Person:
Xu, Yaoda

Profile Picture

Email Address

AA Acceptance Date

Birth Date

Research Projects

Organizational Units

Job Title

Last Name

Xu

First Name

Yaoda

Name

Xu, Yaoda
Author's Publications: search.filters.isAuthorOfPublication.1dba36a9-c826-4bd1-a5d1-9c8a671a82f5

Search Results

Now showing 1 - 10 of 18
  • Thumbnail Image
    Publication
    Understanding location- and feature-based processing along the human intraparietal sulcus
    (American Physiological Society, 2016) Bettencourt, Katherine; Xu, Yaoda
    Based on different cognitive tasks and mapping methods, the human intraparietal sulcus (IPS) has been subdivided according to multiple different organizational schemes. The presence of topographically organized regions throughout IPS indicates a strong location-based processing in this brain region. However, visual short-term memory (VSTM) studies have shown that while a region in the inferior IPS region (inferior IPS) is involved in object individuation and selection based on location, a region in the superior IPS (superior IPS) primarily encodes and stores object featural information. Here, we determined the localization of these two VSTM IPS regions with respect to the topographic IPS regions in individual participants and the role of different IPS regions in location- and feature-based processing. Anatomically, inferior IPS showed an 85.2% overlap with topographic IPS regions, with the greatest overlap seen in V3A and V3B, and superior IPS showed a 73.6% overall overlap, with the greatest overlap seen in IPS0-2. Functionally, there appeared to be a partial overlap between IPS regions involved in location- and feature-based processing, with more inferior and medial regions showing a stronger location-based processing and more superior and lateral regions showing a stronger feature-based processing. Together, these results suggest that understanding the multiplex nature of IPS in visual cognition may not be reduced to examining the functions of the different IPS topographic regions, but rather, it can only be accomplished by understanding how regions identified by different tasks and methods may colocalize with each other.
  • Thumbnail Image
    Publication
    Behaviorally Relevant Abstract Object Identity Representation in the Human Parietal Cortex
    (Society for Neuroscience, 2016) Jeong, Su Keun; Xu, Yaoda
    The representation of object identity is fundamental to human vision. Using fMRI and multivoxel pattern analysis, here we report the representation of highly abstract object identity information in human parietal cortex. Specifically, in superior intraparietal sulcus (IPS), a region previously shown to track visual short-term memory capacity, we found object identity representations for famous faces varying freely in viewpoint, hairstyle, facial expression, and age; and for well known cars embedded in different scenes, and shown from different viewpoints and sizes. Critically, these parietal identity representations were behaviorally relevant as they closely tracked the perceived face-identity similarity obtained in a behavioral task. Meanwhile, the task-activated regions in prefrontal and parietal cortices (excluding superior IPS) did not exhibit such abstract object identity representations. Unlike previous studies, we also failed to observe identity representations in posterior ventral and lateral visual object-processing regions, likely due to the greater amount of identity abstraction demanded by our stimulus manipulation here. Our MRI slice coverage precluded us from examining identity representation in anterior temporal lobe, a likely region for the computing of identity information in the ventral region. Overall, we show that human parietal cortex, part of the dorsal visual processing pathway, is capable of holding abstract and complex visual representations that are behaviorally relevant. These results argue against a “content-poor” view of the role of parietal cortex in attention. Instead, the human parietal cortex seems to be “content rich” and capable of directly participating in goal-driven visual information representation in the brain.
  • Thumbnail Image
    Publication
    Object Ensemble Processing in Human Anterior-Medial Ventral Visual Cortex
    (Society for Neuroscience, 2012) Cant, Jonathan S.; Xu, Yaoda
    Our visual system can extract summary statistics from large collections of similar objects without forming detailed representations of the individual objects in the ensemble. Such object ensemble representation is adaptive and allows us to overcome the capacity limitation associated with representing specific objects. Surprisingly, little is known about the neural mechanisms supporting such object ensemble representation. Here we showed human observers identical photographs of the same object ensemble, different photographs depicting the same ensemble, or different photographs depicting different ensembles. We observed fMRI adaptation in anterior-medial ventral visual cortex whenever object ensemble statistics repeated, even when local image features differed across photographs. Interestingly, such object ensemble processing is closely related to texture and scene processing in the brain. In contrast, the lateral occipital area, a region involved in object–shape processing, showed adaptation only when identical photographs were repeated. These results provide the first step toward understanding the neural underpinnings of real-world object ensemble representation.
