Biomedical subjects

D I Perrett

Publications and source records attributed to D I Perrett.

At least 19 recordsLinked to original sources

PubMed1995

Perception of age in adult Caucasian male faces: computer graphic manipulation of shape and colour information.

This study investigated visual cues to age by using facial composites which blend shape and colour information from multiple faces. Baseline measurements showed that perceived age of adult male faces is on average an accurate index of their chronological age over the age range 20-60 years. Composite images were made from multiple images of different faces by averaging face shape and then blending red, green and blue intensity (RGB colour) across comparable pixels. The perceived age of these composite or blended images depended on the age bracket of the component faces. Blended faces were, however, rated younger than their component faces, a trend that became more marked with increased component age. The techniques used provide an empirical definition of facial changes with age that are biologically consistent across a sample population. The perceived age of a blend of old faces was increased by exaggerating the RGB colour differences of each pixel relative to a blend of young faces. This effect on perceived age was not attributable to enhanced contrast or colour saturation. Age-related visual cues defined from the differences between blends of young and old faces were applied to individual faces. These transformations increased perceived age.

Adult↗

PubMed1994

Facial shape and judgements of female attractiveness.

The finding that photographic and digital composites (blends) of faces are considered to be attractive has led to the claim that attractiveness is averageness. This would encourage stabilizing selection, favouring phenotypes with an average facial structure. The 'averageness hypothesis' would account for the low distinctiveness of attractive faces but is difficult to reconcile with the finding that some facial measurements correlate with attractiveness. An average face shape is attractive but may not be optimally attractive. Human preferences may exert directional selection pressures, as with the phenomena of optimal outbreeding and sexual selection for extreme characteristics. Using composite faces, we show here that, contrary to the averageness hypothesis, the mean shape of a set of attractive faces is preferred to the mean shape of the sample from which the faces were selected. In addition, attractive composites can be made more attractive by exaggerating the shape differences from the sample mean. Japanese and caucasian observers showed the same direction of preferences for the same facial composites, suggesting that aesthetic judgements of face shape are similar across different cultural backgrounds. Our finding that highly attractive facial configurations are not average shows that preferences could exert a directional selection pressure on the evolution of human face shape.

Adult↗

PubMed1994

Visual processing of facial distinctiveness.

Three experiments are reported in which the role of facial distinctiveness in linedrawing representations of famous faces has been examined. In the first subjects were asked to select their impressions of best likeness interactively from a continuous range of drawings generated in real-time. On average, 42% of caricatures were considered to be the best likeness of famous individuals. The distinctiveness of the target faces related by independent observers correlated with the degree of exaggeration faces received to produce an optimal likeness. More distinctive faces required less caricaturing. In the second experiment caricature levels chosen as best likenesses were investigated. Caricatures of famous faces were recognised more quickly (by 36% of subjects) and more accurately (by 28%) than the true veridical drawings. Thus caricature enhancement can improve recognition in terms of both speed and accuracy. In the third experiment the role of distinctiveness and its interaction with external and internal facial features was investigated. The external (outer) hairline present in the previous experiment was found to provide a powerful frame of reference for the perceptual assessment of individuals' appearances; estimations of best likeness without external features present were, on average, veridical. It is concluded that accurate line drawings of even highly familiar faces are poor at conveying identity. Distinctiveness enhancement improves their likeness and their recognisability. Such caricatured drawings provide improved access to memories of famous faces, which lends strong support to models of human-face memory and processing based on norm-based coding. When required to decide upon the veracity of line drawings based only upon internal features subjects were able to make accurate judgments of veridicality. As well as validating the interaction approach to best-likeness judgments, this result further indicates the difficulty in making judgments of identification based on piecemeal and sparse configural information.

Adult↗

PubMed1993

Motion sensitive cells in the macaque superior temporal polysensory area. I. Lack of response to the sight of the animal's own limb movement.

