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Now showing 1 - 10 of 11
  • Publication
    Fast Forward: Supramarginal Gyrus Stimulation Alters Time Measurement
    (2010-01-01) Hamilton, Roy; Turkeltaub, Peter; Wiener, Martin; Coslett, H. Branch; Matell, Matthew S.
    The neural basis of temporal processing is unclear. We addressed this important issue by performing two experiments in which repetitive transcranial magnetic stimulation (rTMS) was administered in different sessions to the left or right supramarginal gyrus (SMG) or vertex; in both tasks, two visual stimuli were presented serially and subjects were asked to judge if the second stimulus was longer than the first (standard) stimulus. rTMS was presented on 50% of trials. Consistent with a previous literature demonstrating the effect of auditory clicks on temporal judgment, rTMS was associated with a tendency to perceive the paired visual stimulus as longer in all conditions. Crucially, rTMS to the right SMG was associated with a significantly greater subjective prolongation of the associated visual stimulus in both experiments. These findings demonstrate that the right SMG is an important element of the neural system underlying temporal processing and, as discussed, have implications for neural and cognitive models of temporal perception and attention.
  • Publication
    Simultanagnosia: When a Rose Is Not Red
    (2008-01-01) Coslett, H. Branch; Lie, Grace
    Information regarding object identity (‘‘what’’) and spatial location (‘‘where/how to’’) is largely segregated in visual processing. Under most circumstances, however, object identity and location are linked. We report data from a simultanagnosic patient (K.E.) with bilateral posterior parietal infarcts who was unable to ‘‘see’’ more than one object in an array despite relatively preserved object processing and normal preattentive processing. K.E. also demonstrated a finding that has not, to our knowledge, been reported: He was unable to report more than one attribute of a single object. For example, he was unable to name the color of the ink in which words were written despite naming the word correctly. Several experiments demonstrated, however, that perceptual attributes that he was unable to report influenced his performance. We suggest that binding of object identity and location is a limited-capacity operation that is essential for conscious awareness for which the posterior parietal lobe is crucial.
  • Publication
    Power in Voxel-based Lesion–Symptom Mapping
    (2007-07-01) Kimberg, Daniel Y.; Coslett, H. Branch; Schwartz, Myrna F.
    Lesion analysis in brain-injured populations complements what can be learned from functional neuroimaging. Voxelbased approaches to mapping lesion–behavior correlations in brain-injured populations are increasingly popular, and have the potential to leverage image analysis methods drawn from functional magnetic resonance imaging. However, power is a major concern for these studies, and is likely to vary regionally due to the distribution of lesion locations. Here, we outline general considerations for voxel-based methods, characterize the use of a nonparametric permutation test adapted from functional neuroimaging, and present methods for regional power analysis in lesion studies.
  • Publication
    Baby Schema in Infant Faces Induces Cuteness Perception and Motivation for Caretaking in Adults
    (2009-03-01) Langleben, Daniel D; Ruparel, Kosha; Loughead, James W; Glocker, Melanie L; Gur, Ruben C; Sachser, Norbert
    Ethologist Konrad Lorenz proposed that baby schema (‘Kindchenschema’) is a set of infantile physical features such as the large head, round face and big eyes that is perceived as cute and motivates caretaking behavior in other individuals, with the evolutionary function of enhancing offspring survival. Previous work on this fundamental concept was restricted to schematic baby representations or correlative approaches. Here, we experimentally tested the effects of baby schema on the perception of cuteness and the motivation for caretaking using photographs of infant faces. Employing quantitative techniques, we parametrically manipulated the baby schema content to produce infant faces with high (e.g. round face and high forehead), and low (e. g. narrow face and low forehead) baby schema features that retained all the characteristics of a photographic portrait. Undergraduate students (n = 122) rated these infants’ cuteness and their motivation to take care of them. The high baby schema infants were rated as more cute and elicited stronger motivation for caretaking than the unmanipulated and the low baby schema infants. This is the first experimental proof of the baby schema effects in actual infant faces. Our findings indicate that the baby schema response is a critical function of human social cognition that may be the basis of caregiving and have implications for infant–caretaker interactions.
  • Publication
    Prefrontal Cortical Response to Conflict during Semantic and Phonological Tasks
    (2007-05-01) Snyder, Hannah R.; Feigenson, Keith; Thompson-Schill, Sharon L.
    Debates about the function of the prefrontal cortex are as old as the field of neuropsychology—often dated to Paul Broca’s seminal work. Theories of the functional organization of the prefrontal cortex can be roughly divided into those that describe organization by process and those that describe organization by material. Recent studies of the function of the posterior, left inferior frontal gyrus (pLIFG) have yielded two quite different interpretations: One hypothesis holds that the pLIFG plays a domain-specific role in phonological processing, whereas another hypothesis describes a more general function of the pLIFG in cognitive control. In the current study, we distinguish effects of increasing cognitive control demands from effects of phonological processing. The results support the hypothesized role for the pLIFG in cognitive control, and more task-specific roles for posterior areas in phonology and semantics. Thus, these results suggest an alternative explanation of previously reported phonology-specific effects in the pLIFG.
