The Journal of Neuroscience, November 8, 2006, ():
Cue-Invariant Networks for Figure and Background Processing in Human Visual Cortex
J. Neurosci. Appelbaum et al.
26: 11695
Supplemental Data
Files in this Data Supplement:
- supplemental material
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Animation 1: Figure Only Stimulus
This animation shows the Figure Only stimulus in which a textured figure is presented on a mean luminance gray background containing no texture. In this stimulus, a centrally presented 5º figure region alternates orientation by 90º at 3.0 Hz. The figure is defined based on this temporal ‘frequency tag’, as well as, the presence of the one-dimensional texture. This stimulus allows us evaluate the figure response in isolation, and to contrast a single frequency tag to that created by two simultaneous frequency tags, as present in the other conditions.
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Animation 2: Orientation-Defined Form
This animation illustrates the Orientation-Defined Form stimulus. In this stimulus the figure and background textures modulate orientation by 90º at 3.0 and 3.6 Hz respectively. Because the rotation rates are different in the two regions, a global stimulus is created in which the figure segments from and disappears into the background. The figure exists only when the two regions are of dissimilar orientation, and the segmentation disappears when they are both in alignment. Thus, the figure region is cued by both a difference in orientation and by a difference in the frequencies of the tags imposed on the two regions.
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Animation 3: Phase-Defined Form Stimulus
This animation shows the Phase-Defined Form stimulus. Here, the figure and background textures rotate orientation by 180º (flipping about the midline) creating a global stimulus in which the figure is defined by local contrast discontinuities in the texture bars occurring at the region borders. The orientation of the figure and background regions is always horizontal, and the segmentation is defined by spatiotemporal luminance discontinuities along the length of the bars occurring at the figure/background border.
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Animation 4: Temporally-Defined Form Stimulus
This animation illustrates such a Temporally-Defined Form stimulus in which orientation information is removed altogether, forcing the segmentation process to rely solely on detection of two different temporal tags. In these stimuli, the pattern of small square elements is updated at 3.0 and 3.6 Hz in the figure and background regions respectively. Because there exists no contrast difference at the region borders in this stimulus, segmentation must be made exclusively on the relative temporal structures of the tagged regions.
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Animation 5: Full Field Stimulus
In the Full Field stimulus the entire field (21º by 21º) is made to alternate orientation by 90º at 3.0 Hz. No figure is present in this stimulus, except for that created at the edge of the field.
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Animation 6: Figure Activity Map, Figure Only, Orientation-, Phase-, and Temporally-Defined Form
Figure region responses are similar for all four cue types. In all conditions the figure responses alternate between a maximum over the occipital pole and maxima over lateral and ventral areas of occipital cortex. The biphasic spread of current flow begins in first-tier visual areas and shifts gradually to lateral visual areas. In the second half of the response cycle, activity again spreads from the occipital pole out to lateral and ventral visual areas. The direction of current flow alternates in the two halves of the response cycle in both medial and lateral areas. This change in current direction is represented by opposite polarity of the red/blue color scale. This apparent alternation of the response is present in all cue conditions, but the precise amplitude and temporal sequence varies between conditions. Current density maxima for each cue type are; Figure Only = 1.60 nAmp/mm2, Orientation 1.15 nAmp/mm2, Phase = 0.65 nAmp/mm2, TDF = 1.15 nAmp/mm2.
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Animation 7: Background Activity Map, Full Field, Orientation-, Phase-, and Temporally-Defined Form
In contrast to the activity evoked by the figure region, the spatiotemporal distribution of activity from the background region is largest over medial regions of the occipital cortex. This activity begins over the occipital pole and extends dorsally, rather than laterally. As was observed in the figure response, the direction of current flow alternates in the two halves of the biphasic response cycle. This spatio-temporal pattern of activity is nearly identical in all four stimulus conditions. From these animations it is readily apparent that figure and background regions thus activate distinct sets of cortical areas. Current density maxima for each cue type are; Full Field = 3.33 nAmp/mm2, Orientation 2.25 nAmp/mm2, Phase = 1.69 nAmp/mm2, TDF = 2.50 nAmp/mm2.
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Supplemental movie legends
