Effects of linear and angular velocity on 2-, 4-, and 6-month-olds'' visual pursuit behaviors

We report on a study with 12 infants at each of 2, 4, and 6 months of age which examines the effects on infant visual pursuit of varying the target linear velocity (m/s) and the target angular velocity (deg/s) independently. Tracking performance is described in terms of five behaviors which characterize infant performance as a tracking trial unfolds: time to initial capture, duration of initial tracking, duration of initial break in tracking, frequency of interruptions in tracking, and mean duration of all tracking intervals. Interruptions in tracking become more frequent as linear velocity increases but less frequent as angular velocity increases. The mean duration of later tracking intervals is diminished relative to the duration of earlier tracking intervals in 4- and 6-month-olds, but not in the 2-month-olds. Differences in angular velocity may account for the conflicting reports of disruptions in object permanence studies relying on a visual tracking paradigm.     

Temporal restriction in apparent motion of two objects by presenting multipartite subframes

Two experiments tested whether proper perception of motion can be realized with a multipartite subframe stimulus. In order to elucidate the constructive processes of visual motion, two motion stimuli were used which differed according to their hierarchical levels of reference. It was found that: (a) stable motion was perceived so long as the temporal interval between the neighboring frames comprising several subframes was held between 30 and 120 ms; (b) visual unification of subframes was properly achieved independently of the number of subframes insofar as the temporal constraint mentioned above was satisfied; (c) when stimuli consisted of two motions of different hierarchical level of reference, perception of the higher-level motion required the prior perception of the lower-level motion.     

Categorization of natural movements by pigeons: visual concept discrimination and biological motion

In three experiments, pigeons were exposed to a discriminated autoshaping procedure in which categories of moving stimuli, presented on videotape, were differentially associated with reinforcement. All stimuli depicted pigeons making defined responses. In Experiment 1, one category consisted of several different scenes of pecking and the other consisted of scenes of walking, flying, head movements, or standing still. Four of the 4 birds for which pecking scenes were positive stimuli discriminated successfully, whereas only 1 of the 4 for which pecking was the negative category did so. In the pecking-positive group, there were differences between the pecking rates in the presence of the four negative actions, and these differences were consistent across subjects. In Experiment 2, only the categories of walking and pecking were used; some but not all birds learned this discrimination, whichever category was positive, and these birds showed some transfer to new stimuli in which the same movements were represented only by a small number of point lights (Johansson's “biological motion” displays). In Experiment 3, discriminations between pecking and walking movement categories using point-light displays were trained. Four of the 8 birds discriminated successfully, but transfer to fully detailed displays could not be demonstrated. Pseudoconcept control groups, in which scenes from the same categories of motion were used in both the positive and negative stimulus sets, were used in Experiments 1 and 3. None of the 8 pigeons trained under these conditions showed discriminative responding. The results suggest that pigeons can respond differentially to moving stimuli on the basis of movement cues alone.     

Visual perception of biological motion in newly hatched chicks as revealed by an imprinting procedure

Day-old chicks were exposed to point-light animation sequences depicting either a walking hen or a rotating cylinder. On a subsequent free-choice test (experiment 1) the chicks approached the novel stimulus, irrespective of this being the hen or the cylinder. In order to obtain equivalent local motion vectors, in experiments 2 and 3 newly hatched chicks were exposed either to a point-light animation sequence depicting a walking hen, or to a positionally scrambled walking hen (i.e. an animation in which exactly the same set of dots in motion as that employed for the walking hen was presented, but with spatially randomized starting positions). Chicks tested on day 1 (experiment 2) or on day 2 (i.e. after a period in the dark following exposure on day 1 (experiment 3)) proved able to discriminate the two animation sequences: males preferentially approached the novel stimulus, females the familiar one. These results indicate that discrimination was not based on local motion vectors, but rather on the temporally integrated motion sequence. Received: 18 August 1999 / Accepted after revision: 14 March 2000     

