Putting culture under the spotlight reveals universal information use for face recognition

Background: Eye movement strategies employed by humans to identify conspecifics are not universal. Westerners predominantly fixate the eyes during face recognition, whereas Easterners more the nose region, yet recognition accuracy is comparable. However, natural fixations do not unequivocally represent information extraction. So the question of whether humans universally use identical facial information to recognize faces remains unresolved. Methodology/Principal Findings: We monitored eye movements during face recognition of Western Caucasian (WC) and East Asian (EA) observers with a novel technique in face recognition that parametrically restricts information outside central vision. We used ‘Spotlights’ with Gaussian apertures of 2°, 5° or 8° dynamically centered on observers’ fixations. Strikingly, in constrained Spotlight conditions (2°, 5°) observers of both cultures actively fixated the same facial information: the eyes and mouth. When information from both eyes and mouth was simultaneously available when fixating the nose (8°), as expected EA observers shifted their fixations towards this region. Conclusions/Significance: Social experience and cultural factors shape the strategies used to extract information from faces, but these results suggest that external forces do not modulate information use. Human beings rely on identical facial information to recognize conspecifics, a universal law that might be dictated by the evolutionary constraints of nature and not nurture

Looking away from faces: influence of high-level visual processes on saccade programming

Human faces capture attention more than other visual stimuli. Here we investigated whether such face-specific biases rely on automatic (involuntary) or voluntary orienting responses. To this end, we used an anti-saccade paradigm, which requires the ability to inhibit a reflexive automatic response and to generate a voluntary saccade in the opposite direction of the stimulus. To control for potential low-level confounds in the eye-movement data, we manipulated the high-level visual properties of the stimuli while normalizing their global low-level visual properties. Eye movements were recorded in 21 participants who performed either pro- or anti-saccades to a face, car, or noise pattern, randomly presented to the left or right of a fixation point. For each trial, a symbolic cue instructed the observer to generate either a pro-saccade or an anti-saccade. We report a significant increase in anti-saccade error rates for faces compared to cars and noise patterns, as well as faster pro-saccades to faces and cars in comparison to noise patterns. These results indicate that human faces induce stronger involuntary orienting responses than other visual objects, i.e., responses that are beyond the control of the observer. Importantly, this involuntary processing cannot be accounted for by global low-level visual factors

An appropriate use of iMap produces correct statistical results: a reply to McManus (2013) "iMAP and iMAP2 produce erroneous statistical maps of eye-movement differences".

McManus (2013, Perception, 42, 1075-1084) contends the validity of the statistical approach adopted in previous versions of iMap (namely, iMap and iMap2; Caldara & Miellet, 2011, Behavior Research Methods, 43, 864-878), casts doubts on earlier results obtained with the toolbox, and offers an altered version of the code. Here we dispute these claims and argue that while some of the arguments put forward are valid, McManus's conclusions are misleading, since they are based on a partial use of the toolbox. Moreover, we compared iMap with the alternative code offered by McManus and objectively demonstrate that McManus's approach is underpowered and flawed. iMap offers an appropriate and effective alternative to the commonly used regions of interest approach for statistical analyses of eye-movement data

Culture shapes how we look at faces

Background: Face processing, amongst many basic visual skills, is thought to be invariant across all humans. From as early as 1965, studies of eye movements have consistently revealed a systematic triangular sequence of fixations over the eyes and the mouth, suggesting that faces elicit a universal, biologically-determined information extraction pattern. Methodology/Principal Findings: Here we monitored the eye movements of Western Caucasian and East Asian observers while they learned, recognized, and categorized by race Western Caucasian and East Asian faces. Western Caucasian observers reproduced a scattered triangular pattern of fixations for faces of both races and across tasks. Contrary to intuition, East Asian observers focused more on the central region of the face. Conclusions/Significance: These results demonstrate that face processing can no longer be considered as arising from a universal series of perceptual events. The strategy employed to extract visual information from faces differs across cultures

Mapping Face Recognition Information Use across Cultures.

