Automatic activation of phonological information in reading: Evidence from the semantic relatedness decision task

A semantic relatedness decision task was used to investigate whether phonological recoding occurs automatically and whether it mediates lexical access in visual word recognition and reading. In this task, subjects read a pair of words and decided whether they were related or unrelated in meaning. In Experiment 1, unrelated word-homophone pairs (e.g., LION-BARE) and their visual controls (e.g., LION-BEAN) as well as related word pairs (e.g., FISH-NET) were presented. Homophone pairs were more likely to be judged as related or more slowly rejected as unrelated than their control pairs, suggesting phonological access of word meanings. In Experiment 2, word-pseudohomophone pairs (e.g., TABLE-CHARE) and their visual controls (e.g., TABLE-CHARK) as well as related and unrelated word pairs were presented. Pseudohomophone pairs were more likely to be judged as related or more slowly rejected as unrelated than their control pairs, again suggesting automatic phonological recoding in reading.     

Dissociating semantic and phonological maintenance using fMRI

Functional magnetic resonance imaging (fMRI) distinguished regions of neural activity associated with active maintenance of semantic and phonological information. Subjects saw a single word for 2 sec, and following a 10-sec delay, made a judgment about that word. In the semantic task, subjects focused on the meaning of the word and decided whether a second word was synonymous with it. In the phonological task, subjects repeated the word silently and decided whether it shared a vowel sound with a nonsense word. Analyses allowed for isolation of neural activity during the maintenance delay. Semantic maintenance elicited greater activity in bilateral inferior frontal gyrus and left middle temporal gyrus regions of interest (ROI). In contrast, there was greater activity for phonological maintenance in the left superior parietal ROI. These results show a frontal-temporal network involved in actively maintaining the meanings of words, and they indicate that semantic and phonological maintenance processes are dissociable within working memory.     

Active maintenance of semantic representations

In research on verbal working memory, articulatory rehearsal, a maintenance mechanism for phonological representations, has undergone intensive and excellent study. Possible mechanisms for semantic representation have received less attention. However, several studies have reported a double dissociation in types of memory deficits (semantic memory difficulties vs. phonological memory difficulties). This suggests the separability of two maintenance mechanisms. The present study focused on this separability in individuals with normal memory abilities, using a dual-task interference paradigm. The results indicate a crossover interaction between memory and interference task effects: Preventing articulatory rehearsal more strongly disrupted the phonological memory task, whereas performing a tapping task that interfered with attentional control more strongly disrupted semantic memory. These results suggest that semantic representations are actively maintained by a mechanism other than phonological maintenance.     

Reduced short-term memory capacity in Alzheimer's disease: The role of phonological,lexical, and semantic processing

Individuals with Alzheimer's disease (AD) are often reported to have reduced verbal short-term memory capacity, typically attributed to their attention/executive deficits. However, these individuals also tend to show progressive impairment of semantic, lexical, and phonological processing which may underlie their low short-term memory capacity. The goals of this study were to assess the contribution of each level of representation (phonological, lexical, and semantic) to immediate serial recall performance in 18 individuals with AD, and to examine how these linguistic effects on short-term memory were modulated by their reduced capacity to manipulate information in short-term memory associated with executive dysfunction. Results showed that individuals with AD had difficulty recalling items that relied on phonological representations, which led to increased lexicality effects relative to the control group. This finding suggests that patients have a greater reliance on lexical/semantic information than controls, possibly to make up for deficits in retention and processing of phonological material. This lexical/semantic effect was not found to be significantly correlated with patients’ capacity to manipulate verbal material in short-term memory, indicating that language processing and executive deficits may independently contribute to reducing verbal short-term memory capacity in AD.     

Reduced short-term memory capacity in Alzheimer's disease: the role of phonological, lexical, and semantic processing

Individuals with Alzheimer's disease (AD) are often reported to have reduced verbal short-term memory capacity, typically attributed to their attention/executive deficits. However, these individuals also tend to show progressive impairment of semantic, lexical, and phonological processing which may underlie their low short-term memory capacity. The goals of this study were to assess the contribution of each level of representation (phonological, lexical, and semantic) to immediate serial recall performance in 18 individuals with AD, and to examine how these linguistic effects on short-term memory were modulated by their reduced capacity to manipulate information in short-term memory associated with executive dysfunction. Results showed that individuals with AD had difficulty recalling items that relied on phonological representations, which led to increased lexicality effects relative to the control group. This finding suggests that patients have a greater reliance on lexical/semantic information than controls, possibly to make up for deficits in retention and processing of phonological material. This lexical/semantic effect was not found to be significantly correlated with patients' capacity to manipulate verbal material in short-term memory, indicating that language processing and executive deficits may independently contribute to reducing verbal short-term memory capacity in AD.     

