Method Of Stimulus Presentation Research Articles

Stimulus Presentation and Analysis Methods for Improving Discrimination Accuracy in P300 Speller

Stimulus Presentation and Analysis Methods for Improving Discrimination Accuracy in P300 Speller

The role of spatial hearing as a key factor in speech perception in noise: Investigating an auditory hypothesis in right hemisphere stroke patients with unilateral spatial neglect

Speech perception in noise is an important function in everyday auditory environments and strongly affects the quality of life. This function depends on the ability of auditory system to separate different streams of sounds and to focus on desired target ones. For this purpose, auditory system uses different sound features. It seems that spatial hearing or auditory lateralization/localization skills plays an important role in speech perception in noise. To test this hypothesis, we recruited the stroke patients with unilateral spatial neglect whose main characteristic of their disorder is multisensory spatial biases. We hypothesized that training of spatial hearing (auditory lateralization training) should improve the speech perception in noise. Participants in our interventional study included 15 patients with right hemisphere stroke and unilateral spatial neglect. Auditory lateralization training consisted of lateralization of sounds simulated by interaural time difference under headphone. Training group received 12 sessions of auditory lateralization training in a modified manner with long-lasting trial time and an oddball stimulus presentation method. To investigate the training program effects, spatial word recognition score in noise test and SSQ questionnaire were conducted three times, before training, after training, and one month later. Patients in training group demonstrated significant improvements in auditory lateralization task and even untrained measures of spatial WRS in noise score (p value ≤ 0.001). Our results suggest that auditory lateralization training could ameliorate auditory spatial biases in neglect patients. Importantly, this training resulted to enhanced spatial word recognition score in noise without any specific speech in noise practices that could support the hypothetical role of spatial hearing in speech perception in noise.

Clustered Volleys Stimulus Presentation for Multifocal Objective Perimetry.

PurposeMultifocal pupillographic objective perimetry (mfPOP) is being developed as an alternative to subjective threshold perimetry for the management of visual and neurological disorders. Here, we evaluate, in normal subjects, differences in signal quality between the original mfPOP method of spatially sparse Continuous stimulus presentation and the new Clustered Volleys (CVs) method. We hypothesized that the CVs method would lead to increased signal-to-noise ratios (SNRs) over the original method due to the stabilization of gain within the pupillary system.MethodsData were collected from six separate studies where otherwise-identical pairs of mfPOP tests using either the original Continuous stimulus presentation method or the new CVs method were undertaken; 440 6-minute tests from 96 normal subjects of varying ages were included. Per-region SNRs were compared between the two methods.ResultsMean SNRs for the CVs mfPOP variants were between 35% and 57% larger than the original Continuous mfPOP variants (P < 0.001 in five of six studies). Similarly, the goodness-of-fit measure (r2) demonstrated large and significant fold increases of between 2.3× and 3.4× over the original method (all P < 0.001). Significant improvements in SNRs were present in all of the 88 test regions (44/eye), ranging between 8.4% and 93.7%; mean SNRs were significantly larger in 98% of test subjects.ConclusionsThe CVs mfPOP stimulus presentation method produced substantial increases in signal quality over the original method. This is likely due to the stabilization of pupillary gain during stimulus presentation.Translational RelevanceThese improvements increase diagnostic accuracy and have enabled shorter, 80-second mfPOP tests to be developed.

Effects of Stimulus Presentation Method on Discourse Comprehension in Healthy Elderly Adults

