SMAC mimetics inhibit human T cell proliferation and fail to augment type 1 cytokine responses

Second mitochondria-derived activator of caspases (SMAC) mimetics are small molecule drugs that mimic the activity of the endogenous SMAC protein. SMAC and SMAC mimetics antagonize inhibitors of apoptosis proteins (IAPs), thereby sensitizing cells to apoptosis. As such, SMAC mimetics are being tested in numerous clinical trials for cancer. In addition to their direct anti-cancer effect, it has been suggested that SMAC mimetics may activate T cells, thereby promoting anti-tumor immunity. Here, we tested the effect of three clinically relevant SMAC mimetics on activation of primary human T cells. As previously reported, SMAC mimetics killed tumor cells and activated non-canonical NF-κB in T cells at clinically relevant doses. Surprisingly, none of the SMAC mimetics augmented T cell responses. Rather, SMAC mimetics impaired T cell proliferation and decreased the proportion of IFNγ/TNFα double-producing T cells. These results question the assumption that SMAC mimetics are likely to boost anti-tumor immunity in cancer patients.

Two Factors in Face Recognition: Whether You Know the Person's Face and Whether You Share the Person's Race

One of the best-known phenomena in face recognition is the other-race effect, the observation that own-race faces are better remembered than other-race faces. However, previous studies have not put the magnitude of other-race effect in the context of other influences on face recognition. Here, we compared the effects of (a) a race manipulation (own-race/other-race face) and (b) a familiarity manipulation (familiar/unfamiliar face) in a 2 × 2 factorial design. We found that the familiarity effect was several times larger than the race effect in all performance measures. However, participants expected race to have a larger effect on others than it actually did. Face recognition accuracy depends much more on whether you know the person’s face than whether you share the same race.

How many faces do people know?

Over our species history, humans have typically lived in small groups of under a hundred individuals. However, our face recognition abilities appear to equip us to recognize very many individuals, perhaps thousands. Modern society provides access to huge numbers of faces, but no one has established how many faces people actually know. Here, we describe a method for estimating this number. By combining separate measures of recall and recognition, we show that people know about 5000 faces on average and that individual differences are large. Our findings offer a possible explanation for large variation in identification performance. They also provide constraints on understanding the qualitative differences between perception of familiar and unfamiliar faces-a distinction that underlies all current theories of face recognition.

The Role of Within-Person Variability in Forming Stable Face Representations

We are usually able to recognise novel instances of familiar faces with little difficulty; yet unfamiliar face recognition can be dramatically impaired by natural within-person variability. Unless otherwise prompted, naturally varying instances of an unfamiliar face are often perceived as belonging to multiple different people (Jenkins, White, Van Montford & Burton, 2011). In Experiment 1 participants sorted naturally varying images of unfamiliar faces into their separate identities; half were told that only two target identities were present (constrained), while half were given no indication of the number of targets (unconstrained). Results indicate that unconstrained participants sorted images into 7.5 identities (mean 5 images per pile). On a subsequent matching test, participants who had performed a constrained sort were more accurate than unconstrained sorters, although matching task accuracy was greater for identities seen in the sorting task than for completely novel faces. To investigate this form of learning, Experiment 2 replicated the design using equally complex non-face stimuli (photographic negative faces from Experiment 1). Results indicate that while sorting and matching accuracy was generally poorer, matching task accuracy was greater for learnt than novel negatives. The implications of these findings are discussed with regards to the importance of within-person variability in developing stable face representations.

Transparency of Geometric Distortions in Face Identity

Research has suggested that processing the spatial interrelationship of facial features is crucial to face perception (Diamond & Carey, 1986; Maurer, Le Grand, & Mondloch, 2002). However, recent research that has examined the effect of stretched and sheared images has suggested that early visual processes do not discriminate between an undistorted image and a severe geometric distortion of the same image (Bindemann, Burton, Leuthold, & Schweinberger, 2008). In two experiments, we show that both familiar and unfamiliar face recognition may be robust to geometric distortions. Using a familiar/unfamiliar judgment task, Experiment 1 compared correct reaction times and accuracy for undistorted face images to vertically and horizontally stretched front-view images. In Experiment 2, we compared undistorted face images to stretched, sheared, and twisted face images seen in front- and three-quarter-viewpoints. Observers saw all familiar and unfamiliar faces randomly in all distorted conditions. In both experiments, we found robust accuracy in all conditions despite effects on correct reaction times and substantial within-image deformation in distorted conditions. The findings suggest that processing the spatial interrelationship of features may not be crucial for correctly recognising a familiar face and correctly rejecting an unfamiliar face. This raises questions about the role of configural information in face processing for identity.

