There are now extensive behavioral and neuropsychological evidence to indicate that semantic information of a word can be activated without conscious awareness. However, semantic activation alone may not be sufficient for observing semantic priming effects in masked lexical decision task. In the following study, two tasks were used: lexical decision and semantic categorization. Conscious awareness of the prime was systematically manipulated by varying the duration of the prime and by varying the placement of the mask in the prime-target presentation sequence. Priming effects were observed in the semantic categorization task at prime durations of 42 milliseconds but no semantic priming was observed for the same prime duration in the lexical decision task. However, semantic priming effects began to emerge in lexical decision at the longer prime durations (55 & 69 ms) and under the least effective prime-mask presentation sequences. It is proposed that semantic activation alone is not sufficient for semantic priming effects in the lexical decision task but that central executive involvement is necessary, if only at the lowest level, for facilitatory effects to be observed. Furthermore, no such central executive involvement appears to be required for the semantic categorization task. The priming effects obtained in this task is interpreted in terms of a "decision priming" effect.

Two semantic priming experiments in the context of lexical decision are reported that examine the joint effects of stimulus quality, semantic context, and strength of association when all these factors are intermixed in a block of trials. A three-way interaction is seen in both experiments in which the typical interaction between semantic context and stimulus quality is eliminated when the strength of association between prime-target pairs is weak. The results support a role for a control mechanism that makes use of local information available within a trial, in addition to a global control mechanism that operates across a block of trials. The interaction between semantic context and stimulus quality when prime-target pairs are strongly related is attributed to the presence of feedback from the semantic system to the lexical system whereas additive effects of semantic context and stimulus quality is attributed to this feedback being eliminated such that semantic and lexical levels are functionally separate modules.

Two semantic priming experiments in the context of lexical decision are reported that examine the joint effects of stimulus quality, semantic context, and strength of association when all these factors are intermixed in a block of trials. A three-way interaction is seen in both experiments in which the typical interaction between semantic context and stimulus quality is eliminated when the strength of association between prime-target pairs is weak. The results support a role for a control mechanism that makes use of local information available within a trial, in addition to a global control mechanism that operates across a block of trials. The interaction between semantic context and stimulus quality when prime-target pairs are strongly related is attributed to the presence of feedback from the semantic system to the lexical system whereas additive effects of semantic context and stimulus quality is attributed to this feedback being eliminated such that semantic and lexical levels are functionally separate modules.

Letter position plays an important role in lexical access. But are some positions more important than the others? Findings from numerous studies support the notion that in lexical access, initial letters produce strongest activation, which weakens towards the end of the word. In order to create a metric for computing the activation produced by each letter position in a correctly spelled word versus a word in which some or all letters are transposed, the formula for calculating a word's orthographic match coefficient (OMC) was developed and tested. Utilizing the masked priming paradigm and a lexical decision task, Experiments 1-5 test the accuracy and reliability of the OMC predictions, and look at neighborhood density in conjunction with different types of letter movement. Results from these experiments provide empirical support for the OMC as a reliable predictor of priming that involves transposed letters, and offer insight into possible mechanisms of word recognition.

The purpose of this research was to study grammatical categories in the Tagalog mental lexicon using lexical decision tasks. Some linguists question whether words in Tagalog can be classified as nouns and verbs (Foley, 1998; Kaufman, 2011) because most root words can be inflected for any grammatical function and because verbs cannot be used in their uninflected form. Previous studies with English and German (Kauschke and Stenneken 2008) have shown that participants respond differently to nouns and verbs in lexical decision tasks. These studies have also shown that participants respond differently to transitive and intransitive verbs in lexical decision tasks. It was assumed that if nouns and verbs exist in Tagalog, response times to Tagalog lexical decision tasks will show similar patterns to those performed in English and German. Two experiments were performed to examine whether words are classified as nouns and verbs in the Tagalog mental lexicon and whether other factors affected that classification. For the experiments, native speakers of Tagalog participated in lexical decision tasks and response times were measured. The first experiment tested the classification of root nouns and verbs. Contrary to findings in other languages, there was no significant difference between response times to nouns and verbs. However, there were differences in response times to nouns from different semantic categories and to verbs with different morphosyntactic structures. The second experiment examined the classification of inflected nouns and verbs. Again, the results showed no difference between response times to nouns and verbs. There was also no difference between transitive and intransitive verbs. However, there was a slight difference between verbs of different voice inflections. The results of the experiments suggest the while the grammatical classes of nouns and verbs may not be the most important features of words in the Tagalog mental lexicon, they may still play a role since different features, semantics or morphosyntactics, did affect the responses to words from the different categories.

