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Vanitha Sampath, Gene Stoner, Karen Dobkins; Direction encoding in infants is sensitive to occlusion cues. Journal of Vision 2007;7(9):408. doi: https://doi.org/10.1167/7.9.408.
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Purpose: Previous studies indicate that by two months of age, infants integrate one- (1D) and two-dimensional (2D) motion signals (Dobkins, Lewis & Fine, 2006). Here, we investigated whether infants are sensitive to depth-ordering (occlusion) cues that determine whether 2D features are seen as intrinsic or extrinsic to moving 1D features. Methods: Modeled after the barber-diamond (BD) stimulus of Duncan, Albright & Stoner (2000), our BD stimulus consisted of vertically moving gratings (0.8 cpd, 8 Hz) presented within 83 diamond-shaped apertures (3 × 3 deg), evenly spaced across the display. Two occluding white bars (3.0 by 0.4 deg) abutted each BD on opposite sides. The two other sides were framed by a black background. We predicted that 2D terminators abutting the occluders would appear as extrinsic to the moving gratings, while 2D terminators along the two (unoccluded) sides would appear as intrinsic. Using a directional (left vs. right) eye movement (DEM) technique, we asked whether infants distinguished between the motion of intrinsic and extrinsic terminators, which moved up/right (45 deg) and up/left (135 deg), respectively (or vice versa). Performance (where 50% = chance) from the BD condition was compared to that from an Equivalent Direction (ED) condition, which consisted of diamond-shaped apertures containing unambiguous grating motion at 45 or 135 deg. For each infant, a BD index (BDI) was calculated as: (DEM performance on the BD condition-50%)/(DEM performance on the ED condition-50%). BDI values greater than 0 indicate a BD effect. Results: For 13 four-month-olds tested thus far, performance in the BD condition was significantly above chance (50%) (p[[lt]]0.001) and the mean BDI was 0.48 (p=0.001). Conclusions: By four months of age, visual motion mechanisms are sensitive to depth-ordering (occlusion) cues. We are currently tracking the development of this phenomenon in infants of different ages.
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