The horizontal and vertical relations in upright faces are transmitted by different spatial frequency ranges

Faces convey distinct types of information: features and their spatial relations, which are differentially vulnerable to inversion. While inversion largely disrupts the processing of vertical spatial relations (e.g. eyes’ height), its effect is moderate for horizontal relations (e.g. interocular distance) and local feature properties. The SF ranges optimally transmitting horizontal and vertical face relations were here investigated to further address their functional role in face perception. Participants matched upright and inverted pairs of faces that differed at the level of local featural properties, horizontal relations in vertical relations. Irrespective of SF, the inversion effect was larger for vertical than horizontal and featural cues. Most interestingly, SF differentially influenced the processing of vertical, horizontal and featural cues in upright faces. Vertical relations were optimally processed in intermediate SF, which are known to carry useful information for face individuation. In contrast, horizontal relations were best conveyed by high SF, which are involved in the processing of local face properties. These findings not only confirm that horizontal and vertical relations play distinct functional roles in face perception, but they also further suggest a unique role of vertical relations in face individuation.     

Face inversion disrupts the perception of vertical relations between features in the right human occipito‐temporal cortex

The impact of inversion on the extraction of relational and featural face information was investigated in two fMRI experiments. Unlike previous studies, the contribution of horizontal and vertical spatial relations were considered separately since they have been shown to be differentially vulnerable to face inversion (Goffaux & Rossion, 2007). Hence, inversion largely affects the perception of vertical relations (e.g. eye or mouth height) while the processing of features (e.g. eye shape and surface) and of horizontal relations (e.g. inter‐ocular distance) is affected to a far lesser extent. Participants viewed pairs of faces that differed either at the level of one local feature (i.e. the eyes) or of the spatial relations of this feature with adjacent features. Changes of spatial relations were divided into two conditions, depending on the vertical or horizontal axis of the modifications. These stimulus conditions were presented in separate blocks in the first (block) experiment while they were presented in a random order in the second event‐related (ER) experiment. Face‐preferring voxels located in the right‐lateralized middle fusiform gyrus (rMFG) largely decreased their activity with inversion. Inversion‐related decreases were more moderate in left‐lateralized middle fusiform gyrus (lMFG). ER experiment revealed that inversion affected rMFG and lMFG activity in distinct stimulus conditions. Whereas inversion affected lMFG processing only in featural condition, inversion selectively affected the processing of vertical relations in rMFG. Correlation analyses further indicated that the inversion effect (IE) observed in rMFG and right inferior occipital gyrus (rIOG) reliably predicted the large behavioural IE observed for the processing of vertical relations. In contrast, lMFG IE correlated with the weak behavioural IE observed for the processing of horizontal relations. Our findings suggest that face configuration is mostly encoded in rMFG, whereas more local aspects of face information, such as features and horizontal spatial relations drive lMFG processing. These findings corroborate the view that the vulnerability of face perception to inversion stems mainly from the disrupted processing of vertical face relations in the right‐lateralized network of face‐preferring regions (rMFG, rIOG).     

The time course of face matching for featural and relational image manipulations

It was found recently that horizontal and vertical relationships of facial features are differently vulnerable to inversion (Goffaux & Rossion, 2007). When faces are upside down manipulations of vertical relations are difficult to detect, while only moderate performance deficits are found for manipulations of horizontal relations, or when features differ. We replicate the findings of Goffaux and Rossion, and record the temporal courses of face matching performance and the effects of inversion. For vertical relations and featural changes inversion effects arise immediately, starting with the first 50 ms of processing. For horizontal relations inversion effects are absent at brief timings, but arise later, after about 200 ms. The final magnitudes of inversion effects are different in all three conditions, reaching 23.4% for vertical displacement, 10.7% for feature replacement, and 5.8% for horizontal displacement. Our results underline the special status of horizontal in contrast to vertical feature relations, and indicate that local and global configural information is handled in parallel by specific routines, as proposed recently (Senunkova & Barton, 2008).     