Learning new meanings for old words: effects of semantic relatedness

Changes to our everyday activities mean that adult language users need to learn new meanings for previously unambiguous words. For example, we need to learn that a "tweet" is not only the sound a bird makes, but also a short message on a social networking site. In these experiments, adult participants learned new fictional meanings for words with a single dominant meaning (e.g., "ant") by reading paragraphs that described these novel meanings. Explicit recall of these meanings was significantly better when there was a strong semantic relationship between the novel meaning and the existing meaning. This relatedness effect emerged after relatively brief exposure to the meanings (Experiment 1), but it persisted when training was extended across 7?days (Experiment 2) and when semantically demanding tasks were used during this extended training (Experiment 3). A lexical decision task was used to assess the impact of learning on online recognition. In Experiment 3, participants responded more quickly to words whose new meaning was semantically related than to those with an unrelated meaning. This result is consistent with earlier studies showing an effect of meaning relatedness on lexical decision, and it indicates that these newly acquired meanings become integrated with participants' preexisting knowledge about the meanings of words.     

Phonological, semantic, and repetition priming with homophones

The current study investigated semantic, repetition, and phonological priming using heterographic homonyms (homophones) as stimuli in a lexical decision task. As in previous research, reliable semantic priming and repetition effects were found. In addition, the statistical additivity of these two effects was replicated using homophones as stimuli. Using homophones, a reliable phonological priming effect was found when 10-16 intervening trials were used. This effect was also statistically independent of semantic priming indicating the independence of the mechanisms responsible for semantic and phonological priming. The magnitude of the phonological priming effect was also significantly less than the magnitude of the repetition effect. This difference in effect magnitude was taken to indicate that the repetition of phonological information is not a primary contributor to the repetition effect.     

工作记忆广度与汉语句子语境效应的关系

采用计算机快速系列视觉呈现技术,以反应时为指标,利用命名法,从工作记忆容量个体差异的角度,探讨汉语句子阅读中的语境效应。本研究将句子的语境效应分为两个来源：一个是自动激活扩散的词汇之间的语义启动,另一个是相互作用的句子水平的主题启动。结果表明：词汇间的语义启动不受工作记忆容量的影响,并且不易受到无关记忆任务的干扰。句子水平的主题启动会受到工作记忆容量的影响：工作记忆广度较高的读者能出现主题水平的语境效应,但是在无关记忆任务的干扰下,句子主题水平的语境效应消失;低广度的读者在无外部记忆负荷和有外部记忆负荷两种条件下都没有出现主题水平的语境效应。工作记忆容量对那些需要较多认知资源的加工过程产生显著的影响,实验结果符合工作记忆容量限制理论     

Orthographic and phonological activation in recognizing Chinese characters

This paper is a contribution to the study of whether visual contact with lexical units in any writing system necessarily arouses their corresponding phonological information. In two experiments it was investigated whether phonological information is automatically activated during the semantic processing of Chinese characters. In these experiments, both using a semantic-categorization task, subjects produced the same proportion of false positive categorization errors and showed the same decision latencies on homophone foils and their non-homophonic controls, thus indicating that phonological information does not seem to affect the semantic task. Experiment 2 further revealed that subjects made more errors and produced longer response times on graphemically similar foils than on the corresponding controls. The absence of phonological effects and the presence of clear effects of visual similarity for Chinese characters in semantic tasks can be taken to indicate that phonological information may not be automatically activated during the processing of meanings of Chinese characters. The present results also cast serious doubts on the hypothesis that phonological activation is a universal principle of lexical processing.     

Visual working memory is enhanced by mixed strategy use and semantic coding

Visual working memory is enhanced by processes related to verbalisation. However, the mechanism underlying this enhancement is unclear. Experiment 1 investigated the potential contribution of the phonological loop of working memory, by assessing the effects of articulatory suppression on two versions of the Visual Patterns Test—one low and one high in availability of verbal coding. The lack of interaction suggested that the phonological loop is not responsible; however, active use of combined verbal and visual strategies, as well as activated semantic knowledge, both appear to be related to increased capacity. Experiment 2 assessed the role of central executive resources. Because central executive suppression removed the benefit of the high verbal coding task version, central executive resources, assumed to relate to the temporary maintenance of multimodal codes in the episodic buffer, appear to underlie the benefit associated with verbalisation.     

