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.     

Masked constituent letter priming in an alphabetic decision task

Abstract

The experiments presented here were designed to test whether the prior presentation of a letter in a word, nonword or a string of Xs facilitates the subsequent identification of this letter. Using briefly presented masked primes, clear facilitatory constituent priming effects were obtained in an alphabetic decision task (letter/non-letter classification) when prime letters were flanked by Xs, but the effects disappeared or were greatly reduced when the prime letter formed part of a consonant array (nonword primes). Evidence for word-letter constituent priming was also obtained but almost only for word-initial letten. These facilitatory constituent priming effects were strongest when the target letter was embedded in a string of hash marks and occupied the same relative position in this string as the prime letter in the prime string. The mediating role of letter representations in word recognition and the position-specific coding of character arrays are discussed in the light of these results.     

Can the dual-route cascaded computational model of reading offer a valid account of the masked onset priming effect?

The masked onset priming effect (MOPE) refers to the empirical finding that target naming is faster when the target (SIB) is preceded by a briefly presented masked prime that starts with the same letter/phoneme (suf) than when it does not (mof; Kinoshita, 2000, Experiment 1). The dual-route cascaded (DRC) computational model of reading (Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001) has offered an explanation for how the MOPE might occur in humans. However, there has been some empirical discrepancy regarding whether for nonword items the effect is limited to the first-letter/phoneme overlap between primes and targets or whether orthographic/phonological priming effects occur beyond the first letter/phoneme. Experiment 1 tested these two possibilities. The human results, which were successfully simulated by the DRC model, showed priming beyond the first letter/phoneme. Nevertheless, two recent versions of the DRC model made different predictions regarding the nature of these priming effects. Experiment 2 examined whether it is facilitatory, inhibitory, or both, in order to adjudicate between the two versions of the model. The human results showed that primes exert both facilitatory and inhibitory effects.     

Phonographic neighbors,not orthographic neighbors,determine word naming latencies

The orthographic neighborhood size (N) of a word—the number of words that can be formed from that word by replacing one letter with another in its place—has been found to have facilitatory effects in word naming. The orthographic neighborhood hypothesis attributes this facilitation to interactive effects. A phonographic neighborhood hypothesis, in contrast, attributes the effect to lexical print-sound conversion. According to the phonographic neighborhood hypothesis, phonographic neighbors (words differing in one letter and one phoneme, e.g., stove and stone) should facilitate naming, and other orthographic neighbors (e.g., stove and shove) should not. The predictions of these two hypotheses are tested. Unique facilitatory phonographic N effects were found in four sets of word naming mega-study data, along with an absence of facilitatory orthographic N effects. These results implicate print-sound conversion—based on consistent phonology—in neighborhood effects rather than word-letter feedback.     

Geometric and semantic similarity in visual masking

Semantic and geometric or physical similarity were manipulated separately in a backward-masking situation. When the target was a word to be read aloud, formal similarity between the letters of target and mask facilitated target recognition, as did associative similarity. Masking a target word by its own anagram also facilitated whole word report. In contrast, formal similarity was inhibitory rather than facilitatory of report when the target was spelled letter-by-letter, rather than read whole. This was true even for the same target words whose whole report was facilitated by formal similarity. A model to account for this reversal in the broader context of the neural substrate of reading is advanced. It is proposed that letter and word processing are fundamentally different in that letters are recognized by hierarchical feature analysis while words are stored and recognized wholistically by diffuse and redundant networks. Implications of the results for the study of reading are discussed.     