An animal's own behaviour can give rise to sensory stimulation that is very similar to stimulation of completely external origin. Much of this self-induced stimulation has little informative value to the animal and may even interfere with the processing of externally induced stimulation. We have measured responses of visual movement sensitive neurons in the anterior part of the dorsal superior temporal sulcus of monkeys to stimulation caused by the animal's own active movements. These cells responded to any stimuli moved by the experimenter, but gave no response to the sight of animal's own limb movements. The cells remained responsive to external stimulation, however, while the monkey's own hand was moving in view. Responses to self-induced movements were recovered if the monkey introduced a novel object in its hand into view. Various possible neural mechanisms for explaining the results are discussed, and it is suggested that the studied neurons belong to a system that detects unexpected and hence behaviourally relevant sensory events.

Animals↗

PubMed1993

Directional tuning of motion-sensitive cells in the anterior superior temporal polysensory area of the macaque.

An investigation was made into the directional sensitivity of cells in the macaque anterior superior temporal polysensory region (STPa) to the motion of objects. The cells studied were sensitive to the presence of motion but showed little or no selectivity for the form of the stimulus. Directional tuning was not continuously distributed about all possible directions. The majority of cells were most responsive to motion in a direction within 15 degrees of one of the three cartesian axes (up/down, left/right, towards/away). Tuning to direction varied in sharpness. For most (34/37) cells the angular change in direction required to reduce response to half maximal was between 45 and 70 degrees (for 3/37 cells it was > 90 degrees). The estimates of the directionality (median Id = 0.97) of STPa cells was similar to that reported for posterior motion processing areas (the middle temporal area, MT, and the medial superior temporal area, MST). The tuning for direction (sharpness, distribution and discrimination) of the motion-sensitive STPa cells were found to be similar to the tuning for perspective view of STPa cells selective for static form of the head and body. On average the STPa responses showed a 100- to 300-ms transient burst of activity followed by a tonic discharge maintained at approximately 20% of the peak firing rate for the duration of stimulation. The responses of motion-sensitive STPa cells occurred at an earlier latency (mean 91 ms) than responses of cells selective for static form (mean 119 ms), but the time course of responses of the two classes of cell were similar in many other respects. The early response latency and directional selectivity indicate that motion sensitivity in STPa cells derives from the dorsal visual pathway via MT/MST. The similarity of tuning for direction and perspective view within STPa may facilitate the integration of motion and form processing within this high-level brain area.

Acoustic Stimulation↗

PubMed1993

Extracting prototypical facial images from exemplars.

A computer graphic method for extracting a natural image of an individual's facial prototype, or average appearance, from a number of different images of that individual is presented. The process improves upon previous photographic and computational techniques. Synthesis of a person's average expression and pose from a sample of images is derived in an automatic and quantitative way. Possible uses of composite faces produced in this manner in psychological investigations of facial qualities (eg attractiveness) and in applied areas such as telecommunication are pointed out.

Attention↗

PubMed1993

What gives a face its gender?

An experiment is reported in which the attribution of gender to isolated facial features and to faces whose features have been interchanged with those of a face of the opposite gender has been examined. Sixteen male faces were averaged to create a prototype male face and sixteen female faces averaged to create a prototype female face. The prototypes were then masked to exclude ears, neck, hair, and hairline. Individual features (brows, eyes, nose, mouth, and chin) and pairs of features (brows & eyes, eyes & nose, nose & mouth, mouth & chin) from the prototypes were then presented in isolation for classification according to their perceived gender. The results showed that, for the faces used, the brows & eyes, brows alone, eyes alone, the whole jaw, the chin, the nose & mouth, the mouth alone (in descending order), ie all the features except the nose, carried some information about gender when they were seen in isolation. In the second part of the experiment different features from one prototype face were grafted into the prototype of the opposite gender and the resulting composite faces classified by their perceived gender. The results of this feature substitution showed the jaw, brows & eyes, chin, and brows (in descending order) effecting significant change in perceived gender. The difference in gender information carried by feature(s) when they were viewed in isolation from that when they were substituted for each other is attributed to the role of configuration in the perception of the gender of a face.

