An investigation of neuronal integrity in severe paediatric traumatic brain injury.

Magnetic Resonance Spectroscopy (MRS) and its association with neuropsychological functioning was examined in the chronic injury phase of paediatric traumatic brain injury (TBI). Fifteen children, aged 10-16 years, with severe TBIs were compared with 15 controls, matched for age and gender. The TBI group was found to have significantly lower levels of -acetyl aspartate (NAA) and Choline (Cho) in the right frontal lobe and generally displayed reduced performances on neuropsychological tests. A correlation between metabolites and reaction times was also obtained. Findings indicate a role of proton MRS as a measure of neuronal integrity following severe paediatric TBI and suggest a potential association of MRS with specific neuropsychological impairments.     

Neurobehavioral deficits,adolescent traumatic brain injury,and transition to college

Outcome following traumatic brain injury (TBI) has been frequently evaluated for adults, although there has been minimal research on adolescents with TBI. It has been argued that TBI sequelae may be more difficult for adolescents to adjust to given developmental changes in physical (puberty), interpersonal (self-concept), and environmental domains (transition to college). In addition, it is commonly acknowledged that moderator variables such as psychiatric history, family functioning, substance use, and sexuality impact functional outcome following TBI, although it is often difficult to objectively evaluate these variables. The current study examined relationships among TBI-related deficits, moderator variables, and academic outcomes for six adolescents transitioning to college. The findings suggest that it may not be appropriate to predict functional outcome based solely on objective neuropsychological results. However, moderator variables appear to have a more direct relationship with outcome, depending on the moderator variable and the individual.     

Locus of semantic priming effects in speeded naming

The locus of semantic priming effects was examined by measuring onset and rime durations as well as response latencies of words with consistent and inconsistent pronunciations, using the postvocalic naming task. We found that the effect of a semantic prime on naming duration was localized rather than spread across the entire word; onset durations were shorter in the related condition than in the unrelated condition, but rime durations were equal in the two prime conditions. Moreover, the priming effect on onset durations was larger for words with inconsistent than for those with consistent pronunciations. These duration results cannot be accounted for by previous proposals, but they can be accounted for by models in which phonemes are activated in parallel rather than serially from left to right and in which motor programs are based on phonemes rather than syllables. Contrary to previous reports of an interaction of prime and regularity (a factor closely related to consistency) on naming latency, we found no interaction of prime and consistency on response latency. We argue that this conflict is only apparent and arises because naming latency conflates response latency and initial phoneme duration for some targets.     

Word-frequency effects in long-term semantic priming and false memory

Several studies have used the lexical decision task (LDT) with the Deese-Roediger-McDermott (DRM) false-memory paradigm to investigate whether long-term semantic priming (LTSP) occurs following presentation of lists of items (e.g., bed, dream, snore) for related non-presented lure words (e.g., sleep). However, results have been mixed, with some studies observing priming, whilst others have not. The present study had four goals: (i) to investigate the existence of LTSP in the LDT; (ii) to investigate effects of LTSP on standard effects of word frequency on LDT performance; (iii) to investigate the effect, if any, of word frequency on true and false recall; and (iv) to compare LDT performance with performance on a subsequent free-recall task. The findings showed (i) a significant effect of LTSP on LDT performance; (ii) no effect of LTSP on standard effects of word frequency on LDT performance; (iii) no effect of word frequency on either true or false free recall; and (iv) a significant relationship between LDT and free-recall performance. Implications of these findings for understanding LTSP and false memories are discussed.     

N200, N250r, and N400 event-related brain potentials reveal three loci of repetition priming for familiar names

The authors assessed immediate repetition effects on event-related potentials (ERPs) while participants performed familiarity decisions for written personal names. For immediately repeated familiar names, the authors observed 3 distinct ERP modulations. At 180-220 ms, a posterior N200 effect occurred for names preceded by same-font primes only. In addition, an increased left temporal negativity (N250r, 220-300 ms) and a reduced central-parietal negativity (N400, 300-400 ms) were seen both for same-font and different-font repetitions. In a 2nd experiment, when names were preceded by either their corresponding face or the face of a different celebrity, only the N400 effect was preserved. These findings suggest that the N200, N250r, and N400 effects reflect facilitated processing at font-specific featural, lexical, and semantic levels of processing, respectively.     

