Word retrieval to letter and semantic cues: A double dissociation in normal subjects using interference tasks

Recent evidence suggests that letter and semantic category verbal fluency tasks may use different component processes of a distributed word retrieval system. We hypothesized that the retrieval of words that begin with the same letter places greater demands on frontal lobe mediated strategic search processes than on temporal lobe mediated semantic knowledge. Conversely, generation of words from the same semantic category places greater demands on semantic knowledge than on strategic search. This hypothesis was tested by requiring subjects to generate lists of words to letter and semantic cues alone and while performing an interference task. A motor sequencing task (developed by Moscovitch, Neuropsychology of Memory, pp. 5–22, 1992) was used to activate frontal regions and an object decision task was used to activate posterior temporal cortex. In support of the hypothesis, letter fluency was reduced to a greater extent by concurrent performance of the motor sequencing task than by the object decision task. The opposite interference pattern was found for semantic category fluency.     

The effects of prime visibility on ERP measures of masked priming

In two experiments, the effect of the duration (40, 80 and 120 ms) of pattern masked prime words on subsequent target word processing was measured using event-related potentials. In Experiment 1, target words were either repetitions of the prior masked prime (car-CAR) or were another unrelated word (job-CAR). In Experiment 2, primes and targets were either semantically related (cap-HAT) or were unrelated (car-HAT). Unrelated target words produced larger N400s than did repeated (Exp 1) or semantically related (Exp 2) words across the different prime durations and these N400 priming effects tended to be smaller overall for semantic than repetition priming. Moreover, there was only a modest decline in the size of N400 repetition priming at the shortest prime durations, and there was no relationship between this N400 effect and a measure of prime categorization performance. However, the size of semantic priming at the shortest durations was relatively smaller than at longer durations and was correlated with prime categorization performance. The findings are discussed in the context of the functional significance of the N400 as well as a model that argues for different mechanisms during masked repetition and semantic priming.     

The effect of word imagery on priming effect under a preconscious condition: An fMRI study

Semantic priming is affected by the degree of association and how readily a word is imagined. In the association effect, activity in the perisylvian structures including the bilateral inferior frontal gyrus, the left middle temporal gyrus, and the supramarginal gyrus was correlated. However, little is known about the brain regions related to the effect of imagery word under the preconscious condition. Forty word pairs for high (HA)‐, low (LA)‐, and nonassociation (NA), nonword (NW) conditions were presented. Each 40 association word pairs (HA and LA) included 20 high (HI) and 20 low (LI) imagery prime stimuli, using a visually presented lexical decision task. A trial consisted of 30 ms prime, 30 ms mask, 500 ms probe, and 2–8 s stimulus onset asynchrony. Brain activation was measured using functional magnetic resonance imaging during word discrimination. Behavioral data indicated that the shortest response time (RT) was given for HA words, followed by LA and NA, and NW showed the longest RT (P < 0.01). RT was faster in HI than LI within HA, but not LA conditions (P < 0.01). Functional neuroimaging showed that differential brain regions for high imagery (HI) and low imagery (LI) words within low prime‐target word association were observed in the left precuneus, left posterior cingulate gyrus, and right cuneal cortex. The present findings demonstrate that the effect of the degree of imagery on semantic priming occurs during the early stage of language processing, indicating an “automatic imagery priming effect.” Our paradigm may be useful to explore semantic deficit related to imagery in various psychiatric disorders. Hum Brain Mapp 35:4795–4804, 2014. © 2014 The Authors. Human Brain Mapping Published by Wiley Periodicals, Inc.     

Semantic category and rhyming processing in the left and right cerebral hemisphere

In this study, the question of hemispheric abilities in processing explicit semantic and phonological information was addressed by measuring response latencies and performances in two judgement tasks. In the semantic task, word pairs were sequentially presented to the left or right visual field and subjects were asked to judge whether these words were categorically related or not. In the phonological task, the same subjects were asked to decide whether pairs of orthographically dissimilar words rhymed or not. Statistical analysis showed that reaction times (RT) were significantly shorter in both tasks when words were presented to the right visual field. Furthermore, in the semantic task, faster responses were observed in both visual fields when the words were related than when they were unrelated. This response facilitation tended to be stronger when words were presented to the left visual field. This result is in accordance with other results obtained by lexical decision studies showing that priming in the right hemisphere is due to controlled processing. By contrast, RT differences between rhyming and non-rhyming word pairs in the phonological task did not reach significance. This supports previous findings showing that phonological facilitation cannot occur when orthographic and phonological indices are in conflict.     