  • Thumbnail Image
    Publication
    The Role of Transverse Occipital Sulcus in Scene Perception and Its Relationship to Object Individuation in Inferior Intraparietal Sulcus
    (MIT Press - Journals, 2013) Bettencourt, Katherine; Xu, Yaoda
    The parietal cortex has been functionally divided into various subregions; however, very little is known about how these areas relate to each other. Two such regions are the transverse occipital sulcus (TOS) scene area and inferior intraparietal sulcus (IPS). TOS exhibits similar activation patterns to the scene selective parahippocampal place area, suggesting its role in scene perception. Inferior IPS, in contrast, has been shown to participate in object individuation and selection via location. Interestingly, both regions have been localized to the same general area of the brain. If these two were actually the same brain region, it would have important implications regarding these regions' role in cognition. To explore this, we first localized TOS and inferior IPS in individual participants and examined the degree of overlap between these regions in each participant. We found that TOS showed only a minor degree of overlap with inferior IPS (∼10%). We then directly explored the role of TOS and inferior IPS in object individuation and scene perception by examining their responses to furnished rooms, empty rooms, isolated furniture, and multiple isolated objects. If TOS and inferior IPS were the same region, we would expect to see similar response patterns in both. Instead, the response of TOS was predominantly scene selective, whereas activity in inferior IPS was primarily driven by the number of objects present in the display, regardless of scene context. These results show that TOS and inferior IPS are nearby but distinct regions, with different functional roles in visual cognition.
  • Thumbnail Image
    Publication
    The association of color memory and the enumeration of multiple spatially overlapping sets
    (Association for Research in Vision and Ophthalmology (ARVO), 2013) Poltoratski, Sonia; Xu, Yaoda
    Using dot displays, Halberda, Sires, and Feigenson (2006) showed that observers could simultaneously encode the numerosity of two spatially overlapping sets and the superset of all items at a glance. With the brief display and the masking used in Halberda et al., the task required observers to encode the colors of each set in order to select and enumerate all the dots in that set. As such, the observed capacity limit for set enumeration could reflect a limit in visual short-term memory (VSTM) capacity for the set color rather than a limit in set enumeration per se. Here, we largely replicated Halberda et al. and found successful enumeration of approximately two sets (the superset was not probed). We also found that only about two and a half colors could be remembered from the colored dot displays whether or not the enumeration task was performed concurrently with the color VSTM task. Because observers must remember the color of a set prior to enumerating it, the under three-item VSTM capacity for color necessarily dictates that set enumeration capacity in this paradigm could not exceed two sets. Thus, the ability to enumerate multiple spatially overlapping sets is likely limited by VSTM capacity to retain the discriminating feature of these sets. This relationship suggests that the capacity for set enumeration cannot be considered independently from the capacity for the set's defining features.
  • Thumbnail Image
    Publication
    Neural Representation of Targets and Distractors during Object Individuation and Identification
    (Massachusetts Institute of Technology Press (MIT Press), 2012) Jeong, Su Keun; Xu, Yaoda
    In many everyday activities, we need to attend and encode multiple target objects among distractor objects. For example, when driving a car on a busy street, we need to simultaneously attend objects such as traffic signs, pedestrians, and other cars, while ignoring colorful and flashing objects in display windows. To explain how multiple visual objects are selected and encoded in visual STM and in perception in general, the neural object file theory argues that, whereas object selection and individuation is supported by inferior intraparietal sulcus (IPS), the encoding of detailed object features that enables object identification is mediated by superior IPS and higher visual areas such as the lateral occipital complex (LOC). Nevertheless, because task-irrelevant distractor objects were never present in previous studies, it is unclear how distractor objects would impact neural responses related to target object individuation and identification. To address this question, in two fMRI experiments, we asked participants to encode target object shapes among distractor object shapes, with targets and distractors shown in different spatial locations and in different colors. We found that distractor-related neural processing only occurred at low, but not at high, target encoding load and impacted both target individuation in inferior IPS and target identification in superior IPS and LOC. However, such distractor-related neural processing was short-lived, as it was only present during the visual STM encoding but not the delay period. Moreover, with spatial cuing of target locations in advance, distractor processing was attenuated during target encoding in superior IPS. These results are consistent with the load theory of visual information processing. They also show that, whereas inferior IPS and LOC were automatically engaged in distractor processing under low task load, with the help of precuing, superior IPS was able to only encode the task-relevant visual information.