The locus of semantic priming effects in person recognition

Semantic priming in person recognition has been studied extensively. In a typical experiment, participants are asked to make a familiarity decision to target items that have been immediately preceded by related or unrelated primes. Facilitation is usually observed from related primes, and this priming is equivalent across stimulus domains (i.e., faces and names prime one another equally). Structural models of face recognition (e.g., IAC: Burton, Bruce, & Johnston, 1990) accommodate these effects by proposing a level of person identity nodes (PINs) at which recognition routes converge, and which allow access to a common pool of semantics. We present three experiments that examine semantic priming for different decisions. Priming for a semantic decision (e.g., British/American?) shows exactly the same pattern that is normally observed for a familiarity decision. The pattern is equivalent for name and face recognition. However, no semantic priming is observed when participants are asked to make a sex decision. These results constrain future models of face processing and are discussed with reference to current theories of semantic priming.     

Priming effects on the N400 in the affective priming paradigm with facial expressions of emotion

We studied the effect of facial expression primes on the evaluation of target words through a variant of the affective priming paradigm. In order to make the affective valence of the faces irrelevant to the task, the participants were assigned a double prime–target task in which they were unpredictably asked either to identify the gender of the face or to evaluate whether the word was pleasant or unpleasant. Behavioral and electrophysiological (event-related potential, or ERP) indices of affective priming were analyzed. Temporal and spatial versions of principal components analyses were used to detect and quantify those ERP components associated with affective priming. Although no significant behavioral priming was observed, electrophysiological indices showed a reverse priming effect, in the sense that the amplitude of the N400 was higher in response to congruent than to incongruent negative words. Moreover, a late positive potential (LPP), peaking around 700 ms, was sensitive to affective valence but not to prime–target congruency. This pattern of results is consistent with previous accounts of ERP effects in the affective priming paradigm that have linked the LPP with evaluative priming and the N400 with semantic priming. Our proposed explanation of the N400 priming effects obtained in the present study is based on two assumptions: a double check of affective stimuli in terms of valence and specific emotion content, and the differential specificities of facial expressions of positive and negative emotions.     

Phonological and semantic priming: Evidence for task-independent effects

The questions asked in the present experiments concern the generality of semantic and phonological priming effects: Do these effects arise automatically regardless of target task, or are these effects restricted to target tasks that specifically require the retrieval of the primed information? In Experiment 1, subjects produced faster color matching times on targets preceded by a masked rhyming prime than on targets preceded by an orthographic control or an unrelated prime. This result suggests that automatic priming effects on the basis of phonological similarity can be obtained even when the target task does not make use of phonological information. This claim was reinforced in Experiment 2 in which a rhyme priming effect and a semantic priming effect were found in a semantic categorization task. In Experiment 3, the target task was phonological (rhyme detection), and, again, both phonological and semantic priming effects were observed. Finally, in Experiments 4 and 5, in a replication and an extension of Experiment 1, phonological and semantic priming effects were found in a color matching task, a task involving neither phonological nor semantic processing. These results are most straightforwardly interpreted by assuming that both semantic and phonological priming effects are, at least in part, due to automatic activation of memorial representations.     

Automatic semantic activation is no myth: semantic context effects on the N400 in the letter-search task in the absence of response time effects

The claim that semantic activation is an automatic process was recently called a myth, on the basis of the finding that if letter search is performed on a prime word, semantic priming effects on response time are eliminated, whereas repetition effects are preserved. The absence of semantic activation, however, cannot be validly inferred from the lack of response time effects, and converging evidence is needed. To this end, we examined the event-related potential correlate of priming, the N400 amplitude modulation, in a letter-search priming paradigm. Our experiment replicated the response time effects and demonstrated that the N400 amplitude successfully differentiates cross-case repetition priming, semantic priming, and neutral conditions. The results clearly indicate that the meaning of the prime word was processed and that semantic activation indeed was present in the letter-search task. The notion that semantic activation is an automatic process should not be abandoned prematurely.     

