance, and the effect increases as interletter distance increases. Location of correctly identified targets follows many of the same patterns as identification performance in the multiple letter conditions. In addition, there is a tendency for incorrectly located targets to be moved foveally and to move to positions occupied by other targets on the trial. The possibility of a limited-capacity attention mechanism operating in the present experiment is discussed.     

Retinal locus and the letter-span error function

The effect of retinal locus on the letter-span error function was investigated by requiring Ss to fixate at the left, middle, or right of lines of letters presented for 100 msec. Stimulus presentations consisted of lines of eight letters presented across the visual field, and lines of four letters presented alternately in the left and right visual hemifields. Locus of fixation and relative letter position were found to be significantly related to whether or not a letter was correctly localized. A significant interaction between locus of fixation and letter position was observed.     

Identification and pronunciation effects in a verbal reaction time task for words,pseudowords, and letters

The question addressed in this investigation was whether faster reading and pronunciation of words than orthographically regular pseudowords is due to faster identification or to faster programming and execution of the motor response. In Experiment I, three different response conditions (naming, threechoice signaled responding, and one-choice signaled responding) were employed to separate the identification and articulation processes in a verbal reaction time task. It was found that, for all intents and purposes, single, isolated letters are processed as if they were very short words. Words are read and pronounced 72 msec faster than pseudowords. Words are also pronounced 30 msec faster than pseudowords even if the reader has longer than 1 sec to identify the stimulus (three-choice condition) or to both identify the stimulus and preprogram the response (one-choice condition). The data indicate that words are identified about 52 msec faster and articulated about 30 msec faster than pseudowords. Since the number of response alternatives (one or three) does not interact with stimulus type (letter, word, or pseudoword) in the signaled response control condition, the 30-msec difference is due to response execution and not to differential response programming. Response programming takes in the neighborhood of 236 msec. Experiment 2 investigated the effect of local orthographic context upon the identification of the first letter of a string of letters. No difference was found in identifying the initial letter of words and pseudowords, but the initial letter of these orthographically regular letter strings was identified and named 10 msec faster than the initial letter of orthographically anomalous strings of letters (anagrams). The data from the two experiments are supportive of theories of reading that assume (1) that the letters of visually presented words are processed simultaneously, in parallel, (2) that there is a relatively direct access and retrieval of the phonological memory codes for the names of words, and (3) that orthographically regular pseudowords having no representation in the phonological lexicon undergo a grapheme-to-phoneme transformation that takes longer to finish than the direct spelling-to-sound process used for words.     

Reading ability and the encoding of item and location information

Two experiments using duration exposures ranging from 20 to 130 msec are reported that link reading skill in adults to the initial encoding of location information. Highly skilled and less skilled readers were equivalent in identifying single letters presented at a central fixation point. When they had to identify the serial position of a letter, however, highly skilled readers performed significantly more accurately than did less skilled readers. A second experiment used displays that consisted of one letter and three dollar signs. Subjects had to identify the letter under two location cuing conditions. When subjects were cued in advance as to which serial position would contain the letter, highly skilled and less skilled readers were equivalent. When the location of the letter had to be resolved prior to identification, highly skilled readers performed significantly more accurately than did less skilled readers. Results are interpreted to suggest that the role of perception in reading has been underestimated because emphasis has been on item perception, and the perception of spatial location has been largely overlooked.     

Effects of informative peripheral cues on eye movements: Revisiting William James’ “derived attention”

Two experiments examined effects of peripheral information on the latency of saccadic eye movements. In Experiment 1, simple target stimuli were presented to the left or right visual field. Prior to each target, a pair of cue letters was presented for 40msec bilaterally. The relative location of the letters (W-S or S-W) was related to target location, but participants were not informed of this contingency. After a brief practice period, saccadic latencies were faster for targets at the likely location, as indicated by the letter pair. This derived peripheral cueing effect was related to participants' awareness of the relation between cue type and target location. Experiments 2A and 2B employed monocular viewing in order to compare performance across the nasal and temporal visual fields. The effect observed in Experiment 1 was confined to the nasal visual field. In a reflexive orienting condition, the effect of a unilateral letter cue was larger in the temporal visual field. It is concluded that the neurocognitive processes responsible for derived peripheral cueing are distinct from those involved in either reflexive or voluntary orienting.     

Evidence for attentional capture by a surprising color singleton in visual search

Three experiments were conducted to investigate whether surprising color singletons capture attention. Participants performed a visual search task in which a target letter had to be detected among distractor letters. Experiments 1 and 2 assessed accuracy as the dependent variable. In Experiment 1, the unannounced presentation of a color singleton 500 ms prior to the letters (and in the same position as the target letter) resulted in better performance than in the preceding conjunction search segment, in which no singleton was presented, and performance was as good in this surprise–singleton trial as in the following feature search segment, in which the singleton always coincided with the target. In contrast, no improvement was observed when the color singleton was presented simultaneously with the letters in Experiment 2, indicating that attentional capture occurred later in the surprise trial than in the feature search segment. In Experiment 3, set size was varied, and reaction time was the dependent variable. Reaction time depended on set size in the conjunction search segment, but not in the surprise trial nor in the feature search segment. The results of the three experiments support the view that surprising color singletons capture attention independently of a corresponding attentional set.     