Sequence learning by action and observation: Evidence for separate mechanisms

In the Serial Reaction Time (SRT) task, participants respond to a set of stimuli the order of which is apparently random, but which consists of repeating sub-sequences. Participants can become sensitive to this regularity, as measured by an indirect test of reaction time, but can remain apparently unaware of the sequence, as measured by direct tests of prediction or recognition. Some researchers have claimed that this learning may take place by observation alone. We suggest that observational learning may be due to explicit acquired knowledge of the sequence, and is not mediated by the same processes which give rise to learning by action. In Expt 1, we show that it is very difficult to acquire explicit sequence knowledge under dual task conditions, even when participants are told that a regular sequence exists. In Expt 2, we use the same conditions to compare actors, who respond to the sequence during learning, and observers, who merely watch the stimuli. Furthermore, we manipulate the salience of the sequence, in order to encourage learning. There is no evidence of observational learning in these conditions, despite the usual effects of learning being demonstrated by actors. In Expt 3, we show that observational learning does occur, but only when observers have no secondary task and even then only reliably for a sequence which has been made salient by chunking subcomponents. We conclude that sequence learning by observation is mediated by explicit processes, and is eliminated under conditions which support learning by action, but make it difficult to acquire explicit knowledge.

Children and adults recall the names of highly familiar faces faster than semantic information

Adults find it harder to remember the names of familiar people than other biographical information such as occupation or nationality. It has been suggested that the opposite effect occurs in children (Scanlan & Johnston, 1997). We failed to replicate the effects found by Scanlan and Johnston and instead found that children were slower to match a name than an occupation to a famous face (Experiment 1). In Experiments 2 and 3, however, we show a temporal advantage for names in both adults and children when highly familiar faces are used. This is the case for famous and personally known faces. These results show that the speed of name retrieval is influenced by familiarity in the same way in both children and adults and indicate that children do not represent knowledge for familiar people differently from adults. The implications of these results for current models of name retrieval difficulties are discussed.

Bereavement after caregiving or unexpected death: effects on elderly spouses

Responses to bereavement have been shown to vary depending on whether death is expected or unexpected, and on the nature of family caregiving experiences, but little previous research has examined these factors simultaneously. To address these issues, we utilized prospective data on bereavement from 193 participants in the Changing Lives of Older Couples (CLOC) study, who were assessed both before their loss and at six and 18 months after the death. Participants who experienced either unexpected loss, or expected loss without caregiving, with low-stress caregiving, or with high-stress caregiving completed measures of psychological, social, and health functioning on each occasion. Results showed that unexpected death was associated with marked increases in depression, while the nature of caregiving did not affect the trajectory of any of the psychological well-being measures. All groups except highly stressed caregivers showed improvements in social activity and support after bereavement, suggesting that highly stressed caregivers may be at an increased risk for social isolation during bereavement. Thus experiencing an unexpected death may put bereaved spouses at risk for depression, while high-stress caregiving may lead to problems with social isolation.

Human and automatic face recognition: a comparison across image formats

Human subjects perform poorly at matching different images of unfamiliar faces. When images are taken by different capture devices (cameras), matching is difficult for human perceivers and also for automatic systems. We test an automatic face recognition system based on principal components analysis (PCA) and compare its performance with that of human subjects tested on the same set of images. A number of variants of the PCA system are compared, using different matching metrics and different numbers of components. PCA performance critically depends on the choice of distance metric, with a Mahalanobis metric consistently outperforming a Euclidean metric. Under optimal conditions, the automatic PCA system exceeds human performance on the same images. We hypothesise that unfamiliar face recognition may be mediated by processes corresponding to rather simple functions of the inputs.