Connectivity among semantic associates: an fMRI study of semantic priming

Semantic priming refers to a reduction in the reaction time to identify or make a judgment about a stimulus that has been immediately preceded by a semantically related word or picture and is thought to result from a partial overlap in the semantic associates of the two words. A semantic priming lexical decision task using spoken words was presented in event-related fMRI and behavioral paradigms. Word pairs varied in terms of semantic relatedness and the connectivity between associates. Thirteen right-handed subjects underwent fMRI imaging and 10 additional subjects were tested in a behavioral version of the semantic priming task. It was hypothesized priming would be greatest, reaction time fastest, and cortical activation reduced the most for related word pairs of high connectivity, followed by related word pairs of low connectivity, and then by unrelated word pairs. Behavioral and fMRI results confirmed these predictions. fMRI activity located primarily in bilateral posterior superior and middle temporal regions showed modulation by connectivity and relatedness. The results suggest that these regions are involved in semantic processing.     

Orthography and phonology in reading Japanese kanji words: Evidence from the semantic decision task with homophones

Correspondences between spelling and sound for Japanese kanji are complex and deep. The meaning of kanji words has generally been assumed to be accessed directly from orthography without phonological mediation. Experiment 1, however, replicated the findings of Van Orden (1987) that subjects made more false-positive errors on homophone foils than they did on nonhomophone controls in a semantic decision task, although they did so only when the foils were orthographically similar to the correct exemplars, which indicates both orthographic and phonological activations of meaning. Experiment 2 showed the same results when subjects were not required to pronounce the target words after semantic decisions, which indicates automatic phonological activation of kanji words. In Experiment 3, under pattern-masking conditions, this homophony effect was reduced but remained on errors, and the orthographic-similarity effect remained strong on both homophone and nonhomophone foils. These results suggest that both orthography and phonology play an important role in the comprehension of kanji words.     

Semantic memory and verbal working memory correlates of N400 to subordinate homographs

N400 is an event-related brain potential that indexes operations in semantic memory conceptual space, whether elicited by language or some other representation (e.g., drawings). Language models typically propose three stages: lexical access or orthographic- and phonological-level analysis; lexical selection or word-level meaning and associate activation; and lexical integration, sentence- and discourse-level operations. The exact stage that N400 reflects is unknown, although opinion favors lexical integration over lexical selection. Surprisingly, little research has assessed relationships between neuropsychological measures of semantic memory fund of information or verbal working memory capacity and N400. Subjects performed a homograph disambiguation comprehension task with minimal working memory load. Short sentences read: The noun was adjective/verb. The nouns were either homographs or unambiguous. The adjective/verb was disambiguating for the homograph, and congruent or incongruent for the unambiguous noun. The primary noun of interest was the subordinate homograph. Comprehension of the subordinate meaning should correlate with semantic memory stores, reflecting greater knowledge. If N400 primarily reflects lexical access operations, it should also correlate with measures of semantic knowledge. If N400 reflects lexical integration, it should correlate with measures of working memory capacity. Comprehension errors were associated with semantic memory stores, but not working memory capacity. N400 was related to working memory capacity, but not semantic knowledge, suggesting that N400 primarily reflects late-stage working memory operations. N400 to subordinate disambiguating words was larger with greater working memory capacity, and thus may index the absolute capacity of working memory rather than difficulty in contextual integration.     

Interference between storage and processing in working memory: Feature overwriting,not similarity-based competition

Eight experiments with the complex span paradigm are presented to investigate why concurrent processing disrupts short-term retention. Increasing the pace of the processing task led to worse recall, supporting the hypothesis that the processing task distracts attention from maintenance operations. Neither phonological nor semantic similarity between memory items and processing-task material impaired memory. In contrast, the degree of phonological overlap between memory items and processing-task material affected recall negatively, supporting feature overwriting as one source of interference in the complex span paradigm. When compared directly, phonological overlap impaired memory, but similarity had a beneficial effect. These findings rule out response competition or confusion as a mechanism of interference between storage and processing.     