Adolescent↗

PubMed1993

Recent developments in the neuropsychology and physiology of face processing.

This chapter will review neuropsychological studies of face processing defects. Recent research in this field has been dominated by evidence of preserved face processing in patients who are unaware of these abilities. This phenomenon is referred to as covert recognition and forms a main focus for this review. The second part of the chapter reviews the advances in physiological studies of the brain mechanisms underlying face processing. The relationship between normal perception of faces and information processing at the single cell level is considered. Finally the chapter discusses how the physiological findings relate to the pathology of face processing.

Agnosia↗

PubMed1992

Organization and functions of cells responsive to faces in the temporal cortex.

Cells selectively responsive to the face have been found in several visual sub-areas of temporal cortex in the macaque brain. These include the lateral and ventral surfaces of inferior temporal cortex and the upper bank, lower bank and fundus of the superior temporal sulcus (STS). Cells in the different regions may contribute in different ways to the processing of the facial image. Within the upper bank of the STS different populations of cells are selective for different views of the face and head. These cells occur in functionally discrete patches (3-5 mm across) within the STS cortex. Studies of output connections from the STS also reveal a modular anatomical organization of repeating 3-5 mm patches connected to the parietal cortex, an area thought to be involved in spatial awareness and in the control of attention. The properties of some cells suggest a role in the discrimination of heads from other objects, and in the recognition of familiar individuals. The selectivity for view suggests that the neural operations underlying face or head recognition rely on parallel analyses of different characteristic views of the head, the outputs of these view-specific analyses being subsequently combined to support view-independent (object-centred) recognition. An alternative functional interpretation of the sensitivity to head view is that the cells enable an analysis of 'social attention', i.e. they signal where other individuals are directing their attention. A cell maximally responsive to the left profile thus provides a signal that the attention (of another individual) is directed to the observer's left. Such information is useful for analysing social interactions between other individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Mapping↗

PubMed1992

The effects of lighting conditions on responses of cells selective for face views in the macaque temporal cortex.

Neural mechanisms underlying recognition of objects must overcome the changes in an object's appearance caused by inconsistent viewing conditions, particularly those that occur with changes in lighting. In humans, lesions to the posterior visual association cortex can impair the ability to recognize objects and faces across different lighting conditions. Inferotemporal lesions in monkey have been shown to produce a similar difficulty in object matching tasks. Here we report on the extent to which cell responses selective for the face and other views of the head in monkey temporal cortex tolerate changes in lighting. For each cell studied the (preferred) head view eliciting maximal response was first established under normal lighting. Cells were then tested with the preferred head view lit from different directions (i.e. front, above, below or from the side). Responses of some cells failed to show complete generalization across all lighting conditions but together as a "population" they responded equally strongly under all four lighting conditions. Further tests on sub-groups of cells revealed that stimulus selectivity was maintained despite unusual lighting. The cells discriminated between head and control stimuli and between different views of the head independent of the lighting direction. The results indicate that constancy of recognition across different lighting conditions is apparent in the responses of single cells in the temporal cortex. Lighting constancy appears to be established by matching the retinal image to view-specific descriptions of objects (i.e. neurons which compute object structure from a limited range of perspective views).

Animals↗

PubMed1992

Use of preferential inspection to define the viewing sphere and characteristic views of an arbitrary machined tool part.

Measurements were made of the way human subjects visually inspected an idealized machined tool part (a 'widget') while learning the three-dimensional shape of the object. Subjects were free to rotate the object about any axis. Inspection was not evenly distributed across all views. Subjects focused on views where the faces of the object were orthogonal to the line of sight and the edges of the object were aligned parallel or at right angles to the gravitational axis. These 'face' or 'plan' views were also the easiest for subjects to bring to mind in a mental imagery task. By contrast, when subjects were instructed to imagine the views displaying the most structural information they visualized views lying midway between face views.

