Biomedical subjects

Quoc C Vuong

Publications and source records attributed to Quoc C Vuong.

12 recordsLinked to original sources

PubMed2006

Planning and online control of goal directed movements when the eyes are 'relocated'.

We investigated the effects of different viewpoints on remapping visuo-motor space, and whether remapping happens differently during the planning and the online control phase of goal-directed movements. Participants tapped targets on a monitor that was placed horizontally flat and flush with the table in front of them. They viewed the layout of the scene, including the monitor, and their hand, through video goggles attached to a camera. The camera could be moved along a semi-circle with the monitor as the circle's center. On each trial, the camera was randomly positioned at one of seven locations on the semi-circle (-90 to +90 degrees in 30 degrees steps), always at eye height. The time needed to tap the target was quickest when the camera was approximately facing the participant and progressively increased when the camera was located more to the sides (Experiment 1). There was no effect of camera location on performance when participants only saw the static layout of the scene and were not allowed to see the scene or their hand during the movement (Experiment 2). By comparison, the dependency of performance on camera location increased when participants did not have information about the layout of the scene at the start of the trial, and could only perform remapping when their hand was visible during the movement (Experiment 3). These results indicate that visuo-motor remapping happens differently during the planning phase when only static information about the layout is available, and during the control phase when dynamic information about the moving hand is also available.

Cognition↗

PubMed2006

An advantage for detecting dynamic targets in natural scenes.

In the present study, we tested the extent to which observers use dynamic information to detect targets in natural scenes. For this purpose, we used composite stimuli in which target sequences were superimposed onto distractor sequences. We varied target visibility in the composite sequence, and the presence or absence of motion. Across four experiments, we found a dynamic advantage for target detection: Observers performed more accurately with dynamic than static target scenes. This advantage depended on the availability of target motion, irrespective of whether the target was upright or inverted in the image plane (Experiments 1-4). The magnitude of this advantage also depended on the availability of segmentation cues (Experiments 1 and 2) and on the distractors used (Experiments 2 and 4). Overall, the dynamic advantage reported extends previous work using isolated dynamic objects to more complex scenes.

Attention↗

PubMed2006

Disparity and shading cues cooperate for surface interpolation.

In two experiments, we tested whether disparity and shading cues cooperated for surface interpolation. Observers adjusted a probe dot to/lie on a surface specified either by a sparse disparity field, a continuous stereo shading or monocular shading gradient, or both cues. Observers' adjustments were very consistent with disparity information but their adjustments were much more variable with shading information. However, observers significantly improved their precision when both cues were present, relative to when only disparity information was present. These results cannot be explained by assuming that separate modules analyze disparity and shading information, even if observers optimally combined these cues. Rather, we attribute this improvement to a process through which the shading gradient constrains the disparity field in regions where disparities cannot be directly measured. This cooperative process may be based on the natural covariation existing between these cues produced by the retinal projection of smooth surfaces.

Adult↗

PubMed2006

Structural similarity and spatiotemporal noise effects on learning dynamic novel objects.

The spatiotemporal pattern projected by a moving object is specific to that object, as it depends on both the shape and the dynamics of the object. Previous research has shown that observers learn to make use of this spatiotemporal signature to recognize dynamic faces and objects. In two experiments, we assessed the extent to which the structural similarity of the objects and the presence of spatiotemporal noise affect how these signatures are learned and subsequently used in recognition. Observers first learned to identify novel, structurally distinctive or structurally similar objects that rotated with a particular motion. At test, each learned object moved with its studied motion or with a non-studied motion. In the non-studied motion condition we manipulated either dynamic information alone (experiment 1) or both static and dynamic information (experiment 2). Across both experiments we found that changing the learned motion of an object impaired recognition performance when 3-D shape was similar or when the visual input was noisy during learning. These results are consistent with the hypothesis that observers use learned spatiotemporal signatures and that such information becomes progressively more important as shape information becomes less reliable.

Face↗

PubMed2006

Dynamic object recognition in pigeons and humans.

We investigated the role of dynamic information in human and pigeon object recognition. Both species were trained to discriminate between two objects that each had a characteristic motion, so that either cue could be used to perform the task successfully. The objects were either easy or difficult to decompose into parts. At test, the learned objects could appear in their learned motions, the reverse of the learned motions, or an entirely new motion, or a new object could appear in one of the learned motions. For humans, any change in the learned motion produced a decrement in performance for both the decomposable and the nondecomposable objects, but participants did not respond differentially to new objects that appeared in the learned motions. Pigeons showed the same pattern of responding as did humans for the decomposable objects, except that pigeons responded differentially to new objects in the learned motions. For the nondecomposable objects, pigeons used motion cues exclusively. We suggest that for some types of objects, dynamic information may be weighted differently by pigeons and humans.

