Neuroscience 2005 Abstract
| Presentation Number: | 389.19 |
|---|---|
| Abstract Title: | High-density EEG analysis of surround suppression in human visual cortex. |
| Authors: |
Wade, A. R.*1
; Petrov, Y.1
; McKee, S. P.1
; Norcia, A. M.1
1Brain Imaging Center, Smith-Kettl Eye Research Inst., San Francisco, CA |
| Primary Theme and Topics |
Sensory and Motor Systems - Vision -- Processing of contrast, orientation, form, and color |
| Secondary Theme and Topics | Techniques in Neuroscience<br />- Staining, Tracing, and Imaging Techniques |
| Session: |
389. Visual Cortex: Surround Mechanisms Poster |
| Presentation Time: | Monday, November 14, 2005 10:00 AM-11:00 AM |
| Location: | Washington Convention Center - Hall A-C, Board # N7 |
| Keywords: | VISUAL CORTEX, EVOKED POTENTIALS, AMBLYOPIA, MASKING |
The response of V1 neurons is suppressed by annular surrounds that fall well beyond their classical receptive fields. The neuronal basis for surround suppression is unknown although there is evidence that it arises via feedback from extra-striate cortex to V1. We have recently demonstrated a psychophysical analog of this surround suppression in the human periphery (SFN, 2004). High contrast annular surrounds, separated from a Gabor target by more than 3 periods raise contrast thresholds by a factor of 2 - 4. Psychophysically, surround suppression is tightly tuned for orientation, peaking at the orientation of the test target. Here we examine the spatiotemporal characteristics of orientation-specific surround suppression using high-density EEG and distributed source modeling.
METHODS
Probes consisting of low-contrast Gabor patches were presented either foveally or peripherally. Probes could be presented either (1) alone, (2) surrounded by a high contrast co-oriented annular grating or (3) surrounded by an orthogonal annular grating. The modulation frequencies of the probe and surround were different so that each component of the visual field was 'frequency tagged'. Subjects viewed the 3 different stimulus types while 128-channel EEG data were acquired. Stimulus-locked waveforms were averaged and analyzed in the frequency domain to identify components related to the probe, the background and their non-linear interactions.
RESULTS
In the peripheral conditions, we found strong suppression when the probe and the surround had the same orientation but not when the surround was orthogonal. We saw little differential effect of orthogonal and co-oriented surrounds for foveally-presented probes. A frequency component corresponding to the sum of the probe and flanker frequencies was present in peripheral conditions.
DISCUSSION
We demonstrate electrophysiological correlates of surround suppression, consistent with our previous psychophysical measurements. Using high density EEG, we have localized the different spatial and temporal components of this phenomenon in visual cortex.
METHODS
Probes consisting of low-contrast Gabor patches were presented either foveally or peripherally. Probes could be presented either (1) alone, (2) surrounded by a high contrast co-oriented annular grating or (3) surrounded by an orthogonal annular grating. The modulation frequencies of the probe and surround were different so that each component of the visual field was 'frequency tagged'. Subjects viewed the 3 different stimulus types while 128-channel EEG data were acquired. Stimulus-locked waveforms were averaged and analyzed in the frequency domain to identify components related to the probe, the background and their non-linear interactions.
RESULTS
In the peripheral conditions, we found strong suppression when the probe and the surround had the same orientation but not when the surround was orthogonal. We saw little differential effect of orthogonal and co-oriented surrounds for foveally-presented probes. A frequency component corresponding to the sum of the probe and flanker frequencies was present in peripheral conditions.
DISCUSSION
We demonstrate electrophysiological correlates of surround suppression, consistent with our previous psychophysical measurements. Using high density EEG, we have localized the different spatial and temporal components of this phenomenon in visual cortex.
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2005 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience, 2005. Online.
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