Capturing multiple interaction effects in L1 and L2 object-naming reaction times in healthy bilinguals: a mixed-effects multiple regression analysis.

BACKGROUND: It is difficult to set up a balanced higher-order full-factorial experiment that can capture multiple intricate interactions between cognitive and psycholinguistic factors underlying bilingual speech production. To capture interactions more fully in one study, we analyzed object-naming reaction times (RTs) by using mixed-effects multiple regression. METHODS: Ten healthy bilinguals (median age: 23 years, seven females) were asked to name 131 colored pictures of common objects in each of their languages. RTs were analyzed based on language status, proficiency, word choice, word frequency, word duration, initial phoneme, time series, and participant's gender. RESULTS: Among five significant interactions, new findings include a facilitating effect of a cross-language shared initial phoneme (mean RT for shared phoneme: 974 ms vs. mean RT for different phoneme: 1020 ms), which profited males less (mean profit: 10 ms) than females (mean profit: 47 ms). CONCLUSIONS: Our data support language-independent phonological activation and a gender difference in inhibitory cognitive language control. Single word production process in healthy adult bilinguals is affected by interactions among cognitive, phonological, and semantic factors.

Reorganization of Motor Representations in Patients with Brain Lesions: A Navigated Transcranial Magnetic Stimulation Study.

This is an explorative study applying presurgical navigated transcranial magnetic stimulation (nTMS) to investigate the spatial distributions of motor sites to reveal tumor-induced brain plasticity in patients with brain tumors. We analyzed nTMS-based motor maps derived from presurgical mapping of 100 patients with motor eloquently located brain tumors (tumors in the frontal lobe, the precentral gyrus [PrG], the postcentral gyrus [PoG], the remaining parietal lobe, or the temporal lobe). Based on these motor maps, we systematically investigated changes in motor evoked potential (MEP) counts among 4 gyri (PrG, PoG, medial frontal gyrus, and superior frontal gyrus) between subgroups of patients according to the tumor location in order to depict the tumor's influence on reorganization. When comparing patients with different tumor locations, high MEP counts were elicited less frequently by stimulating the PrG in patients with tumors directly affecting the PrG (p < 0.05). Still, in more than 50% of these patients, the MEP counts elicited by stimulating the PrG were higher than average, indicating robust motor representations within the primary motor cortex. In contrast, patients with PoG and parietal tumors primarily showed high MEP counts when stimulating the PoG (p < 0.10). The functional reorganization is not likely to induce a shift of motor function from the PrG to adjacent regions but rather leads to a reorganization within anatomical constraints, such as of the PoG. Thus, presurgical nTMS-based motor mapping sensitively depicted the tumor-induced plasticity of the motor cortex.

Non-invasive Mapping of Face Processing by Navigated Transcranial Magnetic Stimulation.

Background: Besides motor and language function, tumor resections within the frontal and parietal lobe have also been reported to cause neuropsychological impairment like prosopagnosia. Objective: Since non-navigated transcranial magnetic stimulation (TMS) has previously been used to map neuropsychological cortical function, this study aims to evaluate the feasibility and spatial discrimination of repetitive navigated TMS (rTMS) mapping for detection of face processing impairment in healthy volunteers. The study was also designed to establish this examination for preoperative mapping in brain tumor patients. Methods: Twenty healthy and purely right-handed volunteers (11 female, 9 male) underwent rTMS mapping for cortical face processing function using 5 Hz/10 pulses. Both hemispheres were investigated randomly with an interval of 2 weeks between mapping sessions. Fifty-two predetermined cortical spots of the whole hemispheres were mapped after baseline measurement. The task consisted of 80 portraits of popular persons, which had to be named while rTMS was applied. Results: In 80% of all subjects rTMS elicited naming errors in the right middle middle frontal gyrus (mMFG). Concerning anomia errors, the highest error rate (35%) was achieved in the bilateral triangular inferior frontal gyrus (trIFG). With regard to similarly or wrongly named persons, we observed 10% error rates mainly in the bilateral frontal lobes. Conclusion: It seems feasible to map the cortical face processing function and to generate face processing impairment via rTMS. The observed localizations are well in accordance with the contemporary literature, and the mapping did not interfere with rTMS-induced language impairment. The clinical usefulness of preoperative mapping has to be evaluated subsequently.