Adolescent↗

PubMed1992

Time course of neural responses discriminating different views of the face and head.

1. Measurements of the magnitude and time course of response were made from 44 cells responsive to static head views at different levels of stimulus effectiveness. In this way responses to complex stimulus patterns evoking good, poor, and midrange responses could be compared across the cell population. 2. Cells exhibiting both good and poor initial discrimination between head views were found at short and long latencies; there was no correlation of any of the temporal response parameters measured with cell response latency. 3. The time course of the population response to the most effective stimuli showed a rapid increase to a peak firing rate (onset to peak, rise time, 58 ms) that was on average 115 spikes/s above spontaneous activity (S/A), followed by slower decay (decay time, 93 ms) to a maintained discharge rate (15% of the peak rate above S/A). 4. Discrimination between responses to different head views exhibited by the population showed a sharp rise and reached highly significant levels within 25 ms after the population's response onset. 5. On average, activity in a single neuron (the Average Cell) rises to 44% of its peak response rate within 5 ms of the response onset. 6. The Average Cell also showed exceptionally fast discrimination between views, significant within 5 ms of response onset. 7. It is argued that the fast rise in firing rate, followed by a decay to a lower rate and the very fast emergence of discrimination are features of pattern processing present in real neural systems that are lacking in many processing models based on artificial networks of neuronlike elements, particularly those where discrimination relies on top-down and/or lateral competitive inhibition. 8. It is concluded that the only way to account for the rapid discrimination is to consider a coding system in which the first spike from multiple sources is used to transmit information between stages of processing.

Animals↗

PubMed1991

Viewer-centred and object-centred coding of heads in the macaque temporal cortex.

An investigation was made into the sensitivity of cells in the macaque superior temporal sulcus (STS) to the sight of different perspective views of the head. This allowed assessment of (a) whether coding was 'viewer-centred' (view specific) or 'object-centred' (view invariant) and (b) whether viewer-centred cells were preferentially tuned to 'characteristic' views of the head. The majority of cells (110) were found to be viewer-centred and exhibited unimodal tuning to one view. 5 cells displayed object-centred coding responding equally to all views of the head. A further 5 cells showed 'mixed' properties, responding to all views of the head but also discriminating between views. 6 out of 56 viewer and object-centred cells exhibited selectivity for face identity or species. Tuning to view varied in sharpness. For most (54/73) cells the angle of perspective rotation reducing response to half maximal was 45-70 degrees but for 19/73 it was greater than 90 degrees. More cells were optimally tuned to characteristic views of the head (the full face or profile) than to other views. Some cells were, however, found tuned to intermediate views throughout the full 360 degree range. This coding of many distinct head views may have a role in the analysis of social signals based on the interpretation of the direction of other individuals' attention.

Animals↗

PubMed1991

Preferential inspection of views of 3-D model heads.

The importance of different perspective views for the recognition of model heads was studied. In experiment 1 subjects were instructed to learn the appearance of six heads placed individually on a turntable free to rotate through 360 degrees. Subjects did not distribute their time evenly but focussed their inspection on particular views (the full face view and a view close to the profile). Despite differential inspection of these two views during the learning phase, the face, half profile, and profile views were recognized with equal efficiency in a subsequent recognition task with static views. Experiment 2 used the inspection paradigm to investigate view preference during the recognition of heads from memory. In this experiment subjects were asked to learn the appearance of three heads each seen rotating at an even speed. In a subsequent retrieval task the subjects actively inspected six model heads on the turntable and were asked to differentiate the three heads previously seen rotating from three novel heads. The pattern of inspection in this retrieval task was equivalent to that in experiment 1. Results suggest that during the encoding into memory subjects construct descriptions of specific prototypical views of the head and that descriptions of these same views are preferentially utilised during recognition.

Adult↗

PubMed1991

Perception and action in 'visual form agnosia'.