Semantic priming of person recognition: categorial priming may be a weaker form of the associative priming effect

An interactive activation and competition account (Burton, Bruce, & Johnston, 1990) of the semantic priming effect in person recognition studies relies on the fact that primes and targets (people) have semantic information in common. However, recent investigations into the type of relationship needed to mediate the semantic priming effect have suggested that the prime and target must be close associates (e.g., Barry, Johnston, & Scanlan, 1998; Young, Flude, Hellawell, & Ellis, 1994). A review of these and similar papers suggests the possibility of a small but non-reliable effect based purely on categorial relationships. Experiment 1 provided evidence that when participants were asked to make a name familiarity decision it was possible to boost this small categorial effect when multiple (four) primes were presented prior to the target name. Results from Experiment 2 indicated that the categorial effect was not due to the particular presentation times of the primes. This boosted categorial effect was shown to cross domains (names to faces) in Experiment 3 and persist in Experiment 4 when the task involved naming the target face. The similarity of the pattern of results produced by the associative priming effect and this boosted categorial effect suggests that the two may be due to the same underlying mechanism in semantic memory.

Learning complex sequences: no role for observation?

Two experiments examined performance in a sequence learning task. Participants were trained on a repeating sequence which was presented as a visual display and learning was measured via the increase in reaction time to respond to a new sequence. Some participants made a response to each stimulus while others merely observed the sequence. In Experiment 1 participants responding to the display via a keypress showed learning, but those merely observing did not. Five possible reasons for the failure to find observational learning were considered and the Experiment 2 attempted to resolve these. This second experiment confirmed the findings of Experiment 1 in a non-spatial sequence display using a cover story which encouraged attention to the display but not rule-search strategies. The results are discussed in relation to applied and theoretical aspects of implicit learning.

Matching identities of familiar and unfamiliar faces caught on CCTV images

People can be inaccurate at matching unfamiliar faces shown in high-quality video images, even when viewpoint and facial expressions are closely matched. However, identification of highly familiar faces appears good, even when video quality is poor. Experiment 1 reported a direct comparison between familiar and unfamiliar faces. Participants who were personally familiar with target items appearing on video were highly accurate at a verification task. Unfamiliar participants doing the same task performed very inaccurately. Familiarity affected discriminability, but not bias. Experiments 2 and 3 showed that brief periods of familiarization have little beneficial effect unless "deep" or "social" processing is encouraged. The results show that video evidence can be used effectively as a probe to identity when the faces shown are highly familiar to observers, but caution should be used where images of unfamiliar people are being compared.

Priming the access to names of famous faces

There is a continuing controversy in models of face identification concerning the level of access to names relative to semantic information. In order to determine whether names are accessed sequentially after or in parallel to semantic information, we studied participants' speeded decisions about famous faces that were primed by partial semantic or partial name information. Decisions that required the access to the celebrity's name (one or more forename syllables, Expt 1) were significantly primed by partial name primes (initials or name fragments). However, at variance with sequential stage models, no reliable priming was observed by partial semantic primes (information about nationality, occupation, or whether a person was dead or alive). Moreover, there was a clear and consistent priming effect by partial semantic primes if the task was a nationality (British or American) decision that required the access to semantic information (Expt 2), demonstrating the effectiveness of these primes. The effects of partial name primes on nationality decisions were less consistent, with a significant effect for name fragments but not initials. However, effects of name primes were generally greater for syllable decisions than nationality decisions, and effects of semantic primes were generally greater for nationality decisions than syllable decisions. Taken together, these results favour a model of parallel rather than sequential access and suggest some degree of independence in the access to personal semantics and names.

A principal component analysis of facial expressions

Pictures of facial expressions from the Ekman and Friesen set (Ekman, P., Friesen, W. V., (1976). Pictures of facial affect. Palo Alto, California: Consulting Psychologists Press) were submitted to a principal component analysis (PCA) of their pixel intensities. The output of the PCA was submitted to a series of linear discriminant analyses which revealed three principal findings: (1) a PCA-based system can support facial expression recognition, (2) continuous two-dimensional models of emotion (e.g. Russell, J. A. (1980). A circumplex model of affect. Journal of Personality and Social Psychology, 39, 1161-1178) are reflected in the statistical structure of the Ekman and Friesen facial expressions, and (3) components for coding facial expression information are largely different to components for facial identity information. The implications for models of face processing are discussed.