Absence of lexical and orthographic effects in a same-different task

Two experiments are reported that investigate whether the lexical and orthographic effects typically found in a simultaneous matching task are due to the facilitating effect of linguistic context on letter identification. The first experiment used a delayed matching task (2-sec SOA), with serial incremental display of the letters of the second stimulus (e.g., B, BR, BRA, BRAI, BRAIN). Lexical and orthographic effects were clearly demonstrated when the letters of the second stimulus were displayed rapidly (40 msec/letter), but these effects were absent at a slower speed (400 msec/letter). The same results were obtained in a second experiment, in which the letters of both stimuli were synchronously presented at either the fast rate or the slow rate. These results were interpreted in terms of a multilevel race model that assumes no interaction between levels of processing and attributes the effects to differing degrees of decision-processing lag.     

Modality-specific coding in matching letters

Auditory and visual similarity was manipulated in a same-different reaction-time task to investigate the use of modality-specific codes in same-different judgments for pairs of letters. Experiment 1 showed that letters presented simultaneously in the auditory and visual modalities were matched on the auditory dimension. In Experiment 2, the letters were presented sequentially, and the modality of the second letter was randomly varied. Subjects matched the pairs on the modality dimension of the second letter even though the modality could not be reliably predicted. In Experiment 3, subjects judged adjacent pairs of letters presented for 50 msec, and in one condition they also named the letters. Matches were made on visual codes in both conditions. In general, the results indicate that when subjects are instructed to determine if two letters are the same, the letters will be matched on a modality-specific code in a way that will minimize the information processing necessary to complete the match.     

Recognition vs recall of visually vs acoustically confusable letter matrices

In an attempt to separate auditory and visual components in short-term memory, five subjects were exposed to letter matrices composed of six visually confusable letters, six acoustically confusable letters, or a mixture of the two, under two response conditions: recognition and recall. A 50-msec stimulus presentation was followed by a variable dark interval of 1, 250, 1,000, or 3,000 msec. In the recall condition, the interval was followed by a buzzer which signaled the subject to recall, in any order, as many letters as possible. In the recognition condition, the variable interval was followed by a second letter matrix which was either identical to the first matrix or differed from is by one letter. Subjects responded either "same" or "different." The results support the notion that the auditory component plays a major role in recall, whereas the visual component dominates in recognition.     

Task- and location-switching effects on visual attention

In two experiments, we examined the effects of task and location switching on the accuracy of reporting target characters in an attentional blink (AB) paradigm. Single-character streams were presented at a rate of 100 msec per character in Experiment 1, and successive pairs of characters on either side of fixation were presented in Experiment 2. On each trial, two targets appeared that were either white letters or black digits embedded in a stream of black letter distractors, and they were separated by between zero and five items in the stream (lags 1-6). Experiment 1 showed that report of the first target was least accurate if it immediately preceded the second target and if the two targets were either both letters or both digits (task repetition cost). Report of the second target was least accurate if one or two distractors intervened between the two targets (the U-shaped AB lag effect) and if one target was a letter and the other a digit (task switch cost). Experiment 2 added location uncertainty as a factor and showed similar effects as Experiment 1, with one exception. Lag 1 sparing (the preserved accuracy in reporting the second of two targets if the second immediately follows the first) was completely eliminated when the task required attention switching across locations. Two-way additive effects were found between task switching and location switching in the AB paradigm. These results suggests separate loci for their attentional effects. It is likely that the AB deficit is due mainly to central memory limitations, whereas location-switching costs occur at early visual levels. Task-switching costs occur at an intermediate visual level, since the present task switch involved encoding differences without changes in stimulus-response mapping rules (i.e., the task was character identification for both letters and digits).     

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.     

Letter identification and lateral masking in dyslexic and average readers

Lateral masking and letter identification in dyslexic and average readers were investigated with a methodology that corrected for some of the weaknesses of the Geiger and Lettvin studies (1986, 1987). Target letters were presented alone or embedded within three-letter arrays at retinal locations from 0 degrees to 15 degrees to the right or left of a fixation point. A foveal letter, which was the same as or different from a target letter, appeared as a distractor, and comparisons were made between scaled and unscaled stimuli. Dyslexic readers were found to be better than average readers at detecting scaled letters embedded in an array in some of the peripheral locations tested. Unlike the results of Geiger and Lettvin, however, this finding of better letter detection in the periphery by dyslexics was limited to selected conditions of the study. Reading groups were also found to differ in responding to the foveal distractor in the letter task. Detection of letters by average readers was affected by the type of distractor, but this variable was not found to influence the dyslexic readers. These findings suggest some differences between dyslexic and average readers in attention to stimuli presented at multiple locations in the visual field.     