Parafoveal letter-position coding in reading

The masked-priming lexical decision task has been the paradigm of choice for investigating how readers code for letter identity and position. Insight into the temporal integration of information between prime and target words has pointed out, among other things, that readers do not code for the absolute position of letters. This conception has spurred various accounts of the word recognition process, but the results at present do not favor one account in particular. Thus, employing a new strategy, the present study moves out of the arena of temporal- and into the arena of spatial information integration. We present two lexical decision experiments that tested how the processing of six-letter target words is influenced by simultaneously presented flanking stimuli (each stimulus was presented for 150 ms). We manipulated the orthographic relatedness between the targets and flankers, in terms of both letter identity (same/different letters based on the target’s outer/inner letters) and letter position (intact/reversed order of letters and of flankers, contiguous/noncontiguous flankers). Target processing was strongly facilitated by same-letter flankers, and this facilitatory effect was modulated by both letter/flanker order and contiguity. However, when the flankers consisted of the target’s inner-positioned letters alone, letter order no longer mattered. These findings suggest that readers may code for the relative position of letters using words’ edges as spatial points of reference. We conclude that the flanker paradigm provides a fruitful means to investigate letter-position coding in the fovea and parafovea.     

Effects of binding in the identification of objects

The binding problem requires a solution at the level of individual neurons, but no definite mechanism has yet be given. Therefore, the neuronal level is as yet inadequate for modeling cognitive processes in which binding plays a crucial role. Moreover, the neuronal level involves too many details that are unlikely to be essential for understanding cognition. A general model of cognitive brain functioning is described in which cognitive tasks are represented in a network of cell assemblies. In the network, binding is functionally defined in a way that is compatible with the neuronal level. A computer simulation of the model clarifies how the binding of location and identity of a set of simultaneously presented letters takes place and how questions about the location and identity of the letters are answered. From the simulation of the task three predictions on the logistics of neural processes are derived: 1. When the cell assembly representing a letter participates in more than one temporary excitation loop, it will reach its critical threshold faster. At the behavioral level this means that as the number of identical letters in the display increases, responses will be faster. 2. In order to answer questions about the location and identity of presented letters cell assemblies representing the target location and the target identity have to become bound to their appropriate values. As a consequence the facilitatory effect of identical letters will be stronger if they involve the target location or the target identity than when identical non-targets are involved. 3. Negative identifications are more dependent on the presentation time of the letters than positive identifications because the excitation loops involved take more time to reach the critical threshold. Therefore, the facilitatory effect of identical letters is stronger when the external activation is relatively strong, i.e., when presentation time of the letters is sufficiently long. The reaction times obtained in three behavioral experiments support these hypotheses. Effects of binding can therefore be predicted on the basis of the general logistics of neural processes, without assumptions about a specific binding mechanism at the neuronal level.     

Word-to-letter inhibition: Word-inferiority and other interference effects

Four experiments were run to determine whether the interactive activation model would more accurately reflect the effect of context in letter perception by including word-to-letter inhibition resulting from word-to-word inhibition produced when multiple word units become active. The first three experiments found less accurate target letter discrimination in word than in nonword strings when a string was altered halfway through the exposure through adding or dropping a nontarget letter. The alteration changed a word to a different word or a nonword to a different nonword. Unaltered strings produced the typical word-superiority effect. The last experiment found an inverse relationship between target discrimination performance and the number of word substrings contained in each of a set of word quadrigrams that were individually exposed.     

The category effect in visual search depends on physical rather than conceptual differences

Is a target letter (digit) more readily detected in a digit (letter) background because of conceptual-level differences between letters and digits or because of physical-level differences? When letters and digits were matched on physical features, both for the target set and the background set, no letter vs. digit category effect was found. With physical differences eliminated, search was faster and more accurate for letter than for digit targets and distractors, presumably because of the greater familiarity of letters. Presenting the same characters in normal and mirrorreversed orientation, which also minimized featural differences between categories, produced only a small normal vs. reversed category effect. In a normal background, a reversed target lost much more from its unfamiliarity than it gained from mismatching the background. The present results indicate that the category effect vanishes when only conceptual level differences are present.     