The variability of motor evoked potential latencies in neurosurgical motor mapping by preoperative navigated transcranial magnetic stimulation.

BACKGROUND: Recording of motor evoked potentials (MEPs) is used during navigated transcranial magnetic stimulation (nTMS) motor mapping to locate motor function in the human brain. However, factors potentially underlying MEP latency variability in neurosurgical motor mapping are vastly unknown. In the context of this study, one hundred brain tumor patients underwent preoperative nTMS-based motor mapping of the tumor hemisphere between 2010 and 2013. Fourteen predefined predictor variables were recorded, and MEP latencies of abductor pollicis brevis muscle (APB), abductor digiti minimi muscle (ADM), and flexor carpi radialis muscle (FCR) were analyzed using linear mixed-effect multiple regression analysis with the forward step-wise model comparison approach. RESULTS: Common factors (relevant to APB, ADM, and FCR) for MEP latency variability were gender, most likely due to body height, and antiepileptic drug (AED) intake. Muscle-specific factors (relevant to APB, ADM, or FCR) for MEP latency variability were resting motor threshold (rMT), tumor side, and tumor location. CONCLUSIONS: Based on a large cohort of neurosurgical patients, this study provides data on a wide range of clinical factors that may underlie MEP latency variability. The factors that significantly contributed to MEP latency variability should be standardly recorded and taken into consideration during neurosurgical motor mapping.

Cortical plasticity of motor-eloquent areas measured by navigated transcranial magnetic stimulation in patients with glioma.

OBJECTIVE The goal of this study was to obtain a better understanding of the mechanisms underlying cerebral plasticity. Coupled with noninvasive detection of its occurrence, such an understanding has huge potential to improve glioma therapy. The authors aimed to demonstrate the frequency of plastic reshaping, find clues to the patterns behind it, and prove that it can be recognized noninvasively using navigated transcranial magnetic stimulation (nTMS). METHODS The authors used nTMS to map cortical motor representation in 22 patients with gliomas affecting the precentral gyrus, preoperatively and 3-42 months postoperatively. Location changes of the primary motor area, defined as hotspots and map centers of gravity, were measured. RESULTS Spatial normalization and analysis of hotspots showed an average shift of 5.1 ± 0.9 mm (mean ± SEM) on the mediolateral axis, and 10.7 ± 1.6 mm on the anteroposterior axis. Map centers of gravity were found to have shifted by 4.6 ± 0.8 mm on the mediolateral, and 8.7 ± 1.5 mm on the anteroposterior axis. Motor-eloquent points tended to shift toward the tumor by 4.5 ± 3.6 mm if the lesion was anterior to the rolandic region and by 2.6 ± 3.3 mm if it was located posterior to the rolandic region. Overall, 9 of 16 (56%) patients with high-grade glioma and 3 of 6 (50%) patients with low-grade glioma showed a functional shift > 10 mm at the cortical level. CONCLUSIONS Despite the small size of this series, analysis of these data showed that cortical functional reorganization occurs quite frequently. Moreover, nTMS was shown to detect such plastic reorganization noninvasively.

Clinical Factors Underlying the Inter-individual Variability of the Resting Motor Threshold in Navigated Transcranial Magnetic Stimulation Motor Mapping.

Correctly determining individual's resting motor threshold (rMT) is crucial for accurate and reliable mapping by navigated transcranial magnetic stimulation (nTMS), which is especially true for preoperative motor mapping in brain tumor patients. However, systematic data analysis on clinical factors underlying inter-individual rMT variability in neurosurgical motor mapping is sparse. The present study examined 14 preselected clinical factors that may underlie inter-individual rMT variability by performing multiple regression analysis (backward, followed by forward model comparisons) on the nTMS motor mapping data of 100 brain tumor patients. Data were collected from preoperative motor mapping of abductor pollicis brevis (APB), abductor digiti minimi (ADM), and flexor carpi radialis (FCR) muscle representations among these patients. While edema and age at exam in the ADM model only jointly reduced the unexplained variance significantly, the other factors kept in the ADM model (gender, antiepileptic drug intake, and motor deficit) and each of the factors kept in the APB and FCR models independently significantly reduced the unexplained variance. Hence, several clinical parameters contribute to inter-individual rMT variability and should be taken into account during initial and follow-up motor mappings. Thus, the present study adds basic evidence on inter-individual rMT variability, whereby some of the parameters are specific to brain tumor patients.

