물체가 관찰자를 향하여 다가올 때, 그 물체가 이루는 각, 즉 물체각의 상대적 팽창률의 역수는 그 물체의 도착시간과 일치한다. 관찰자는 tau라고 명명된 이 광학정보를 이용하여 움직이는 물체를 잡거나 다가오는 물체를 피하는 행동을 시간적으로 통제할 수 있다. 하지만 회전하며 날아오는 럭비공 같은 비대칭 비등방형 물체는 광흐름을 교란시키며, 그 결과 tau의 추출을 어렵게 한다. Gray와 Regan(2000)은 이러한 가능성을 검증하였으며, 그 결과 인간시각체계가 tau라는 단안정보에 입각하여 회전하며 접근하는 비원형 물체의 접촉시간을 탐지할 능력이 결여되었다고 주장하였다. 그에 반해, 다양한 결무늬를 입힌 비원형 물체를 이용하여 접촉시간 지각능력을 검증한 김남균(2009)은 기존의 접촉시간 연구에서 보고한 결과들과 비슷하거나 더 우수한 결과를 발견하였다. 하지만 김남균의 연구는 물체 내부 결 조직이 묘사되었다는 점을 제외하고는 참가자들이 어떤 정보에 근거하여 접촉시간을 탐지할 수 있었는지를 규명하기가 어려운 문제점을 내재하고 있다. 이 연구에서는 이러한 문제점을 보완하여, 물체를 검은색의 무선점들로 묘사하였으며, 무선점들의 숫자도 조작하여, tau가 광흐름 속에서 명시되는 정도를 변화시켰다. 이런 물체들을 이용하여 접촉시간 탐지능력을 실험 1에서 검증한 결과, 접근시간 예측이 기존의 문헌에서 보고된 수행능력과 크게 차이가 나지 않는다는 사실을 발견하였다. 하지만 4점 결밀도에서의 수행능력은 다른 3개의 고밀도 조건에서의 수행능력과는 차이가 있었다. 낮은 수행능력이 지각능력을 반영하는지를 평가하기 위해서 실험 2를 실시하여, 실험 1의 결과가 정확한 광패턴, 즉 팽창여부의 탐지에 근거하였는지를 검증하였다. 그 결과 정확한 광패턴 지각능력이 발견되었다. 특히 4점 결밀도 조건에서도 80%이상의 정확도를 보였다. 하지만 럭비공 물체에서 광패턴을 추출하는 것이 다른 물체에 비해 더 어려웠다는 사실을 발견하였으며, 이런 결과는 동일한 물체를 사용한 Gray와 Regan의 연구가 연구에 사용한 물체의 특수성에 근거하여 발생했을 가능성을 제기한다.
The present study examined human observers’ perceptual capacity to estimate time-to-contact (TTC) of an approaching object under severely perturbed or impoverished optic flow that compromised TTC information, in particular, local tau1. In Experiment 1, non-spherical objects approached the observation point while rotating either about one (horizontal or vertical) or two axes. The objects were depicted using random dots that varied in density (4, 16, 64, or 256 dots), half of which were projected to the observer. Under object rotation, the surface dots were displaced or even disappeared. These manipulations severely compromised the optical pattern specifying local tau1. In Experiment 1, performance degraded with decreasing dot density. Particularly, performance in the 4 dot density condition differed significantly from performance in the three higher density conditions. Experiment 2 examined whether these results accurately depicted the capacity of the human visual system. Objects either approached, or retreated from, the observation point; and participants were asked to judge the direction of the object’s motion. With an overall accuracy of 89%, most objects’ motion directions were identified reliably, even in the 4 dot density condition. Taken together, the present study demonstrated that the human visual system is capable of coping with adverse conditions by extracting requisite information, in particular, local tau1, that specifies the TTC of an approaching object, even from severely perturbed and impoverished optic flow. However, the present results also demonstrate that, under certain extreme conditions such as those engendered by rugby ball shaped object that rotated 90 deg over their approaches to the observation point, the visual system can fail, a finding consistent with that reported by Gray and Regan (2000).
The present study examined human observers’ perceptual capacity to estimate time-to-contact (TTC) of an approaching object under severely perturbed or impoverished optic flow that compromised TTC information, in particular, local tau1. In Experiment 1, non-spherical objects approached the observation point while rotating either about one (horizontal or vertical) or two axes. The objects were depicted using random dots that varied in density (4, 16, 64, or 256 dots), half of which were projected to the observer. Under object rotation, the surface dots were displaced or even disappeared. These manipulations severely compromised the optical pattern specifying local tau1. In Experiment 1, performance degraded with decreasing dot density. Particularly, performance in the 4 dot density condition differed significantly from performance in the three higher density conditions. Experiment 2 examined whether these results accurately depicted the capacity of the human visual system. Objects either approached, or retreated from, the observation point; and participants were asked to judge the direction of the object’s motion. With an overall accuracy of 89%, most objects’ motion directions were identified reliably, even in the 4 dot density condition. Taken together, the present study demonstrated that the human visual system is capable of coping with adverse conditions by extracting requisite information, in particular, local tau1, that specifies the TTC of an approaching object, even from severely perturbed and impoverished optic flow. However, the present results also demonstrate that, under certain extreme conditions such as those engendered by rugby ball shaped object that rotated 90 deg over their approaches to the observation point, the visual system can fail, a finding consistent with that reported by Gray and Regan (2000).