ë°°ê²½ 및 ëª©ì  ë ¸ì¸ì˜ 담화이해 ëŠ¥ë ¥ì€ ìžê·¹ì œì‹œ 방법에 따라 달라질 수 있음에도 ë¶ˆêµ¬í•˜ê³ ê´€ë ¨ 연구는 ì œí•œì ì´ë‹¤. 본 연구에서는 일반 ë ¸ì¸ì„ 대상으로 담화의 ìžê·¹ì œì‹œ 방법에 따른 담화이해 ëŠ¥ë ¥ì˜ 차이를 ì•Œì•„ë³´ê³ , 담화 ìžê·¹ì œì‹œ 방법의 효과가 ì‚¬ì‹¤ì  ì •ë³´ë‚˜ ì¶”ë¡ ê³¼ 같은 ì§ˆë¬¸ìœ í˜•ì— 따라 다르게 나타나는지 알아보는 것을 ëª©ì ìœ¼ë¡œ 하였다. 방법 본 연구는 일반 ë ¸ì¸ 48ëª ì„ 대상으로 하였다. 담화 ê³¼ì œëŠ” 이야기를 ë“£ê³ ì§ˆë¬¸ì— 답하는 íšŒìƒê³¼ì œë¥¼ 사용하였으며, 1회 ì œì‹œ, 반복 ì œì‹œ, 그림 병행의 ìžê·¹ì œì‹œ 방법을 사용하였다. ì§ˆë¬¸ìœ í˜•ì€ ì‚¬ì‹¤ì  ì •ë³´ì´í•´, í ìŠ¤íŠ¸ ì—°ê²°ì¶”ë¡ ë° ë¹ ì§„ ì •ë³´ì¶”ë¡ ìœ¼ë¡œ 구성하였다. ê²°ê³¼ 첫째, 담화의 반복 ì œì‹œ, 그림 병행 방법 모두 1회 ì œì‹œì— 비해 담화이해 ì ìˆ˜ê°€ 높았으며, 반복 ì œì‹œ, 그림 병행 사이의 차이는 ìœ ì˜í•˜ì§€ 않은 것으로 나타났다. 둘째, ì‚¬ì‹¤ì  ì •ë³´ì´í•´ì˜ 경우 반복에서의 수행이 가장 높은 반면, í ìŠ¤íŠ¸ ì—°ê²°ì¶”ë¡ ì˜ 경우 그림 병행의 수행이 가장 높았다. ì ‹ì§¸, ë¹ ì§„ ì •ë³´ì¶”ë¡ ì˜ 경우 ìžê·¹ì œì‹œ 방법에 따른 담화이해 ëŠ¥ë ¥ì˜ 차이가 ìœ ì˜í•˜ì§€ 않았다. ë ¼ì˜ 및 ê²°ë¡ ì´ëŸ¬í•œ 결과는 일반 ë ¸ì¸ì„ 대상으로 담화의 í‘œë©´ì ì¸ ì •ë³´ì´í•´ 향상을 위해서는 담화를 ë°˜ë³µì ìœ¼ë¡œ ì œì‹œí•˜ëŠ” 것이 더 íš¨ê³¼ì ì´ë©°, í ìŠ¤íŠ¸ 사이의 연결 및 통합을 위한 ë ¼ë¦¬ì  ì¶”ë¡ ì˜ 향상을 위해서는 ì‹œê°ì ì¸ 자료를 병행하는 것이 더 íš¨ê³¼ì ì´ë¼ëŠ” 것을 시사한다. Keywords: 담화이해, ìžê·¹ì œì‹œ 방법, 반복, 그림 병행 ì œì‹œ

No effect of feedback, level of processing or stimulus presentation protocol on perceptual learning when easy and difficult trials are interleaved

The role of feedback during training is a topic of great theoretical importance in perceptual learning. Feedback can be provided externally by the environment or internally by the observer. In order to evaluate the effectiveness of learning with internal versus external feedback, we performed a large multi-level experiment, varying the type of training task (Motion or Form), the level of processing (Local or Global), the presence of feedback (With or Without) and finally the method of stimulus presentation (Adaptive staircase or Method of constant stimuli). 140 participants were randomly assigned to one of ten groups and undertook 3 days of training in one condition only. Detection thresholds were measured daily before and after training with a pre- and post-assessment. A 75% detection threshold was calculated and used to estimate that day’s training levels (65% and 85% accuracy for difficult and easy trials respectively). The group trained with MOCS were presented with predefined randomly interleaved easy and difficult trials ranging from 50% to 95% stimulus intensity. Our findings indicate that improvement was generally robust across training-tasks, processing levels and feedback conditions. This suggests that internal reinforcement is as effective as external feedback in a discrete-noise-paradigm for local and global tasks when easy and difficult trials are interleaved.

Motion correction for infant functional near-infrared spectroscopy with an application to live interaction data.

Correcting for motion is an important consideration in infant functional near-infrared spectroscopy studies. We tested the performance of conventional motion correction methods and compared probe motion and data quality metrics for data collected at different infant ages (5, 7, and 12 months) and during different methods of stimulus presentation (video versus live). While 5-month-olds had slower maximum head speed than 7- or 12-month-olds, data quality metrics and hemodynamic response recovery errors were similar across ages. Data quality was also similar between video and live stimulus presentation. Motion correction algorithms, such as wavelet filtering and targeted principal component analysis, performed well for infant data using infant-specific parameters, and parameters may be used without fine-tuning for infant age or method of stimulus presentation. We recommend using wavelet filtering with [Formula: see text]; however, a range of parameters seemed acceptable. We do not recommend using trial rejection alone, because it did not improve hemodynamic response recovery as compared to no correction at all. Data quality metrics calculated from uncorrected data were associated with hemodynamic response recovery error, indicating that full simulation studies may not be necessary to assess motion correction performance.