Incidental learning of real-world regularities

The large literature on incidental learning relies almost exclusively on laboratory experiments. Whenever researchers have attempted to demonstrate incidental learning of real-world regularities, they have typically failed to show learning. For example, it is well established that people do not learn regularities in everyday objects, such as the left-right orientation of faces on coins, despite a very large exposure to them. In this report, we examine this apparent contradiction. We argue that most studies exploring real-life incidental learning use tests that are not as sensitive to low-confidence information as those traditionally used in laboratory tasks. Using more sensitive measures, we show that it is possible to learn regularities from British and Japanese cultural life as a direct result of exposure to these regularities. Further, confidence measures suggest that although the information may be acquired incidentally, it can be expressed with and without concomitant awareness of that knowledge.

Covert face recognition in neurologically intact participants

Prosopagnosic patients may maintain some ability to recognize familiar faces, although they remain unaware of this ability. This phenomenon--called covert face recognition--was investigated in neurologically intact participants, using priming techniques. Participants were quicker to indicate that a target-name was familiar when the preceding prime-face belonged to the same person compared with an unrelated familiar person. This was observed both when prime-faces could be recognized overtly and when they were presented too briefly to be recognized overtly (Exps. 1 and 2). Thus, covert face recognition was observed in neurologically intact participants. In Exp. 3, participants were quicker to recognize a familiar face when that person's face had been seen previously, but only when it had been recognized overtly on the first encounter. These results are interpreted within the framework of an interactive activation model of face recognition.

Perceptual priming is not a necessary consequence of semantic classification of pictures

Four experiments investigated how repetition priming of object recognition is affected by the task performed in the prime and test phases. In Experiment 1 object recognition was tested using both vocal naming and two different semantic decision tasks (whether or not objects were manufactured, and whether or not they would be found inside the house). Some aspects of the data were inconsistent with contemporary models of object recognition. Specifically, object priming was eliminated with some combinations of prime and test tasks, and there was no evidence of perceptual (as opposed to conceptual or response) priming in either semantic classification task, even though perceptual identification of the objects is required for at least one of these tasks. Experiment 2 showed that even when perceptual demands were increased by brief presentation, the inside task showed no perceptual priming. Experiment 3 showed that the inside task did not appear to be based on conceptual priming either, as it was not primed significantly when the prime decisions were made to object labels. Experiment 4 showed that visual sensitivity could be restored to the inside task following practice on the task, supporting the suggestion that a critical factor is whether the semantic category is preformed or must be computed. The results show that the visual representational processes revealed by object priming depend crucially on the task chosen.

Lighting direction affects recognition of untextured faces in photographic positive and negative

Face recognition in photographic positive and negative was examined in a same/different matching task in five lighting direction conditions using untextured 3-D laser-scanned faces. The lighting directions were +60, +30, 0, -30 and -60 degrees, where negative values represent bottom lighting and positive values represent top lighting. Recognition performance was better for faces in positive than in negative when lighting directions were at +60 degrees. In one experiment, the same effect was also found at +30 degrees. However, faces in negative were recognized better than positive when the direction was -60 degrees. There was no difference in recognition performance when the lighting direction was 0 and -30 degrees. These results confirm that the effect of lighting direction can be a determinant of the photographic negative effect. Positive faces, which normally appear to be top-lit, may be difficult to recognize in negative partly because of the accompanying change in apparent lighting direction to bottom-lit.

Asymmetric dependencies in perceiving identity and emotion: experiments with morphed faces

We investigated whether an asymmetric relationship between the perception of identity and emotional expressions in faces (Schweinberger & Soukup, 1998) may be related to differences in the relative processing speed of identity and expression information. Stimulus faces were morphed across identity within a given emotional expression, or were morphed across emotion within a given identity. In Experiment 1, consistent classifications of these images were demonstrated across a wide range of morphing, with only a relatively narrow category boundary. At the same time, classification reaction times (RTs) reflected the increased perceptual difficulty of the morphed images. In Experiment 2, we investigated the effects of variations in the irrelevant dimension on judgments of faces with respect to a relevant dimension, using a Garner-type speeded classification task. RTs for expression classifications were strongly influenced by irrelevant identity information. In contrast, RTs for identity classifications were unaffected by irrelevant expression information, and this held even for stimuli in which identity was more difficult and slower to discriminate than expression. This suggests that differences in processing speed cannot account for the asymmetric relationship between identity and emotion perception. Theoretical accounts proposing independence of identity and emotion perception are discussed in the light of these findings.