Word semantics is processed even without attentional effort

We examined the attentional modulation of semantic priming and the N400 effect for spoken words. The aim was to find out how the semantics of spoken language is processed when attention is directed to another modality (passive task), to the phonetics of spoken words (phonological task), or to the semantics of spoken words (word task). Equally strong behavioral priming effects were obtained in the phonological and the word tasks. A significant N400 effect was found in all tasks. The effect was stronger in the word and the phonological tasks than in the passive task, but there was no difference in the magnitude of the effect between the phonological and the word tasks. The latency of the N400 effect did not differ between the tasks. Although the N400 effect had a centroparietal maximum in the phonological and the word tasks, it was largest at the parietal recording sites in the passive task. The effect was more pronounced at the left than right recording sites in the phonological task, but there was no laterality effect in the other tasks. The N400 effect in the passive task indicates that semantic priming occurs even when spoken words are not actively attended. However, stronger N400 effect in the phonological and the word tasks than in the passive task suggests that controlled processes modulate the N400 effect. The finding that there were no differences in the N400 effect between the phonological and the word tasks indicates that the semantics of attended spoken words is processed regardless of whether semantic processing is relevant for task performance.     

Effects of Task Structure on Category Priming in Patients With Parkinson's Disease and in Healthy Individuals

Lexical decision tasks have been used to study both shifts of attention and semantic processing in Parkinson's Disease (PD). Whereas other laboratories have reported normal levels of semantic priming among PD patients, our laboratory has reported abnormally large levels. In this study, two experiments were performed to determine the influence of task structure on the extent of semantic priming during lexical decision-making and pronunciation tasks among PD patients and neurologically healthy controls. In Experiment 1, the effect of Prime Dominance (the ratio of category to neutral trials) on lexical decision-making was studied. Although equal numbers of word and nonword trials were presented, half of the PD patients and controls were studied under Category Prime Dominance (category : neutral prime ratio of 2:1) and half were studied under Neutral Prime Dominance (category : neutral prime ratio of 1:2). In Experiment 2, PD and control participants were studied on lexical decision-making and pronunciation tasks where twice as many words as nonword trials were presented, consistent with other studies from our laboratory. In Experiment 1, we found no group differences in the magnitude of priming and no effect of Prime Dominance. Moreover, the findings were similar in pattern and magnitude to results published by Neely (1977). In Experiment 2, we observed larger priming effects among PD patients than among controls, but only on the lexical decision (LD) task. These results support the hypothesis that abnormally large category-priming effects appear in LD studies of PD patients when the number of word trials exceeds the number of nonword trials. Furthermore, increased lexical priming in PD appears to be due to processes operating during the decision-making period that follows presentation of the lexical target.     

Effects of task structure on category priming in patients with Parkinson's disease and in healthy individuals

Lexical decision tasks have been used to study both shifts of attention and semantic processing in Parkinson's Disease (PD). Whereas other laboratories have reported normal levels of semantic priming among PD patients, our laboratory has reported abnormally large levels. In this study, two experiments were performed to determine the influence of task structure on the extent of semantic priming during lexical decision-making and pronunciation tasks among PD patients and neurologically healthy controls. In Experiment 1, the effect of Prime Dominance (the ratio of category to neutral trials) on lexical decision-making was studied. Although equal numbers of word and nonword trials were presented, half of the PD patients and controls were studied under Category Prime Dominance (category : neutral prime ratio of 2:1) and half were studied under Neutral Prime Dominance (category : neutral prime ratio of 1:2). In Experiment 2, PD and control participants were studied on lexical decision-making and pronunciation tasks where twice as many words as nonword trials were presented, consistent with other studies from our laboratory. In Experiment 1, we found no group differences in the magnitude of priming and no effect of Prime Dominance. Moreover, the findings were similar in pattern and magnitude to results published by Neely (1977). In Experiment 2, we observed larger priming effects among PD patients than among controls, but only on the lexical decision (LD) task. These results support the hypothesis that abnormally large category-priming effects appear in LD studies of PD patients when the number of word trials exceeds the number of nonword trials. Furthermore, increased lexical priming in PD appears to be due to processes operating during the decision-making period that follows presentation of the lexical target.     