Modulating semantic feedback in visual word recognition

According to the interactive activation framework proposed by McClelland and Rumelhart (1981), activation spreads both forward and backward between some levels of representation during visual word recognition. An important boundary condition, however, is that the spread of activation from lower to higher levels can be prevented (e.g., explicit letter processing during prime processing eliminates the well-documented semantic priming effect). Can the spread of activation from higher to lower levels also be prevented? This question was addressed with a choice task procedure in which subjects read a prime word and then responded to a target, performing either lexical decision or letter search depending on the color of the target. A semantic context effect was observed in lexical decision, providing evidence of semantic-level activation. In contrast, there was no semantic context effect in the letter search task, despite evidence of lexical involvement: Words were searched faster than nonwords. Further evidence of lexical involvement in the letter search task appeared in Experiment 2 in the form of greater identity priming for words than for nonwords. The results of these experiments are consistent with the conclusion that feedback from the semantic level to the lexical level can be blocked. Hence, between-level activation blocks can be instantiated in both bottom-up and top-down directions.     

An event-related brain potential analysis of visual word priming effects

Two experiments are reported that provide evidence on task-induced effects during visual lexical processing in a prime-target semantic priming paradigm. The research focuses on target expectancy effects by manipulating the proportion of semantically related and unrelated word pairs. In Experiment 1, a lexical decision task was used and reaction times (RTs) and event-related brain potentials (ERPs) were obtained. In Experiment 2, subjects silently read the stimuli, without any additional task demands, and ERPs were recorded. The RT and ERP results of Experiment 1 demonstrate that an expectancy mechanism contributed to the priming effect when a high proportion of related word pairs was presented. The ERP results of Experiment 2 show that in the absence of extraneous task requirements, an expectancy mechanism is not active. However, a standard ERP semantic priming effect was obtained in Experiment 2. The combined results show that priming effects due to relatedness proportion are induced by task demands and are not a standard aspect of online lexical processing.     

Interaction of semantic and perceptual processes in repetition blindness

Two experiments examined the effect of activation of higher-level semantic representations on lower-level perceptual representations. A forced-choice discrimination paradigm was used, a method known to produce repetition blindness (RB) for words unconfounded by memory demands or response bias. In Experiment 1, equivalent reductions in RB (as measured by omission error rate and by d') occurred when successive word pairs were identical in: (1) form, pronunciation, and meaning (both uppercase versions of the same word); (2) pronunciation and meaning but not form (lowercase versus uppercase; lexical identity); and (3) pronunciation, but not form or meaning (homonyms; phonological identity), relative to when the words were unrelated on all dimensions. The RB effect was markedly attenuated, but not eliminated, when the words were semantically related. Similar results were obtained in Experiment 2 using a larger group of subjects. These findings show that higher-order semantic representations can have a top-down influence on judgements based on lower-order perceptual representations. The results are discussed within the framework of a cascade model of object processing in the human brain.     

Hemispheric differences in the time-course of semantic priming processes: evidence from event-related potentials (ERPs)

To investigate hemispheric differences in the timing of word priming, the modulation of event-related potentials by semantic word relationships was examined in each cerebral hemisphere. Primes and targets, either categorically (silk-wool) or associatively (needle-sewing) related, were presented to the left or right visual field in a go/no-go lexical decision task. The results revealed significant reaction-time and physiological differences in both visual fields only for associatively related word pairs, but an electrophysiological difference also tended to reach significance for categorically related words when presented in the left visual field. ERP waveforms showed a different time-course of associative priming effects according to the field of presentation. In the right visual field/left hemisphere, both N400 and Late Positive Component (LPC/P600) were modulated by semantic relatedness, while only a late effect was present in the left visual field/ right hemisphere.     

Concreteness effects in different tasks: implications for models of short-term memory

This study investigates concreteness effects in tasks requiring short-term retention. Concreteness effects were assessed in serial recall, matching span, order reconstruction, and free recall. Each task was carried out both in a control condition and under articulatory suppression. Our results show no dissociation between tasks that do and do not require spoken output. This argues against the redintegration hypothesis according to which lexical-semantic effects in short-term memory arise only at the point of production. In contrast, concreteness effects were modulated by task demands that stressed retention of item versus order information. Concreteness effects were stronger in free recall than in serial recall. Suppression, which weakens phonological representations, enhanced the concreteness effect with item scoring. In a matching task, positive effects of concreteness occurred with open sets but not with closed sets of words. Finally, concreteness effects reversed when the task asked only for recall of word positions (as in the matching task), when phonological representations were weak (because of suppression), and when lexical semantic representations overactivated (because of closed sets). We interpret these results as consistent with a model where phonological representations are crucial for the retention of order, while lexical-semantic representations support maintenance of item identity in both input and output buffers.