Publications (4)22.45 Total impact
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Article: Category expectation modulates baseline and stimulus-evoked activity in human inferotemporal cortex.
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ABSTRACT: Expectation of locations and low-level features increases activity in extrastriate visual areas even in the absence of a stimulus, but it is unclear whether or how expectation of higher-level stimulus properties affects visual responses. Here, we used event-related functional magnetic resonance imaging (fMRI) to test whether category expectation affects baseline and stimulus-evoked activity in higher-level, category-selective inferotemporal (IT) visual areas. Word cues indicating an image category (FACE or HOUSE) were followed by a delay, then a briefly presented image of a face or a house. On most trials, the cue correctly predicted the upcoming stimulus. Baseline activity in regions within the fusiform face area (FFA) and parahippocampal place area (PPA) was modulated such that activity was higher during expectation of the preferred (e.g., FACE for FFA) vs. non-preferred category. Stimulus-evoked responses reflected an initial bias (higher overall activity) followed by increased selectivity (greater difference between activity to a preferred vs. non-preferred stimulus) after expectation of the preferred vs. non-preferred category. Consistent with the putative role of a frontoparietal network in top-down modulation of activity in sensory cortex, expectation-related activity in several frontal and parietal areas correlated with the magnitude of baseline shifts in the FFA and PPA across subjects. Furthermore, expectation-related activity in lateral prefrontal cortex also correlated with the magnitude of expectation-based increases in stimulus selectivity in IT areas. These findings demonstrate that category expectation influences both baseline and stimulus-evoked activity in category-selective inferotemporal visual areas, and that these modulations may be driven by a frontoparietal attentional control network.Brain research 09/2009; 1301:89-99. · 2.46 Impact Factor -
Article: Interactions between endogenous and exogenous attention during vigilance.
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ABSTRACT: The ability to remain vigilant over long periods of time is critical for many everyday tasks, but controlled studies of visual sustained attention show that performance declines over time when observers are required to respond to rare stimulus events (targets) occurring in a sequence of standard stimulus events (nontargets). When target discrimination is perceptually difficult, this vigilance decrement manifests as a decline in perceptual sensitivity. We examined whether sudden-onset stimuli could act as exogenous attentional cues to improve sensitivity during a traditional sustained attention task. Sudden-onset cues presented immediately before each stimulus attenuated the sensitivity decrement, but only when stimulus timing (the interstimulus interval [ISI]) was constant. When stimulus timing was variable, exogenous cues increased overall sensitivity but did not prevent performance decline. Finally, independent of the effects of sudden onsets, a constant ISI improved vigilance performance. Our results demonstrate that exogenous attention enhances perceptual sensitivity during vigilance performance, but that this effect is dependent on observers' being able to predict the timing of stimulus events. Such a result indicates a strong interaction between endogenous and exogenous attention during vigilance. We relate our findings to a resource model of vigilance, as well as to theories of endogenous and exogenous attention over short time periods.Attention Perception & Psychophysics 08/2009; 71(5):1042-58. · 2.04 Impact Factor -
Article: Expectation both helps and hinders object perception.
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ABSTRACT: We examined how expectation influences perception of complex objects. Participants discriminated between normal and distorted images of famous faces or places. Word cues (mostly valid) indicated either the general category or the exact identity of the upcoming image pair. Whereas category cues did not affect performance, valid exemplar expectation led to performance benefits. Furthermore, discrimination was slower after exemplar cues from the incorrect category than after invalid exemplar cues from the correct category, indicating costs of invalid category expectation. Thus, expectation of a specific exemplar facilitates perception of that object, but hinders perception of an object from a different category.Vision Research 03/2008; 48(4):589-97. · 2.41 Impact Factor -
Article: Attention increases neural selectivity in the human lateral occipital complex.
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ABSTRACT: It is well established that attention increases the efficiency of information processing, but the neural mechanisms underlying this improvement are not fully understood. Evidence indicates that neural firing rates increase for attended stimuli, but another possibility is that attention could increase the selectivity of the neural population representing an attended stimulus. We tested this latter hypothesis by using functional magnetic resonance imaging (fMRI) to measure population selectivity for object views under different attention conditions in the human lateral occipital complex (LOC). Our data not only show increased neural activity (or 'gain') with attention, consistent with existing models, but also increased population selectivity that cannot be accounted for by gain mechanisms alone. Our results suggest that attention increases the specificity of the neural population representing an attended object.Nature Neuroscience 02/2004; 7(1):70-4. · 15.53 Impact Factor
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Institutions
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2004–2008
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University of California, Davis
- Center for Neuroscience
Davis, CA, USA
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