Yes / Pattern-related visual stress (PRVS) is a form of sensory hypersensitivity that some people experience when viewing high contrast repeating patterns, notably alternating dark and light stripes. Those susceptible to PRVS typically have a strong aversion to such stimuli, and this is often accompanied by experiences of visual discomfort and disturbance. The patterns most likely to elicit symptoms of PRVS have a square-wave grating configuration of spatial frequency ~3 cycles/degree. Such stimuli are characteristic of printed text in which lines of words and the spaces between them present a high contrast grating-like stimulus. Consequently, much printed reading material has the potential to elicit PRVS that may impair reading performance, and this problem appears to be common in individuals with reading difficulties including dyslexia. However, the manner in which PRVS affects reading ability is unknown. One possibility is that the early sensory visual stress may interfere with the later cognitive word recognition stage of the reading process, resulting in reading performance that is slower and/or less accurate. To explore the association of PRVS with word recognition ability, lexical decision performance (speed and accuracy) to words and pronounceable non-words was measured in two groups of adults, having low and high susceptibility to PRVS. Results showed that lexical decisions were generally faster but less accurate in high-PRVS, and also that high-PRVS participants made decisions significantly faster for words than for non-words, revealing a strong lexicality effect that was not present in low-PRVS. These findings are novel and, as yet, unconfirmed by other studies.

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This thesis describes basic research into visual word recognition and decision making. Determining the best matching lexical representation for a given stimulus involves interactions between representations. The standard task for studying these processes is the lexical decision task (LDT), but there is still debate regarding the factors that affect how individuals make lexical decisions. The nature of lexical interactions and the processes underlying lexical decision-making were addressed here by testing response congruency effects in the masked priming variant of the LDT. The results of seven masked priming experiments showed a robust response congruency effect that depends on the difficulty of the word-nonword discrimination. This finding resolved apparent inconsistencies in previous research. The experiments were simulated using the Bayesian Reader and the Spatial Coding Model (SCM). The probability based Bayesian Reader model failed to accommodate the findings. However, a good fit to the data was provided by a modified version of the SCM in which the assumptions regarding the nature of lexical interactions were changed such that word nodes inhibit only (closely) related competitors. The model also assumes that the difficulty of the word-nonword discrimination affects the degree to which stimulus typicality informs lexical decisions. A critical issue for these experiments involved the definition of orthographic typicality. An algorithm for measuring orthographic typicality and for generating nonwords with a specific level of orthographic typicality (OT3) was developed. An unprimed LDT experiment showed that OT3 affected decision latency even when other standard measures of orthographic typicality were controlled. Two additional masked priming experiments showed that highly typical primes lead to faster word responses and slower nonword responses than less typical primes. Overall, the results of this research enhance our understanding of the processes underlying visual word recognition and lexical decision making, and also have important methodological implications for the field.

It has long been held that processing at the single word level during reading is automatic. However, research has recently begun to emerge that challenges this view. The literature surrounding the processing of emotion while recognizing printed words is limited, but some findings in the processing of emotion in faces suggest that negative stimuli (especially threat stimuli) promote quick and accurate processing. The purpose of the present experiments is to investigate whether negative emotionally-laden words are afforded priority processing in visual word recognition compared to positive emotionally-laden words. Two experiments are reported that manipulated the lexicality and valence of the target and distractor stimuli (Experiments 1 & 2), the validity of a spatial pre-cue (Experiments 1 & 2), and the presence of a distractor item (Experiment 2). Participants were asked to determine whether the target stimulus spelled a word or not. Response times on valid trials were faster compared to invalid trials, response times to negative emotionally-laden words were slower compared to positive emotionally-laden words, and the presence of a distractor item encouraged better focus on the target stimuli in the absence of any evidence that the valence of the distractor itself was processed. These results are consistent with the hypothesis that visual word recognition is not automatic given that processing benefited from the accurate direction of spatial attention. Furthermore, negative emotionally-laden words benefited equally compared to positive emotionally-laden words and therefore provide no evidence of automatic processing.

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