Non-invasive mapping of calculation function by repetitive navigated transcranial magnetic stimulation.

Concerning calculation function, studies have already reported on localizing computational function in patients and volunteers by functional magnetic resonance imaging and transcranial magnetic stimulation. However, the development of accurate repetitive navigated TMS (rTMS) with a considerably higher spatial resolution opens a new field in cognitive neuroscience. This study was therefore designed to evaluate the feasibility of rTMS for locating cortical calculation function in healthy volunteers, and to establish this technique for future scientific applications as well as preoperative mapping in brain tumor patients. Twenty healthy subjects underwent rTMS calculation mapping using 5 Hz/10 pulses. Fifty-two previously determined cortical spots of the whole hemispheres were stimulated on both sides. The subjects were instructed to perform the calculation task composed of 80 simple arithmetic operations while rTMS pulses were applied. The highest error rate (80 %) for all errors of all subjects was observed in the right ventral precentral gyrus. Concerning division task, a 45 % error rate was achieved in the left middle frontal gyrus. The subtraction task showed its highest error rate (40 %) in the right angular gyrus (anG). In the addition task a 35 % error rate was observed in the left anterior superior temporal gyrus. Lastly, the multiplication task induced a maximum error rate of 30 % in the left anG. rTMS seems feasible as a way to locate cortical calculation function. Besides language function, the cortical localizations are well in accordance with the current literature for other modalities or lesion studies.

Cortical distribution of speech and language errors investigated by visual object naming and navigated transcranial magnetic stimulation.

Navigated transcranial magnetic stimulation (nTMS) gains increasing importance in presurgical language mapping. Although bipolar direct cortical stimulation (DCS) is regarded as the gold standard for intraoperative mapping of language-related areas, it cannot be used to map the healthy human brain due to its invasive character. Therefore, the present study employed a non-invasive virtual-lesion modality to provide a causality-confirmed cortical language map of the healthy human brain by repetitive nTMS (rTMS) with functional specifications beyond language-positive/language-negative distinction. Fifty right-handed healthy volunteers underwent rTMS language mapping of the left hemisphere combined with an object-naming task. The induced errors were categorized and frequency maps were calculated. Moreover, a principal component analysis (PCA) was performed on the basis of language-positive cortical regions for each error category. The left hemisphere was stimulated at 258-789 sites (median: 361.5 sites), and 12-241 naming errors (median: 72.5 errors) were observed. In male subjects, a total number of 2091 language errors were elicited by 9579 stimulation trains, which is equal to an error rate of 21.8 %. Within females, 10,238 stimulation trains elicited 2032 language errors (19.8 %). PCA revealed that the inferior parietal lobe (IPL) and middle frontal gyrus (MFG) were causally involved in object naming as a semantic center and an executive control center. For the first time, this study provides causality-based data and a model that approximates the distribution of language-related cortical areas grouped for different functional aspects of single-word production processes by PCA.

Task type affects location of language-positive cortical regions by repetitive navigated transcranial magnetic stimulation mapping.

OBJECTIVES: Recent repetitive TMS (rTMS) mapping protocols for language mapping revealed deficits of this method, mainly in posterior brain regions. Therefore this study analyzed the impact of different language tasks on the localization of language-positive brain regions and compared their effectiveness, especially with regard to posterior brain regions. METHODS: Nineteen healthy, right-handed subjects performed object naming, pseudoword reading, verb generation, and action naming during rTMS language mapping of the left hemisphere. Synchronically, 5 Hz/10 pulses were applied with a 0 ms delay. RESULTS: The object naming task evoked the highest error rate (14%), followed by verb generation (13%) and action naming (11%). The latter revealed more errors in posterior than in anterior areas. Pseudoword reading barely generated errors, except for phonological paraphasias. CONCLUSIONS: In general, among the evaluated language tasks, object naming is the most discriminative task to detect language-positive regions via rTMS. However, other tasks might be used for more specific questions.

Impairment of preoperative language mapping by lesion location: a functional magnetic resonance imaging, navigated transcranial magnetic stimulation, and direct cortical stimulation study.

