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Parallel processing in the brain's visual form system: an fMRI study.

Shigihara Y, Zeki S - Front Hum Neurosci (2014)

Bottom Line: Our results show that all three categories of form activate all three visual areas with which we were principally concerned (V1-V3), with angles producing the strongest and rhombuses the weakest activity in all three.The difference between the activity produced by angles and rhombuses was significant, that between lines and rhombuses was trend significant while that between lines and angles was not.Taken together with our earlier MEG results, the present ones suggest that a parallel strategy is used in processing forms, in addition to the well-documented hierarchical strategy.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Laboratory of Neurobiology, University College London London, UK.

ABSTRACT
We here extend and complement our earlier time-based, magneto-encephalographic (MEG), study of the processing of forms by the visual brain (Shigihara and Zeki, 2013) with a functional magnetic resonance imaging (fMRI) study, in order to better localize the activity produced in early visual areas when subjects view simple geometric stimuli of increasing perceptual complexity (lines, angles, rhombuses) constituted from the same elements (lines). Our results show that all three categories of form activate all three visual areas with which we were principally concerned (V1-V3), with angles producing the strongest and rhombuses the weakest activity in all three. The difference between the activity produced by angles and rhombuses was significant, that between lines and rhombuses was trend significant while that between lines and angles was not. Taken together with our earlier MEG results, the present ones suggest that a parallel strategy is used in processing forms, in addition to the well-documented hierarchical strategy.

No MeSH data available.


Stimuli were viewed using the right eye only and were presented in the lower region of the visual field in either the nasal or temporal quadrant. All stimuli consisted of 16 white lines, presented either separately (A), joined to form eight angles (B) or joined to form four rhombuses (C).
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Figure 1: Stimuli were viewed using the right eye only and were presented in the lower region of the visual field in either the nasal or temporal quadrant. All stimuli consisted of 16 white lines, presented either separately (A), joined to form eight angles (B) or joined to form four rhombuses (C).

Mentions: In general, we tried to keep our stimulus presentation and paradigm as similar to the ones we used in our MEG study, to allow for a direct comparison. The stimuli were generated in the same way as in our previous MEG study (Shigihara and Zeki, 2013) but differed in (a) the addition of a further category (angles) constituted from the same lines and intermediate in perceptual complexity between lines and rhombuses and (b) a reduction in the size of all the form stimuli by 14%, because of the smaller fMRI scanner screen size. To match our previous study MEG study, subjects viewed the fixation cross (subtending 0.9 × 0.9°) at the center of the screen monocularly with the right eye (a patch covered the left eye). All stimuli were displayed separately in either the lower left (nasal) or lower right (temporal) quadrants of the visual field, between 1.1 and 10.5° below the fixation cross and 1.9–11.8° on either side. Three different form stimuli were used: 16 lines, 8 angles, or 4 rhombuses (Figures 1A–C), all consisting of the same16 white lines. The vertices of angled stimuli varied from 54 to 108° and those of rhombuses from 18 to 162°. The same image (e.g., oriented lines) flashed at 8 Hz (67 ms between flashes) without changing the orientation of the line, to maximize the activation during the scans (Kwong et al., 1992); it continued to flash for 4 s, then disappeared and was replaced by a new stimulus which could be another oriented line or one of the two other categories (angles and rhombuses), the sequence being randomized.


Parallel processing in the brain's visual form system: an fMRI study.

Shigihara Y, Zeki S - Front Hum Neurosci (2014)

Stimuli were viewed using the right eye only and were presented in the lower region of the visual field in either the nasal or temporal quadrant. All stimuli consisted of 16 white lines, presented either separately (A), joined to form eight angles (B) or joined to form four rhombuses (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4115635&req=5

Figure 1: Stimuli were viewed using the right eye only and were presented in the lower region of the visual field in either the nasal or temporal quadrant. All stimuli consisted of 16 white lines, presented either separately (A), joined to form eight angles (B) or joined to form four rhombuses (C).
Mentions: In general, we tried to keep our stimulus presentation and paradigm as similar to the ones we used in our MEG study, to allow for a direct comparison. The stimuli were generated in the same way as in our previous MEG study (Shigihara and Zeki, 2013) but differed in (a) the addition of a further category (angles) constituted from the same lines and intermediate in perceptual complexity between lines and rhombuses and (b) a reduction in the size of all the form stimuli by 14%, because of the smaller fMRI scanner screen size. To match our previous study MEG study, subjects viewed the fixation cross (subtending 0.9 × 0.9°) at the center of the screen monocularly with the right eye (a patch covered the left eye). All stimuli were displayed separately in either the lower left (nasal) or lower right (temporal) quadrants of the visual field, between 1.1 and 10.5° below the fixation cross and 1.9–11.8° on either side. Three different form stimuli were used: 16 lines, 8 angles, or 4 rhombuses (Figures 1A–C), all consisting of the same16 white lines. The vertices of angled stimuli varied from 54 to 108° and those of rhombuses from 18 to 162°. The same image (e.g., oriented lines) flashed at 8 Hz (67 ms between flashes) without changing the orientation of the line, to maximize the activation during the scans (Kwong et al., 1992); it continued to flash for 4 s, then disappeared and was replaced by a new stimulus which could be another oriented line or one of the two other categories (angles and rhombuses), the sequence being randomized.

Bottom Line: Our results show that all three categories of form activate all three visual areas with which we were principally concerned (V1-V3), with angles producing the strongest and rhombuses the weakest activity in all three.The difference between the activity produced by angles and rhombuses was significant, that between lines and rhombuses was trend significant while that between lines and angles was not.Taken together with our earlier MEG results, the present ones suggest that a parallel strategy is used in processing forms, in addition to the well-documented hierarchical strategy.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Laboratory of Neurobiology, University College London London, UK.

ABSTRACT
We here extend and complement our earlier time-based, magneto-encephalographic (MEG), study of the processing of forms by the visual brain (Shigihara and Zeki, 2013) with a functional magnetic resonance imaging (fMRI) study, in order to better localize the activity produced in early visual areas when subjects view simple geometric stimuli of increasing perceptual complexity (lines, angles, rhombuses) constituted from the same elements (lines). Our results show that all three categories of form activate all three visual areas with which we were principally concerned (V1-V3), with angles producing the strongest and rhombuses the weakest activity in all three. The difference between the activity produced by angles and rhombuses was significant, that between lines and rhombuses was trend significant while that between lines and angles was not. Taken together with our earlier MEG results, the present ones suggest that a parallel strategy is used in processing forms, in addition to the well-documented hierarchical strategy.

No MeSH data available.