客体运动方向的视觉工作记忆存储方式

采用变化觉察范式,以独立运动的客体为对象,通过两个实验,探讨多个客体的运动方向在视觉工作记忆中的存储机制,即单个对象独立存储,抑或其存储受多个客体构型的影响。实验一和实验二相继考察了非目标客体运动方向变化,以及是否存在非目标客体对觉察目标客体运动方向的影响。结果发现,非目标客体运动方向变化条件下的觉察正确率显著低于不变的条件,然而只呈现目标客体条件下的觉察正确率与同时呈现目标和非目标条件无显著差异。该结果与前人在静态条件下对目标客体的觉察受目标客体和非目标客体整体构型影响的结论不一致。本研究的结果支持多个客体的运动方向信息在工作记忆中是以独立方式存储的假设。     

基于时空变化的步态识别算法研究

本文提出了一种八椭圆人体模型,并在此基础上提出了基于变化信息的步态识别算法。对每个视频序列,采用基于贝叶斯规则的检测算法检测出目标人体区域;将目标人体区域按比例划分为八个区域并分别用椭圆拟合,建立人体椭圆模型;用人体姿势的时空变化——相邻帧间的模型参数的差值作为特征,用归一化后的Mahalanobis距离和Euclidean距离分别进行相似性度量,NN和KNN技术用于最终的分类。实验结果表明,该算法拥有较高的识别率和较低的计算代价。     

内源性眼跳前的空间注意转移

采用线运动错觉(illusory line motion)测量的单任务范式,以色块为眼跳提示刺激,用三个实验对内源性眼跳前是否存在空间注意转移进行了探讨。实验一要求被试将眼睛跳往提示刺激处,通过对线运动错觉的分析确定该条件下的空间注意转移规律;实验二要求被试在将视线保持在注视点处的条件下判断目标色块是否出现,以探明线运动错觉是否受对目标色块前注意阶段加工的影响;实验三要求被试将眼睛跳往提示刺激的对侧,分析眼跳位置与提示刺激空间方位的一致性对空间注意转移的影响。获得以下主要结果：(1)内源性眼跳前存在注意转移;(2)在视线保持在注视点处的条件下,注意未受对提示刺激前注意加工的引导;(3)眼跳目标位置与提示目标位置的空间一致性对眼跳前空间注意转移无显著影响。     

视觉运动知觉脑机制的研究现状

视觉运动是探索脑功能的一个重要研究途径,该对视觉运动通路与色彩的关系、视觉运动知觉的产生,对于视觉信息的不同阶段的处理以及立体视觉等若干问题进行了回顾与讨论,并概述了其中若干理论及其争论,提出了未来视觉研究可能存在的问题与研究方向。     

生物运动加工特异性：整体结构和局部运动的作用

人类具有很强的识别生物体运动信息的能力, 甚至当运动信息仅是由附着在头部和一些重要关节上的光点的运动组成时, 观察者对该信息检测和编码的优势依然存在。光点生物运动信息包含整体信息(如整体形状)和局部信息(如各个点的运动轨迹)。先前的绝大部分研究强调整体形状在生物运动知觉中的作用。最近有研究表明去除了整体结构信息的局部生物运动仍然存在加工优势, 揭示了局部生物运动本身可能包含了一些特异性信息。因此生物运动知觉并非单一现象, 而是一种具有不同加工机制(基于整体结构和基于局部运动)的多水平现象。     

Creation and the Symbiosis of Science and Judaism

It seems to me that the critical questions that science and natural philosophy raise for Jewish theology are the following: Does God evolve? Does the universe have or even need an interpretation, specifically with reference to the fact that most of the universe most of the time is uninhabitable, and there may be many more than one universe? Does the universe need a beginning? What is distinctive about human consciousness, intelligence, and ethics in the light of evidence for evolution from all of the life sciences? Finally, will both life and the universe end? These questions are not only modern. They contain all the primary issues that have dominated rabbinic thought. That agenda can be summarized in six topics: How should we model what we believe about (1) God, (2) the world, and (3) the human being; and how should we understand the relations between them, that is, between (4) God and the world (or, creation), (5) God and the human (or, revelation), and (6) the human and the world (or, redemption)? In this paper I focus on the fourth issue, creation. My answer is presented in detail in my Judaism and the Doctrine of Creation(Samuelson 1994). Here I shall summarize my conclusions there concerning science, Jewish texts, and the correlation between them.