Reduced sensitivity to contrast signals from the eye region in developmental prosopagnosia

Contrast-related signals from the eye region are known to be important for the processing of facial identity. Individuals with developmental prosopagnosia (DP) have severe face recognition problems, which may be linked to deficits in the perceptual processing of identity-related information from the eyes. We tested this hypothesis by measuring N170 components in DP participants and age-matched controls in response to face images where the contrast polarity of the eyes and of other face parts was independently manipulated. In different trials, participants fixated either the eye region or the lower part of a face. In the Control group, contrast-reversal of the eyes resulted in enhanced and delayed N170 components, irrespective of the contrast of other face parts and of gaze location. In the DP group, these effects of eye contrast on N170 amplitudes were strongly and significantly reduced, demonstrating that perceptual face processing in DP is less well tuned to contrast information from the eye region. Inverting the contrast of other parts of the face affected N170 amplitudes only when fixation was outside the eye region. This effect did not differ between the two groups, indicating that DPs are not generally insensitive to the contrast polarity of face images. These results provide new evidence that a selective deficit in detecting and analysing identity-related information provided by contrast signals from the eye region may contribute to the face recognition impairment in DP

The cognitive and neural basis of developmental prosopagnosia

Developmental prosopagnosia (DP) is a severe impairment of visual face recognition in the absence of any apparent brain damage. The factors responsible for DP have not yet been fully identified. This article provides a selective review of recent studies investigating cognitive and neural processes that may contribute to the face recognition deficits in DP, focusing primarily on event-related brain potential (ERP) measures of face perception and recognition. Studies that measured the face-sensitive N170 component as a marker of perceptual face processing have shown that the perceptual discrimination between faces and non-face objects is intact in DP. Other N170 studies suggest that faces are not represented in the typical fashion in DP. Individuals with DP appear to have specific difficulties in processing spatial and contrast deviations from canonical upright visual-perceptual face templates. The rapid detection of emotional facial expressions appears to be unaffected in DP. ERP studies of the activation of visual memory for individual faces and of the explicit identification of particular individuals have revealed differences between DPs and controls in the timing of these processes and in the links between visual face memory and explicit face recognition. These observations suggest that the speed and efficiency of information propagation through the cortical face network is altered in DP. The nature of the perceptual impairments in DP suggests that atypical visual experience with the eye region of faces over development may be an important contributing factor to DP

Effects of contrast inversion on face perception depend on gaze location: evidence from the N170 component

Face recognition is known to be impaired when the contrast polarity of the eyes is inverted. We studied how contrast affects early perceptual face processing by measuring the face-sensitive N170 component to face images when the contrast of the eyes and of the rest of the face was independently manipulated. Fixation was either located on the eye region or on the lower part of a face. Contrast-reversal of the eyes triggered delayed and enhanced N170 components independently of the contrast of other face parts, and regardless of gaze location. Similar N170 modulations were observed when the rest of a face was contrast-inverted, but only when gaze was directed away from the eyes. Results demonstrate that the contrast of the eyes and of other face parts can both affect face perception, but that the contrast polarity of the eye region has a privileged role during early stages of face processing

Facial misidentifications arise from the erroneous activation of visual face memory

Misidentifications are a common phenomenon in unfamiliar face processing, but little is known about the underlying cognitive and neural mechanisms. We used the face identity-sensitive N250r component of the event-related brain potential as a measure of identity-sensitive face matching process in visual working memory. Two face images were presented in rapid succession, and participants had to judge whether they showed the same or two different individuals. Identity match and mismatch trials were presented in random sequence. On similar mismatch trials, perceptually similar faces of two different individuals were shown, while two physically distinct faces were presented on dissimilar mismatch trials. Misidentification errors occurred on 40% of all similar mismatch trials. N250r components were elicited not only in response to an identity match, but also on trials with misidentification errors. This misidentification N250r was smaller and emerged later than the N250r to correctly detected identity repetitions. Importantly, N250r components were entirely eliminated on similar mismatch trials where participants correctly reported two different facial identities. Results show that misidentification errors are not primarily a post-perceptual decision-related phenomenon, but are generated during early visual stages of identity-related face processing. Misidentification errors occur when stored representations of a particular individual face in visual working memory are incorrectly activated by a perceptual match with a different face

