ISSN : 1226-9654
시지각 연구에서 물체는 지각적 처리 단위로 간주되곤 하지만, 복잡한 물체의 형태를 지각하려면 세부 부분들에 대한 처리가 필요하다. 오목한 극점 원리(minima rule)에 따르면, 물체 윤곽선에서 오목하게 들어간 곳은 부분 간 경계로 지각되며, 부분 간 경계부가 더 오목하게 들어갈수록 각 부분이 독립적으로 지각되는 부분 현저성(part salience)이 증가한다. 본 연구는 비일관적인 운동 중첩(inconsistent kinetic occlusion)이라는 새로운 자극 패러다임을 사용하여, 오목한 극점 원리에 따라 정의되는 부분 간 구조(part structure)의 생태적/물리적 타당성을 살펴보았다. 표적 도형이 정지된 물체를 가로질러 이동하는 애니메이션이 실험 자극으로 사용되었는데, 표적이 정지된 물체를 지나칠 때 그 윗부분은 정지된 물체에 의해 가려지고, 동시에 아래 부분은 정지된 물체를 덮고 지나가도록 하여, 중첩단서를 비일관적으로 할당하였다. 이 자극은 경합하는 두 지각적 해석을 유발하여, 움직이는 표적이 정지된 물체를 깊이 상에서 둘로 분할하면서 통과하거나, 혹은 움직이는 표적이 고정된 물체의 모서리에 의해 둘로 잘리는 것처럼 지각 가능하였다. 직사각형 자극의 윤곽선 곡률을 조작하여, 중앙부가 오목하게 들어가거나 불록하게 튀어나온 6개의 표적 도형을 구성하였다. 실험 결과, 중앙부가 오목한 조건에서 볼록할 때보다 표적이 두 부분으로 잘리는 것으로 지각되는 경향성이 높았으나, 표적의 폭은 이 경향성에 영향을 주지 않았다. 이 결과는 부분 표상의 지각적 원리로 제안된 오목한 극점 원리의 심리적, 그리고 생태적 타당성을 시사하며, 또한 물체의 부분 간 구조에 대한 지각적 처리가 표면 표상에 영향을 미치는 시지각 초기 단계의 과정임을 시사한다.
Many theories of shape perception assume that objects are the perceptual units, but complex objects are composed of distinct parts and thus the visual system can also represent object shapes at the level of smaller parts. The minima rule proposes that the visual system uses negative minima of curvature to define boundaries between parts. We employed a new experimental paradigm, globally inconsistent kinetic occlusion, to test whether the minima rule reliably mirrors regularities in the physical world, where concave contour segments often correspond to part boundaries. Participants observed animations of a target object moving across another static object, where the top half of the target was occluding, and simultaneously the bottom half occluded by the static object. This situation generated two competing perceptual interpretations: either the target cleaving the static object into two separated in depth, or the target being cleaved into two surfaces by the static one. We manipulated the sign and magnitude of contour curvature between the top and bottom halves of an object, so that 6 shapes were employed as moving targets. This result showed that targets with concave minima were more likely perceived as splitting into two surfaces than those with convex maxima or zero curvature. This finding suggests that the visual system parses shapes into parts, taking advantage of negative minima of curvature, and that part structure affects surface representations in accordance with ecological/physical regularities of the visual world.
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