An attempt to simulate letter-by-letter dyslexia in normal readers

We attempted to simulate the main features of letter-by-letter (LBL) dyslexia in normal readers through stimulus degradation (i.e. contrast reduction and removal of high spatial frequencies). The results showed the word length and the letter confusability effects characteristic of LBL dyslexia. However, the interaction of letter confusability and N size (i.e. a facilitatory effect only for low confusability targets) previously observed in LBL dyslexics [Arguin, M., Fiset, S., & Bub, D. (2002). Sequential and parallel letter processing in letter-by-letter reading. Cognitive Neuropsychology, 19, 535-555; Arguin, M., & Bub, D. (2006). Parallel processing blocked by letter similarity in letter dyslexia: a replication. Cognitive Neuropsychology, 22, 589-602; Fiset, D., Arguin, M. & McCabe, E. (2005a). The breakdown of parallel letter processing in letter-by-letter dyslexia. Cognitive Neuropsychology, 22, 1-22] was not found. Our results suggest that the type of visual degradation employed here may only partially correspond to the visual deficit present in LBL dyslexia and that this degradation may have prevented the normal readers from accessing visual information available to LBL dyslexics when they use the compensatory strategy of serial letter processing.     

The influence of visualization of orthography on the recognition of written words]

This paper reviews the main research that has been conducted on the role of orthographic neighbourhood in visual word recognition. We focus here on the traditionally defined neighbourhood, that is corresponding to the set of words of the same length sharing all but one letter with the stimulus. Two major theoretical frameworks, namely the activation verification and the interactive activation models, assume that orthographic neighbours are activated when a written word is presented. Predictions formulated by both models for words and pseudowords on the effects of neighbourhood size (N), neighbourhood frequency (NF), and neighbourhood distribution (P), are examined in order to assess the plausibility of serial versus interactive processes. Findings from 27 empirical studies including more than 80 experiments suggest that neighbourhood effects depend on the neighbourhood indexes (N, NF, and P), on the particular tasks (lexical decision, naming, semantic categorization, perceptual identification, and reading), and on the languages (English, French, Spanish, and Dutch) that are used. The results for words can be summarized as follows: (1) In the lexical decision task, the N effect is facilitatory. The NF effect is rather inhibitory, particularly in French and Spanish experiments. The P effect is rather inhibitory in English studies, whereas the P effect for higher frequency neighbours is facilitatory in French. (2) In the perceptual identification task with a single identification response, N and NF effects are inhibitory whatever the language. (3) In the naming task, N and NF effects are facilitatory whatever the language. (4) In the semantic categorization task, an interaction effect between N and NF is found in both English and Spanish. (5) In eye movement studies, the NF effect is inhibitory in both English and French. The issue of lexical versus task-specific processes underlying neighbourhood effects in lexical identification tasks is also examined. On the whole, facilitatory N effects are usually attributed to nonlexical processes of the lexical decision task and of the naming task, whereas inhibitory neighbourhood frequency effects are usually attributed to lexical processes, at least in lexical-decision experiments and in eye-movement studies on normal reading. The distribution of higher frequency neighbours which is found to have a facilitatory effect on French words in lexical-decision experiments can be attributed to lexical processes in the interactive activation framework. The theoretical implications of the data are discussed in light of the original activation verification and interactive activation models and in recently extended versions of these models. We conclude that the lexical inhibition hypothesis which is central in the interactive activation framework is the most appropriate to account for the role of orthographic neighbourhoods in visual word recognition.     

The crossmodal facilitation of visual object representations by sound: evidence from the backward masking paradigm

We report a series of experiments designed to demonstrate that the presentation of a sound can facilitate the identification of a concomitantly presented visual target letter in the backward masking paradigm. Two visual letters, serving as the target and its mask, were presented successively at various interstimulus intervals (ISIs). The results demonstrate that the crossmodal facilitation of participants' visual identification performance elicited by the presentation of a simultaneous sound occurs over a very narrow range of ISIs. This critical time-window lies just beyond the interval needed for participants to differentiate the target and mask as constituting two distinct perceptual events (Experiment 1) and can be dissociated from any facilitation elicited by making the visual target physically brighter (Experiment 2). When the sound is presented at the same time as the mask, a facilitatory, rather than an inhibitory effect on visual target identification performance is still observed (Experiment 3). We further demonstrate that the crossmodal facilitation of the visual target by the sound depends on the establishment of a reliable temporally coincident relationship between the two stimuli (Experiment 4); however, by contrast, spatial coincidence is not necessary (Experiment 5). We suggest that when visual and auditory stimuli are always presented synchronously, a better-consolidated object representation is likely to be constructed (than that resulting from unimodal visual stimulation).     