Unimpaired automatic processing of verbal information in the course of clinical depression

In this study automatic processing of verbal information was investigated in 22 clinically depressed inpatients and 22 healthy controls in a longitudinal design. A semantic priming task with word pronunciation was administered twice, about 7 weeks apart. Following brief presentations of prime words, subjects had to read target words aloud as quickly as possible. Prime words were directly related, indirectly related, or unrelated to the target words. Stimulus onset asynchrony (SOA) of prime and target was 250 ms. In the course of inpatient treatment, patients recovered significantly. Semantic priming occurred in both study groups for the directly and indirectly related conditions across both testing times. As expected, directly related primes resulted in stronger priming than indirectly related primes. Patients and controls did not differ in semantic priming at either time or relatedness condition. Size of priming was not associated with depression severity, anxiety level, intelligence, medication, or clinical features. We conclude that depression is not characterized by dysfunctional automatic processing of verbal information.     

The effects of inter-stimulus interval and prime modality in a semantic priming task

Background: Semantic priming studies are employed in order to examine how various semantic contexts can influence visual word recognition processes. Although research has shown numerous factors can have an influence on the magnitude of the semantic priming effects found in lexical decision tasks, the majority of these factors have been related to the prime–target relationship itself. However, other factors have also been shown to alter the priming effect. Two such factors are the inter-stimulus interval (ISI) and presentation modality. The inter-stimulus interval may be used to independently assess automatic and strategic processes, whereas presentation modality is typically used to assess the different processing time courses that occur with spoken or written words. These factors have not been adequately investigated in the normal population. A more in-depth understanding of the relationships between prime modality, inter-stimulus interval, and word recognition processes in a sample of individuals with typical language abilities may provide valuable when examining lexical access and storage in language disordered populations such as those with aphasia.

Aims: The focus of the present study was to examine the impact of relatively short and long inter-stimulus intervals on processing time in a visual and cross-modal lexical decision task. Previous research has not fully addressed whether convergent processes occur during cross-modal tasks or if an amodal semantic system exists. The utilisation of slow and fast inter-stimulus intervals should allow for a clearer distinction relative to processing.

Methods & Procedures: A series of four lexical decision tasks was used to investigate reaction time and accuracy. The four tasks resulted from the combination of the independent variables ISI (0 ms or 400 ms) and prime modality (auditory or visual).

Outcomes & Results: Results indicated that participants exhibited a larger priming effect when stimuli were presented in the 0 ms condition. Results also indicated that participants responded more accurately when the target word was presented auditorily.

Conclusions: It was concluded that automatic spreading activation occurred in both the visual and auditory modalities, providing further evidence of an amodal semantic system. These observations are helpful in developing a clearer understanding of lexical storage and access in language impairments such as aphasia.     

Semantic category fluency versus initial letter fluency over 60 seconds as a measure of automatic and controlled processing in healthy school-aged children

Verbal fluency was operationalized as the number of words produced in a restricted category (i.e., semantic category [SCF] and words beginning with a given letter [ILF]) in 60 seconds. Word production in the first 15 seconds of either type of fluency task was defined as a measure of automatic information processing, whereas word production in the remaining 45 seconds (in 15-second periods) was taken as a measure of controlled information processing. Data revealed that over 60 seconds healthy children aged 8.4-9.7 years (n = 91) produced significantly more words and less incorrect responses on the SCF task than on the ILF task. Although word production was a function of both type of task and time, it was highest in the initial time slice of either type of fluency and decreased as time on task increased. Finally, no sex differences were found for any measure of performance on either type of fluency task. In contrast, the level of occupational achievement of the caregiver (LOA) appeared to be a determinant of the child's performance on either type of fluency task, indicating that LOA affects higher-order processes, such as the automation of newly learned verbal skills and effortful processing.     

Another look at categorical priming in the cerebral hemispheres.

This study investigated the effect of exemplar dominance on semantic priming in the left and right visual fields for words that are members of the same category, but not strongly associated. A low proportion of related primes was employed in lexical decision and word pronunciation tasks to assess the automatic activation of word meanings in each cerebral hemisphere. Priming was reliably obtained only in the LVF/right hemisphere. In addition, this effect did not vary with category dominance of the prime:equivalent LVF priming was observed for ROBIN-CROW (high dominant) and DUCK-CROW (low dominant) pairs. These findings support the view that a broader range of related meanings is activated during word recognition in the right, than in the left, hemisphere.     

