Biomedical subjects

Yaoda Xu

Publications and source records attributed to Yaoda Xu.

8 recordsLinked to original sources

PubMed2006

Understanding the object benefit in visual short-term memory: the roles of feature proximity and connectedness.

Past research has identified visual objects as the units of information processing in visual short-term memory (VSTM) and has shown that two features from the same object can be remembered in VSTM as well (or almost as well) as one feature of that object and are much better remembered than the same two features from two spatially separated objects. It is not clear, however, what drives this object benefit in VSTM. Is it the shared spatial location (proximity), the connectedness among features of an object, or both? In six change detection experiments, both location/proximity and connectedness were found to be crucial in determining the magnitude of the object benefit in VSTM. Together, these results indicate that location/proximity and connectedness are essential elements in defining a coherent visual object representation in VSTM.

Adolescent↗

PubMed2005

Dissociable neural mechanisms supporting visual short-term memory for objects.

Using visual information to guide behaviour requires storage in a temporary buffer, known as visual short-term memory (VSTM), that sustains attended information across saccades and other visual interruptions. There is growing debate on whether VSTM capacity is limited to a fixed number of objects or whether it is variable. Here we report four experiments using functional magnetic resonance imaging that resolve this controversy by dissociating the representation capacities of the parietal and occipital cortices. Whereas representations in the inferior intra-parietal sulcus (IPS) are fixed to about four objects at different spatial locations regardless of object complexity, those in the superior IPS and the lateral occipital complex are variable, tracking the number of objects held in VSTM, and representing fewer than four objects as their complexity increases. These neural response patterns were observed during both VSTM encoding and maintenance. Thus, multiple systems act together to support VSTM: whereas the inferior IPS maintains spatial attention over a fixed number of objects at different spatial locations, the superior IPS and the lateral occipital complex encode and maintain a variable subset of the attended objects, depending on their complexity. VSTM capacity is therefore determined both by a fixed number of objects and by object complexity.

Humans↗

PubMed2005

Revisiting the role of the fusiform face area in visual expertise.

It has previously been reported (Gauthier et al., 2000, Nat. Neurosci., 3:191-197) in a functional magnetic resonance imaging (fMRI) study that objects of visual expertise (cars and birds) activate the right fusiform face area (FFA) more strongly than non-expertise stimuli, and it was argued that the right FFA is involved in expertise specific rather than face specific visual processing. This expertise effect, however, may be due to experts taking advantage of the 'faceness' of the stimuli: birds have faces and three-quarter frontal views of cars resemble faces. This expertise effect may also be caused by a biased attentional modulation: with a blocked fMRI design, experts may attend more to a block of expertise than a block of non-expertise stimuli. In this study, using both side-view car images that do not resemble faces and bird images in an event-related fMRI design that minimizes attentional modulation, an expertise effect in the right FFA is observed in both car and bird experts (although a baseline bias makes the bird expertise effect less reliable). These results are consistent with those of Gauthier et al., and suggest the involvement of the right FFA in processing non-face expertise visual stimuli.

Adult↗

PubMed2004

The M170 is selective for faces, not for expertise.

Are the mechanisms for face perception selectively involved in processing faces per se, or do they also participate in the processing of any class of visual stimuli that share the same basic configuration and for which the observer has gained substantial visual expertise? Here we tested the effects of visual expertise on the face-selective "M170", a magnetoencephalography (MEG) response component that occurs 170 ms after stimulus onset and is involved in the identification of individual faces. In Experiment 1, cars did not elicit a higher M170 response (relative to control objects) in car experts compared to controls subjects. In Experiment 2, the M170 amplitude was correlated with successful face identification, but not with successful car identification in car experts. These results indicate that the early face processing mechanisms marked by the M170 are involved in the identification of faces in particular, not in the identification of any objects of expertise.

Adult↗

PubMed2002

Limitations of object-based feature encoding in visual short-term memory.

The present study investigated object-based feature encoding in visual short-term memory for 2 features within the same dimension that occur on different parts of an object. Using the change-detection paradigm, this experiment studied objects with 2 colors and objects with 2 orientations. Participants found it easier to monitor 1 rather than both features of such objects, even when decision noise was properly controlled for. However, no object-based benefit was observed for encoding the 2 features of each object that were of the same dimension. When similar stimuli were used but the 2 features of each object were from different dimensions (color and orientation), an object-based benefit was observed. These results thus impose a major constraint on object-based feature encoding theories by showing that only features from different dimensions can benefit from object-based encoding.

Adolescent↗

PubMed2002

Feature integration across parts in visual search.

In the present study, participants searched for a conjunction of color and orientation either from the same part of an object (same-part display), or from different parts of an object (different-part display). While no difference was found between the two display conditions in single feature searches, conjunction search in the same-part display was significantly faster than that in the different-part display. This same-part advantage applies to both the inner part as well as the outer part of an object. These results suggest that features are more readily integrated if they are from the same part of an object than if they are from different parts of an object. The formation of object part representations thus influences how features are integrated and encoded during visual information processing.

Adolescent↗

PubMed2002

Early computation of part structure: evidence from visual search.

The visual system represents object shapes in terms of intermediate-level parts. The minima rule proposes that the visual system uses negative minima of curvature to define boundaries between parts. We used visual search to test whether part structures consistent with the minima rule are computed preattentively--or at least, rapidly and early in visual processing. The results of Experiments 1 and 2 showed that whereas the search for a non-minima-segmented shape is fast and efficient among minima-segmented shapes, the reverse search is slow and inefficient. This asymmetry is expected if parsing at negative minima occurs obligatorily. The results of Experiments 3 and 4 showed that although both minima- and non-minima-segmented shapes pop out among unsegmented shapes, the search for minima-segmented shapes is significantly slower. Together, these results demonstrate that the visual system segments shapes into parts, using negative minima of curvature, and that it does so rapidly in early stages of visual processing.

Adolescent↗

PubMed2002

Encoding color and shape from different parts of an object in visual short-term memory.

Can we find an object-based encoding benefit in visual short-term memory (VSTM) when the features to be remembered are from different parts of an object? Using object parts defined by either figure-ground separation or negative minima of curvature, results from five experiments in which the visual change detection paradigm was used showed that the object-based encoding benefit in VSTM is modulated by how features are assigned to parts of an object: Features are best retained when the color and shape features to be remembered belong to the same part of an object. Although less well retained in comparison, features from different parts of an object are still better remembered than features from spatially separated objects. An object-based feature binding therefore exists even when the color and shape features to be remembered are from different parts of an object.

Adolescent↗