The influence of multiple readings on the missing-letter effect revisited

In searching for a target letter while reading, participants make more omissions when the target letter is embedded in frequent function words than when it is embedded in less frequent content words. According to the guidance-organization (GO) model, this occurs because high-frequency function words are processed faster than low-frequency content words, leaving less time available for letter processing. We tested this hypothesis in three experiments by increasing word-processing speed through text repetition, which should translate into higher omission rates. Participants either read the text and searched for the target letter once or read the text three times and searched for a target letter on all readings or the final reading only. In all the experiments in which participants could not anticipate the target letter to be used, results revealed the presence of a large missing-letter effect that was unaffected by familiarity with the text. In addition, when participants knew from the start the target letter to be used on the final reading, the missing-letter effect was eliminated. Repeated search of the same text for different targets increased omissions equally for function words and content words, but this finding was present even when a new text was used, suggesting that repetition of the search task, rather than familiarity with the text, was responsible.     

Effects of noise letters on decisions: Discrete or continuous flow of information?

Four forced-choice letter-detection experiments examined the effect on detection latency of noise letters that were visually similar to target letters. A single target letter was present in each display. Noise letters were similar to the target letter present in the display (the signal), to a different target letter assigned to the same response as the signal, or to a target letter assigned to the opposite response from the signal. Noise letters were present in either relevant or irrelevant display positions, and two quite different stimulus sets were used. The experiments were designed to test a prediction of models in which information about noise letters is transmitted continuously from the recognition to the decision process. These models predict that responses should be faster when noise letters are visually similar to a target assigned to the same response as the signal than when noise letters are similar to a target assigned to the opposite response. Statistically reliable effects of the type predicted by continuous models were obtained when noise letters appeared in relevant display positions, but not when they appeared in irrelevant positions.     

Graphemes are perceptual reading units

Graphemes are commonly defined as the written representation of phonemes. For example, the word 'BREAD' is composed of the four phonemes /b/, /r/, /e/ and /d/, and consequently, of the four graphemes 'B', 'R', 'EA', and 'D'. Graphemes can thus be considered the minimal 'functional bridges' in the mapping between orthography and phonology. In the present study, we investigated the hypothesis that graphemes are processed as perceptual units by the reading system. If the reading system processes graphemes as units, then detecting a letter in a word should be harder when this letter is embedded in a multi-letter grapheme than when it corresponds to a single-letter grapheme. In Experiment 1A, done in English, participants were slower to detect a target letter in a word when the target letter was embedded in multi-letter grapheme (i.e. 'A' in 'BEACH') than when it corresponded to a single-letter grapheme (i.e. 'A' in 'PLACE'). In Experiment 1B, this effect was replicated in French. In Experiment 2, done in English, this grapheme effect remained when phonemic similarity between the target letter alone and the target letter inside the word was controlled. Together, the results are consistent with the assumption that graphemes are processed as perceptual reading units in alphabetic writing systems such as English or French.     

Neighborhood effects in visual word recognition: Facilitatory or inhibitory?