A comparison of stimulus presentation methods in temporal discrimination testing

The temporal discrimination threshold (TDT) is the shortest time interval at which an individual detects two stimuli to be asynchronous (normal = 30–50 ms). It has been shown to be abnormal in patients with disorders affecting the basal ganglia including adult onset idiopathic focal dystonia (AOIFD). Up to 97% of patients have an abnormal TDT with age- and sex-related penetrance in unaffected relatives, demonstrating an autosomal dominant inheritance pattern. These findings support the use of the TDT as a pre-clinical biomarker for AOIFD. The usual stimulus presentation method involves the presentation of progressively asynchronous stimuli; when three sequential stimuli are reported asynchronous is taken as a participant’s TDT. To investigate the robustness of the ‘staircase’ method of presentation, we introduced a method of randomised presentation order to explore any potential ‘learning effect’ that may be associated with this existing method. The aim of this study was to investigate differences in temporal discrimination using two methods of stimulus presentation. Thirty healthy volunteers were recruited to the study (mean age 33.73 ± 3.4 years). Visual and tactile TDT testing using a staircase and randomised method of presentation order was carried out in a single session. There was a strong relationship between the staircase and random method for TDT values. This observed consistency between testing methods suggests that the existing experimental approach is a robust method of recording an individual’s TDT. In addition, our newly devised randomised paradigm is a reproducible and more efficient method for data acquisition in the clinic setting. However, the two presentation methods yield different absolute TDT results and either of the two methods should be used uniformly in all participants in any one particular study.

Visual stimulus presentation methods that capture the temporal traits of sentence processing and their evaluation

Visual stimulus presentation methods that capture the temporal traits of sentence processing and their evaluation

Sensitivity evaluation of the visual, tactile, and auditory detection response task method while driving

ABSTRACTObjectives: In this article, we evaluate the sensitivity to cognitive load of 3 versions of the Detection Response Task method (DRT), proposed in ISO Draft Standard DIS-17488.Methods: We present a user study with 30 participants in which we compared the sensitivity to cognitive load of visual, audio, and tactile DRT in a simulated driving environment. The amount of cognitive load was manipulated with secondary n-back tasks at 2 levels of difficulty (0-back and 1-back). We also explored whether the DRT method is least sensitive to cognitive load when the stimuli and secondary task are of the same modality. For this purpose, we used 3 forms to present the n-back task stimuli: visual, audio, and tactile. Responses to the task were always vocal. The experiment was based on a between-subject design (the DRT modalities) with 2 levels of within-subject design study (modalities and difficulty of the secondary n-back tasks). The participants' primary task in the study was to drive safely, and a second priority was to answer to DRT stimuli and perform secondary tasks.Results: The results indicate that all 3 versions of the DRT tested were sensitive to detecting the difference in cognitive load between the reference driving period and driving and engaging in the secondary tasks. Only the visual DRT discriminated between the 0-back and 1-back conditions on mean response time. Contrary to expectations, no interaction was observed between DRT modality and the stimuli modality used for presentation of the secondary tasks.Conclusions: None of the 3 methods of presenting DRT stimuli showed a consistent advantage in sensitivity in differentiating multiple levels of cognitive load if all response times, hit rates, and secondary task performance are considered. If only response time is considered, the visual presentation of the DRT stimulus used in this study showed some advantages. In interpreting these data, it should be noted that the methods of DRT stimulus presentation varied somewhat from the currently proposed draft ISO standard and it is possible that the relative salience level of the visual DRT stimulus influenced the findings. It is further suggested that more than 2 levels of difficulty of the n-back task should be considered for further investigation of the relative sensitivity of different DRT stimuli modalities. Parameters that indicate change in cognitive load (response time, hit rate, task performance) should be analyzed together in assessing the overall impact on the driver and not individually, in order to obtain a fuller insight of the assessed cognitive load.