  • Publication
    The Representation of Parts and Wholes in Face-selective Cortex
    (2008-05-01) Harris, Alison; Aguirre, Geoffrey Karl
    Although face perception is often characterized as depending on holistic, rather than part-based, processing, there is behavioral evidence for independent representations of face parts. Recent work has linked ‘‘face-selective’’ regions defined with functional magnetic resonance imaging (fMRI) to holistic processing, but the response of these areas to face parts remains unclear. Here we examine part-based versus holistic processing in ‘‘face-selective’’ visual areas using face stimuli manipulated in binocular disparity to appear either behind or in front of a set of stripes [Nakayama, K., Shimojo, S., & Silverman, G. H. Stereoscopic depth: Its relation to image segmentation, grouping, and the recognition of occluded objects. Perception, 18, 55–68, 1989]. While the first case will be ‘‘filled in’’ by the visual system and perceived holistically, we demonstrate behaviorally that the latter cannot be completed amodally, and thus is perceived as parts. Using these stimuli in fMRI, we found significant responses to both depth manipulations in inferior occipital gyrus and middle fusiform gyrus (MFG) ‘‘faceselective’’ regions, suggesting that neural populations in these areas encode both parts and wholes. In comparison, applying these depth manipulations to control stimuli (alphanumeric characters) elicited much smaller signal changes within faceselective regions, indicating that the part-based representation for faces is separate from that for objects. The combined adaptation data also showed an interaction of depth and familiarity within the right MFG, with greater adaptation in the back (holistic) condition relative to parts for familiar but not unfamiliar faces. Together, these data indicate that face-selective regions of occipito-temporal cortex engage in both part-based and holistic processing. The relative recruitment of such representations may be additionally influenced by external factors such as familiarity.
  • Publication
    Functional Neuroimaging Can Support Causal Claims about Brain Function
    (2011-01-01) Weber, Matthew J.; Thompson-Schill, Sharon L.
    Cognitive neuroscientists habitually deny that functional neuroimaging can furnish causal information about the relationship between brain events and behavior. However, imaging studies do provide causal information about those relationships although not causal certainty. Although popular portrayals of functional neuroimaging tend to attribute too much inferential power to the technique, we should restrain ourselves from ascribing it too little.
  • Publication
    The Neural Basis for Spatial Relations
    (2009-01-01) Amorapanth, Prin X.; Widick, Page; Chatterjee, Anjan
    Studies in semantics traditionally focus on knowledge of objects. By contrast, less is known about how objects relate to each other. In an fMRI study, we tested the hypothesis that the neural processing of categorical spatial relations between objects is distinct from the processing of the identity of objects. Attending to the categorical spatial relations compared with attending to the identity of objects resulted in greater activity in superior and inferior parietal cortices (especially on the left) and posterior middle frontal cortices bilaterally. In an accompanying lesion study, we tested the hypothesis that comparable areas would be necessary to represent categorical spatial relations and that the hemispheres differ in their biases to process categorical or coordinate spatial relations. Voxelbased lesion symptom mapping results were consistent with the fMRI observations. Damage to a network comprising left inferior frontal, supramarginal, and angular gyri resulted in behavioral impairment on categorical spatial judgments. Homologous right brain damage also produced such deficits, albeit less severely. The reverse pattern was observed for coordinate spatial processing. Right brain damage to the middle temporal gyrus produced more severe deficits than left hemisphere damage. Additional analyses suggested that some areas process both kinds of spatial relations conjointly and others distinctly. The left angular and inferior frontal gyrus processes coordinate spatial information over and above the categorical processing. The anterior superior temporal gyrus appears to process categorical spatial information uniquely. No areas within the right hemisphere processed categorical spatial information uniquely. Taken together, these findings suggest that the functional neuroanatomy of categorical and coordinate processing is more nuanced than implied by a simple hemispheric dichotomy.
  • Publication
    The Relation Between Color Discrimination and Color Constancy: When Is Optimal Adaptation Task Dependent?
    (2007-01-01) Abrams, Alicia B.; Hillis, James M.; Brainard, David H.
    Color vision supports two distinct visual functions: discrimination and constancy. Discrimination requires that the visual response to distinct objects within a scene be different. Constancy requires that the visual response to any object be the same across scenes. Across changes in scene, adaptation can improve discrimination by optimizing the use of the available response range. Similarly, adaptation can improve constancy by stabilizing the visual response to any fixed object across changes in illumination. Can common mechanisms of adaptation achieve these two goals simultaneously?We develop a theoretical framework for answering this question and present several example calculations. In the examples studied, the answer is largely yes when the change of scene consists of a change in illumination and considerably less so when the change of scene consists of a change in the statistical ensemble of surface reflectances in the environment.
  • Publication
    Bayesian Online Learning of the Hazard Rate in Change-Point Problems
    (2010-01-01) Nassar, Matthew R.; Wilson, Robert C.; Gold, Joshua I.
    Change-point models are generative models of time-varying data in which the underlying generative parameters undergo discontinuous changes at different points in time known as change points. Changepoints often represent important events in the underlying processes, like a change in brain state reflected in EEG data or a change in the value of a company reflected in its stock price. However, change-points can be difficult to identify in noisy data streams. Previous attempts to identify change-points online using Bayesian inference relied on specifying in advance the rate at which they occur, called the hazard rate (h). This approach leads to predictions that can depend strongly on the choice of h and is unable to deal optimally with systems in which h is not constant in time. In this letter, we overcome these limitations by developing a hierarchical extension to earlier models. This approach allows h itself to be inferred from the data, which in turn helps to identify when change-points occur. We show that our approach can effectively identify change-points in both toy and real data sets with complex hazard rates and how it can be used as an ideal-observermodel for human and animal behavior when faced with rapidly changing inputs.