OBJECT: Language mapping by repetitive navigated transcranial magnetic stimulation (rTMS) is increasingly used and has already replaced functional MRI (fMRI) in some institutions for preoperative mapping of neurosurgical patients. Yet some factors affect the concordance of both methods with direct cortical stimulation (DCS), most likely by lesions affecting cortical oxygenation levels. Therefore, the impairment of the accuracy of rTMS and fMRI was analyzed and compared with DCS during awake surgery in patients with intraparenchymal lesions. METHODS: Language mapping was performed by DCS, rTMS, and fMRI using an object-naming task in 27 patients with left-sided perisylvian lesions, and the induced language errors of each method were assigned to the cortical parcellation system. Subsequently, the receiver operating characteristics were calculated for rTMS and fMRI and compared with DCS as ground truth for regions with (w/) and without (w/o) the lesion in the mapped regions. RESULTS: The w/ subgroup revealed a sensitivity of 100% (w/o 100%), a specificity of 8% (w/o 5%), a positive predictive value of 34% (w/o: 53%), and a negative predictive value (NPV) of 100% (w/o: 100%) for the comparison of rTMS versus DCS. Findings for the comparison of fMRI versus DCS within the w/ subgroup revealed a sensitivity of 32% (w/o: 62%), a specificity of 88% (w/o: 60%), a positive predictive value of 56% (w/o: 62%), and a NPV of 73% (w/o: 60%). CONCLUSIONS: Although strengths and weaknesses exist for both rTMS and fMRI, the results show that rTMS is less affected by a brain lesion than fMRI, especially when performing mapping of language-negative cortical regions based on sensitivity and NPV.

Stimulation frequency determines the distribution of language positive cortical regions during navigated transcranial magnetic brain stimulation.

BACKGROUND: Although language mapping by repetitive navigated transcranial magnetic stimulation (rTMS) gains importance in neuropsychological research and clinical utility, neuroscientists still use different mapping protocols including different stimulation frequencies. To refine the existing language protocol, we tested two different repetition rates of 5 Hz/10 pulses and 7 Hz/10 pulses with a 0 ms delay in 19 healthy subjects. We furthermore investigated differences between both frequencies in case of performance of four different language tasks: object naming, pseudoword reading, verb generation, and action naming. RESULTS: Even the small variance in frequencies revealed statistically significant differences concerning the number and type of language errors. Stimulation with 5 Hz evoked a higher number of all occurred language errors in all language tasks (error rate object naming 14% (5 Hz) vs. 12% (7 Hz); pseudoword reading 4% (5 Hz) vs. 3% (7 Hz); verb generation 13% (5 Hz) vs. 11% (7 Hz); action naming 11% (5 Hz) vs. 9% (7 Hz)), whereas 7 Hz evoked specifically more total speech arrests. CONCLUSION: These findings suggest that the stimulation frequency has to be adapted to the aim of the rTMS language investigation.

Cortical regions involved in semantic processing investigated by repetitive navigated transcranial magnetic stimulation and object naming.

BACKGROUND: Knowledge about the cortical representation of semantic processing is mainly derived from functional magnetic resonance imaging (fMRI) or direct cortical stimulation (DCS) studies. Because DCS is regarded as the gold standard in terms of language mapping but can only be used during awake surgery due to its invasive character, repetitive navigated transcranial magnetic stimulation (rTMS)­a non-invasive modality that uses a similar technique as DCS­seems highly feasible for use in the investigation of semantic processing in the healthy human brain. METHODS: A total number of 100 (50 left-hemispheric and 50 right-hemispheric) rTMS-based language mappings were performed in 50 purely right-handed, healthy volunteers during an object-naming task. All rTMS-induced semantic naming errors were then counted and evaluated systematically. Furthermore, since the distribution of stimulations within both hemispheres varied between individuals and cortical regions stimulated, all elicited errors were standardized and subsequently related to their cortical sites by projecting the mapping results into the cortical parcellation system (CPS). RESULTS: Overall, the most left-hemispheric semantic errors were observed after targeting the rTMS to the posterior middle frontal gyrus (pMFG; standardized error rate: 7.3‰), anterior supramarginal gyrus (aSMG; 5.6‰), and ventral postcentral gyrus (vPoG; 5.0‰). In contrast to that, the highest right-hemispheric error rates occurred after stimulation of the posterior superior temporal gyrus (pSTG; 12.4‰), middle superior temporal gyrus (mSTG; 6.2‰), and anterior supramarginal gyrus (aSMG; 6.2‰). CONCLUSIONS: Although error rates were low, the rTMS-based approach of investigating semantic processing during object naming shows convincing results compared to the current literature. Therefore, rTMS seems a valuable, safe, and reliable tool for the investigation of semantic processing within the healthy human brain.