Prolongation of ERP latency and reaction time (RT) in simultaneous EEG/fMRI data acquisition

BackgroundRecording EEG and fMRI data simultaneously inside a fully-operating scanner has been recognized as a novel approach in human brain research. Studies have demonstrated high concordance between the EEG signals and hemodynamic response. However, a few studies reported altered cognitive process inside the fMRI scanner such as delayed reaction time (RT) and reduced and/or delayed N100 and P300 event-related brain potential (ERP) components. New methodThe present study investigated the influence of electromagnetic field (static magnetic field, radio frequency (RF) pulse, and gradient switching) and experimental environment on posterior N100 and P300 ERP components in four different settings with six healthy subjects using a visual oddball task: (1) classic fMRI acquisition inside the scanner (e.g., supine position, mirror glasses for stimulus presentation), (2) standard behavioral experiment outside the scanner (e.g., seated position, keyboard response), (3) controlled fMRI acquisition inside the scanner (e.g., organic light-emitting diode (OLED) goggles for stimulus presentation) inside; and (4) modified behavioral experiment outside the scanner (e.g., supine position, OLED goggles). ResultsThe study findings indicated that the experimental environment in simultaneous EEG/fMRI acquisition could substantially delay N1P, P300 latency, and RT inside the scanner, and was associated with a reduced N1P amplitude. Comparison with existing methodsThere was no effect of electromagnetic field in the prolongation of RT, N1P and P300 latency inside the scanner. N1P, but not P300, latency was sensitive to stimulus presentation method inside the scanner. ConclusionFuture simultaneous EEG/fMRI data collection should consider experimental environment in both design and analysis.

1-A-D-18. A Study on improvement of character input performance for a P300 speller

A P300 speller, which is equipment for character input utilizing an event-related potential (ERP), was tested clinically in patients with amyotrophic lateral sclerosis (ALS). Improvement of character input speed and reduction of data acquisition time for pre-training were evaluated. The authors developed a stimulus presentation method named reliability based automatic repeat request (RB-ARQ), which dynamically discontinues stimulus presentation based on the reliability of discriminant function, an N-gram method which calculates this reliability based on the transition probabilities of Japanese letters, and an incremental learning method which uses on-line EEG data for updating the discriminant function on-line. The P300 speller incorporating the RB-ARQ and N-gram method was tested with four ALS patients on ventilator in sickrooms with plural beds in two hospitals. The utility, an index for character input speed, of the proposed method was 3.3 times higher than that of the conventional averaging method. It took approximately 10 s to input a character on average. The incremental learning method was tested in simulation using EEG data collected from two patients a half year ago and another patient a week ago for the pre-training. The proposed method achieved zero acquisition time at the start of re-use of the speller.

Reliability and validity of the computerized Revised Token Test: comparison of reading and listening versions in persons with and without aphasia.

This study assessed the reliability and validity of intermodality associations and differences in persons with aphasia (PWA) and healthy controls (HC) on a computerized listening and 3 reading versions of the Revised Token Test (RTT; McNeil & Prescott, 1978). Thirty PWA and 30 HC completed the test versions, including a complete replication. Reading versions varied according to stimulus presentation method: (a) full-sentence presentation, (b) self-paced word-by-word full-sentence construction, and (c) self-paced word-by-word presentation with each word removed with the onset of the next word. Participants also received tests of aphasia and reading severity. The listening version produced higher overall mean scores than each of the reading versions. Differences were small and within 1 standard error of measurement of each version. Overall score test-retest reliability among versions for PWA ranged from r=.89 to r=.97. Correlations between the listening and reading versions ranged from r=.79 to r=.85. All versions correlated highly with aphasia and reading severity. Correlations were generally low for the HC due to restricted variability. Factor analysis yielded a 2-factor solution for PWA and a single-factor for HC. Intermodality differences were small, and all 4 versions were reliable, concurrently valid, and sensitive to similar linguistic processing difficulties in PWA.

Neural bases of syntax-semantics interface processing.