Prime time advertisements: repetition priming from faces seen on subject recruitment posters

Repetition priming is defined as a gain in item recognition after previous exposure. Repetition priming of face recognition has been shown to last for several months, despite contamination by everyday exposure to both experimental and control faces in the interval. Here we show that gains in face recognition in the laboratory are found from faces initially seen in a rather different context--on subject recruitment posters, even when the advertisements make no specific mention of experiments involving face recognition. The priming was greatest when identical pictures were shown in the posters and in the test phase, although different views of faces did give significant priming in one study. Follow-up studies revealed poor explicit memory for the faces shown on the posters. The results of these experiments are used to develop a model in which repetition priming reflects the process of updating representations of familiar faces.

Investigating the relation between imagery and perception: evidence from face priming

The relation between imagery and perception was investigated in face priming. Two experiments are reported in which subjects either saw or imagined the faces of celebrities. They were later given a speeded perceptual test (familiarity judgement to pictures of celebrities) or a speeded imagery test (in which they were told the names of celebrities and asked to make a decision about their appearance). Seeing faces primed the perceptual test, and imaging faces primed the imagery test; however, there was no priming between seeing and imaging faces. These results show that perception and imagery can be dissociated in normal subjects. In two further experiments, we examined the effects of imaging faces on a subsequent face-naming task and on a task requiring familiarity judgements to partial faces. Both these tasks were facilitated by prior imaging of faces. These results are discussed in relation to those of McDermott & Roediger (1994), who found that imagery promoted object priming in a perceptual test involving naming partial line drawings. The implications for models of face recognition are also discussed.

An artificial neural network system for diagnosis of acute myocardial infarction (AMI) in the accident and emergency department: evaluation and comparison with serum myoglobin measurements

Recent studies have confirmed that artificial neural networks (ANNs) are adept at recognising patterns in sets of clinical data. The diagnosis of acute myocardial infarction (AMI) in patients presenting with chest pain remains one of the greatest challenges in emergency medicine. The aim of this study was to evaluate the performance of an ANN trained to analyse clinical data from chest pain patients. The ANN was compared with serum myoglobin measurements--cardiac damage is associated with increased circulating myoglobin levels, and this is widely used as an early marker for evolving AMI. We used 39 items of clinical and ECG data from the time of presentation to derive 53 binary inputs to a back propagation network. On test data (200 cases), overall accuracy, sensitivity, specificity and positive predictive value (PPV) of the ANN were 91.8, 91.2, 90.2 and 84.9% respectively. Corresponding figures using linear discriminant analysis were 81.0, 77.9, 82.6 and 69.7% (P < 0.01). Using a further test set from a different centre (91 cases), the accuracy, sensitivity, specificity and PPV for the admitting physicians were 65.1, 28.5, 76.9 and 28.6% respectively compared with 73.6, 52.4, 80.0 and 44.0% for the ANN. Although myoglobin at presentation was highly specific, it was only 38.0% sensitive, compared with 85.7% at 3 h. Simple strategies to combine clinical opinion, ANN output and myoglobin at presentation could greatly improve sensitivity and specificity of AMI diagnosis. The ideal support for emergency room physicians may come from a combination of computer-aided analysis of clinical factors and biochemical markers such as myoglobin. This study demonstrates that the two approaches could be usefully combined, the major benefit of the decision support system being in the first 3 h before biochemical markers have become abnormal.

Modelling face recognition

Much early work in the psychology of face processing was hampered by a failure to think carefully about task demands. Recently our understanding of the processes involved in the recognition of familiar faces has been both encapsulated in, and guided by, functional models of the processes involved in processing and recognizing faces. The specification and predictive power of such theory has been increased with the development of an implemented model, based upon an ‘interactive activation and competition’ architecture. However, a major deficiency in most accounts of face processing is their failure to spell out the perceptual primitives that form the basis of our representations for faces. Possible representational schemes are discussed, and the potential role of three-dimensional representations of the face is emphasized.