In five experiments, in which subjects were to identify a target word as it was gradually clarified, we manipulated the target's frequency of occurrence in the language and its neighborhood size—the number of words that can be constructed from a target word by changing one letter, while preserving letter position. In Experiments 1–4, visual identification performance to screen-fragmented words was measured. In Experiments 1 and 2, we used the ascending method of limits, whereas Experiments 3 and 4 presented a fixed-level fragment. In Experiment 1, there was no relation between overall accuracy and neighborhood size for-words-between three and six letters in length. However, more errors of commission (guesses) were made for high-neighborhood words and more errors of omission (blanks) were made for low-neighborhood words. Letter errors within guesses occurred at serial positions having many neighbors, and these positions were also likely to contain consonants rather than vowels. In Experiment 2, a smallfacilitatory effect of neighborhood size on bothhigh- and low-frequency words was found. In contrast, in Experiments 3 and 4, using the same set of words,inhibitory effects of neighborhood size, but only for low-frequency words, were found. Experiment 5, using a speeded identification task, showed results parallel to those of Experiments 3 and 4. We suggest that whether neighborhood effects are facilitatory or inhibitory depends on whether feedback allows subjects to disconfirm initial hypotheses that the target is a high-frequency neighbor.     

Effects of letter-names on visual search

When a subject searches through a list of letters of mixed case in a letter cancellation task search is slowed if the background items include the target letter in the other case. This effect is largest when target and confusing background have visual analogue similarity (e.g., cC) but still obtains when no special visual similarity exists (e.g., aA). In searches for two targets, one of either case, search is facilitated when the targets are both cases of the same letter.     

Interaction between endogenous and exogenous orienting in crossmodal attention

Using a cue-target paradigm, we investigated the interaction between endogenous and exogenous orienting in cross-modal attention. A peripheral (exogenous) cue was presented after a central (endogenous) cue with a variable time interval. The endogenous and exogenous cues were presented in one sensory modality (auditory in Experiment 1 and visual in Experiment 2) whereas the target was presented in another modality. Both experiments showed a significant endogenous cuing effect (longer reaction times in the invalid condition than in the valid condition). However, exogenous cuing produced a facilitatory effect in both experiments in response to the target when endogenous cuing was valid, but it elicited a facilitatory effect in Experiment 1 and an inhibitory effect in Experiment 2 when endogenous cuing was invalid. These findings indicate that endogenous and exogenous cuing can co-operate in orienting attention to the crossmodal target. Moreover, the interaction between endogenous and exogenous orienting of attention is modulated by the modality between the cue and the target.     

Evidence for early selection: precuing target location reduces interference from same-category distractors

In this study, we evaluated whether uncertainty about target location and category overlap between the target and the flankers played a role in recent findings (Miller, 1987) of semantic interference of irrelevant stimuli. In each of four testing conditions, subjects were required to identify a target letter surrounded by irrelevant flankers whose identity predicted the correct response. We varied (1) whether or not the target location was precued, and (2) the flanker's category (digits vs. letters). We found a substantial effect of letter flankers when subjects were uncertain of the precise target location. However, this effect was greatly attenuated when attention was predirected to the target location. Similarly, a reduced flanker effect was observed when the flankers (digits) belonged to a different semantic category than the target. However, when the target location was precued, no effect of the semantic congruity of target and flankers was found. Coupled with previous research, these findings converge in establishing that both failures to maintain attention on the target location and the semantic congruity of target and flankers modulate the size of the effects from irrelevant stimuli. These results are discussed in the context of early and late selection views of selective attention.     

The impact of familiarization strategies on the missing-letter effect

When reading a text and searching for a target letter, readers make more omissions of the target letter if it is embedded in frequent function words than if it is in rare content words. While word frequency effects are consistently found, few studies have examined the impacts of passage familiarity on the missing-letter effect and studies that have present conflicting evidence. The present study examines the effects of passage familiarity, as well as the impacts of passage familiarization strategy promoting surface or deep encoding, on the missing-letter effect. Participants were familiarized with a passage by retyping a text, replacing all common nouns with synonyms, or generating a text on the same topic as that of the original text, and then completed a letter search task on the familiar passage as well as an unfamiliar passage. In Experiment 1, when both familiar and unfamiliar passages use the same words, results revealed fewer omissions for the retyping and synonyms conditions. However, in Experiment 2, when different words are used in both types of texts, no effect of familiarization strategy was observed. Furthermore, the missing-letter effect is maintained in all conditions, adding support to the robustness of the effect regardless of familiarity with the text.