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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2005)
In nature, organisms not only process what is in the environment, but also continuously use the sensory information gathered in planning and acting upon the environment. Thus a theory of perception which regards it as a passive, receptive process is not likely to provide a complete picture. Instead, we can view perception as intimately related to processes and brain areas which were traditionally viewed as motor or executive in nature. I have studied the neural substrates of human perception in different modalities and at different levels of complexity. There are three main research areas represented in this dissertation: 1) The sensorimotor neural bases of language; 2) Sensory and motor areas involved in biological motion perception; 3) Representations of visual space in higher cortical areas and their response properties. First, in neuropsychological studies, I have examined the extent to which language comprehension shares processing and neural resources with other complex non-linguistic skills. The results support a view of language as a system which has considerable behavioral and neural links with related non- linguistic skills and sensorimotor substrates. Second, I explored brain areas involved in the visual perception of actions represented with motion cues (point-light biological motion) in both neuropsychological and neuroimaging (fMRI) experiments. The results suggest that these stimuli are processed in not only posterior, motion- sensitive areas of the brain, but also in premotor areas in frontal cortex. Third, using fMRI, I have aimed to identify retinotopic maps in the human brain and to explore their functional properties. I found significant, well-defined retinotopic maps in multiple areas in the brain, including some which are not traditionally thought to be visual areas. Furthermore, retinotopic responses were affected both by the complexity of stimuli and by attention, with attention as important as visual stimuli in several areas. These experiments highlight the embodied nature of perception and show that perceptual processes show a great deal of flexibility to subserve a variety of goals, and rely on multiple levels of representations across multiple modalities, often times including significant involvement of motor or executive neural resources
    Cover page: Embodied perception : neuropsychological and neuroimaging studies of language, vision, and attention
    • Article
    • Peer Reviewed
    Proceedings of the Annual Meeting of the Cognitive Science Society, Volume 32 (2010)
      Cover page: The Perception of Humans and Robots: Uncanny Hills in Parietal Cortex
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2004)

      We tested aphasic patients’ comprehension of actions to examine processing deficits in the linguistic and non-linguistic domains and their lesion correlates. 29 left-hemisphere injured patients and 18 age-matched control subjects matched pictured actions (with the objects missing) or their linguistic equivalents (printed sentences with the object missing) to one of two visually-presented pictures of objects. Aphasic patients performed poorly not only in the linguistic domain but also in the non-linguistic domain. A subset of the patients, largely consisting of severe and non-fluent aphasics, showed a greater deficit in the linguistic domain compared with the non-linguistic domain and across the patient group, deficits in the linguistic and non-linguistic domains were not tightly correlated. Poor performance in pantomime interpretation was associated with lesions in the inferior frontal, premotor and motor cortex, a portion of somatosensory cortex, and the caudate, while poor reading comprehension of actions was associated with lesions around the anterior superior temporal lobe, the anterior insula and the anterior portion of the inferior parietal lobe. Lesion size did not correlate with deficits. The lesion results for pantomime interpretation deficits demonstrate that lesions in the frontal component of the human analog of the “mirror neuron system” are associated with deficits in non-linguistic action understanding. For reading comprehension deficits, the lesion correlates are brain areas known to be involved in linguistic tasks including sentence processing and speech articulation; the parietal lesion site may also correspond to a subpart of the human mirror neuron system. These results indicate that brain areas important for the production of language and action are also recruited in their comprehension. Similar findings have been reported in electrophysiological and neuroimaging studies. Our findings now also lend neuropsychological support to an embodied view of brain organization for action processing.

        Cover page: Action comprehension in aphasia: Linguistic and non-linguistic deficits and their lesion correlates.
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2004)

        Motion cues can be surprisingly powerful in defining objects and events. Specifically, a handful of point-lights attached to the joints of a human actor will evoke a vivid percept of action when the body is in motion. The perception of point-light biological motion activates posterior cortical areas of the brain. On the other hand, observation of others' actions is known to also evoke activity in motor and premotor areas in frontal cortex. In the present study, we investigated whether point-light biological motion animations would lead to activity in frontal cortex as well. We performed a human functional magnetic resonance imaging study on a high-field-strength magnet and used a number of methods to increase signal, as well as cortical surface-based analysis methods. Areas that responded selectively to point-light biological motion were found in lateral and inferior temporal cortex and in inferior frontal cortex. The robust responses we observed in frontal areas indicate that these stimuli can also recruit action observation networks, although they are very simplified and characterize actions by motion cues alone. The finding that even point-light animations evoke activity in frontal regions suggests that the motor system of the observer may be recruited to "fill in" these simplified displays.