ERPs and morphological processing: the N400 and semantic composition

Both behavioral and electrophysiological evidence suggests that fluent readers decompose morphologically complex words into their constituent parts. Previous event-related potential (ERP) research has been equivocal with regard to whether the N400 component indexes morphological decomposition or the integration of the products of decomposition, a process called semantic composition. In a visual lexical decision task with college students, we recorded ERPs to a well-controlled set of words and nonwords made up of bound morphemes (discern, predict; disject, percern) or free morphemes (cobweb, earring; cobline, bobweb) and monomorphemic control words and nonwords (garlic, minnow; gartus, buzlic). For each of the three morphological types, participants were faster to respond to words than to nonwords. Furthermore, for each of the three morphological types, the amplitude of the N400 was more negative to nonwords than to matched words, an effect indicating that the N400 is more sensitive to the lexicality of the whole stimulus than to the meaningfulness of the constituent parts of the stimulus. The N400 lexicality effect was not significantly different across the three morphological types. To our knowledge, this is the first ERP study to directly compare the processing of printed sets of words composed of bound and free morphemes and monomorphemic control stimuli in order to explore the relative sensitivity of the N400 to morphological decomposition (i.e., the status of the parts) and semantic composition (i.e., the status of the whole). Our findings are consistent with an interpretation of the N400 as an index of a process of semantic composition.     

Category size effects revisited: frequency and masked priming effects in semantic categorization

Previous work indicates that semantic categorization decisions for nonexemplars (e.g., deciding that TURBAN is not an animal name) are faster for high-frequency words than low-frequency words. However, there is evidence that this result might depend on category size. When narrow categories are used (e.g., Months, Numbers), there is no frequency effect for nonexemplars. This result is confirmed, and is explained in terms of a category search model, which allows a "No" decision to be generated without access to the lexical entry for the target word. This explains the absence of a frequency effect, but not the presence of a strong masked repetition priming effect, which is assumed to have a lexical source. It is shown that this effect may not be lexical, since nonwords also show similar priming. Both of these priming effects disappear when a larger category is used. This pattern of results is explained on the assumption that category search is only possible with small categories, and that tentative category decisions are generated for the unconsciously perceived prime, which leads to a marked response congruence effect.     

Neurobehavioural profile following cumulative mild traumatic brain injury in adolescent rugby players in South Africa

The study investigated the neurobehavioural components of executive dysfunction following sport-related Mild Traumatic Brain Injury (MTBI) in Grade 12 adolescent rugby players over a rugby season. In a non-equivalent quasi-experimental design, a rugby group (n?=?90) were compared with demographically equivalent noncontact sport controls (n?=?59). The Behaviour Rating Inventory of Executive Functions – Self Report (BRIEF-SR) was employed to assess the neurobehavioural component of executive functions. Independent and dependent t-test analyses were conducted to compare the groups at baseline and end-of-season intervals. The overall findings suggest more pronounced deleterious effects on executive functioning from exposure to the concussive and sub-concussive events among the rugby group. High school rugby players experience adverse neurobehavioural effects in executive dysfunction from contact rugby sport injuries.     

Age-related differences in semantic priming: evidence from event-related brain potentials

Hasher and Zacks (1988) suggested that aging may affect processes involved in the inhibition of irrelevant information during language processing. Our experiment tested this hypothesis using the N400 event-related brain potential in a priming paradigm and assessed whether older subjects could benefit from the constraints of a sentence context. Twenty older (63 to 88 years) and 20 young (19 to 29 years) subjects read sentences and word pairs. Each final word varied on the degree of relatedness to the preceding context, with some being highly related (BC), moderately related (R), or unrelated (U). Younger subjects showed the expected N400 effect gradient (U > R > BC) in both the sentence and word-pair contexts, while older adults showed no discrimination between the conditions (U = R = BC) for the sentence and limited discrimination (U > BC) for the word pairs. These results support the inhibition-deficit hypothesis, whereby older adults fail to inhibit related items in working memory, and suggest that older adults do not benefit from the constraints of a sentence context.     

Severe traumatic brain injury: some effects on family caregivers

This study assesses the effects of severe traumatic brain injuries on family members and functioning-a topic of interest for those working with survivors and their families. This issue is receiving increased attention as recent findings suggest that family adjustment influences outcome for brain-injured persons. The Family Environment Scale and the Profile of Mood States were completed by 25 individuals who had a family member with a severe traumatic brain injury. These scales were also completed by a comparison group of 32 individuals who had no brain-injured family member. In terms of family functioning, the findings suggest that, when a family member suffers a severe traumatic brain injury, depression may be elevated, along with a decreased ability to express feelings, decreased time and energy for social and recreational activities, and increased control in comparison to families without a brain-injured member. While this might contribute to family isolation which could last for many years, the overall finding of the present study was that caregiver families were coping adequately.     