  • Thumbnail Image
    Publication
    The Neural Fate of Task-Irrelevant Features in Object-Based Processing
    (Society for Neuroscience, 2010) Xu, Yaoda
    Objects are one of the most fundamental units in visual attentional selection and information processing. Studies have shown that, during object-based processing, all features of an attended object may be encoded together, even when these features are task irrelevant. Some recent studies, however, have failed to find this effect. What determines when object-based processing may or may not occur? In three experiments, observers were asked to encode object colors and the processing of task-irrelevant object shapes was evaluated by measuring functional magnetic resonance imaging responses from a brain area involved in shape representation. Whereas object-based task-irrelevant shape processing was present at low color-encoding load, it was attenuated or even suppressed at high color-encoding load. Moreover, such object-based processing was short-lived and was not sustained over a long delay period. Object-based processing for task-irrelevant features of attended objects thus does exist, as reported previously; but it is transient and its magnitude is determined by the encoding demand of the task-relevant feature.
  • Thumbnail Image
    Publication
    The impact of item clustering on visual search: It all depends on the nature of the visual search
    (Association for Research in Vision and Ophthalmology (ARVO), 2010) Xu, Yaoda
    Decades of vision research on how people search for a target item among distractor items have always avoided item clustering. Instead, researchers made sure that items were evenly distributed in search displays. This, however, is rarely the case in our everyday visual environment. Consequently, it is largely unknown how item clustering may impact visual search performance. In this study, I manipulated item clustering in search displays. In an easy feature search, observers looked for a target letter “T” among distractor letters “Os” and reported whether the target was pointing to the left or to the right. In a difficult spatial configuration search, observers searched and reported the orientation of the target letter “T” among distractor letters “Ls”. The two types of searches thus had the same target but different distractors. In two experiments, I found that while item clustering slowed down the easy feature search, it speeded up the difficult spatial configuration search. Together, these results show that item clustering significantly affects visual search performance and its exact impact (negative or positive) depends on the nature of the visual search.
  • Thumbnail Image
    Publication
    The impact of top-down spatial attention on laterality and hemispheric asymmetry in the human parietal cortex
    (The Association for Research in Vision and Ophthalmology, 2016) Jeong, Su Keun; Xu, Yaoda
    The human parietal cortex exhibits a preference to contralaterally presented visual stimuli (i.e., laterality) as well as an asymmetry between the two hemispheres with the left parietal cortex showing greater laterality than the right. Using visual short-term memory and perceptual tasks and varying target location predictability, this study examined whether hemispheric laterality and asymmetry are fixed characteristics of the human parietal cortex or whether they are dynamic and modulated by the deployment of top-down attention to the target present hemifield. Two parietal regions were examined here that have previously been shown to be involved in visual object individuation and identification and are located in the inferior and superior intraparietal sulcus (IPS), respectively. Across three experiments, significant laterality was found in both parietal regions regardless of attentional modulation with laterality being greater in the inferior than superior IPS, consistent with their roles in object individuation and identification, respectively. Although the deployment of top-down attention had no effect on the superior IPS, it significantly increased laterality in the inferior IPS. The deployment of top-down spatial attention can thus amplify the strength of laterality in the inferior IPS. Hemispheric asymmetry, on the other hand, was absent in both brain regions and only emerged in the inferior but not the superior IPS with the deployment of top-down attention. Interestingly, the strength of hemispheric asymmetry significantly correlated with the strength of laterality in the inferior IPS. Hemispheric asymmetry thus seems to only emerge when there is a sufficient amount of laterality present in a brain region.
  • Thumbnail Image
    Publication
    Inferior frontal junction biases perception through neural synchrony
    (Elsevier BV, 2014) Xu, Yaoda
    How the primate attentional control network interacts with posterior sensory regions to bias perception is not fully understood. Using magnetoencephalography (MEG) supplemented by functional magnetic resonance imaging (fMRI), a recent study reported that human inferior frontal junction (IFJ) could play a key role in biasing perception through neural synchrony with posterior sensory regions.