Neural evidence for faster and further automatic spreading activation in schizophrenic thought disorder

It has been proposed that the loose associations characteristic of thought disorder in schizophrenia result from an abnormal increase in the automatic spread of activation through semantic memory. We tested this hypothesis by examining the time course of neural semantic priming using event-related potentials (ERPs). ERPs were recorded to target words that were directly related, indirectly related, and unrelated to their preceding primes, while thought-disordered (TD) and non-TD schizophrenia patients and healthy controls performed an implicit semantic categorization task under experimental conditions that encouraged automatic processing. By 300-400 milliseconds after target word onset, TD patients showed increased indirect semantic priming relative to non-TD patients and healthy controls, while the degree of direct semantic priming was increased in only the most severely TD patients. By 400-500 milliseconds after target word onset, both direct and indirect semantic priming were generally equivalent across the 3 groups. These findings demonstrate for the first time at a neural level that, under automatic conditions, activation across the semantic network spreads further within a shorter period of time in specific association with positive thought disorder in schizophrenia.     

Amnesic patients' impaired category exemplar production priming.

This study examined the effect of varying the number of potential target words on amnesic patients' category exemplar production performance. In Experiment 1, 4 words from each of 6 categories were presented to amnesic patients and normal control participants. This was followed by an indirect task in which each participant produced the first 8 words that came to mind when presented with a category cue. On this task the amnesic patients were impaired. This outcome stands in sharp contrast to most other category exemplar production tasks that have been reported. However, these other paradigms tend to restrict participants' processing during target item presentation while our procedure allowed them to analyze the target words as they chose. Our procedure may have allowed the control participant more opportunity to "cluster" target words from the same category during list presentation and this, in turn, may have given them an advantage at the time of category exemplar production. Therefore, in Experiment 2, only 1 word per category was presented in the target list and only 2 words per category were requested during category exemplar production. Surprisingly, the amnesic patients still exhibited impaired performance. Therefore, it was suggested that perhaps amnesic patients' known inability to perform semantic levels of processing during individual target word presentation may have resulted in impaired priming for categorical features for these patients.     

Depth-of-processing effects on semantic activation deficits in schizophrenia: an electrophysiological investigation

N400, an event-related brain potential (ERP) waveform elicited by meaningful stimuli, is normally reduced (made less negative) by relatedness between the eliciting stimulus and preceding ones (N400 semantic priming). Schizophrenia patients' N400 semantic priming deficits suggest impairment in using meaningful context to activate related concepts in semantic memory. We aimed to examine the degree to which this impairment can be ameliorated by task instructions that more explicitly require processing of stimulus meaning. We recorded ERPs from 16 schizophrenia patients and 16 controls who viewed prime words each followed at 750-ms stimulus-onset asynchrony by an unrelated or related target word, or a nonword, in a non-semantic task (indicating whether a letter occurred in the target) compared to an explicit semantic task (judging prime-target relatedness). Consistent with previous work, controls exhibited greater N400 semantic priming (larger amplitude reductions for related versus unrelated targets) in the semantic task than in the orthographic task. Schizophrenia patients showed this same pattern, although their N400 semantic priming effects were smaller than controls' across tasks. Nevertheless, patients' priming effects increased as much as did controls' from the orthographic to the semantic task. Thus, connections among related concepts in schizophrenia patients' semantic memory appear grossly intact, such that, given a meaningful stimulus, they can make use of explicit cues to activate related concepts at a neurophysiological level, although their ability to do so remains less than normal. These data provide support for further research on semantic-cueing strategies for cognitive remediation of verbal memory in schizophrenia.     

Gamma band synchronization and the formation of representations in visual word processing: evidence from repetition and homophone priming

The formation of an object's cortical representation seems to rely on synchronized neuronal activity within the gamma band frequency range (gamma band activity [GBA]). In this study, we investigated whether electroencephalogram (EEG) GBA, and its phase synchronization between electrodes, is necessary for the formation of nonobject higher-order cognitive representations, using both repetition and homophone priming tasks. In a repetition priming task, the formation of orthographic, phonological, and semantic representations is promoted by a prime word, whereas in the homophone priming task, the formation of only phonological representations is promoted. In the present study, the lexical processing of a target word induced GBA. In the repetition priming task, induced GBA and phase synchronization were decreased by presentation of the prime word (i.e., a repetition suppression effect) within both 200-300 msec and 400-500 msec time windows. In the homophone priming task, the repetition suppression effect was observed only within the 400-500 msec time window. The fact that repetition suppression effects were found in both priming tasks indicates that GBA and phase synchronization are necessary for the formation of phonological and semantic representations of a word. These results also suggest that formation of orthographic and higher-order cognitive representations occurred over different time courses.     