Face recognition is not rooted in a universal eye movement information-gathering strategy. Western observers favor a local facial feature sampling strategy, whereas Eastern observers prefer sampling face information from a global, central fixation strategy. Yet, the precise qualitative (the diagnostic) and quantitative (the amount) information underlying these cultural perceptual biases in face recognition remains undetermined. To this end, we monitored the eye movements of Western and Eastern observers during a face recognition task, with a novel gaze-contingent technique: the Expanding Spotlight. We used 2° Gaussian apertures centered on the observers' fixations expanding dynamically at a rate of 1° every 25 ms at each fixation - the longer the fixation duration, the larger the aperture size. Identity-specific face information was only displayed within the Gaussian aperture; outside the aperture, an average face template was displayed to facilitate saccade planning. Thus, the Expanding Spotlight simultaneously maps out the facial information span at each fixation location. Data obtained with the Expanding Spotlight technique confirmed that Westerners extract more information from the eye region, whereas Easterners extract more information from the nose region. Interestingly, this quantitative difference was paired with a qualitative disparity. Retinal filters based on spatial-frequency decomposition built from the fixations maps revealed that Westerners used local high-spatial-frequency information sampling, covering all the features critical for effective face recognition (the eyes and the mouth). In contrast, Easterners achieved a similar result by using global low-spatial-frequency information from those facial features. Our data show that the face system flexibly engages into local or global eye movement strategies across cultures, by relying on distinct facial information span and culturally tuned spatially filtered information. Overall, our findings challenge the view of a unique putative process for face recognition

When East meets West: Gaze-contingent Blindspots abolish cultural diversity in eye movements for faces

Culture impacts on how people sample visual information for face processing. Westerners deploy fixations towards the eyes and the mouth to achieve face recognition. In contrast, Easterners reach equal performance by deploying more central fixations, suggesting an effective extrafoveal information use. However, this hypothesis has not been yet directly investigated, i.e. by providing only extrafoveal information to both groups of observers. We used a parametric gaze-contingent technique dynamically masking central vision - the Blindspot - with Western and Eastern observers during face recognition. Westerners shifted progressively towards the typical Eastern central fixation pattern with larger Blindspots, whereas Easterners were insensitive to the Blindspots. These observations clearly show that Easterners preferentially sample information extrafoveally for faces. Conversely, the Western data also show that culturally-dependent visuo-motor strategies can flexibly adjust to constrained visual situations

iMap4: An Open Source Toolbox for the Statistical Fixation Mapping of Eye Movement data with Linear Mixed Modeling.

A major challenge in modern eye movement research is to statistically map where observers are looking, by isolating the significant differences between groups and conditions. Compared to signals of contemporary neuroscience measures, such as M/EEG and fMRI, eye movement data are sparser with much larger variations in space across trials and participants. As a result, the implementation of a conventional linear modeling approach on two-dimensional fixation distributions often returns unstable estimations and underpowered results, leaving this statistical problem unresolved (Liversedge, Gilchrist, & Everling. 2011). Here, we present a new version of the iMap toolbox (Caldara and Miellet, 2011) which tackles this issue by implementing a statistical framework comparable to those developped in state-of the- art neuroimaging data processing toolboxes. iMap4 uses univariate, pixel-wise Linear Mixed Models (LMM) on the smoothed fixation data, with the flexibility of coding for multiple between- and within- subject comparisons and performing all the possible linear contrasts for the fixed effects (main effects, interactions, etc.). Importantly, we also introduced novel nonparametric tests based on resampling to assess statistical significance. Finally, we validated this approach by using both experimental and Monte Carlo simulation data. iMap4 is a freely available MATLAB open source toolbox for the statistical fixation mapping of eye movement data, with a user-friendly interface providing straightforward, easy to interpret statistical graphical outputs. iMap4 matches the standards of robust statistical neuroimaging methods and represents an important step in the data-driven processing of eye movement fixation data, an important field of vision sciences

Meeting abstract: iMap 4: An Open Source Toolbox for the Statistical Fixation Mapping of Eye Movement data with Linear Mixed Modeling.

A major challenge in modern eye movement research is to statistically map where observers are looking at, as well as isolating statistical significant differences between groups and conditions. Compared to signals of contemporary neuroscience measures, such as M/EEG and fMRI, eye movement data are sparse with much larger variations across trials and participants. As a result, the implementation of a conventional Hierarchical Linear Model approach on two-dimensional fixation distributions often returns unstable estimations and underpowered results, leaving this statistical problem unresolved. Here, we tackled this issue by using the statistical framework implemented in diverse state-of-the-art neuroimaging data processing toolboxes: Statistical Parametric Mapping (SPM), Fieldtrip and LIMO EEG. We first estimated the mean individual fixation maps per condition by using trimmean to account for the sparseness and the high variations of fixation data. We then applied a univariate, pixel-wise linear mixed model (LMM) on the smoothed fixation data with each subject as a random effect, which offers the flexibility to code for multiple between- and within- subject comparisons. After this step, our approach allows to perform all the possible linear contrasts for the fixed effects (main effects, interactions, etc.). Importantly, we also introduced a novel spatial cluster test based on bootstrapping to assess the statistical significance of the linear contrasts. Finally, we validated this approach by using both experimental and computer simulation data with a Monte Carlo approach. iMap 4 is a freely available MATLAB open source toolbox for the statistical fixation mapping of eye movement data, with a user-friendly interface providing straightforward, easy to interpret statistical graphical outputs and matching the standards in robust statistical neuroimaging methods. iMap 4 represents a major step in the processing of eye movement fixation data, paving the way to a routine use of robust data-driven analyses in this important field of vision sciences. Meeting abstract presented at VSS 2015