          Cover page: Point-light biological motion perception activates human premotor cortex.
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2015)
          Identifying the movements of those around us is fundamental for many daily activities, such as recognizing actions, detecting predators, and interacting with others socially. A key question concerns the neurobiological substrates underlying biological motion perception. Although the ventral "form" visual cortex is standardly activated by biologically moving stimuli, whether these activations are functionally critical for biological motion perception or are epiphenomenal remains unknown. To address this question, we examined whether focal damage to regions of the ventral visual cortex, resulting in significant deficits in form perception, adversely affects biological motion perception. Six patients with damage to the ventral cortex were tested with sensitive point-light display paradigms. All patients were able to recognize unmasked point-light displays and their perceptual thresholds were not significantly different from those of three different control groups, one of which comprised brain-damaged patients with spared ventral cortex (n > 50). Importantly, these six patients performed significantly better than patients with damage to regions critical for biological motion perception. To assess the necessary contribution of different regions in the ventral pathway to biological motion perception, we complement the behavioral findings with a fine-grained comparison between the lesion location and extent, and the cortical regions standardly implicated in biological motion processing. This analysis revealed that the ventral aspects of the form pathway (e.g., fusiform regions, ventral extrastriate body area) are not critical for biological motion perception. We hypothesize that the role of these ventral regions is to provide enhanced multiview/posture representations of the moving person rather than to represent biological motion perception per se.
            Cover page: Ventral aspect of the visual form pathway is not critical for the perception of biological motion
            • Article
            • Peer Reviewed
            Proceedings of the Annual Meeting of the Cognitive Science Society, Volume 34 (2012)
              Cover page: Temporal Dynamics of Action Perception: The Role of Biological Appearance and Motion Kinematics
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2010)

              Background

              Perception of biological motion is linked to the action perception system in the human brain, abnormalities within which have been suggested to underlie impairments in social domains observed in autism spectrum conditions (ASC). However, the literature on biological motion perception in ASC is heterogeneous and it is unclear whether deficits are specific to biological motion, or might generalize to form-from-motion perception.

              Methodology and principal findings

              We compared psychophysical thresholds for both biological and non-biological form-from-motion perception in adults with ASC and controls. Participants viewed point-light displays depicting a walking person (Biological Motion), a translating rectangle (Structured Object) or a translating unfamiliar shape (Unstructured Object). The figures were embedded in noise dots that moved similarly and the task was to determine direction of movement. The number of noise dots varied on each trial and perceptual thresholds were estimated adaptively. We found no evidence for an impairment in biological or non-biological object motion perception in individuals with ASC. Perceptual thresholds in the three conditions were almost identical between the ASC and control groups.

              Discussion and conclusions

              Impairments in biological motion and non-biological form-from-motion perception are not across the board in ASC, and are only found for some stimuli and tasks. We discuss our results in relation to other findings in the literature, the heterogeneity of which likely relates to the different tasks performed. It appears that individuals with ASC are unaffected in perceptual processing of form-from-motion, but may exhibit impairments in higher order judgments such as emotion processing. It is important to identify more specifically which processes of motion perception are impacted in ASC before a link can be made between perceptual deficits and the higher-level features of the disorder.
                Cover page: Unaffected Perceptual Thresholds for Biological and Non-Biological Form-from-Motion Perception in Autism Spectrum Conditions
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2010)
                The human visual system must perform complex visuospatial extrapolations (VSE) across space and time in order to extract shape and form from the retinal projection of a cluttered visual environment characterized by occluded surfaces and moving objects. Even if we exclude the temporal dimension, for instance when judging whether an extended finger is pointing towards one object or another, the mechanisms of VSE remain opaque. Here we investigated the neural correlates of VSE using functional magnetic resonance imaging in sixteen human observers while they judged the relative position of, or saccaded to, a (virtual) target defined by the extrapolated path of a pointer. Using whole brain and region of interest (ROI) analyses, we compared the brain activity evoked by these VSE tasks to similar control judgements or eye movements made to explicit (dot) targets that did not require extrapolation. The data show that activity in an occipitotemporal region that included the lateral occipital cortex (LOC) was significantly greater during VSE than during control tasks. A similar, though less pronounced, pattern was also evident in regions of the fronto-parietal cortex that included the frontal eye fields. However, none of the ROIs examined exhibited a significant interaction between target type (extrapolated/explicit) and response type (oculomotor/perceptual). These findings are consistent with a close association between visuoperceptual and oculomotor responses, and highlight a critical role for the LOC in the process of VSE.
                  Cover page: The Neural Correlates of Visuospatial Perceptual and Oculomotor Extrapolation
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