Project: Research project

Project Details


Recordings from primate cortex have shown that different features of visual
stimuli are analyzed in distinct cortical fields. How does the perceptual
system recombine these features to form a coherent percept? Clues are
available from studies of visual search . Subjects rapidly detect targets
distinguished from distracting stimuli by single features (e.g., color) but
are slow and error-prone when targets are distinguished by conjointed
features (e.g., color and orientation). According to Treisman's feature
integration theory, single features of stimuli are processed automatically
and in parallel in different feature maps. However, visual feature
integration (VFI) requires a serial process in which objects must first be
localized before their features can be bound together by an attentional
scan. Unfortunately, it is difficult to study the physiology of VFI in search
tasks since the experimenter can never be certain which stimulus the
subject is processing. A new paradigm, rapid serial visual presentation
(RSVP), permits VFI to be studied for stimuli presented one-by-one. Four
experiments are proposed using RSVP tasks. For comparison, a fifth
experiment utilizing visual search is also included. In all experiments,
behavioral analysis will be combined with multi-channel recording of event-
related brain potentials (ERPs). ERP difference waves associated with the
processing of individual stimulus features and with feature integration
will be isolated to provide insight into the localization and timing of
VHI. Preliminary results show ERP difference waves related to feature
conjunction over frontal and parietal regions at latencies of 200-250 ms.
Event-related difference spectra (ERDs) will also be used to localize
cortical activity associated with VFI. Preliminary data show ERD changes
related to visual feature processing over the right parietal and occipital
scalp. In all experiments, behavioral and electrophysiological results from normal
subjects will be compared with data from patients with focal cortical
lesions of the lateral parietal lobe, dorsolateral prefrontal cortex, or
posterior superior temporal plane. Lesions in the regions have been shown
to impair VFI in visual search tasks. Behavioral and electrophysiological
results from normal subjects and patients will be used to test a model in
which different VFI operations are localized to distinct cortical regions;
the "master map" of locations in lateral parietal cortex, the scan of the
master map controlled by dorsolateral prefrontal cortex with a variable
aperture of attentional scan controlled by the temporal/parietal junction.
Effective start/end date6/1/945/31/00


  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health


  • Medicine(all)
  • Neuroscience(all)

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