The focus of spatial attention determines the number and precision of face representations in working memory

The capacity of visual working memory for faces is extremely limited, but the reasons for these limitations remain unknown. We employed event-related brain potential (ERP) measures to demonstrate that individual faces have to be focally attended in order to be maintained in working memory, and that attention is allocated to only a single face at a time. When two faces have to be memorized simultaneously in a face identity matching task, the focus of spatial attention during encoding predicts which of these faces can be successfully maintained in working memory and matched to a subsequent test face. We also show that memory representations of attended faces are maintained in a position-dependent fashion. These findings demonstrate that the limited capacity of face memory is directly linked to capacity limits of spatial attention during the encoding and maintenance of individual face representations. We suggest that the capacity and distribution of selective spatial attention is a dynamic resource that constrains the capacity and fidelity of working memory for faces

Neural responses in a fast periodic visual stimulation paradigm reveal domain-general visual discrimination deficits in developmental prosopagnosia

We investigated selective impairments of visual identity discrimination in developmental prosopagnosia (DP), using a fast periodic identity oddball stimulation paradigm with electroencephalography (EEG). In Experiment 1, neural responses to unfamiliar face identity changes were strongly attenuated for individuals with DP as compared to Control participants, to the same extent for upright and inverted faces. This reduction of face identity discrimination responses, which was confirmed in Experiment 2, provides direct evidence for deficits in the visual processing of unfamiliar facial identity in DP. Importantly, Experiment 2 demonstrated that DPs showed attenuated neural responses to identity oddballs not only with face images, but also with non-face images (cars). This result strongly suggests that rapid identity-related visual processing impairments in DP are not restricted to faces, but also affect familiar classes of non-face stimuli. Visual discrimination deficits in DP do not appear to be face-specific. To account for these findings, we propose a new account of DP as a domain-general deficit in rapid visual discrimination

The transformation of Galway: an urban history of a port town 1600-1700

Galway’s wealth and position as a major Irish trading port at the beginning of the seventeenth century stemmed from a mixture of geography and politics. Its staunch support of the Crown, since its foundation in the early thirteenth century, enabled it to secure a range of special privileges. This situation allowed it to evolve as a settlement akin to a ‘city state’, exempt in the main from much of the fiscal duties imposed on commerce and trade within the English mercantile system. This special relationship began to fall apart as the Reformation and Protestant interests began to impact on what was an almost exclusively Catholic community, with power residing in the hands of a monopolistic clique of powerful and wealthy merchant families. Until the Gaelic uprising of 1641, there was little visible evidence of a conflict of interest between Catholics and Protestants in terms of their political affiliations, and even during the early stages of the formation of the Confederacy, the Galway community was reluctant to join forces with the other Old English communities. However, the siege and subsequent surrender of Galway to the Cromwellian forces in 1652, resulted in the town being left in a state of stagnation by the time of the Restoration of Charles II in1660. During the closing decades of the seventeenth century, Galway’s trading activity dwindled as the town struggled to regain its former markets. For a brief period in the late 1680s, Catholics regained control of Galway’s municipal affairs. They subsequently supported James II in the Williamite Wars, only to lose control once more following the surrender of the town to General Ginckle on 21 July 1691. To date, no published work has closely researched the significant transformations, from 1600-1700, in Galway’s economy, morphology, politics and society. This study seeks to address this lacuna by assembling and interpreting a vast range of historical evidence, so as to produce an original, integrated, meticulous and far-reaching narrative and analysis that reconstructs the urban history of seventeenth-century Galway. As well as making extensive use of the primary and secondary historical sources relating to aspects of Galway’s urban history, this study is also informed by recent scholarship on the seventeenth-century colonial policies that England adopted in its conquest of Ireland, particularly those which contributed to the outbreak of the Confederate Wars, the subsequent Cromwellian settlement of Ireland and the economic changes brought about by the Cattle Acts and the Navigation Acts after the Restoration. As a whole, this study relies not only on the perspective of the historian, but upon interdisciplinary perspectives drawn from cognate disciplines such as geography and archaeology