Picture-plane inversion leads to qualitative changes of face perception

Presenting a face stimulus upside-down generally causes a larger deficit in perceiving metric distances between facial features ("configuration") than local properties of these features. This effect supports a qualitative account of face inversion: the same transformation affects the processing of different kinds of information differently. However, this view has been recently challenged by studies reporting equal inversion costs of performance for discriminating featural and configural manipulations on faces. In this paper I argue that these studies did not replicate previous results due to methodological factors rather than largely irrelevant parameters such as having equal performance for configural and featural conditions at upright orientation, or randomizing trials across conditions. I also argue that identifying similar diagnostic features (eyes and eyebrows) for discriminating individual faces at upright and inverted orientations by means of response classification methods does not dismiss at all the qualitative view of face inversion. Considering these elements as well as both behavioral and neuropsychological evidence, I propose that the generally larger effect of inversion for processing configural than featural cues is a mere consequence of the disruption of holistic face perception. That is, configural relations necessarily involve two or more distant features on the face, such that their perception is most dependent on the ability to perceive simultaneously multiple features of a face as a whole.     

A feature-inversion effect: can an isolated feature show behavior like the face-inversion effect?

The face-inversion effect (FIE) is explained by the configural-processing hypothesis. It proposes that inversion disrupts configural information processing (spatial links among facial features) and leaves the processing of featural information (eyes, nose, and mouth) comparatively intact. According to this hypothesis, an inverted isolated facial feature cannot show a feature-inversion effect--that is, behavior similar to the FIE--since all the spatial links between it and the other features in a face are eliminated; that is, the configural information is removed. The findings of the present study, which show that isolated eyes do exhibit the feature-inversion effect, support the extended configural-processing hypothesis. This proposes that inversion also impairs processing of the configural information within the eyes themselves. Removal of the brows in whole faces tended to interfere with processing of the configural information in the upright position but to facilitate processing in the inverted position.     

When feature information comes first! Early processing of inverted faces

We investigated the early stages of face recognition and the role of featural and holistic face information. We exploited the fact that, on inversion, the alienating disorientation of the eyes and mouth in thatcherised faces is hardly detectable. This effect allows featural and holistic information to be dissociated and was used to test specific face-processing hypotheses. In inverted thatcherised faces, the cardinal features are already correctly oriented, whereas in undistorted faces, the whole Gestalt is coherent but all information is disoriented. Experiment 1 and experiment 3 revealed that, for inverted faces, featural information processing precedes holistic information. Moreover, the processing of contextual information is necessary to process local featural information within a short presentation time (26 ms). Furthermore, for upright faces, holistic information seems to be available faster than for inverted faces (experiment 2). These differences in processing inverted and upright faces presumably cause the differential importance of featural and holistic information for inverted and upright faces.     

Beyond U-Shaped Development in Infants' Processing of Faces: An Information-Processing Account

The development of the "inversion" effect in face processing was examined in infants 3 to 6 months of age by testing their integration of the internal and external features of upright and inverted faces using a variation of the "switch" visual habituation paradigm. When combined with previous findings showing that 7-month-olds use integrative processing of an upright face, but featural processing of an inverted face (Cohen & Cashon, 2001a), the present findings suggest that from 3 to 7 months, infants' ability to integrate facial features follows an N-shaped developmental pattern for upright faces and an inverted U-shaped pattern for inverted faces. We discuss these results in terms of a set of domain-general information-processing principles.     

The effect of inversion on the encoding of normal and “thatcherized” faces

In the “Thatcher illusion” a face, in which the eyes and mouth are inverted relative to the rest of the face, looks grotesque when shown upright but not when inverted. In four experiments we investigated the contribution of local and global processing to this illusion in normal observers. We examined inversion effects (i.e., better performance for upright than for inverted faces) in a task requiring discrimination of whether faces were or were not “thatcherized”. Observers made same/different judgements to isolated face parts (Experiments 1-2) and to whole faces (Experiments 3-4). Face pairs had the same or different identity, allowing for different process- ing strategies using feature-based or configural information, respectively. In Experiment 1, feature-based matching of same-person face parts yielded only a small inversion effect for normal face parts. However, when feature-based matching was prevented by using the face parts of different people on all trials (Experiment 2) an inversion effect occurred for normal but not for thatcherized parts. In Experiments 3 and 4, inversion effects occurred with normal but not with thatcherized whole faces, on both same- and different-person matching tasks. This suggests that a common configural strategy was used with whole (normal) faces. Face context facilitated attention to misoriented parts in same-person but not in different-person matching. The results indicate that (1) face inversion disrupts local configural processing, but not the processing of image features, and (2) thatcherization disrupts local configural processing in upright faces.     

