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Hugh R Wilson

Publications and source records attributed to Hugh R Wilson.

At least 19 recordsLinked to original sources
PubMed2006

Learning alters local face space geometry.

The effects of learning on the geometry of face space were investigated by measuring thresholds for discrimination and recognition of synthetic faces. This was based on a novel experimental technique that permitted measurement of psychometric functions for face recognition. Two major results were obtained. First, thresholds for face recognition were significantly better than thresholds for discrimination among novel faces. Second, rapid discrimination in the neighborhood of learned faces was better than discrimination near novel faces. Control experiments showed that this discrimination improvement occurred only with learned faces, and it could not be explained by generalized discrimination learning. Thus, face learning selectively alters or distorts face space in the vicinity of learned faces. This alteration may be due to an improvement in the signal/noise ratio as a result of face learning.

Discrimination, Psychological↗
PubMed2006

A biologically plausible model of human radial frequency perception.

Several recent studies have used radial frequency patterns to investigate intermediate-level shape perception, a critical precursor to object recognition. Here, we developed the first neural model of RF perception based on known V4 properties that exhibits many of the characteristics of human RF perception. The model is composed of two main parts: (1) recovery of object position using large-scale non-Fourier V4-like concentric units that respond at the center of concentric contour segments across orientations, and (2) curvature detectors that encode local shape information. Each curvature mechanism combines multiplicatively the responses of three oriented filters, the positions and orientation preferences of which determine the curvature mechanism's tuning properties for position, orientation, and degree of curvature. When responding to RF patterns, peak responses occur at points of maximum curvature. Shape is represented as curvature responses as a function of orientation around the object center, and the cross-correlation of that function with a sine wave peaks when the frequency of the sine wave matches the number of peaks in the stimulus. Cross-correlation strength can be used to model human performance. Model and human performance are comparable for detection, identification, and lateral masking tasks. Moreover, the model also shows size invariance of detection performance due to scaling of the curvature mechanisms. The model is then used to make novel predictions.

Form Perception↗
PubMed2006

Size-invariant but viewpoint-dependent representation of faces.

The present study investigated the role of size and view on face discrimination, using a novel set of synthetic face stimuli. Face discrimination thresholds were measured using a 2AFC match-to-sample paradigm, where faces were discriminated from a mean face. In Experiment 1, which assessed the effect of size alone, subjects had to match faces that differed in size up to four-fold. In Experiment 2 where only viewpoint was manipulated, a target face was presented at one of four different views (0 degree front, 6.7 degrees, 13.3 degrees, and 20 degrees side) and subsequent matches appeared either at the same or different view. Experiment 3 investigated how face view interacts with size changes, and subjects matched faces differing both in size and view. The results were as follows: (1) size changes up to four-fold had no effect on face discrimination; (2) threshold for matching different face views increased with angular difference from frontal view; (3) size differences across different views had no effect on face discrimination. Additionally, the present study found a perceptual boundary between 6.7 degrees and 13.3 degrees side views, grouping 0 degrees front and 6.7 degrees side views together and 13.3 degrees and 20 degrees side views together. This suggests categorical perception of face view. The present study concludes that face view and size are processed by parallel mechanisms.

Adult↗
PubMed2006

Selective preference in visual fixation away from negative images in old age? An eye-tracking study.

Recent studies have suggested that older individuals selectively forget negative information. However, findings on a positivity effect in the attention of older adults have been more mixed. In the current study, eye tracking was used to record visual fixation in nearly real-time to investigate whether older individuals show a positivity effect in their visual attention to emotional information. Young and old individuals (N = 64) viewed pairs of synthetic faces that included the same face in a nonemotional expression and in 1 of 4 emotional expressions (happiness, sadness, anger, or fear). Gaze patterns were recorded as individuals viewed the face pairs. Older adults showed an attentional preference toward happy faces and away from angry ones; the only preference shown by young adults was toward afraid faces. The age groups were not different in overall cognitive functioning, suggesting that these attentional differences are specific and motivated rather than due to general cognitive change with age.

Adolescent↗
PubMed2006

Is there an age-related positivity effect in visual attention? A comparison of two methodologies.