Combined noninvasive language mapping by navigated transcranial magnetic stimulation and functional MRI and its comparison with direct cortical stimulation.

OBJECT: Repetitive navigated transcranial magnetic stimulation (rTMS) is now increasingly used for preoperative language mapping in patients with lesions in language-related areas of the brain. Yet its correlation with intraoperative direct cortical stimulation (DCS) has to be improved. To increase rTMS's specificity and positive predictive value, the authors aim to provide thresholds for rTMS's positive language areas. Moreover, they propose a protocol for combining rTMS with functional MRI (fMRI) to combine the strength of both methods. METHODS: The authors performed multimodal language mapping in 35 patients with left-sided perisylvian lesions by using rTMS, fMRI, and DCS. The rTMS mappings were conducted with a picture-to-trigger interval (PTI, time between stimulus presentation and stimulation onset) of either 0 or 300 msec. The error rates (ERs; that is, the number of errors per number of stimulations) were calculated for each region of the cortical parcellation system (CPS). Subsequently, the rTMS mappings were analyzed through different error rate thresholds (ERT; that is, the ER at which a CPS region was defined as language positive in terms of rTMS), and the 2-out-of-3 rule (a stimulation site was defined as language positive in terms of rTMS if at least 2 out of 3 stimulations caused an error). As a second step, the authors combined the results of fMRI and rTMS in a predefined protocol of combined noninvasive mapping. To validate this noninvasive protocol, they correlated its results to DCS during awake surgery. RESULTS: The analysis by different rTMS ERTs obtained the highest correlation regarding sensitivity and a low rate of false positives for the ERTs of 15%, 20%, 25%, and the 2-out-of-3 rule. However, when comparing the combined fMRI and rTMS results with DCS, the authors observed an overall specificity of 83%, a positive predictive value of 51%, a sensitivity of 98%, and a negative predictive value of 95%. CONCLUSIONS: In comparison with fMRI, rTMS is a more sensitive but less specific tool for preoperative language mapping than DCS. Moreover, rTMS is most reliable when using ERTs of 15%, 20%, 25%, or the 2-out-of-3 rule and a PTI of 0 msec. Furthermore, the combination of fMRI and rTMS leads to a higher correlation to DCS than both techniques alone, and the presented protocols for combined noninvasive language mapping might play a supportive role in the language-mapping assessment prior to the gold-standard intraoperative DCS.

Language and its right-hemispheric distribution in healthy brains: an investigation by repetitive transcranial magnetic stimulation.

OBJECT: Repetitive navigated transcranial magnetic stimulation (rTMS) is increasingly used for preoperative cortical language mapping. Unlike direct cortical stimulation (DCS), and due to its non-invasive character, this technique can provide a map of the distribution of human language in the healthy brain as well as a dysfunctional brain. Although functional magnetic resonance imaging (fMRI) studies have reported interhemispheric functional connectivity between language structures, the way in which the right hemisphere helps bring about language function remains only partially investigated. The present study therefore uses rTMS as a virtual lesion model to investigate the right hemisphere's contribution to language processing in the healthy human brain. METHODS: Fifty healthy right-handed volunteers (25 males, 25 females, mean age 25.9 ± 5.4 years) underwent language mapping of the right hemisphere by rTMS combined with an object naming task. All errors induced by rTMS were categorized into six different error groups (no-response error, hesitation, performance error, neologism, semantic error, and phonological error). Afterwards, the error rates for each category were calculated and visualized through the results' being projected into the cortical parcellation system (CPS). To reveal CPS regions having similar functional properties, an additional principal component analysis (PCA) was performed. RESULTS: rTMS induced 1485 naming errors out of the 9839 stimulation trains (error rate 15.1%). These errors were located mainly in the right hemisphere's homologues of the left hemisphere's visually cued overt speech area (middle superior temporal gyrus: mSTG) and in the sound-to-articulation dorsal pathway consisting of opercular inferior frontal gyrus (opIFG) and anterior and posterior supramarginal gyrus (aSMG, pSMG) in both male and female brains. In addition, rTMS caused many errors in the global language comprehension area in female brains (right posterior superior temporal gyrus: pSTG), in speech motor areas in the middle and ventral precentral and postcentral gyri (mPrG, vPrG, mPoG, vPoG), and in executive-function areas in the middle and posterior middle frontal gyri (mFMG, pMFG). CONCLUSIONS: For the first time, the present study provides data on the right hemisphere's cortical regions causally related to single word production function (right opIFG, aSMG, pSMG, mSTG), and selectively in female brains (right pSTG), from a large sample of 50 healthy adult brains in a virtual-lesion design. Moreover, speech-motor control regions (right mPrG, vPrG, mPoG, vPoG) and cortical regions supporting language task performance (mMFG, pMFG) in the language-non-dominant right hemisphere are described.