Diversidade genética intrapopulacional e variabilidade de genes ligados a determinação do sexo: investigando um caso de reversão sexual em Akodon montensis

O primeiro caso de reversão sexual em Akodon foi relatado em 1967 e desde então há registro de casos de fêmeas XY em nove espécies do gênero. Na maioria dos casos não há concesso sobre o motivo/causa da reversão, mas para muitos autores essas fêmeas XY são resultantes de problemas no gene Sry. No caso de A. montensis o sugerido é que o cromossomo X teria um de seus genes participantes da cascata sexual alterado. Para essas espécies também se identificou a presença do gene Sry, porém a integridade da cópia identificada, o número de cópias e a funcionalidade da proteína do gene não havia sido testada. Outro dado importante é que só há registro de fêmeas XY em uma única população, Iguape SP, sendo necessário assim se investigar qual seria o diferencial nessa populacional que estivesse favorecendo o surgimento ou a manutenção dessas fêmeas. O presente estudo se propôs a investigar o papel dos genes ligados à determinação do sexo e dos processos que envolvem esses genes, tomando como base um organismo modelo como fêmeas XY de Akodon montensis, verificando a integridade/funcionalidade de alguns genes ligados ao sexo bem como seu número de cópias e estruturação genética e demográfica das populações de A. montensis, assim como verificar se historicamente os nove casos de reversão sexual no gênero Akodon possuem uma origem comum. Para tal, foram extraídos DNA de 94 indivíduos de A. montensis (incluindo fêmeas XY) e comparado com o DNA de pelo menos 6 espécies do gênero. Com esse DNA foram feitos estudos populacionais (como desvio de neutralidade, teste mismatch, analise de diversidade nucleotídica, haplotípica estimativa de tempo de expansão, Φst, Nm, análise filogenéticas) com uso da região controle do DNA mitocondrial. Também foi investigada a presença e integridade estrutural dos genes Dax-1 e Sry por meio de sequenciamento genético analisando-se diversidade genética entre diversas espécies. Em especial para o gene Sry investigou-se a estrutura primária da proteína e sua estrutura terciária, como uso de programas específicos para modelagem tridimensional. Também empregou-se técnicas de pcr em tempo real para se estimar o número de cópias desses genes no genoma de A. montensis. Sequencias do gene citocromo b foram usadas para se inferir uma filogenia do gênero e por mapeamento de caráter filogenético mapeou-se a origem das fêmeas XY dentro de Akodon. Os resultados encontrados apontam que apenas população de Iguape apresenta sinais de expansão populacional recente, devido a possível gargalo populacional, que pode ter feito com que as fêmeas XY subissem de frequência nessa população. Além disso, demostrou-se que essas fêmeas surgiram a cerca de 15 mil anos atrás. A integridade do gene Sry foi confirmada por todas as metodologias empregadas, incluindo a modelagem tridimensional das proteínas, esse gene demonstrou-se espécie específico, mas não houve diferenças entre machos e fêmeas XY nesse gene para A. montensis. Por problemas com anelamento de iniciadores devido a falta de informações disponíveis na literatura, somente o exon2 de Dax-1 pode ser analisado. As analises feitas para esse gene também indicam que não há diferenças entre machos e fêmeas XY nessa espécie que possa ser a causa da reversão sexual. Como PCR em tempo real pode-se inferir que não há diferenças entre o número de cópias do gene Sry entre machos e fêmeas XY.A filogenia obtida corrobora filogenias anteriores propostas para o gênero Akodon e o mapeamento do caráter reversão sexual nessa filogenia indica que essa característica tem múltiplas origens dentro do gênero. Assim pode-se concluir que não são mutações exon 2 de Dax-1, ou alterações do gene Sry, ou em sua proteína que levam a reversão sexual, mas que outros genes da cascata da sexual devam ser determinantes para o caso de fêmeas XY em A. montensis