The respective role of low and high spatial frequencies in supporting configural and featural processing of faces

One distinctive feature of processing faces, as compared to other categories, is thought to be the large dependence on configural cues such as the metric relations among features. To test the role of low spatial frequencies (LSFs) and high spatial frequencies (HSFs) in configural and featural processing, subjects were presented with triplets of faces that were filtered to preserve either LSFs (below 8 cycles per face width), HSFs (above 32 cycles per face width), or the full frequency spectrum. They were asked to match one of two probe faces to a target face. The distractor probe face differed from the target either configurally, featurally, or both featurally and configurally. When the difference was at the configural level, performance was better with LSF faces than with HSF faces. In contrast, with a featural difference, a strong performance advantage was found for HSF faces as compared to LSF faces. These results support the dominant role that LSFs play in the configural processing of faces, whereas featural processing is largely dependent on HSFs.     

The face inversion effect—Parts and wholes: Individual features and their configuration

The face inversion effect (FIE) is a reduction in recognition performance for inverted faces (compared to upright faces) that is greater than that typically observed with other stimulus types (e.g., houses). The work of Diamond and Carey, suggests that a special type of configural information, “second-order relational information” is critical in generating this inversion effect. However, Tanaka and Farah concluded that greater reliance on second-order relational information did not directly result in greater sensitivity to inversion, and they suggested that the FIE is not entirely due to a reliance on this type of configural information. A more recent review by McKone and Yovel provides a meta-analysis that makes a similar point. In this paper, we investigated the contributions made by configural and featural information to the FIE. Experiments 1a and1b investigated the link between configural information and the FIE. Remarkably, Experiment 1b showed that disruption of all configural information of the type considered in Diamond and Carey's analysis (both first and second order) was effective in reducing recognition performance, but did not significantly impact on the FIE. Experiments 2 and 3 revealed that face processing is affected by the orientation of individual features and that this plays a major role in producing the FIE. The FIE was only completely eliminated when we disrupted the single feature orientation information in addition to the configural information, by using a new type of transformation similar to Thatcherizing our sets of scrambled faces. We conclude by noting that our results for scrambled faces are consistent with an account that has recognition performance entirely determined by the proportion of upright facial features within a stimulus, and that any ability to make use of the spatial configuration of these features seems to benefit upright and inverted normal faces alike.     

Featural and configurational processes in the recognition of faces of different familiarity

Previous research suggests that face recognition may involve both configurational and piecemeal (featural) processing. To explore the relationship between these processing modes, we examined the patterns of recognition impairment produced by blurring, inversion, and scrambling, both singly and in various combinations. Two tasks were used: recognition of unfamiliar faces (seen once before) and recognition of highly familiar faces (celebrities). The results provide further support for a configurational-featural distinction. Recognition performance remained well above chance if faces were blurred, scrambled, inverted, or simultaneously inverted and scrambled: each of these manipulations disrupts either configurational or piecemeal processing, leaving the other mode available as a route to recognition. However, blurred/scrambled and blurred/inverted faces were recognised at or near chance levels, presumably because both configurational processing and featural processing were disrupted. Similar patterns of effects were found for both familiar and unfamiliar faces, suggesting that the relationship between configurational and featural processing is qualitatively similar in both cases.     

The effects of face inversion on the perception of long-range and local spatial relations in eye and mouth configuration

A recent study hypothesized a configurational anisotropy in the face inversion effect, with vertical relations more difficult to process. However, another difference in the stimuli of that report was that the vertical but not horizontal shifts lacked local spatial references. Difficulty processing long-range spatial relations might also be predicted from a relevance-interaction explanation, which proposes that in inverted faces, spatial relations are processed efficiently only within high-relevance local regions. The authors performed 2 experiments to distinguish between these hypotheses. Experiment 1 showed that the inversion effect for vertical shifts of the eyes alone was more similar to that for horizontal eye shifts than for vertical shifts of the eyes and eyebrows. In Experiment 2, focused attention reduced the inversion effect for vertical mouth position more than that for vertical shifts of the eyes and brows. The authors concluded that face inversion impairs the perception of both local spatial relations in low-relevance regions and long-range spatial relations extending across multiple facial regions, consistent with a loss of efficient whole-face processing of the spatial relations between features.     