Optimal timing of pulse onset for language mapping with navigated repetitive transcranial magnetic stimulation.

OBJECT: Within the primary motor cortex, navigated transcranial magnetic stimulation (nTMS) has been shown to yield maps strongly correlated with those generated by direct cortical stimulation (DCS). However, the stimulation parameters for repetitive nTMS (rTMS)-based language mapping are still being refined. For this purpose, the present study compares two rTMS protocols, which differ in the timing of pulse train onset relative to picture presentation onset during object naming. Results were the correlated with DCS language mapping during awake surgery. METHODS: Thirty-two patients with left-sided perisylvian tumors were examined by rTMS prior to awake surgery. Twenty patients underwent rTMS pulse trains starting at 300 ms after picture presentation onset (delayed TMS), whereas another 12 patients received rTMS pulse trains starting at the picture presentation onset (ONSET TMS). These rTMS results were then evaluated for correlation with intraoperative DCS results as gold standard in terms of differential consistencies in receiver operating characteristics (ROC) statistics. Logistic regression analysis by protocols and brain regions were conducted. RESULTS: Within and around Broca's area, there was no difference in sensitivity (onset TMS: 100%, delayed TMS: 100%), negative predictive value (NPV) (onset TMS: 100%, delayed TMS: 100%), and positive predictive value (PPV) (onset TMS: 55%, delayed TMS: 54%) between the two protocols compared to DCS. However, specificity differed significantly (onset TMS: 67%, delayed TMS: 28%). In contrast, for posterior language regions, such as supramarginal gyrus, angular gyrus, and posterior superior temporal gyrus, early pulse train onset stimulation showed greater specificity (onset TMS: 92%, delayed TMS: 20%), NPV (onset TMS: 92%, delayed TMS: 57%) and PPV (onset TMS: 75%, delayed TMS: 30%) with comparable sensitivity (onset TMS: 75%, delayed TMS: 70%). Logistic regression analysis also confirmed the greater fit of the predictions by rTMS that had the pulse train onset coincident with the picture presentation onset when compared to the delayed stimulation. Analyses of differential disruption patterns of mapped cortical regions were further able to distinguish clusters of cortical regions standardly associated with semantic and pre-vocalization phonological networks proposed in various models of word production. Repetitive nTMS predictions by both protocols correlate well with DCS outcomes especially in Broca's region, particularly with regard to TMS negative predictions. CONCLUSIONS: With this study, we have demonstrated that rTMS stimulation onset coincident with picture presentation onset improves the accuracy of preoperative language maps, particularly within posterior language areas. Moreover, immediate and delayed pulse train onsets may have complementary disruption patterns that could differentially capture cortical regions causally necessary for semantic and pre-vocalization phonological networks.

'Be prepared': an implemental mindset for alleviating social-identity threat.

Stereotype threat occurs when people who belong to socially devalued groups experience a fear of negative evaluation, which interferes with the goal of staying task focused. The current study was designed to examine whether priming socially devalued individuals with an implemental (vs. a deliberative) mindset, characterized by forming a priori goal-directed plans, would help these individuals to overcome threat-induced distracting states. Participants from low and high socioeconomic status backgrounds (measured by maternal education; SESm ) completed a speeded mental arithmetic test, an intellectually threatening task. Low-SESm individuals performed comparably and exhibited similar confidence levels to high-SESm counterparts only when induced with an implemental mindset, suggesting that implemental mindset priming may help to create equity in the face of stereotype threat.