The binding problem-question of how information between the modules of the linguistic system is integrated during language processing-is as yet unresolved. The remarkable speed of language processing and comprehension (Pulvermüller et al. 2009) suggests that at least coarse semantic information (e.g. noun animacy) and syntactically-relevant information (e.g. verbal template) are integrated rapidly to allow for coarse comprehension. This EEG study investigated syntax-semantics interface processing during word-by-word sentence reading. As alpha-band neural activity serves as an inhibition mechanism for local networks, we used topographical distribution of alpha power to help identify the timecourse of the binding process. We manipulated the syntactic parameter of verbal event structure, and semantic parameter of noun animacy in reduced relative clauses (RRCs, e.g. "The witness/mansion seized/protected by the agent was in danger"), to investigate the neural bases of interaction between syntactic and semantic networks during sentence processing. The word-by-word stimulus presentation method in the present experiment required manipulation of both syntactic structure and semantic features in the working memory. The results demonstrated a gradient distribution of early components (biphasic posterior P1-N2 and anterior N1-P2) over function words "by" and "the", and the verb, corresponding to facilitation or conflict resulting from the syntactic (telicity) and semantic (animacy) cues in the preceding portion of the sentence. This was followed by assimilation of power distribution in the α band at the second noun. The flattened distribution of α power during the mental manipulation with high demand on working memory-thematic role re-assignment-demonstrates a state of α equilibrium with strong functional coupling between posterior and anterior regions. These results demonstrate that the processing of semantic and syntactic features during sentence comprehension proceeds in highly integrated fashion using gating of attentional resources to facilitate rapid comprehension, with attentional suppression of global alpha power to facilitate interaction of local networks.

Laterality of Tickle Sensation Produced by Self-Stimulation,

Numerous authors have reported that people cannot create a tickling reaction in themselves. However, Provine (2000) claimed that ticklishness was felt even if he stimulated his own leg with his fingers. Ticklishness was stronger when the hand and leg were on opposite sides of the body. Provine's findings were replicated with 30 university students. Two types of stimulus presentation methods were adopted: a participant's fingers and a paintbrush. Ticklishness was assessed by self-rating and evaluation by observers. Provine's claim was supported only by the self-rating of stimulation with the fingers.

Infants Need More Variety – Increased Data Acquisition with Reduced Participant Attrition in Infant ERP Studies

Infant ERP studies often feature high attrition rates with large numbers of trials excluded from statistical analyses. The number of experimental conditions is conventionally limited to reduce the test-sessions’ durations and to ensure that reasonable trial-numbers will be obtained for each condition. Here, we designed an ERP study involving eight conditions originating from three previously published studies and presented them to 18 1-year-olds. We expected to replicate original results at least partly. Additionally, we were interested in the effect this novel method of stimulus presentation would have on infant attention. Due to the requirement for sustained attention, interest may decrease. Alternatively, the stimulus-variability may extend attention, allowing the acquisition of more valid trials. Our main finding was that the variability of the stimulus presentation sustained the infants’ attention beyond normal parameters. This is apparent from the markedly increased number of artifact-free trials obtained and from the substantially decreased attrition rates. Results from a gap-/no gap-task were fully replicated whereas others, related to face-processing, were replicated in part. Additionally, effects that were not reported in the original studies were found. This is most probably due to interference in the information processing between these conditions. The results show that presenting infants with varied stimuli extends their attention, allowing the acquisition of at least four times more data than via current infant ERP methods. However, stimuli from separate sub-experiments must be cognitively and perceptually distinct, otherwise contamination between related factors will occur.

A Study on Assisting System for Inputting Character using NIRS by the Stimulus Presentation Method of Bit Form

A Study on Assisting System for Inputting Character using NIRS by the Stimulus Presentation Method of Bit Form

Optimizing reliability and sensitivity of Semmes–Weinstein monofilaments for establishing point tactile thresholds

Semmes–Weinstein monofilaments (SWM) are widely used to assess tactile point pressure sensitivity. However, the reliability of SWMs has been questioned, standardization of stimulus presentation procedures is lacking, and the sensitivity measure is commonly confounded by the response criterion. This study sought to assess the reliability of two versions of a forced-choice single staircase SWM test with the goal of optimizing test reliability with a minimum number of test trials. Test–retest and intra-test reliability coefficients for SWM threshold values from the plantar halluces of 24 normal subjects were obtained using two versions of a forced-choice single-staircase procedure. One version followed a two-down one-up rule (2D) and the other a three-down one-up rule (3D). The 3D procedure was significantly more reliable than the 2D procedure for all sequential combinations of reversal pairs. A total of four 3D reversal pairs (i.e., eight reversals) were sufficient to achieve test–retest and intra-test reliability coefficients>0.90. High reliability with the minimum number of trials was obtained by calculating the threshold as the mean of eight reversals (test–retest r=0.93, p<0.001; Sessions 1 and 2 intra-test rs=0.87 and 0.92; ps<0.001). Identical median detection thresholds were noted for the two repeated test sessions (5.1g/mm2). The threshold values correlated with subject age despite the small range of ages tested, suggesting high sensitivity (Sessions 1 and 2 rs=0.61 and 0.63, ps<0.001). This study demonstrates that SWMs provide highly reliable and sensitive point pressure thresholds with very few trials when an appropriate psychophysical paradigm is employed. The brief forced-choice procedure described herein could serve as a basis for standardizing SWM stimulus presentation methods.