Discrimination of spatially confusable letters by young children

A study of the ability of young children to discriminate spatially confusable letters using four different methods of discrimination (matching, copying, naming, and writing to dictation) was carried out. The subjects were 31 English children whose ages ranged from 5 years 6 months to 6 years 10 months. The test material consisted of 10 spatially confusable letters, i.e., letters whose differential features depend upon their spatial orientation: p, q, d, b, u, and n, and to a lesser extent h and y and w and m. The results show that the accuracy of discrimination of spatially confusable letters is dependent upon the method of assessment employed. The highest accuracy is achieved when the method requires copying confusable letters from a given sample, followed by the method that requires matching a given letter with other possible alternatives. Naming the confusable letters and writing them in response to dictation are the most difficult tasks to perform. The results also indicate that there is a significant correlation between individual performances in the matching, naming, and writing to dictation tests; but in the copying task individual performances varied independently of the performances in the other tests. Some theoretical implications of the findings are discussed.     

Lateral masking in visual information processing

When unrelated letter strings are presented tachistoscopically, the end letters are reported more often than their neighbors; and when spaces are inserted into strings, performance on certain adjacent letters is superior to performance on those letters when no spaces were present. An experiment was conducted to determine the nature of those spacing effects. Letter strings were presented at a variety of retinal locations, and spaces were inserted into different positions in the instructed left-right processing order. The space effect was unrelated to processing order, but it was dependent on retinal location. To account for the various asymmetries, it was necessary to postulate that letters tend to interact with adjacent lettersand that the interaction was not spatially symmetric. Furthermore, it was found that spaces had greater effects on “right-hand” letters than on symmetric letters. It was therefore concluded that letters interact at the feature level.     

Allocation of attention according to informativeness in visual recognition

In visual identification, is visual attention attracted to more informative elements, i.e. to elements which are more critical for identification? This question was investigated by having subjects detect some visual probes while performing a primary task that involved identification. The probes were located in the neighbourhood of highly or poorly informative parts of the identified stimuli. Three experiments that followed this rationale were conducted. In Experiment I, it was found that when subjects searched for a target letter in lines of identical background letters, they detected more dots near the feature that distinguished between the target and the background letters. In Experiment 11, it was found that native Hebrew-speaking subjects detected more lines above a letter that distinguished between two English words. Experiment III showed that the effect was reduced but did not vanish when spatial uncertainty was introduced. On the whole, the data are interpreted as suggesting that more attention may indeed be directed to informative regions, and that this effect cannot be solely attributed to retinal factors.     

Influence of category identity on letter matching: conceptual penetration of visual processing or response competition?

Participants performed same-different matching tasks, with physical-identity instructions, on letter pairs composed from the letters B, b, and p. The letters in a pair were presented simultaneously or sequentially, with the experiments differing in whether (1) the letters could appear in two or four positions, (2) two or five SOAs were used, (3) the font was Arial or one in which the two loops of the letter B were of the same size, and (4) p did or did not occur in same pairs. With sequential presentation, different RTs were longer when the letters had the same name (Bb; within-category pair) than when they did not (Bp; between-category pair), replicating a finding by Lupyan et al. (2010). However, unlike in their study, this category effect was also significant with simultaneous presentation, tending to be nonsignificantly smaller for RTs but larger for accuracy than that obtained with sequential presentation. A similar pattern was observed when we removed a bias to respond different whenever the letter p was detected in the experiments in which p did not appear in same pairs. The presence of a category effect with simultaneous presentation is predicted by a response competition account, but not by Lupyan et al.'s conceptual-penetration-of-visual-processing account.     

Immediate and delayed recognition of sequentially presented random shapes.

Two experiments tested whether short-term memory accounts for the recency effect observed with rapid sequential presentation of nonverbal stimuli. Four random shapes were presented sequentially (with no interstimulus interval) on each trial at rates of 150 msec, 250 msec, 500 msec, and 1,000 msec per stimulus. Subsequent recognition varied positively with exposure duration, ranging from 57% at 150 msec to 77% at 1,000 msec. Two serial position effects were observed: a slight decrease in recognition accuracy for the first stimulus in each sequence and a large increase in recognition for the last stimulus in each sequence. The recency effect was not altered by an intervening 30-sec delay, an intervening 30-sec copying task, or an intervening 30-sec copying and counting task. Since neither visual nor verbal distractors altered recognition accuracy, it was suggested that all shapes were processed directly into long-term memory storage. It also was hypothesized that long-term storage of a nonverbal stimulus requires identification of a distinctive feature of the stimulus and that this process may continue for a brief period after actual stimulus offset.     

Repetition blindness for locations: evidence for automatic spatial coding in an RSVP task

The authors report a new phenomenon called repetition blindness (RB) for locations: When 3 or 4 letters are presented rapidly and sequentially at random locations within a spatial array, experimental participants have difficulty reporting pairs of letters appearing in the same location within 250 ms of each other. This deficit occurs both during report of letter identities and during report of the locations in which the letters appear; it can also be found using a partial report task. During letter report, the deficit is found for 4-location arrays but not for 8-location arrays. In contrast, letter RB is not found during location report even when the letters are always chosen from a set of 4. These results indicate that a small number of locations--but not letters--can be encoded automatically even when they are not explicitly reported. The authors argue that RB for locations results from a difficulty individuating 2 tokens at the same spatial location.