Two loci of repetition priming in the recognition of familiar faces

Four experiments examining the repetition priming of familiar face recognition are reported. The experiments showed that the speed of deciding whether a face is familiar was facilitated by prior presentation of the face, but not by reading the written name or by producing the name in response to a definition. In contrast, reading names and producing names to definitions both primed subsequent naming of the corresponding faces (Experiments 1 and 2). Face naming was primed more by face naming than by either familiarity decisions or naming from description (Experiments 3 and 4). The authors propose that repetition priming of familiar face recognition occurs at 2 distinct loci. The first involves the perceptual recognition of a face as familiar and is domain-specific. The second involves name retrieval and is susceptible to both within- and cross-domain priming.

Early diagnosis of acute myocardial infarction using clinical and electrocardiographic data at presentation: derivation and evaluation of logistic regression models

The aim of this study was to determine which, and how many, data items are required to construct a decision support algorithm for early diagnosis of acute myocardial infarction using clinical and electrocardiographic data available at presentation. Logistic regression models were derived using data items from 600 consecutive patients at one centre (Edinburgh), then tested prospectively on 510 cases from the same centre and 662 consecutive cases from another centre (Sheffield). Although performance of the models increased with progressive addition of data inputs when applied to training data, a simple six-factor model was the most effective on test data, yielding accuracies of 84.3 and 83.6% on the two test sets. A model constructed solely of electrocardiographic data performed nearly as well as those incorporating clinical data. Previously published logistic regression models did not perform so well as the models derived from data collected for this study.

Two loci of repetition priming in the recognition of familiar faces

Four experiments examining the repetition priming of familiar face recognition are reported. The experiments showed that the speed of deciding whether a face is familiar was facilitated by prior presentation of the face, but not by reading the written name or by producing the name in response to a definition. In contrast, reading names and producing names to definitions both primed subsequent naming of the corresponding faces (Experiments 1 and 2). Face naming was primed more by face naming than by either familiarity decisions or naming from description (Experiments 3 and 4). The authors propose that repetition priming of familiar face recognition occurs at 2 distinct loci. The first involves the perceptual recognition of a face as familiar and is domain-specific. The second involves name retrieval and is susceptible to both within- and cross-domain priming.

Face processing: human perception and principal components analysis

Principal components analysis (PCA) of face images is here related to subjects' performance on the same images. In two experiments subjects were shown a set of faces and asked to rate them for distinctiveness. They were subsequently shown a superset of faces and asked to identify those that had appeared originally. Replicating previous work, we found that hits and false positives (FPs) did not correlate: Those faces easy to identify as being "seen" were unrelated to those faces easy to reject as being "unseen." PCA was performed on three data sets: (1) face images with eye position standardized, (2) face images morphed to a standard template to remove shape information, and (3) the shape information from faces only. Analyses based on PCA of shape-free faces gave high predictions of FPs, whereas shape information itself contributed only to hits. Furthermore, whereas FPs were generally predictable from components early in the PCA, hits appeared to be accounted for by later components. We conclude that shape and "texture" (the image-based information remaining after morphing) may be used separately by the human face processing system, and that PCA of images offers a useful tool for understanding this system.

What's distinctive about a distinctive face?

In this study we examine the relationship between objective aspects of facial appearance and facial "distinctiveness". Specifically, we examine whether the extent to which a face deviates from "average" correlates with rated distinctiveness and measures of memorability. We find that, provided the faces are rated with hair concealed, reasonable correlations can be achieved between their physical deviation and their rated distinctiveness. More modest correlations are obtained between physical deviation and the extent to which faces are remembered, either correctly or falsely, after previous study. Furthermore, memory ratings obtained to "target" faces when they have been previously seen (i.e. "hits") do not show the expected negative correlation with the scores obtained to the same faces when acting as distractors (i.e. "false positives"), though each correlates with rated distinctiveness. This confirms the theory of Vokey and Read (1992) that the typicality/distinctiveness dimension can be broken down into two orthogonal components: "memorability" and "context-free familiarity".