Research suggests a positivity effect in older adults' memory for emotional material, but the evidence from the attentional domain is mixed. The present study combined 2 methodologies for studying preferences in visual attention, eye tracking, and dot-probe, as younger and older adults viewed synthetic emotional faces. Eye tracking most consistently revealed a positivity effect in older adults' attention, so that older adults showed preferential looking toward happy faces and away from sad faces. Dot-probe results were less robust, but in the same direction. Methodological and theoretical implications for the study of socioemotional aging are discussed.

Adolescent↗
PubMed2005

Quantifying facial expression recognition across viewing conditions.

Facial expressions are key to social interactions and to assessment of potential danger in various situations. Therefore, our brains must be able to recognize facial expressions when they are transformed in biologically plausible ways. We used synthetic happy, sad, angry and fearful faces to determine the amount of geometric change required to recognize these emotions during brief presentations. Five-alternative forced choice conditions involving central viewing, peripheral viewing and inversion were used to study recognition among the four emotions. Two-alternative forced choice was used to study affect discrimination when spatial frequency information in the stimulus was modified. The results show an emotion and task-dependent pattern of detection. Facial expressions presented with low peak frequencies are much harder to discriminate from neutral than faces defined by either mid or high peak frequencies. Peripheral presentation of faces also makes recognition much more difficult, except for happy faces. Differences between fearful detection and recognition tasks are probably due to common confusions with sadness when recognizing fear from among other emotions. These findings further support the idea that these emotions are processed separately from each other.

Adult↗
PubMed2005

fMRI evidence for the neural representation of faces.

fMRI (functional magnetic resonance imaging) studies on humans have shown a cortical area, the fusiform face area, that is specialized for face processing. An important question is how faces are represented within this area. This study provides direct evidence for a representation in which individual faces are encoded by their direction (facial identity) and distance (distinctiveness) from a prototypical (mean) face. When facial geometry (head shape, hair line, internal feature size and placement) was varied, the fMRI signal increased with increasing distance from the mean face. Furthermore, adaptation of the fMRI signal showed that the same neural population responds to faces falling along single identity axes within this space.

Brain Mapping↗
PubMed2005

Global shape coding for motion-defined radial-frequency contours.

The visual system is highly skilled at recovering the shape of complex objects defined exclusively by motion cues. But while low-level and high-level mechanisms involved in shape-from-motion have been studied extensively, intermediate computational stages remain poorly understood. In the present study, we used motion-defined radial-frequency contours--or motion RFs--to probe intermediate stages involved in the computation of motion-defined shape. Motion RFs consisted of a virtual circle of Gabor elements whose carriers drifted at speeds determined by a sinusoidal function of polar angle. Motion RFs elicited vivid percepts of shape, and observers could detect and discriminate radial frequencies up to approximately five cycles. Randomizing Gabor speeds over a small contour segment impaired detection and discrimination performance significantly more than predicted by probability summation. Threshold comparisons between spatial-RF and motion-RF contours ruled out that motion-induced shifts in perceived position (i.e., the DeValois effect) determine shape perception in motion RFs. Together, results indicate that the shape of motion RFs is processed by synergistic mechanisms that perform a global analysis of motion cues over space. These results are integrated with data on perceptual interactions between motion RFs and spatial-RFs and are discussed in terms of cue-specific and cue-invariant representations of object shape in human vision.

Cues↗
PubMed2005

Configural masking of faces: evidence for high-level interactions in face perception.

The perception of a stimulus can be impaired when presented in the context of a masking pattern. To determine the timing and the nature of face processing, the effect of various masks on the discriminability of faces was investigated. Results reveal a strong configural effect: the magnitude of masking depends on the similarity between mask and target. Masking is absent for non-face masks (noise, houses), modest for scrambled and inverted faces and strongest for upright faces, even when they differ in size, gender or viewpoint from the targets. This suggests an extra-striate location for the masking (possibly FFA). Reduced but significant masking for isolated face parts (internal features or head shape) is consistent with holistic computations in face perception. The duration over which a face mask can impair face discrimination (130 ms) is markedly longer than previously assumed and is sufficient for iterative and feedback computations to be part of face processing.

Contrast Sensitivity↗
PubMed2005

The nature of synthetic face adaptation.

