Presenting words without interior letters: Superiority over single letters and influence of postmask boundaries.

In 5 experiments with a total of 32 Ss, exterior letter pairs from 4-letter words (e.g., d??k from dark) were presented in pattern-postmasked displays, in the positions they would occupy if the whole word were shown. In Exp 1, letter pairs (d??k) were reported more accurately than single letters (d) (the pair–letter effect). In Exps 2 and 3, performances with letter pairs dropped to those for single letters when each letter in a pair was masked individually or when masks were much wider than letter pairs. In Exps 4 and 5, the pair–letter effect and mask influence were both removed when one letter in each pair was replaced by a number sign (d??#) or when letter pairs were not the exterior letters of real words (e.g., y??f). These findings suggest that the exterior letter combinations of words are represented psychologically and access to these representations is affected by mask configuration. Implications for current word-recognition models are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Probability effects on stimulus evaluation and response processes.

Investigated the effects of probability information on response preparation and stimulus evaluation. Eight Ss responded with 1 hand to the target letter H and with the other to the target letter S. The target letter was surrounded by noise letters that were either the same as or different from the target letter. In 2 conditions, the targets were preceded by a warning stimulus unrelated to the target letter. In 2 other conditions, a warning letter predicted that the same letter or the opposite letter would appear as the imperative stimulus with .80 probability. Correct reactions times (RTs) were faster and error rates were lower when imperative stimuli confirmed the predictions of the warning stimulus. Probability information affected (1) the preparation of motor responses during the foreperiod, (2) the development of expectancies for a particular target letter, and (3) a process sensitive to the identities of letter stimuli but not to their locations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Testing the role of vertical symmetry in letter matching

A series of experiments tested a recent suggestion that vertical symmetry of a stimulus display can serve as a visual diagnostic for responding "same" in a letter-matching task. The data of chief interest were same reaction times to vertically symmetric (e.g., AA) and asymmetric (e.g., LL) displays, each composed of two side-by-side uppercase letters. Overall, the data argue against subjects' use of vertical symmetry as a diagnostic in dealing with letter pairs. The results were interpreted within the context of recent work on symmetry. In particular, it was suggested that the importance of structural diagnostics in a matching task may be inversely related to the codability of the stimulus elements being compared.     

Preferences for letters of the alphabet.

"To determine whether or not consistent preferences for letters of the alphabet exist in the populations, and to identify pairs of letters which have equal preference value, seven letters presented pair-wise in all possible combinations to 182 students (138 males, 44 females) at the University of Minnesota. Only seven letters were used in order to reduce the Ss' task, these seven being chosen on the basis of two preliminary studies as having the least likelihood of being different from each other in appeal. By lowering the significance level of the statistical test, a few pairs can be found for which the probability is high that they are nearly equal. The following pairs showed a preference for the letter listed first at the 1% level: SK, SG, SP, ST, GK." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence of preliminary response preparation from a divided attention task.

In a divided attention situation, preliminary response activations produced by stimuli on one channel were revealed through their effects on responses to stimuli on a secondary probe channel. Subjects performed concurrent but independent four-choice reaction-time tasks using the same four response fingers (middle and index fingers on both hands). In the main task, targets were large and small Ss and Ts, and medium-sized Ss and Ts sometimes appeared as distractors. Targets in the probe task were squares differing in location. A response to a probe square was faster if a distractor letter presented just before it had the same name as the target letter corresponding to that square (i.e., assigned to the same response key) than if the distractor letter had a different name—a result indicating that distractor letters cause partial response preparation. The timecourse of the effect demonstrated that preparation was based on preliminary information about distractor name that was available before distractor size had been determined. The results support models in which response preparation can sometimes begin before stimulus recognition has finished. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Why is word recognition impaired by disorientation while the identification of single letters is not?