The effects of associative and semantic priming in the lexical decision task

Four lexical decision experiments were conducted to examine under which conditions automatic semantic priming effects can be obtained. Experiments 1 and 2 analyzed associative/semantic effects at several very short stimulus-onset asynchronies (SOAs), whereas Experiments 3 and 4 used a single-presentation paradigm at two response-stimulus intervals (RSIs). Experiment 1 tested associatively related pairs from three semantic categories (synonyms, antonyms, and category coordinates). The results showed reliable associative priming effects at all SOAs. In addition, the correlation between associative strength and magnitude of priming was significant only at the shortest SOA (66 ms). When prime-target pairs were semantically but not associatively related (Experiment 2), reliable priming effects were obtained at SOAs of 83 ms and longer. Using the single-presentation paradigm with a short RSI (200 ms, Experiment 3), the priming effect was equal in size for associative + semantic and for semantic-only pairs (a 21-ms effect). When the RSI was set much longer (1,750 ms, Experiment 4), only the associative + semantic pairs showed a reliable priming effect (23 ms). The results are interpreted in the context of models of semantic memory.     

Sexual offenses and traumatic brain injury

A sample of 476 male sexual offenders, seen at a university psychiatric hospital for forensic assessment, was examined for the incidence of traumatic head injuries. A total of 49.3% had sustained head injuries that led to unconsciousness and of these 22.5% sustained significant neurological insults. A major causative factor was motor vehicle accidents, but lifestyle variables including alcohol and drug abuse and history of violence also contributed. The brain-injured group was convicted for a wide range of sexual offenses and was comparable to the non-injured group in this respect, but tended more often to offend against adults than against children and to show somewhat more exhibiting and polymorphous sexual behavior. In spite of the serious legal implications for these men and the additional distress to their families, psychologists, psychiatrists, and the professional literature have been relatively silent on the subject which calls for more attention to sexual behavior as part of assessments and treatment planning.     

Masked priming effects in semantic categorization are independent of category size

The question whether subliminal primes can activate their semantic meaning or not is still of interest today. Three different competing theories have tried to account for the often inconsistent research results: The semantic categorization hypothesis, the direct motor specification hypothesis, and the category search model. The present study aimed to shed light on these different points of view by examining the role of category size in response congruency effects when novel primes are used. Three experiments were conducted and a transparent pattern of results emerged: Significant priming effects were obtained across different tasks, irrespective of category size and irrespective of stimulus set size. The findings are discussed in terms of the three theoretical frameworks. It becomes clear that the present results provide strong evidence in favor of the semantic categorization hypothesis, which assumes semantic processing of subliminal primes.     

Pretrial EEG coherence as a predictor of semantic priming effects

Twenty subjects were presented 240 randomized trials of a lexical decision task (LDT) while connected to a 16-electrode EEG montage. EEG data were acquired for 2 sec prior to the onset of each LDT trial. Alpha (9-13 Hz) coherence, alpha power, and 3- to 30-Hz power from five different combinations of EEG electrodes were used to predict semantic effects in the LDT trials. High pretrial coherence in the Right Hemisphere and Left Posterior-Parietal regions was associated with greater semantic facilitation (faster reaction times) in related-prime trials and greater semantic inhibition (slower reaction times) in unrelated-prime trials, relative to neutral-prime trials. No power variables were associated with semantic effects. Results support an information flow model of the functional significance of EEG coherence to cognitive processing.     

The (un)reliability of item-level semantic priming effects

Many researchers have tried to predict semantic priming effects using a myriad of variables (e.g., prime–target associative strength or co-occurrence frequency). The idea is that relatedness varies across prime–target pairs, which should be reflected in the size of the priming effect (e.g., cat should prime dog more than animal does). However, it is only insightful to predict item-level priming effects if they can be measured reliably. Thus, in the present study we examined the split-half and test–retest reliabilities of item-level priming effects under conditions that should discourage the use of strategies. The resulting priming effects proved extremely unreliable, and reanalyses of three published priming datasets revealed similar cases of low reliability. These results imply that previous attempts to predict semantic priming were unlikely to be successful. However, one study with an unusually large sample size yielded more favorable reliability estimates, suggesting that big data, in terms of items and participants, should be the future for semantic priming research.