Naming faces and naming names: exploring an interactive activation model of person recognition

In this paper we present an interactive activation and competition (IAC) model of name recognition. This is an extension of a previous account of name retrieval (Burton & Bruce, 1992) and is based on a functional model due to Valentine, Bredart, Lawson, and Ward (1991). Several empirical effects of name recognition are simulated: (1) names that are known are read faster than names that are unknown; (2) common names are read faster than rare names; and (3) rare names are recognised as familiar faster than common names. The simulations demonstrate that these complex effects can arise as a natural consequence of the architecture of the IAC model. Finally, we explore a modification of the Valentine et al. functional model, and conclude that the model as originally proposed is best able to account for the available data.

Sex discrimination: how do we tell the difference between male and female faces?

People are remarkably accurate (approaching ceiling) at deciding whether faces are male or female, even when cues from hair style, makeup, and facial hair are minimised. Experiments designed to explore the perceptual basis of our ability to categorise the sex of faces are reported. Subjects were considerably less accurate when asked to judge the sex of three-dimensional (3-D) representations of faces obtained by laser-scanning, compared with a condition where photographs were taken with hair concealed and eyes closed. This suggests that cues from features such as eyebrows, and skin texture, play an important role in decision-making. Performance with the laser-scanned heads remained quite high with 3/4-view faces, where the 3-D shape of the face should be easiest to see, suggesting that the 3-D structure of the face is a further source of information contributing to the classification of its sex. Performance at judging the sex from photographs (with hair concealed) was disrupted if the photographs were inverted, which implies that the superficial cues contributing to the decision are not processed in a purely 'local' way. Performance was also disrupted if the faces were shown in photographic negatives, which is consistent with the use of 3-D information, since negation probably operates by disrupting the computation of shape from shading. In 3-D, the 'average' male face differs from the 'average' female face by having a more protuberant nose/brow and more prominent chin/jaw. The effects of manipulating the shapes of the noses and chins of the laser-scanned heads were assessed and significant effects of such manipulations on the apparent masculinity or femininity of the heads were revealed. It appears that our ability to make this most basic of facial categorisations may be multiply determined by a combination of 2-D, 3-D, and textural cues and their interrelationships.

What's the difference between men and women? Evidence from facial measurement

Human subjects are able to identify the sex of faces with very high accuracy. Using photographs of adults in which hair was concealed by a swimming cap, subjects performed with 96% accuracy. Previous work has identified a number of dimensions on which the faces of men and women differ. An attempt to combine these dimensions into a single function to classify male and female faces reliably is described. Photographs were taken of 91 male and 88 female faces in full face and profile. These were measured in several ways: (i) simple distances between key points in the pictures; (ii) ratios and angles formed between key points in the pictures; (iii) three-dimensional (3-D) distances derived by combination of full-face and profile photographs. Discriminant function analysis showed that the best discriminators were derived from simple distance measurements in the full face (85% accuracy with 12 variables) and 3-D distances (85% accuracy with 6 variables). Combining measures taken from the picture plane with those derived in 3-D produced a discriminator approaching human performance (94% accuracy with 16 variables). Performance of the discriminant function was compared with that of human perceivers and found to be correlated, but far from perfectly. The difficulty of deriving a reliable function to distinguish between the sexes is discussed with reference to the development of automatic face-processing programs in machine vision. It is argued that such systems will need to incorporate an understanding of the stimuli if they are to be effective.

I recognize your face but I can't remember your name: a simple explanation?

When shown the faces of familiar people, subjects are typically slower and less accurate at retrieving names than other semantic information. This finding, along with converging evidence from neuropsychological studies, has influenced most theoretical accounts of face recognition (e.g. Bruce & Young, 1986). These accounts propose that names are stored separately from semantic information, and that they may not be retrieved in the absence of other information. Here we show that it is possible to account for empirical findings without positing a separate store for names. The account is based on an implemented simulation with an interactive activation and competition architecture. We demonstrate that the fact that most names are unique leads naturally to the patterns of recall found in experimental studies.

