As social primates, one of the most important cognitive tasks we conduct, dozens of times a day, is to look at a face and extract the person's identity. During the last decade, the neural basis of face processing has been extensively investigated in humans with event-related potential (ERP) and functional MRI (fMRI). These two methods provide complementary information about the temporal and spatial aspects of the neural response, with ERPs allowing high temporal resolution of milliseconds but low spatial resolution of the neural generator and fMRI displaying a slow hemodynamic response but better spatial localization of the activated regions. Despite the extensive fMRI and ERP research of faces, only a few studies have assessed the relationship between the two methods and no study to date have collected simultaneous ERP and fMRI responses to face stimuli. In the current paper we will try to assess the spatial and temporal aspects of the neural response to faces by simultaneously collecting functional MRI and event-related potentials (ERP) to face stimuli. Our goals are twofold: 1) ERP and fMRI show a robust selective response to faces. In particular, two well-established face-specific phenomena, the RH superiority and the inversion effect are robustly found with both ERP and fMRI. Despite the extensive research of these effects with ERP and fMRI, it is still unknown to what extent their spatial (fMRI) and temporal (ERP) aspects are associated. In Study 1 we will employ an individual differences approach, to assess the relationship between these ERP and fMRI face-specific responses. 2) Face processing involves several stages starting from structural encoding of the face image through identity processing to storage for later retrieval. This representation undergoes several manipulations that take place at different time points and in different brain regions before the final percept is generated. By simultaneously recording ERP and fMRI we hope to gain a more comprehensive understanding of the timecourse that different brain areas participate in the generation of the face representation.
Prosopagnosic individuals suffer from severe difficulties in face perception and recognition. Interventions that improve their face recognition abilities are scarce and mostly involve extended training on perceptual information. Given that most individuals with developmental prosopagnosia appear to make trait judgments about faces normally, in the current study we took advantage of recent reports on a semantic encoding benefit in face recognition and examined whether semantic encoding will also improve face recognition in developmental prosopagnosia (DP). Recent studies show that making trait inferences about faces (e.g., how intelligent does the face look like?) during encoding improves face recognition relative to making perceptual inferences about facial features (e.g., how round is the face?) or no evaluations. This semantic manipulation during encoding was also shown to improve face recognition for other race faces, suggesting that it can enhance poor recognition abilities. Thus, we ran a group of DPs (N = 17) on a face recognition task in which participants evaluated faces socially, perceptually, or made no evaluations during the study phase. During the test phase they were presented with different images of the learned identities and were asked to decide whether the face was old or new. Results show a robust semantic encoding benefit that was comparable in prosopagnosics and controls. Surprisingly, the overall performance of prosopagnosics across all conditions of this task was not worse than controls. These findings are the first to show that a non-perceptual, social manipulation can enhance face recognition in prosopagnosia. This may be consistent with a previous report that oxytocin enhances face recognition in prosopagnosia, suggesting that social processing mechanisms may help DPs to alleviate their face recognition difficulties.
Primate face processing depends on a distributed network of interlinked face-selective areas composed of face-selective neurons. In both humans and macaques, the network is divided into a ventral stream and a dorsal stream, and the functional similarities of the areas in humans and macaques indicate they are homologous. Neural correlates for face detection, holistic processing, face space, and other key properties of human face processing have been identified at the single neuron level, and studies providing causal evidence have established firmly that face-selective brain areas are central to face processing. These mechanisms give rise to our highly accurate familiar face recognition but also to our error-prone performance with unfamiliar faces. This limitation of the face system has important implications for consequential situations such as eyewitness identification and policing.
Summary Recent studies show significant similarities between the representations humans and deep neural networks (DNNs) generate for faces. However, two critical aspects of human face recognition are overlooked by these networks. First, human face recognition is mostly concerned with familiar faces, which are encoded by visual and semantic information, while current DNNs solely rely on visual information. Second, humans represent familiar faces in memory, but representational similarities with DNNs were only investigated for human perception. To address this gap, we combined visual (VGG-16), visual-semantic (CLIP), and natural language processing (NLP) DNNs to predict human representations of familiar faces in perception and memory. The visual-semantic network substantially improved predictions beyond the visual network, revealing a new visual-semantic representation in human perception and memory. The NLP network further improved predictions of human representations in memory. Thus, a complete account of human face recognition should go beyond vision and incorporate visual-semantic, and semantic representations.
Abstract It is well established that faces are processed by mechanisms that are not used with other objects. Two prominent hypotheses have been proposed to characterize how information is represented by these special mechanisms. The spacing hypothesis suggests that face-specific mechanisms primarily extract information about spacing among parts rather than information about the shape of the parts. In contrast, the holistic hypothesis suggests that faces are processed as nondecomposable wholes and, therefore, claims that both parts and spacing among them are integral aspects of face representation. Here we examined these hypotheses by testing a group of developmental prosopagnosics (DPs) who suffer from deficits in face recognition. Subjects performed a face discrimination task with faces that differed either in the spacing of the parts but not the parts (spacing task), or in the parts but not the spacing of the parts (part task). Consistent with the holistic hypothesis, DPs showed lower performance than controls on both the spacing and the part tasks, as long as salient contrast differences between the parts were minimized. Furthermore, by presenting similar spacing and part tasks with houses, we tested whether face-processing mechanisms are specific to faces, or whether they are used to process spacing information from any stimulus. DPs' normal performance on the tasks of two houses indicates that their deficit does not result from impairment in a general-purpose spacing mechanism. In summary, our data clearly support face-specific holistic hypothesis by showing that face perception mechanisms extract both part and spacing information.
Language is a high-level cognitive function, so exploring the neural correlates of unconscious language processing is essential for understanding the limits of unconscious processing in general. The results of several functional magnetic resonance imaging studies have suggested that unconscious lexical and semantic processing is confined to the posterior temporal lobe, without involvement of the frontal lobe—the regions that are indispensable for conscious language processing. However, previous studies employed a similarly designed masked priming paradigm with briefly presented single and contextually unrelated words. It is thus possible, that the stimulation level was insufficiently strong to be detected in the high-level frontal regions. Here, in a high-resolution fMRI and multivariate pattern analysis study we explored the neural correlates of subliminal language processing using a novel paradigm, where written meaningful sentences were suppressed from awareness for extended duration using continuous flash suppression. We found that subjectively and objectively invisible meaningful sentences and unpronounceable nonwords could be discriminated not only in the left posterior superior temporal sulcus (STS), but critically, also in the left middle frontal gyrus. We conclude that frontal lobes play a role in unconscious language processing and that activation of the frontal lobes per se might not be sufficient for achieving conscious awareness.
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