Explicit semantic tasks are necessary to study semantic priming effects with high rates of repetition

ObjectiveThe purpose of the present study was to clarify in which experimental conditions the semantic processing of repeated words is preserved.MethodsWe contrasted a short (250 ms) and a long (1000 ms) stimulus onset asynchrony (SOA) in two different experiments, using a relatively low proportion of related words (30%). One group of participants performed a lexical decision task (LDT) and a second group performed an explicit semantic matching task with the same words (except for pseudowords) and the same task parameters. In both tasks, word stimuli consisted solely of two prime and two target words repeated throughout the experiment.ResultsThe effects of semantic priming on reaction time (RT) and the amplitude of the N400 ERP were absent for both the short and the long SOA in the LDT. In contrast, in the explicit semantic task, these effects were significant. In this task, the activity of N400 generators in the left superior temporal gyrus and the inferior parietal cortex significantly differentiated primed and unprimed trials but this effect did not interact with SOA.ConclusionsOur results indicate that task instruction is critical to preserve semantic processing with repeated presentations.SignificanceUsing explicit semantic designs, it may be possible to study associative or categorical relations between individual concepts.     

Lexical and semantic priming deficits in patients with Alzheimer's disease

Two experiments utilizing priming procedures examined the status of semantic memory in demented and amnesic patients. In the first investigation, lexical priming was assessed in patients with dementia of the Alzheimer type (DAT), Huntington's Disease (HD), alcoholic Korsakoff's syndrome (KS), and in intact control subjects. Subjects were first exposed to a list of words in a rating task and then required to complete three-letter stems with the "first word that comes to mind". Half of the stems could be completed with the previously presented words and the other half were used to assess baseline guessing rates. Recall and recognition of incidentally exposed words was also assessed. Although all three patient groups were impaired on tests of recall and recognition, only the DAT patients exhibited a priming deficit on the stem-completion task. In the second experiment, DAT, HD, and intact control subjects were administered a semantic priming test which required the subject to "free associate" to the first words of previously presented semantically associated word pairs. The results for this association task showed that DAT patients were significantly less likely to produce the second word of the semantically related pair than were the other subject groups. The results of these two experiments suggest that the memory capacities of DAT patients are characterized by a breakdown in the structure of semantic memory and that this impairment is evident on some "automatic" as well as "effortful" processing tasks.     

Lack of inhibition in Parkinson's disease: evidence from a lexical decision task

Persons affected by Parkinson's disease (PD) often show an increased semantic priming effect from target words in lexical decision tasks (hyper-priming) as compared to age-matched controls. In this study, a lexical decision task was used to investigate both semantic priming (Experiment 1) and repetition priming (Experiment 2) from distractor words in PD patients and age-matched controls. With this negative priming procedure, target words in successive trials are never related, and therefore participants always have to switch between unrelated target words. Instead, it is the distractor prime word that is either related or unrelated to the subsequent target, giving the measure of priming. Results showed that PD patients demonstrated a robust effect of positive semantic priming from distractor words. Participants from the control group did not show any semantic priming effect (positive or negative) from distractors. Similarly, PD patients showed positive repetition priming from distractor words, but the control group showed significant repetition negative priming. These results support the view that the hyper-priming effect typically shown by persons with Parkinson's disease is the result of impaired inhibitory processes required to control word activation during reading.     

Automatic processing in mildly retarded and nonretarded persons

ABSTRACT. Mildly retarded adults, equal mental age nonretarded children, high mental age nonretarded children, equal chronological age nonretarded adults and young nonretarded adults were required to perform a priming task (letters/digits) in which some primes were masked (visual noise mask) at just below detection levels to assess automatic processing. The critical (just below detection level) prime-mask stimulus onset asynchronies (SOAs) were established individually for each subject using the method of limits and reassessed after the experimental trials. The mean critical SOA for each of the five groups was comparable and the critical SOAs remained stable across the 120 experimental trials for all groups. The nonretarded adult subjects demonstrated semantic, categorical and orthographic priming. The mildly retarded, the equal-MA and the high-MA groups failed to demonstrate priming, and in fact, demonstrated superior performance for prime-target conditions which should have been poorest. This finding was discussed in terms of the level of specificity engendered in the priming task. Under the mask procedure, the nonretarded adult groups demonstrated semantic (letter) priming and orthographic priming, suggesting that letters (not digits) function as an analog to words which were employed in earlier masked prime lexical decision tasks. The mentally retarded, the equal-MA and the high-MA groups again failed to demonstrate priming under the mask procedure