Brand familiarity and tasting in conjoint analysis

PurposeThe aims of this paper is to determine, via an empirical study of beer consumers in Croatia, the influence of tasting on the validity of conjoint analysis (CA) under presence of familiar or unfamiliar brands.Design/methodology/approachThe research comprised a face‐to‐face survey with 403 beer consumers. The respondents were divided into four groups regarding CA experiment (familiar/unfamiliar beer brand in combination with presence or absence of beer tasting). CA validity was measured with five criteria: face validity, convergent validity, internal validity, predictive validity and subjective evaluation of conjoint task. In addition to the CA experiment, a structured questionnaire was used consisting of a few questions regarding respondents' socio‐economic characteristics, beer purchasing, and consuming behaviour.FindingsThe research results confirmed that tasting as an additional presentation method has significant influence on validity of CA. However, the results of the study indicate that tasting should be used as a stimulus presentation method for CA with food and beverage products/brands, which are unfamiliar to the consumers. When testing familiar brands and brands with established perceptions, simpler and less expensive verbal stimulus presentation can be used.Practical implicationsAccording to the research results, it could be concluded that when performing CA with strong familiar brands, it is not necessary to use CA with tasting since tasting increases research complexity and costs and it does not achieve better results. However, tasting as a stimuli presentation method gives better results than pure verbal CA in the case of unfamiliar brands.Originality/valueThe paper is one of the first to deal with tasting as a presentation method in conjoint analysis and its results have direct implications for the future use of CA with food and beverages.

Gender differences in brain areas involved in silent counting by means of fMRI

BackgroundPattern of brain asymmetries varies with handedness, gender, age, and with variety of genetic and social factors. Large-scale neuroimaging analyses can optimize the detection of asymmetric features and confirm the factors that might modulate pattern of brain asymmetries. We attempted to evaluate eventual differences between genders in hemodynamic responses to a simple language task.Methods12 healthy right-handed volunteers (age 24-46), 6 men and 6 women underwent fMRI scanning while performing the simple cognitive - language processing task – silent number counting in Serbian. ResultsGroup analysis of hemodynamic responses shows activation in expected brain language areas of inferior frontal gyrus (IFG) and superior temporal gyrus (STG) in both hemispheres. In the male group, aside from dedicated language areas in IFG and STG, activation was noted in right frontal region and interhemispheric supplementary motor area. On the other hand, in the female group, besides activation in dedicated language areas, activation was noted, in right hippocampus, limbic brain and cerebellum bilaterally.ConclusionsOur results on differences in silent counting by means of fMRI suggest that those differences may be based on different brain pattern activation in men and women. The relation between performance, strategies and regional brain activation should be the topic of further studies when considering not only gender differences in language processing but also differences that may be attributed to the variations in the task details, stimuli, and the stimulus presentation methods.

Whole not hole: Expert face recognition requires holistic perception

Face recognition is an important ability of the human brain, yet its underlying mechanisms are still poorly understood. Two opposite views have been proposed to account for human face recognition expertise: the ability to extract the most diagnostic local information, feature-by feature (analytical view), or the ability to process all features at once over the whole face (holistic view). To help clarifying this debate, we used an original gaze-contingent stimulus presentation method to compare normal observers and a brain-damaged patient specifically impaired at face recognition (prosopagnosia). When a single central facial feature was revealed at a time through a gaze-contingent window, normal observers’ performance at an individual face matching task decreased to the patient level. However, when only the central feature was masked, forcing normal observers to rely on the whole face but the fixated feature, their performance was almost not affected. In contrast, the prosopagnosic patient's performance decreased dramatically in this latter condition. These results were independent of the absolute size of the face and window/mask. This dissociation indicates that expertise in face recognition does not rest on the ability to analyze diagnostic local detailed features sequentially but rather on the ability to see the individual features of a face all at once, a function that is critically impaired in acquired prosopagnosia.