Recent evidence demonstrates that adapting to a face will systematically bias the perception of faces that lie along the same identity trajectory in geometric face space but not faces that lie along different identity trajectories. We explored this configural aftereffect using synthetic face stimuli developed to measure face-specific processing. Adapting to synthetic "anti-faces" resulted in an identity-specific aftereffect that was characterized by a marked decrease in the slope of the psychometric functions. Adaptation transferred across different face sizes, but not different face viewpoints nor faces constructed about a non-mean face. Performance was captured by a model where responses were modulated through a divisive gain control and an additive constant reflecting a shift in the origin of perceived face space. Together, these results suggest that face adaptation reflects activity from mechanisms common to various processing stages along the visual pathway.

Adaptation, Biological↗
PubMed2004

Global shape discrimination at reduced contrast in enucleated observers.

Previous research has shown that observers with early unilateral enucleation have selectively better sensitivity to luminance contrast than monocular viewing controls [González et al., 2002; Vision Research 36 (1) (1996) 175; Vision Research 36 (1996) 3011; Vision Research 37 (17) (1997) 2465]. We asked whether unilateral enucleation specifically enhances all levels of luminance processing. Enucleated observers, as well as binocular and monocular viewing controls, detected global shape in radial frequency (RF) patterns [Vision Research 38 (1998) 2555] at low contrast. Control observers were tested in two monocular conditions in which the stimulus was presented to one eye, while the fellow eye: (1) viewed a luminance-matched grey field or (2) was covered by a dark eye patch. Sensitivity to low-contrast global shape was equivalent in enucleated observers and binocular controls. More importantly, enucleated observers showed superior performance to that of controls in either monocular condition. At low contrast, the dichoptic control group was more sensitive than controls wearing an eye patch, which suggests that dichoptic viewing is a superior method of testing when comparing monocular control performance to that of monocularly deprived populations. The previously reported enhanced sensitivity to luminance-defined form in early enucleated observers also occurs for low-contrast global shape discrimination.

Adolescent↗
PubMed2004

The influence of motion-defined form on the perception of spatially-defined form.

It is well established that the visual system is sensitive to the global structure--or "form"--of objects defined exclusively by spatial or motion cues, but it remains unclear how form perception combines spatial and motion cues if these are presented concurrently. In the present study, we introduce a novel class of stimuli where spatial-form and motion-form can be superimposed and manipulated independently. In both the spatial and motion domains, global structure consisted of radial-frequency (RF) contours defined by a virtual circle of Gabor elements whose positions and/or drift speeds were sinusoidally modulated at a specified frequency of polar angle. The first two experiments revealed that observers encode the global structure of spatial-RF and motion-RF contours presented in isolation. In a third experiment, observers detected a spatial-RF modulation superimposed on a motion-RF pedestal of identical radial frequency: results showed little facilitation at low pedestal amplitudes but significant masking at higher pedestal amplitudes, especially if the RF modulations of test and pedestal were in anti-phase. Additional experiments demonstrated that masking of the spatial-RF test is abolished if the global structure of the motion-RF pedestal is altered or destroyed while local motion cues are preserved. We argue these results cannot be explained by local neural interactions between spatial and motion cues and propose instead that data reflect higher-level interactions between separate visual pathways encoding spatial-form and motion-form.

Cues↗
PubMed2004

Curvature population coding for complex shapes in human vision.

In the primate visual system relatively complex patterns such as curved shapes are first represented at intermediate levels of the ventral pathway. Furthermore, there is now evidence for the existence of curvature population coding in primate V4. We sought to determine whether similar encoding occurs in the human visual system by using a context-dependent lateral masking paradigm. In this paradigm a central closed contour comprising the test pattern is masked by surrounding larger or smaller patterns with various configurations. Results indicate that test thresholds are not affected by a circular control mask, and that elevations are greatest when curvature extrema of the mask are aligned with those of the target. These lateral interactions extend over greater than 1 degrees and are tuned for target shape. Masking increases with the number of local curvature extrema aligned with the target. Finally, masking persists when target and mask have orthogonal local orientations and increases with mask amplitude. These findings are incompatible with local orientation-selective interactions (V1-mediated) but are consistent with the existence of population codes based on curvature maxima at intermediate levels of processing (presumably V4) in human vision. The paradigm we introduce provides a new tool for evaluating the representation of complex percepts.