Past research has shown that speed of identifying single letters or digits is largely indifferent to orientation, whereas the recognition of single words or connected text is markedly disrupted by disorientation. In a series of four experiments, we attempted to reconcile these findings. The results suggest that disorientation does not impair the identification of the characters but disrupts the perception of their spatial arrangement. When spatial order information is critical for distinguishing between different stimuli, disorientation is disruptive because some rectification process is required to restore order information. Utilizing the similarity between the letter B and the number 13, we found strong effects of orientation when a stimulus was interpreted as the two-digit number 13 but not when interpreted as the single letter B. This, however, occurred only when the set of numbers to be classified included permutations of the same digits. Odd–even decisions on single-digit and two-digit numbers (Experiment 3) yielded strong effects of stimulus orientation for order-dependent numbers (e.g., 32), weaker effects for order-independent numbers (e.g., 24), and none for repeated-digit (e.g., 22) or single-digit numbers. Classification time for two-letter Hebrew words evidenced strong effects of orientation for words that differed only in letter order but much weaker effects for words that had no letters in common, even when these were embedded within some words that did (Experiment 4). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of stimulus arrangement on hemispheric differences and interhemispheric interaction for processing letter trigrams.

Observers identified consonant-vowel-consonant (CVC) nonsense syllables with the letters arranged horizontally. In each of 2 experiments, there were fewer errors when stimuli were presented to the right visual field (RVF) and left hemisphere (LH) than when stimuli were presented to the left visual field (LVF) and right hemisphere (RH), and the extent to which the number of last-letter errors exceeded the number of first-letter errors was greater on LVF/RH than on RVF/LH trials. When the same stimulus was presented simultaneously to both visual fields (Experiment 2), the qualitative error pattern was very similar to the pattern obtained on LVF/RH trials. These effects replicate results obtained in earlier CVC identification experiments with letters arranged vertically. However. when a single stimulus was presented in the center of the visual field (Experiment 1), so that the first letter of the CVC projected to the LVF/RH and the last letter projected to the RVF/LH, the error pattern was a mixture of the LVF/RH and RVF/LH patterns, as if each hemisphere took the lead for processing the letter it received directly. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison requirements and attention in identical-nonidentical stimulus discriminations.

Perceptual matching data show several puzzling effects. Particularly problematic are the disparities between the processing rates for same and different stimuli—the fast–same effect—and between the processing rates for two same–different judgment tasks that are related as mirror images—the task effect. Current models have difficulty accounting simultaneously for both effects. Central to these models is a stimulus comparison process that derives relative judgments of sameness and difference from tests of the congruence of stimulus representations. A contrasting view holds that same–different judgments can be modeled as absolute, rather than relative, judgments. This latter view is shown to be supported by experimental data. Reaction times (RTs) for judgments of identical letter strings increase with string length at the same rate whether judgments are based on all the information in the strings or just the information in a single pair of component letters. The data show that stimulus comparisons of the sort described by previous models are not involved in these judgments. An attentional model accounts for the data and for the fast–same and task effects as well. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Word superiority over isolated letters: The neglected role of flanking mask contours.

When stimuli are presented in pattern-postmasked displays, performance is better for words than for isolated letters. Contemporary accounts of this word advantage emphasize the role played by mask contours that overlay the positions of letters in each stimulus; however, the precise effect of these overlying mask contours has never been empirically determined. The role of overlying and flanking (falling to the left and right of each word and isolated letter) mask contours in the word advantage over isolated letters was examined. A word advantage was obtained only when more flanking mask contours were shown with isolated letters than with words; when masks covered only the positions of letters in each stimulus, and thus no flanking mask contours were presented, the word advantage was removed or reversed. Implications for contemporary accounts of the word advantage over isolated letters are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of letters and random dot patterns by pigeons and humans.

Conducted 2 exploratory experiments to compare pigeon and human perception of visual stimuli. In a 3-choice discrimination task, 3 white Carneaux pigeons learned to distinguish each letter of the alphabet from all the other letters and each of 16 random dot patterns from all the others, and Ss' discrimination errors were used to generate a matrix of interletter and interpattern similarities. Human estimates of letter similarity were obtained from previous literature, and 6 human adults rated the similarity of the dot patterns. Performances of the humans and of 6 pigeons were described and compared through correlation, multidimensional scaling, and cluster analysis, and fits of the data by simple-feature and template models were computed and compared. The correlation between pigeon and human similarity matrices was .68 for letters and .72 for dot patterns. The other analyses revealed broadly similar patterns of results from the 2 species but suggested that, relative to human data, the best fits to the pigeon data required fewer dimensions, fewer features, and fuzzier templates. There was some indication that pigeon discriminations depended on relatively simple features, and several of these were tentatively identified. It is suggested that the different methods employed could have influenced these apparent differences between pigeons and humans, but, overall, findings suggest considerable cross-task and cross-species generality in the processing of these simple forms. (47 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Establishing global and local correspondence between successive stimuli: The holistic nature of backward alignment.