Holistic face perception is impaired in developmental prosopagnosia

Individuals with developmental prosopagnosia (DP) have severe difficulties recognising familiar faces. A current debate is whether these face recognition impairments derive from problems with face perception and in particular whether individuals with DP cannot utilize holistic representations of individual faces. To assess this hypothesis, we recorded event-related potentials (ERPs) during a sequential face identity matching task where successively presented pairs of upright faces were either identical or differed with respect to their internal features, their external features, or both. Participants with DP and age-matched controls reported on each trial whether the face pair was identical or different. To track the activation of cortical visual face memory representations, we measured N250r components over posterior face-selective regions. N250r components to full face repetitions were strongly attenuated for DPs as compared to control participants, indicating impaired face identity matching processes in DP. In the Control group, the N250r to full face repetitions was superadditive (i.e., larger than the sum of the two N250r components to partial repetitions of external or internal features). This demonstrates that holistic face representations were involved in identity matching processes. In the DP group, N250r components to full and partial identity repetitions were strictly additive, indicating that the identity matching of external and internal features operated in an entirely part-based fashion, without any involvement of holistic representations. In line with this conclusion, DPs also made a disproportionate number of errors on partial repetition trials, where they often failed to report a change of internal facial features. This suggests an atypical strategy for encoding external features as cues to identity in DP. These results provide direct electrophysiological and behavioural evidence for qualitative differences in the representation of face identity in the occipital-temporal face processing system in developmental prosopagnosia

Response of face-selective brain regions to trustworthiness and gender of faces

Neuropsychological and neuroimaging studies have demonstrated a role for the amygdala in processing the perceived trustworthiness of faces, but it remains uncertain whether its responses are linear (with the greatest response to the least trustworthy-looking faces), or quadratic (with increased fMRI signal for the dimension extremes). It is also unclear whether the trustworthiness of the stimuli is crucial or if the same response pattern can be found for faces varying along other dimensions. In addition, the responses to perceived trustworthiness of face-selective regions other than the amygdala are seldom reported. The present study addressed these issues using a novel set of stimuli created through computer image-manipulation both to maximise the presence of naturally occurring cues that underpin trustworthiness judgments and to allow systematic manipulation of these cues. With a block-design fMRI paradigm, we investigated neural responses to computer-manipulated trustworthiness in the amygdala and core face-selective regions in the occipital and temporal lobes. We asked whether the activation pattern is specific for differences in trustworthiness or whether it would also track variation along an orthogonal male–female gender dimension. The main findings were quadratic responses to changes in both trustworthiness and gender in all regions. These results are consistent with the idea that face-responsive brain regions are sensitive to face distinctiveness as well as the social meaning of the face features

The activation of visual face memory and explicit face recognition are delayed in developmental prosopagnosia

Individuals with developmental prosopagnosia (DP) are strongly impaired in recognizing faces, but the causes of this deficit are not well understood. We employed event-related brain potentials (ERPs) to study the time-course of neural processes involved in the recognition of previously unfamiliar faces in DPs and in age-matched control participants with normal face recognition abilities. Faces of different individuals were presented sequentially in one of three possible views, and participants had to detect a specific Target Face (“Joe”). EEG was recorded during task performance to Target Faces, Nontarget Faces, or the participants' Own Face (which had to be ignored). The N250 component was measured as a marker of the match between a seen face and a stored representation in visual face memory. The subsequent P600f was measured as an index of attentional processes associated with the conscious awareness and recognition of a particular face. Target Faces elicited reliable N250 and P600f in the DP group, but both of these components emerged later in DPs than in control participants. This shows that the activation of visual face memory for previously unknown learned faces and the subsequent attentional processing and conscious recognition of these faces are delayed in DP. N250 and P600f components to Own Faces did not differ between the two groups, indicating that the processing of long-term familiar faces is less affected in DP. However, P600f components to Own Faces were absent in two participants with DP who failed to recognize their Own Face during the experiment. These results provide new evidence that face recognition deficits in DP may be linked to a delayed activation of visual face memory and explicit identity recognition mechanisms