Humans↗
PubMed2004

A window on the normal development of sensitivity to global form in Glass patterns.

We studied the development of sensitivity to global form in 6-year-olds, 9-year-olds, and adults (n = 24 in each group) using Glass patterns with varying ratios of paired signal dots to noise dots. The developmental pattern was similar whether the global structure within the Glass patterns was concentric or parallel. Thresholds were equally immature for both types of pattern at 6 years of age (about twice the adult value) but were adult-like at 9 years of age. Together, the results indicate that the cortical structures involved in the processing of global form achieve functional maturity between 6 and 9 years of age. During middle childhood, the mechanisms mediating sensitivity to concentric structure develop at the same rate as those mediating sensitivity to parallel structure.

Adolescent↗
PubMed2003

Computational evidence for a rivalry hierarchy in vision.

Cortical-form vision comprises multiple, hierarchically arranged areas with feedforward and feedback interconnections. This complex architecture poses difficulties for attempts to link perceptual phenomena to activity at a particular level of the system. This difficulty has been especially salient in studies of binocular rivalry alternations, where there is seemingly conflicting evidence for a locus in primary visual cortex or alternatively in higher cortical areas devoted to object perception. Here, I use a competitive neural model to demonstrate that the data require at least two hierarchic rivalry stages for their explanation. This model demonstrates that competitive inhibition in the first rivalry stage can be eliminated by using suitable stimulus dynamics, thereby revealing properties of a later stage, a result obtained with both spike-rate and conductance-based model neurons. This result provides a synthesis of competing rivalry theories and suggests that neural competition may be a general characteristic throughout the form-vision hierarchy.

Evoked Potentials, Visual↗
PubMed2003

Local and global contributions to shape discrimination.

Humans are remarkably sensitive in detecting small deviations from circularity. In tasks involving discrimination between closed contours, either circular in shape or defined by sinusoidal modulations of the circle radius, human performance has been shown to be limited by global processing. We assessed the amount of global pooling for different pattern shapes (different radial modulation frequencies, RF) when circular deformation was restricted to a fraction of the contour. The results show that the improvement in performance depends on the modulation frequency (the pattern shape) when increasing the number of cycles of an RF pattern. Global processing only extends up to modulation frequencies between 5 and 10. For higher frequencies, performance can be predicted by probability summation. Position uncertainty cannot explain these effects. In a circumstance where global pooling exceeds probability summation (RF=5), we split the pattern up into five identical segments conserving the total amount of information presented. Thresholds are significantly affected by different global arrangements of these segments: (a) Occluding small parts of the pattern shows a significant effect on the position of occluders with performance lowest when gaps are placed at the points of maximum curvature. (b) Shifting segments away from the pattern centre (exploded condition) or displaying them out of concentric context (spiral condition) shuts down global processing. (c) Jittering segments radially disrupts both global and local processing. We conclude that RF patterns in the global processing range are analysed by detecting the points of maximum curvature and that, in this range, the visual system can only reliably process up to about 5 local curvature extrema.

Discrimination, Psychological↗
PubMed2002

Symmetry perception: a novel approach for biological shapes.

The majority of quantitative studies on symmetry perception have employed random dot patterns, yet symmetrical random patterns are not common in nature. Here we explore symmetry perception utilizing sums of radial frequency (RF) patterns to define complex shapes. When a pair of RF patterns with different frequencies are added, the relative phase of the two components provides a precise measure of the degree of deviation from bilateral symmetry. Sums of RF2-RF7 define such diverse biological shapes as human heads, animal heads, torsos, and many fruit, so discrimination of symmetries defined by these patterns is highly relevant to biological vision. Here we show that symmetry discrimination during brief presentations is best for RF2+RF3 but becomes impossible for RF2+RF7. Further experiments demonstrate that the underlying neural mechanisms differ from those involved in random dot symmetry detection. These results were used to predict symmetry thresholds for deviations from bilateral symmetry of head shapes based on a principal components analysis of 30 female heads. Human V4 is hypothesized to be the site for symmetry discrimination of RF patterns but not of random dot patterns.

Computer Graphics↗