Reflection decisions on alphanumeric characters display systematic effects of disorientation, suggesting that subjects mentally rotate the stimulus to the upright (the uprighting process). However, response time also increases with increasing angular disparity between the current and preceding orientations. This occurs only when the current stimulus is a rotational transform of the preceding stimulus, suggesting that the current stimulus is brought into congruence with the preceding one (the backward alignment process). In the present study, we examined the hypothesis that the transformation that occurs in backward alignment is holistic even in tasks in which the uprighting process is likely to be piecemeal. Evidence supporting this hypothesis is presented on the basis of tasks requiring either classification of numbers (Experiments 1 and 3) and words (Experiment 2), or mirror image discrimination on letter pairs (Experiment 4). The results indicated that backward alignment establishes global correspondence between successive stimuli and is indifferent to local correspondence at the level of the constituent elements. The establishment of this global correspondence decreases with the number of elements in the stimulus (Experiment 5), but its effects are still observed for four-letter strings (Experiment 6). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Do alphabet letters help prereaders acquire phonemic segmentation skill?

Tested the assumptions that phonemic segmentation skill is learned best in the oral mode and that teaching segmentation with alphabet letters confuses learners. Three treatment groups of 8 prereaders (mean age 67.8 mo) were formed. The letter group was taught to segment nonword blends using letter tokens. The nonletter group was taught to segment blends with tokens lacking letters. A control group received no training. Experimental groups took about the same time and number of trials to reach criterion during training, indicating that neither method was more difficult or time consuming. Errors indicated that letters helped Ss learn to distinguish phoneme-size units and to remember the correct sounds during the task. On a segmentation posttest, letter and nonletter Ss segmented unpracticed blends better than controls, indicating that both groups acquired general segmentation skill. Letter Ss were superior to nonletter Ss in segmenting practiced sounds, with both groups surpassing controls. It is suggested that letters provide learners with a mental symbol system for representing and thinking about specific phonemes. (53 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Letter encoding in visual word identification: More evidence for a word-integration explanation for parafoveal preview effects in reading.

A letter string presented briefly in the parafovea facilitates naming a foveally presented word provided that the two stimuli are orthographically similar. The facilitation is asymmetrical in that to obtain it, both letter strings must have the first letters in common. One possible explanation, a letter-integration hypothesis, proposes that readers only identify the letters at the beginning of the parafoveal stimulus, an action that facilitates processing the target. Another explanation, a word-integration hypothesis, postulates that all the letters of the parafoveal stimulus are identified and that the asymmetry occurs because the first letters of the parafoveal stimulus are weighted more heavily than the later ones. The two accounts differ in the way the position of the first letter is determined. To distinguish the views, English and Hebrew stimuli were presented to 7 bilingual readers. 12 normal students participated as controls. Readers could not anticipate the position of the first letters; hence, if the letter-integration explanation is correct, the asymmetry in the priming should be attenuated. Consistent with the word-integration explanation, however, priming occurred when the target shared the beginning letters with the prime in both languages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Crowding affects letters and symbols differently.

Five experiments examined crowding effects with letter and symbol stimuli. Experiments 1 through 3 compared 2-alternative forced-choice (2AFC) identification accuracy for isolated targets presented left and right of fixation with targets flanked either by 2 other items of the same category or a single item situated to the right or left of targets. Interference from flankers (crowding) was significantly stronger for symbols than letters. Single flankers generated performance similar to the isolated targets when the stimuli were letters but closer to the 2-flanker condition when the stimuli were symbols. Experiment 4 confirmed this pattern using a partial-report bar probe procedure. Experiment 5 showed that another measure of crowding, critical spacing, was greater for symbols than for letters. The results support the hypothesis that letter-string processing involves a specialized system developed to limit the spatial extent of crowding for letters in words. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A theory of order relations in perceptual matching.