Understanding covert recognition

An implementation of Bruce and Young's (1986) functional model of face recognition is used to examine patterns of covert face recognition previously reported in a prosopagnosic patient, PH. Although PH is unable to recognize overly the faces of people known to him, he shows normal patterns of face processing when tested indirectly. A simple manipulation of one set of connections in the implemented model induces behaviour consistent with patterns of results from PH obtained in semantic priming and interference tasks. We compare this account with previous explanations of covert recognition and demonstrate that the implemented model provides the most natural and parsimonious account available. Two further patients are discussed who show deficits in person perception. The first (MS) is prosopagnosic but shows no covert recognition. The second (ME) is not prosopagnosic, but cannot access semantic information relating to familiar people. The model provides an account of recognition impairments which is sufficiently general also to be useful in describing these patients.

Understanding face recognition with an interactive activation model

In this paper we describe how the microstructure of the Bruce & Young (1986) functional model of face recognition may be explored and extended using an interactive activation implementation. A simulation of the recognition of familiarity of individuals is developed which accounts for a range of published findings on the effects of semantic priming, repetition priming and distinctiveness. Finally, we offer some speculative predictions made by the model, and point to an empirical programme of research which it suggests.

Parturition in the guinea-pig; plasma levels of steroid hormones, steroid-binding proteins, and oxytocin, and the effect of corticosteroids, prostaglandins and adrenocorticotrophin

Parturition in the guinea-pig is not preceded by any consistent change in the maternal plasma concentrations of progesterone, total unconjugated oestrogens or corticosteroids, or by a significant change in the concentration of progesterone-binding globulin (PBG). The onset of parturition was delayed by high doses of oestrogens (stilboestrol and oestradiol), but was not affected by oestriol or an antiserum raised against oestradiol. Premature parturition was achieved by the intra-carotid infusion of adrenocorticotrophin or prostaglandins (PGF2α, PGE2, I.C.I. 80,996) in conscious animals with indwelling catheters. I.C.I. 80,996, a potent analogue of PGF2α, induced parturition in all seven guinea-pigs treated; delivery occurred within 6 h of starting the infusion in six animals, and within 48 h in the seventh. The undesirable side-effects that accompanied treatment with PGF2α or PGE2 were not encountered with I.C.I. 80,996. Parturition induced experimentally resembled normal delivery but was not preceded by any significant change in the maternal levels of progesterone, total unconjugated oestrogens, corticosteroids, PBG or CBG in the circulation. Oxytocin was not detected until the delivery of the first foetus.

Parturition was not induced by maternal or foetal injections of corticosteroids or dexamethasone. Earlier findings are confirmed that the foetal adrenal grows steadily throughout late pregnancy and, unlike the foetal lamb adrenal, undergoes no rapid phase of growth immediately before term. Foetal adrenal weight decreased relative to foetal body weight.

The trigger for parturition in this species remains unidentified.

The maintenance of pregnancy, and parturition, in guinea-pigs hypophysectomized within 4 days of mating

Pregnancy was sustained to term (>63 days) in 15 out of a total of 46 guinea-pigs, hypophysectomized within 4 days after mating. The majority (22/29) of complete or partial abortions occurred between 20 and 35 days post coitum. Analysis of plasma samples showed that the pregnant hypophysectomized animals with live foetuses had high progesterone and progesterone-binding protein concentrations, equivalent to those found in intact pregnant guinea-pigs. Animals that received daily injections of cortisone acetate from day 55 (7/15) gave birth to live young at the normal time (67–68 days). Plasma samples from one animal taken during parturition showed no measurable oxytocin in maternal plasma, but oxytocin was present in foetal plasma at the moment of birth.

Observations on the release and clearance of neurophysin and the neurohypophysial hormones in the rat

Circulating levels of neurophysin, oxytocin and vasopressin were determined in rats under various physiological conditions using bovine neurophysin as the reference standard. Under resting conditions the mean plasma concentration of immunoreactive neurophysin was 6·2 ± 2·4 ng/ml while oxytocin and vasopressin were undetectable.

Neurophysin and vasopressin were released in response to haemorrhage in Wistar and heterozygous Brattleboro rats; in the homozygous strain haemorrhage resulted in a release of oxytocin and neurophysin. Infusion of 0·1 M-calcium chloride into Wistar rats caused a rise in plasma neurophysin, oxytocin and vasopressin. The half-times for the disappearance from the plasma of arginine-vasopressin and neurophysin in the circulation were 1·6 ± 0·8 (S.D.) and 3·4 ± 0·9 min respectively.