A single case study of a patient with 'visual form agnosia' is presented. A severe visual recognition deficit was accompanied by impairments in discriminating shape, reflectance, and orientation, although visual acuity and colour vision, along with tactile recognition and intelligence, were largely preserved. Neuropsychological and behavioural investigations have indicated that the patient is able to utilize visual pattern information surprisingly well for the control of hand movements during reaching, and can even read many whole words, despite being unable to make simple discriminative judgements of shape or orientation. She seems to have no awareness of shape primitives through Gestalt grouping by similarity, continuity or symmetry. It is proposed that many of these perceptual disorders might be the combined result of (1) a selective loss of the cortical elaboration of the magnocellular visual processing stream, and (2) a selective output disconnection from a central processor of visual boundaries and shape primitives in the occipital cortex.

Adult↗

PubMed1990

Visual and somatosensory processing in the macaque temporal cortex: the role of 'expectation'.

The somatosensory and visual properties of cells in a polymodal region of temporal cortex were studied in 4 awake behaving macaque monkeys. When stimulated passively and out of sight, cells with tactile responses were found to have very large receptive fields covering most of the body surface and an apparent lack of selectivity for size, shape or texture of the tactile stimulus. These properties are equivalent to those described for the anaesthetized preparation (Bruce et al. 1981). Our study revealed that tactile responses were influenced by the degree to which stimuli could be 'expected'. Tactile stimulation arising from active exploration of novel surfaces produced vigourous neuronal responses but equivalent stimulation of the skin arising when the monkey contacted 'expected' surfaces such as itself or items with which it had become familiar produced no responses. The responses of cells to active or passive tactile stimulation were attenuated when the monkey could see the objects causing the stimulation. For cells responsive to more than one sensory modality, visual and somatosensory responses were associated in a compatible manner. Cells responsive to the onset of touch were selective for the sight of objects moving towards the monkey, whereas cells selective for the offset of touch were responsive to the sight of movements away from the monkey.

Animals↗

PubMed1990

Perceptual dysfunction in poor readers: evidence for visual and auditory segmentation problems in a sub-group of poor readers.

The purpose of this study was to consider reading disorders in children within the context of their general perceptual development. A review of the literature suggested that visual and auditory perceptual skills advance from a holistic to an analytical approach, and that reading skills also show this progression. It was proposed that poor readers might show impairments in visual and auditory segmentation tasks, if these skills are important factors in reading development. This hypothesis was tested on a sample (N = 20) of poor readers in the primary age range who were assessed against reading age and chronological age control groups. The hypothesis was partially borne out, a quarter of the sample performing very poorly on both types of tasks. It was argued that segmentation problems in perceptual tasks may underlie reading failure in some children, although the direction of the causation has yet to be determined.

Auditory Perceptual Disorders↗

PubMed1989

Frameworks of analysis for the neural representation of animate objects and actions.

A variety of cell types exist in the temporal cortex providing high-level visual descriptions of bodies and their movements. We have investigated the sensitivity of such cells to different viewing conditions to determine the frame(s) of reference utilized in processing. The responses of the majority of cells in the upper bank of the superior temporal sulcus (areas TPO and PGa) found to be sensitive to static and dynamic information about the body were selective for one perspective view (e.g. right profile, reaching right or walking left). These cells can be considered to provide viewer-centred descriptions because they depend on the observer's vantage point. Viewer-centred descriptions could be used in guiding behaviour. They could also be used as an intermediate step for establishing view-independent responses of other cell types which responded to many or all perspective views selectively of the same object (e.g. head) or movement. These cells have the properties of object-centred descriptions, where the object viewed provides the frame of reference for describing the disposition of object parts and movements (e.g. head on top of shoulders, reaching across the body, walking forward 'following the nose'). For some cells in the lower bank of the superior temporal sulcus (area TEa) the responses to body movements were related to the object or goal of the movements (e.g. reaching for or walking towards a specific place). This goal-centred sensitivity to interaction allowed the cells to be selectively activated in situations where human subjects would attribute causal and intentional relationships.

Animals↗