Animals↗

PubMed2005

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.

Adult↗

PubMed2004

The role of surface pigmentation for recognition revealed by contrast reversal in faces and Greebles.

Faces are difficult to recognize when viewed as negatives [Galper (1970). Recognition of faces in photographic negative. Psychonomic Science, 19, 207]. Here we examined the contribution of surface properties to this contrast effect, and whether it is modulated by object category. We tested observers in a matching task using faces or Greebles, presented with or without pigmentation. When stimulus pairs were shown with mismatched contrast (e.g., positive-negative), there was a decrement in performance. This decrement was larger when the stimuli were shown with pigmentation, and this difference was more pronounced with faces than with Greebles. Overall, contrast reversal disrupts the recognition of both faces and objects to a greater degree in the presence of pigmentation, suggesting that surface properties are important components of the object representation.

Color Perception↗

PubMed2004

Incidental processing of biological motion.

The successful detection of biological motion can have important consequences for survival. Previous studies have demonstrated the ease and speed with which observers can extract a wide range of information from impoverished dynamic displays in which only an actor's joints are visible. Although it has often been suggested that such biological motion processing can be accomplished relatively automatically, few studies have directly tested this assumption by using behavioral methods. Here we used a flanker paradigm to assess how peripheral "to-be-ignored" walkers affect the processing of a central target walker. Our results suggest that task-irrelevant dynamic figures cannot be ignored and are processed to a level where they influence behavior. These findings provide the first direct evidence that complex dynamic patterns can be processed incidentally, a finding that may have important implications for cognitive, neurophysiological, and computational models of biological motion processing.

Analysis of Variance↗

PubMed2004

Rotation direction affects object recognition.

What role does dynamic information play in object recognition? To address this question, we probed observers' memory for novel objects rotating in depth. Irrespective of object discriminability, performance was affected by an object's rotation direction. This effect was obtained despite the same shape information and views being shown for different rotation directions. This direction effect was eliminated when either static images or animations that did not depict globally coherent rotation were used. Overall, these results suggest that dynamic information, that is, the spatiotemporal ordering of object views, provides information independent of shape or view information to a recognition system.

Contrast Sensitivity↗

PubMed2004

Evidence for patchwork approximation of shape primitives.

Investigators have proposed that qualitative shapes are the primitive information of spatial vision: They preserve an approximately one-to-one mapping between surfaces, images, and perception. Given their importance, we examined how the visual system recovers these primitives from sparse disparity fields that do not provide sufficient information for their recovery. We hypothesized that the visual system interpolates sparse disparities with planes, resulting in a patchwork approximation of the implicitly defined shapes. We presented observers with stereo displays simulating planar or smooth curved surfaces having different curvatures. The observers' task was to detect whether dots deviated from these surfaces or to discriminate planar from curved or planar from scrambled surfaces. Consistent with our hypothesis, increasing curvature had detrimental effects on observers' performance (Experiments 1-3). Importantly, this patchwork approximation leads to the recovery of the proposed shape primitives, since observers were more accurate at discriminating planar-from-curved than planar-from-scrambled surfaces with matched disparity range (Experiment 4).

Computer Graphics↗

PubMed2003

A chimeric point-light walker.

Ambiguity has long been used as a probe into visual processing. Here, we describe a new dynamic ambiguous figure-the chimeric point-light walker--which we hope will prove to be a useful tool for exploring biological motion. We begin by describing the construction of the stimulus and discussing the compelling finding that, when presented in a mask, observers consistently fail to notice anything odd about the walker, reporting instead that they are watching an unambiguous figure moving either to the left or right. Some observers report that the initial percept fluctuates, moving first to the left, then to the right, or vice versa; others always perceive a constant direction. All observers, when briefly shown the unmasked ambiguous figure, have no difficulty in perceiving the novel motion pattern once the mask is returned. These two findings--the initial report of unambiguous motion and the subsequent 'primed' perception of the ambiguity--are both consistent with an important role for top-down processing in biological motion. We conclude by suggesting several domains within the realm of biological-motion processing where this simple stimulus may prove to be useful.

Humans↗

PubMed2002

Temporal integration in structure from motion.

A temporal integration model is proposed that predicts the results reported in 4 psychophysical experiments. The main findings were (a) the initial part of a structure-from-motion (SFM) sequence influences the orientation evoked by the final part of that sequence (an effect lasting for more than 1 s), and (b) for oscillating SFM sequences, perceived slant is affected by the oscillation frequency and by the sign of the final gradient. For contracting optic flows (i.e., rotations away from the image plane), the sequence with the lowest oscillation frequency appeared more slanted; for expanding optic flows (i.e., rotations toward the image plane), the sequence with the highest oscillation frequency appeared more slanted.

Humans↗