Older adults' configural processing of faces: role of second-order information

Problems with face recognition are frequent in older adults. However, the mechanisms involved have only been partially discovered. In particular, it is unknown to what extent these problems may be related to changes in configural face processing. Here, we investigated the face inversion effect (FIE) together with the ability to detect modifications in the vertical or horizontal second-order relations between facial features. We used a same/different unfamiliar face discrimination task with 33 young and 33 older adults. The results showed dissociations in the performances of older versus younger adults. There was a lack of inversion effect during the recognition of original faces by older adults. However, for modified faces, older adults showed a pattern of performance similar to that of young participants, with preserved FIE for vertically modified faces and no detectable FIE for horizontally modified faces. Most importantly, the detection of vertical modifications was preserved in older relative to young adults whereas the detection of horizontal modifications was markedly diminished. We conclude that age has dissociable effects on configural face-encoding processes, with a relative preservation of vertical compared to horizontal second-order relations processing. These results help to understand some divergent results in the literature and may explain the spared familiar face identification abilities in the daily lives of older adults.     

Configural processing and perceptions of head tilt

Configural processing is important for face recognition, but its role in other types of face processing is unclear. In the present study, participants made judgments of head tilt for faces in which the vertical position of the internal facial region was varied. We found a highly reliable relationship between inner-face position and perceived head tilt. We also found that changes in inner-face position affected the perceived dimensions of an individual unchanged facial feature: compared to control faces, nearly two-thirds of faces in which the features had been moved down were judged to have a longer nose. This finding suggests an early integration of configural and featural processing to create a stable holistic percept of the face. The demonstration of holistic processing at a basic perceptual level (as opposed to during face recognition) is important as it constrains possible models of the relationships between featural and configural processing.     

Neural developmental changes in processing inverted faces

We explored developmental changes in neural substrates for face processing, using fMRI. Children and adults performed a perceptual-matching task with upright and inverted face and animal stimuli. Behaviorally, inversion disrupted face processing more than animal processing for adults and older children. In line with this behavioral pattern, the left middle occipital gyrus showed a stronger face than animal inversion effect in adults. Moreover, a superior aspect of this region showed a greater face inversion effect in older than in younger children, indicating a developmental change in the processing of inverted faces. The visual regions recruited for inverted face processing in adults also overlapped more with brain regions involved in the viewing of upright objects than with regions involved in the viewing of upright faces in an independent localizer task. Hence, when faces are inverted, adults recruit regions normally engaged for recognizing objects, possibly pointing to a role for the featural processing of inverted faces.     

The other-race effect: Holistic coding differences and beyond

We evaluate claims that the other-race effect in face memory reflects stronger holistic coding of own-race than other-race faces. Considering evidence from a range of paradigms, including the inversion effect, part–whole effect, composite effect, and the scrambled/blurred task, we find considerable inconsistency, both between paradigms and between participant ethnicities. At the same time, however, studies that isolate configural and component feature processing consistently show better featural, as well as better configural, processing of own-race faces, for both Caucasian and Asian participants. These results raise the possibility that the key feature of own-race face processing is not stronger holistic processing per se, but rather more effective processing of all types of face information (featural as well as holistic).     

