Onat Selim, Açık Alper, Schumann Frank, König Peter
Institute of Cognitive Science, University of Osnabrück, Osnabrück, Germany.
PLoS One. 2014 Apr 15;9(4):e93254. doi: 10.1371/journal.pone.0093254. eCollection 2014.
During free-viewing of natural scenes, eye movements are guided by bottom-up factors inherent to the stimulus, as well as top-down factors inherent to the observer. The question of how these two different sources of information interact and contribute to fixation behavior has recently received a lot of attention. Here, a battery of 15 visual stimulus features was used to quantify the contribution of stimulus properties during free-viewing of 4 different categories of images (Natural, Urban, Fractal and Pink Noise). Behaviorally relevant information was estimated in the form of topographical interestingness maps by asking an independent set of subjects to click at image regions that they subjectively found most interesting. Using a Bayesian scheme, we computed saliency functions that described the probability of a given feature to be fixated. In the case of stimulus features, the precise shape of the saliency functions was strongly dependent upon image category and overall the saliency associated with these features was generally weak. When testing multiple features jointly, a linear additive integration model of individual saliencies performed satisfactorily. We found that the saliency associated with interesting locations was much higher than any low-level image feature and any pair-wise combination thereof. Furthermore, the low-level image features were found to be maximally salient at those locations that had already high interestingness ratings. Temporal analysis showed that regions with high interestingness ratings were fixated as early as the third fixation following stimulus onset. Paralleling these findings, fixation durations were found to be dependent mainly on interestingness ratings and to a lesser extent on the low-level image features. Our results suggest that both low- and high-level sources of information play a significant role during exploration of complex scenes with behaviorally relevant information being more effective compared to stimulus features.
在自由观看自然场景时，眼球运动受刺激本身固有的自下而上因素以及观察者固有的自上而下因素引导。这两种不同信息来源如何相互作用并影响注视行为的问题最近受到了广泛关注。在此，我们使用了一组15种视觉刺激特征来量化在自由观看4种不同类别图像（自然、城市、分形和粉红噪声）时刺激属性的贡献。通过让另一组独立的受试者点击他们主观上认为最有趣的图像区域，以地形兴趣度图的形式估计行为相关信息。我们使用贝叶斯方法计算了描述给定特征被注视概率的显著性函数。对于刺激特征，显著性函数的精确形状强烈依赖于图像类别，总体而言与这些特征相关的显著性通常较弱。当联合测试多个特征时，个体显著性的线性加性整合模型表现良好。我们发现与有趣位置相关的显著性远高于任何低级图像特征及其任何两两组合。此外，发现低级图像特征在那些已经具有高兴趣度评分的位置最为显著。时间分析表明，具有高兴趣度评分的区域在刺激开始后的第三次注视时就被注视了。与这些发现一致，注视持续时间主要取决于兴趣度评分，在较小程度上取决于低级图像特征。我们的结果表明，在探索复杂场景时，低级和高级信息源都起着重要作用，行为相关信息比刺激特征更有效。