Relates order relations to research on retrieval processes and the representation of order information in memory. In 2 experimental tests, presentation of a study string of letters was followed by a test string to which the 6 undergraduate Ss responded "same" or "different." When adjacent letters were switched, RT was long and accuracy low, suggesting that a test letter is not simply compared to the letter in the same position in the study string; rather, the comparison is distributed across positions. The memory model assumes that the representation of a letter is distributed over position and that the comparison process assesses the amount of overlap between the test string and the memory representation. The diffusion retrieval model and overlap memory model are fitted to the data and goodness-of-fit is assessed. Shortcomings of alternative models are considered and applications of the model to related matching tasks, such as D. Taylor's (1976) converse of the perceptual matching task, and Angiolillo-Bent and L. Rips's (1981) multiple-element comparison task, are described. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the recognition of words with inverted letters.

Conducted 2 experiments in which 24 Ss were asked to identify words with all or some of their letters inverted. The experiments differed only in the explicitness of the instructions given to Ss. In some cases the letters appearing upside down were inverted as 1 unit, and in other cases they were inverted by letter. It was found that when all the letters were inverted, recognition time was faster for unit inversion. When just a few of the letters in the words were inverted, recognition time was shorter when the inversion was letter by letter rather than by unit. Data are consistent with a model that assumes that when the stimulus is homogeneously misoriented unit correction is applied, and when such homogeneity does not exist piecemeal correction is applied. (French abstract) (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Right hemisphere superiority in visual orientation matching.

"Same" or "different" judgments were made by 22 right-handed college students in 2 orientation matching tasks. In 1 task pairs of lines were presented 4. left or right of fixation. Reaction times for both "same" and "different" judgments were faster if stimulus pairs were presented to the left visual field, indicating superiority of the right hemisphere for handling spatial information. In the other task the orientation of a standard line, held in memory, was compared with the orientation of a single test line projected to the left or right of fixation. Results were in the same direction as before, although the right hemisphere superiority was significant only for the "different" responses. Data do not support the idea that "same" and "different" judgments need be differentially lateralized. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Making letters distinctive.

Results of a study with 77 kindergartners, 24 1st graders, 21 2nd graders, and 6 college students show that small graphic changes made in normal letters of the alphabet changed the similarity relations among those letters. All Ss classified letters of this distinctive font faster and with fewer errors than they classified normal letters. It is shown that it is not features alone but relations between features within letters, and relations between letters in the stimulus set, that determine how difficult any particular letter is to classify. The advantage of the distinctive font is such that many children had less difficulty classifying distinctive letters into bins labeled with normal letters than doing the conceptually easier match-to-sample task of placing normal letters into bins labeled with normal letters. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of imagery-perception interaction.

A number of different research findings have shown that mental imagery can affect the perceptual processing of stimuli. The present research was aimed at characterizing the representations and processes underlying imagery–perception interactions. In 4 experiments, Ss mentally projected images of letters into the visual field, and either detected or detected and localized point threshold stimuli that fell on or off the image. Stimuli falling on the image were detected more often than stimuli falling off the image, consistent with the hypothesis that the representations at the interface between imagery and perception have an array format. When the facilitation was analyzed in terms of signal detection theory, it was found to consist only of criterion lowering, and not of enhanced sensitivity. The local criterion-lowering effect of imaged letters was then compared with the effect of perceiving a letter and attending to a letter. Perceiving a letter had no discernible effect on stimulus detection, whereas attending to the letter caused the same local criterion lowering, without sensitivity changes, as imaging the letter. This is consistent with the claims of U. Neisser (1976) and others that imagery is an attentional state. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taking a bright view of negative priming in the light of dim stimuli: Further evidence for memory confusion during episodic retrieval.

A same–different letter-matching task was used to examine the effects of stimulus intensity on negative priming, which is poorer performance when target letters have been presented as distractor letters on the immediately preceding trial. In Exp 1, with 68 college students, stimulus intensity was manipulated between-participants, whereas in Exp 2, with 32 college students, it varied randomly from trial-to-trial within-participants. In Exp 1, negative priming was equivalent for both stimulus intensities. In Exp 2, negative priming effects were larger for repeated intensity stimuli than for nonrepeated intensity stimuli, when stimulus intensity was dim. Furthermore, for repeated intensity stimuli, negative priming effects were enhanced when the overt response required to the stimulus was repeated from prime to probe trial. These results are consistent with the hypothesis that negative priming may be due to memory confusion, rather than to inhibition of the distractor stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)