Explaining the face-inversion effect: the face–scheme incompatibility (FSI) model

The face-inversion effect (FIE) can be viewed as being based on two kinds of findings. According to the face(UI) effect, perception and recognition are better for faces presented upright (U) than for faces presented inverted (I). According to the face/object(UI) effect, inversion impairs the processing of faces more than the processing of nonfacial objects (e.g., buildings or cars). Part I of this article focuses on the face(UI) effect and the configural-processing hypothesis, which is considered the most popular explanatory hypothesis of the FIE. In this hypothesis, it is proposed that inversion impairs the processing of configural information (the spatial relations between features) but hardly (if at all) impairs the processing of featural information (e.g., eyes, nose, and mouth). Part II of the article starts from the conclusion reached in part I, that the configural-processing hypothesis has not succeeded in explaining a substantial number of the findings and in resolving certain theoretical problems. The part then goes on to outline a new alternative model, the face–scheme incompatibility (FSI) model, which contends with these theoretical problems, accounts for the configural-processing hypothesis, succeeds in explaining a considerable portion of the empirical findings related to the face(UI) effect, and proposes a relatively new research program on the concept of the face scheme. The basic assumption of the FSI model is that schemes and prototypes are involved in processing a visual stimulus of a face and in transforming it to a “meaning-bearing” face, and that different schemes are involved if the face is presented upright or inverted.     

Understanding the role of configural processing in face emotion recognition in Parkinson’s disease

This investigation examined whether impairment in configural processing could explain deficits in face emotion recognition in people with Parkinson’s disease (PD). Stimuli from the Radboud Faces Database were used to compare recognition of four negative emotion expressions by older adults with PD (n = 16) and matched controls (n = 17). Participants were tasked with categorizing emotional expressions from upright and inverted whole faces and facial composites; it is difficult to derive configural information from these two types of stimuli so featural processing should play a larger than usual role in accurate recognition of emotional expressions. We found that the PD group were impaired relative to controls in recognizing anger, disgust and fearful expressions in upright faces. Then, consistent with a configural processing deficit, participants with PD showed no composite effect when attempting to identify facial expressions of anger, disgust and fear. A face inversion effect, however, was observed in the performance of all participants in both the whole faces and facial composites tasks. These findings can be explained in terms of a configural processing deficit if it is assumed that the disruption caused by facial composites was specific to configural processing, whereas inversion reduced performance by making it difficult to derive both featural and configural information from faces.     

Effects of geometric distortions on face-recognition performance

The importance of 'configural' processing for face recognition is now well established, but it remains unclear precisely what it entails. Through four experiments we attempted to clarify the nature of configural processing by investigating the effects of various affine transformations on the recognition of familiar faces. Experiment 1 showed that recognition was markedly impaired by inversion of faces, somewhat impaired by shearing or horizontally stretching them, but unaffected by vertical stretching of faces to twice their normal height. In experiment 2 we investigated vertical and horizontal stretching in more detail, and found no effects of either transformation. Two further experiments were performed to determine whether participants were recognising stretched faces by using configural information. Experiment 3 showed that nonglobal vertical stretching of faces (stretching either the top or the bottom half while leaving the remainder undistorted) impaired recognition, implying that configural information from the stretched part of the face was influencing the process of recognition--ie that configural processing involves global facial properties. In experiment 4 we examined the effects of Gaussian blurring on recognition of undistorted and vertically stretched faces. Faces remained recognisable even when they were both stretched and blurred, implying that participants were basing their judgments on configural information from these stimuli, rather than resorting to some strategy based on local featural details. The tolerance of spatial distortions in human face recognition suggests that the configural information used as a basis for face recognition is unlikely to involve information about the absolute position of facial features relative to each other, at least not in any simple way.     

Hemispheric asymmetry in discriminating faces differing for featural or configural (second-order relations) aspects

The human capacity to discriminate among different faces relies on distinct parallel subprocesses, based either on the analysis of configural aspects or on the sequential analysis of the single elements of a face. A particular type of configural processing consists of considering whether two faces differ in terms of internal spacing among their features, referred to as second-order relations processing. Findings from electrophysiological, neuroimaging, and lesion studies suggest that, overall, configural processes rely more on the right hemisphere, whereas analysis of single features would involve more the left. However, results are not always consistent, and behavioral evidence for a right-hemisphere specialization in second-order relations processing is lacking. Here, we used divided visual field presentation to investigate the possible different contributions of the two hemispheres to face discrimination based on relational versus featural processing. Our data indicate a right-hemispheric specialization in relational processing of upright (but not inverted) faces. Furthermore, we provide evidence regarding the involvement of both the right and left hemispheres in the processing of faces differing for inner features, suggesting that both analytical and configural modes of processing are at play.